While the information we provide is universal enough to apply to most hardwood flooring types, it is important to always read and follow instructions as they are given to you by a manufacturer for your specific hardwood flooring. Manufacturer instructions will vary, and individual companies may provide instructions which vary from those you see here, particularly in the laying of specialty hardwood flooring.
Before beginning any hardwood flooring installation project, please read this entire manual. If you happen to come across a situation that has not been addressed here, you can contact the Technical Department of NOFMA for assistance. Call (901) 526-5016 for general information and to have questions answered. The office is open between 8:30 a.m. and 4:30 p.m. Central Time, weekdays.
Please remember that this brochure only contains information about hardwood flooring installation methods. If you would like to learn more about hardwood flooring finishing procedures, please request a separate manual from the WFI.
NOFMA 9 HARDWOOD FLOORING
NOFMA/WFI TECHNICAL SERVICE
HANDLING AND STORAGE FOR HARDWOOD FLOORING INSTALLATION
Solid hardwood is the best for floors that are on or above ground level. These types of flooring options are ideal for the Chicagoland area. This flooring type is very durable and long lasting, and can be refinished and re-coated over years. However, if you are the type of homeowner who enjoys the rustic look of minor dents, cracks and scratches in your flooring to add character to your home, you may prefer to leave them be. Solid hardwood shrinks and expands depending on the level of humidity, so it is very important to keep temperatures and humidity levels in your home to around 40% for the entire year. In order to achieve this, you may want to run a humidifier in the winter time, and the air conditioner on during the summer time.
Store kiln-dried hardwood flooring in an enclosed building with weather-proof windows that is well ventilated and located in an area where similar fine millwork is stored. The storage area for the prefinished or unfinished hardwood flooring should be clean and dry. Leave adequate room for good air circulation around the bamboo, oak, cherry, walnut or white oak materials. Remember that over-heating hardwood flooring with continual dry heat may dry out the hardwood flooring too much. This could lead to buckled hardwood flooring later on, due to hardwood flooring delivery and installation without proper spacing or acclimation.
JOB SITE CONDITIONS FOR FLOOR CONTRACTORS
It is a best practice to check every job site before delivery of hardwood floor installation materials have been placed in the scene. You want to avoid extended exposure to high humidity or moisture. Ideally, the surface grade or slope of construction of the job site should direct water away from the building. Only use basements and crawl spaces which are dry and well-ventilated. If a joint construction site has no basement, you are required to use outside cross ventilation through vents or other openings in the foundation walls with no dead air areas. To hinder the presence of vapor in crawl space construction at a flooring site, use a surface cover of 6 mil polyethylene film. This type of film can be bought online or at most home and garden stores.
When executing the job, please keep in mind that the building of the job site needs to be closed in. Outside windows and doors should be fixed in place. Before delivering hardwood flooring materials, all concrete, masonry, sheetrock and framing members, etc. should be thoroughly dry, especially in an area like Chicago where temperatures vary greatly depending on the time of year. You will need to carefully control temperatures and ventilation of the job site. In warm months, the building must be well-ventilated; during cold months, heating should be kept near occupancy levels. Do this for at least five days before the flooring is delivered and until dustless floor sanding and hardwood floor finishing are complete.
You may need to delay delivery and installation of flooring to allow any moisture trapped during construction to evaporate. As most professional flooring contractors know, excessive dampness can accumulate in a residence due to materials used to provide energy efficient structures trap moisture. Before delivery of hardwood flooring materials, the average moisture content of framing members and subflooring should be below 12-14 percent. Levels above this can cause aesthetic issues for hardwood floor installation and hardwood floor refinishing.
Once you have confirmed that job site conditions adhere to these standards, the next step would be to deliver the hardwood flooring materials. It is wise to not pile up all the materials in one spot, but to scatter the materials into small groups and to store them in specific rooms where the hardwood floor installation will occur. The next step would be to wait four to five days (sometimes more) for the flooring to acclimate to the job site.
Next, open or remove packaging of any hardwood flooring materials so that they can adjust to the local environment. After delivery, temperature and humidity should be maintained at or near occupancy levels until the hardwood flooring installation takes place. Continue to control the environment even after occupancy in order to avoid elevated moisture conditions. This is important in order to maintain a beautiful finish of your hardwood flooring after installation is complete.
Another tip is to keep hardwood flooring away from excessive heat. You may see cracks appear in hardwood flooring if it’s installed over a heating plant or un-insulated heating ducts and no protection is provided. Adequate protection can be created if you use a double layer of 15 lb. asphalt felt/building paper, or a single layer of 30 lb. asphalt felt/building paper. Another option for your hardwood flooring is to use 1⁄2" standard insulation boards between joists under the flooring in the areas where heat is applied. If the hardwood floor installation happens over a heating plant, the insulation used should be non-flammable. As a flooring contractor, it is your responsibility not only to provide a high-quality product to your customer but also to ensure safety in their home. Wood floor installation is an intricate process. Be sure to consult this guide or call the Technical Department of NOFMA for extra help.
Fig. 1. This represents the plywood-on-slab method for strip hardwood floor installation.
Fig. 2. This illustration represents the Screeds method of installing strip flooring on slab.
HARDWOOD FLOOR INSTALLATION OVER A CONCRETE SLAB
You can successfully install hardwood flooring over a slab which is on-grade or above grade. We do not recommend below-grade hardwood floor installations. Be sure the slab has been constructed properly (check that it is dry and flat with a trowel finish). Keep an eye out for water when you are getting ready to install the wood flooring. New concrete tends to be very full of moisture, which is wood’s worst enemy. The last thing you want to do is ruin a beautiful piece of cherry, maple or white oak wood simply by forgetting to accommodate for moisture in the on-grade concrete slab. Proper on-grade slab construction requires the use of something to hold back vapor. Usually 6 mil polyethylene film is placed between the gravel fill and the slab. This not only prevents moisture from entering through the slab, but the membrane also curing of the slab. Even if the slab has been in place for over two years, test it for dryness. If a slab is younger than 60 days old, it’s probably still too wet for flooring installation. Keep this timeline in mind when you are planning a hardwood floor installation project so your client understands the amount of time it will take to complete installation.
TESTING CONCRETE FOR EXCESSIVE MOISTURE
NOTE: Test both old and new slabs in several areas of each room where the wood flooring is going to be installed. If a test indicates there is too much moisture in a slab, do not proceed with hardwood floor installation. You have several options if a wet slab prevents hardwood flooring installation from proceeding. You can wait until moist slabs dry naturally, or accelerate drying with heat and ventilation and then test the slab again.
Here are several tests you can use to test a slab for moisture.
1. The Rubber Mat Test. Lay a smooth, non-corrugated rubber mat over the slab. Place a weight on top of it to prevent moisture from escaping. Leave the mat in place for 24 hours. If the covered area shows water marks when the mat is removed, the mat is too wet to begin hardwood floor installation.
Note: you should not use this test if the slab surface is not light in color originally because you could detect false water marks.
2. The Polyethylene Film Test. Cut out a one-foot square of 6 mil clear polyethylene film and tape it to the slab, sealing all edges with plastic, moisture resistant tape. After 24 hours, if there is not any visible “clouding” or noticeable drops of moisture on the underside of the film, the slab can be considered dry enough to proceed with the hardwood flooring installation process.
3. The Calcium Chloride Test. Place 1/4 teaspoon dry (anhydrous) Calcium Chloride crystals inside a 3-inch diameter putty ring. Place on the slab. Cover the putty ring with a glass so that the crystals are totally sealed off from the air. You’ll know the slab is still too wet if the crystals dissolve within 12 hours.
4. The Phenolphthalein Test. Create a solution of a 3% Phenolphthalein solution in grain alcohol such as ethanol. Place several drops at various spots on the slab. If a red color develops in a few minutes, there is too much moisture present in the slab. You must wait to begin hardwood flooring installation.
It’s important for every professional flooring contractor to practice and understand these tests in order to ensure hardwood flooring installation that avoids moisture. For your Chicago area wood flooring needs, contact Great Flooring, Inc.
SLAB PREPARATION BEFORE WOOD FLOOR INSTALLATION
Be sure the slab is sound and flat. Grind off any high spots and fill low spots so that the surface is smooth. Remember to clean up grease, oil or any other contaminants, and sweep clean. If the slab feels mealy or gritty, or if its texture is excessively dusty, it may not be of proper strength.
VAPOR RETARDER USE OVER A SLAB
Proper vapor retarders must be used on top of every slab to ensure moisture does not reach the finished floor. It is your responsibility as a flooring company to know which vapor retarders are appropriate for the hardwood flooring job.
Where you place a vapor retarder depends on the type of system used. Check that the vapor retarder has a U.S. perm rating of less than 1 perm. You will often see 6 mil polyethylene film used since it has a 0.04 perm rating which is considered a good choice. The recommended vapor retarders are affixed to the slab with 3⁄4" plywood which is used as a nailing base. These systems can either be a 4-6 mil polyethylene film, 2 membrane asphalt felt/building paper and mastic, or an equivalent system as described below.
Fig. 3. Image of a moisture retarder using two layers of asphalt felt or building paper.
Fig. 4. This illustration shows wood joist construction using square-edge board subfloor.
Two membrane asphalt felt or building paper system.
First, prepare and apply a cold cut-back asphalt mastic with a notched trowel. Be sure to use the rate of 50 sq. ft per gallon. Let the asphalt set and air dry for two hours. Roll out 15 lb. asphalt felt/building paper, with lapping edges of 4". Align the ends. Apply a second layer over the first one of similar coating of mastic and roll out a second layer of asphalt felt/building paper. Lay both layers of felt in the same direction, but stagger the overlaps to achieve a more even thickness.
If the slabs at your installation site are well above grade and the expected annual rainfall is light to moderate (such as in an area like Chicago), cover the entire slab with 4- to 6-mil polyethylene film. Use overlapping edges which measure 4-6" and be sure to allow enough to extend under the baseboard on all sides.Where moisture conditions are considered more severe, prime and apply a cold-type cut-back asphalt mastic with a straight-edge or fine tooth trowel over the entire slab surface (100 sq. ft. per gallon). Allow the surface to dry for about one hour. Lay the 4-6 mil polyethylene film over the slab, covering the entire area and lapping edges 4-6". To ensure proper adhesion of the film, walk or roll on it, stepping on every square inch of the floor. Don’t worry about any small bubbles that appear, since these may be punctured to allow captive air to escape.
This system uses 3⁄4" or thicker sheathing grade exterior plywood as the subfloor over the appropriate vapor retarder. Lay 3⁄4" plywood panels loosely over entire floor. You can prevent cracks associated with panel edges by aying plywood on a diagonal to the direction of the finished floor. Remember to stagger plywood and joints every 4' by cutting the first sheet of every other run in half.
Between panels, leave 1⁄4" to 1⁄2" and leave 3⁄4" space at all wall lines. Cut your plywood to fit within 1⁄8" near and around door jambs and other obstructions where finish trim will not be used. The plywood should be fastened with a powder-actuated concrete nailer or hammer-driven concrete nails. Start at the center of the panel and work toward the edges so you are sure to flatten out the plywood. Use at least nine nails per panel fasten securely. At your discretion, you may want to use more.
Here is an alternate method: start by gluing the 3⁄4" plywood over the vapor retarder systems (this includes the cut-back mastic). Cut the 3⁄4" plywood into 4' x 4' squares or 16” x 8’ planks. Score the back 3⁄8" deep on a 12" x 12" grid, and remember to lay the panels in the cut-back mastic applied with a 1⁄4" x 1⁄4" notched trowel (35 sq. ft. per gal.). Be sure to stagger panel joints by 2 ft.
This system uses a flat, dry 2" x 4" screeds of Group 1 density wood (sometimes called sleepers) of random lengths from 18" to 48" to create a nailing base. The pieces of wood must be treated with a preservative that is suitable for interior hardwood installation. If saturation with water is involved, screeds must be dried to a moisture content of 12 percent or less after this preservative treatment.
Lay out all screeds on their flat face in rivers of mastic. Screed runs should be 12" on center at right angles to the direction of the finished floor. Sweep your slab clean, prime it with anasphalt primer and let it dry completely. Apply hot (poured) or cold (cut-back) asphalt mastic. Then embed the screeds. It’s important to stagger joints and to lap the ends at least 4"as well as leave 1/2" space between lapped edges. Be sure there is enough mastic for complete contact between the screeds and the slab. With a continuous run of screeds at end walls, leave 3⁄4" of space between the ends of the screeds and the walls.
The flooring contractor should lay a 4- to 6-mil polyethylene vapor retarder with edges lapped over the rows of screeds. Avoid bunching or puncturing the polyethylene, especially between screeds. The finished hardwood flooring will be nailed to the screeds through the film.
This system – with screeds spaced 12" on center and a moisture retarder without a subfloor – is satisfactory for all 3⁄4" Strip Flooring and Plank Flooring less than 4" wide. If plank flooring is 4" or wider, it requires either the Plywood-On-Slab subfloor, or screeds plus a wood subfloor, to provide an adequate nailing surface. The subfloor over screeds may be 5⁄8" or thicker plywood, 3⁄4" OSB (performance rated), or 3⁄4" Group 1 dense softwood boards or equivalent no wider than 6". Allow 1⁄2" spacing between boards if the subfloor boards are used over sleepers or screeds.
NOTE: Especially when area moisture conditions are considered high (such as in the Gulf coastal area), glue the vapor retarder directly to the slab system. You can do this in addition to or in substitution for the film draped over screeds. Flooring companies in the Chicago area shouldn’t have to worry about this step.
HARDWOOD FLOORING INSTALLATION OVER WOOD JOIST CONSTRUCTION
You must be sure that outside cross ventilation in the foundation walls is provided through vents or other openings. There should be no dead air areas present. Use a surface cover throughout the entire crawl space of 6 mil polyethylene film in order to retard moisture.
For 3⁄4" thick strip flooring, use either kiln-dried boards of No. 1 or No. 2 Common Pine or other dense, Group 1 softwoods suitable for subfloors over wood joists. Exterior sheathing grade plywood can also be substituted. If you’re using plywood, be sure to find 5⁄8" (19⁄32") or 3⁄4" (23⁄32") performance rated products. Using 3⁄4" (23⁄32") OSB is a comparable alternative. If you are building 1⁄2" thick strip flooring, use a 3⁄4" (23⁄32") subfloor.
Fig. 5. Drawing showing the establishing starter line for nailing the first strip of a hardwood floor.
Subfloor materials should not be thin. For specific information, you can request a summary of subfloor test results. Be sure to follow all panel manufacturer instructions when installing subfloor panels. Unless a manufacturer recommends otherwise, subfloor panels should be installed with grain of faces at right angles to joists and nailed every 6” along each joist. Of course, flooring companies should utilize appropriate nails and appropriate spacing at panel ends and edges.
Use only flat, dry 3⁄4" dressed square edge boards no wider than 6" for board subfloors. Lay them diagonally across the joists, allowing 1⁄4" to 3⁄8" of expansion space between the boards. Also, be sure to avoid using tongue and groove boards. Nail the boards to each bearing point (including blocking) with two 8d common nails. Mitered joints should rest on joists. Mark the locations of joists so that hardwood flooring can be nailed into them accurately.
Good nailing is an essential step of the hardwood flooring installation process. As a top-quality flooring contractor, Great Flooring, Inc. prides itself on a high level of detail and accuracy in this process. Precise nailing keeps the boards rigid, which prevents creeping which is sometimes caused by shrinkage in subfloor lumber. By providing adequate nailing, a flooring company ensures that clients will have solid, non-squeaking floors.
LAYING AND FASTENING THE HARDWOOD FLOORING
Use the following instructions when laying strip flooring on plywood- on-slab, on screeds, and plywood or board subfloors.
(NOTE: Flooring “SHORTS” - 11⁄4' or 2' bundles of flooring strips are “Strip Flooring” and should be installed accordingly.)
We do not recommend gluing shorts directly to slabs.
If you have plywood or board subfloors, start by re-nailing any loose areas and sweeping the subfloor clean. Mark the locations of joists on perimeter walls. This will ensure that the starting runs and finishing runs, which require face nailing, can be nailed into joists. Next, cover the subfloor with a good grade of 15 lb. asphalt felt/building paper, with 2"-4" lapped by the edge seams. Doing this will help keep out dust, limit moisture movement from below, and prevent squeaks in the wood flooring during dry seasons.
Direction of Finished Flooring
As shown in figure 4, finished hardwood flooring should be at directed right angles to the joists. Generally finish flooring is used for the longest dimension of the room or building, giving it the best appearance. Begin hardwood flooring installation along the longest continuous wall that is parallel to the flooring direction of most rooms. An example of this is hardwood flooring used down a long hallway wall. You will want to work from the longest continuous wall into the room where you are completing the hardwood floor installation. Use a slip-tongue to reverse direction and complete the rooms. Glue and blind, then nail the slip tongue. Wherever any change of direction occurs, always provide tongue and groove engagement either with a slip tongue or factory edge or end.
Starting to lay the hardwood floor.
Two of the most important factors when you start to install a hardwood floor are location and straight alignment of the first course of flooring materials. These can mean the difference between a straight and smooth cherry hardwood floor that your friends and neighbors will talk about for years, versus and a crooked, dejected white oak hardwood floor which your customer will regret installing.
To start a quality hardwood floor installation, place a mark 3⁄4" plus the width of flooring (3" for 2 1⁄4" flooring) on the end wall near a corner of starting wall. See figure 5 for an illustration of this step. Place a similar mark at the opposite corner of the hardwood floor and insert nails into each mark. Pull a line of string between the nails, pulling it taut. With the leading edge along this line, nail the first strip carefully.
Fig. 6. Demonstration of how to use the power nailer for installation of strip flooring.
Fig. 7. This illustration shows how to countersink screws in plank flooring, and then cover them with plugs.
The gap between that strip and the wall is needed to allow expansion space. It will be hidden by the shoe mold (Fig. 1) so that the appearance is still aesthetically appealing. If you’re working with screeds on slabs, make the same measurements and stretch a line between the nails. After you get the starter board in place, remove the line. With its tongue facing outward, lay the first strip along the starting string line. Next, drive 6d or 8d flooring nails or casing nails 1” from the grooved edge. Generally galvanized or screw shank nails hold best. Nails should be driven into the top surface of the strips and then counter sunk (face nailing). Position each nail over a supporting joist, and near the end of a strip or into each screed crossed. Remember to keep the starter strip aligned with the string line. (You can pre-drill nail holes tp prevent splits.) According to the nailing schedule, blind the nail starting strip through the tongue.
Rack the hardwood flooring.
Lay out seven or eight rows of hardwood flooring end to end in a staggered pattern with the end joints at least 6" apart. Find pieces which fit within 1⁄2" of the end wall; if needed, you can cut some. Carefully watch your pattern for even distribution of long and short pieces and to avoid clusters of short boards (see figure 6 for details on this).
Nailing the hardwood flooring.
The face nails should be cut to slightly less than 1.5" for plywood on-slab construction. Once the starter run is complete, fit each run of successive strips snugly, placing them groove-to-tongue. According to the schedule shown in the table, proceed with blinding each nail through the tongue along the length of the strip. Countersink all of the nails. Once the second or third run is firmly in place, you can change from a hammer to a floor nailing machine. This type of machine drives nails mechanically or pneumatically, and does not require additional countersinking. Various floor nailing machines use either a barbed cleat or staples which are fed into the machine in clips. The nailing machine drives fasteners through the tongue of the hardwood flooring at the proper angle.
Be sure to use a 1.5" cleat when using the floor nailing machine to fasten 3⁄4" thick strip or plank flooring to plywood laid on a slab. Avoid the usual 2" cleat which may come out the back of the plywood and prevent nails from countersinking properly and which could tear the vapor retarder. For all other applications, the 2" cleat is preferable. Continue installing across the room, ending up on the far wall with the same 3⁄4" expansion space as you used for the beginning wall.
Keep in mind you may also need to rip a strip to fit. Do not nail into subfloor joints. Position the flooring strips so that they do not meet over subfloor joints. In spots where the nailing machine can’t be used, you will need to blind nail by hand. Face nail the last runs when you are unable to blind nail by hand. With 2.25" strip face-nailing is required the last two or three runs and in a ripped piece of a strip if one has been used. To tighten these last face nailed runs all at once before face-nailing, use an offset pry bar or lever device.
Nailing the hardwood flooring to screeds.
If you are nailing directly to screeds (no solid subfloor), be sure to nail at all screed intersections and to both screeds where a strip passes over a lapped screed joint. Since flooring ends are tongue and grooved, all end joints do not need to meet over screeds. However, keep in mind that end joints of adjacent rows should not break over the same void between screeds. You’ll find that some boards may not be straight. You can use a large screwdriver, sharpened pry bar, or wedges to force such boards into position or pull two or three runs together.
Shoe molding for the hardwood flooring.
After the entire floor is in place, nail shoe molding to the baseboard, not the hardwood flooring.
NOTE: With wide planks over 4", use extra care. Since units tend to move more with changing conditions, proper acclimation before and after installation is especially critical. Here’s an additional tip: sealing the back surface may help prevent some cupping normally associated with wider widths after acclimation and before installation as well. By learning techniques like this, Chicago-based flooring company Great Flooring, Inc. has become a trusted hardwood floor installation business in the area.
Plank flooring is normally made in 3" to 8" widths. It may involve using countersunk holes filled with wood plugs for securing planks with wood screws. Random width plank flooring is installed in the same manner as strip flooring, whereby you alternate courses by widths.
Start with widest boards, then move down to smaller ones, repeating the pattern. Follow manufacturers’ instructions for fastening the flooring. The most common practice is to blind nail through the tongue as with conventional strip flooring.
Afterward, you should countersink one or more drywall screws, flat head screws, or No. 7 - No. 9 Phillips head screws at each end of each plank. Place the screws at intervals along the plank to hold them securely, and then cover them with wood plugs glued into the holes.
Be careful not to use too many screws because once the plugs are in place, this will tend to give the flooring a polka-dotted appearance. Also, use care to select screws at the appropriate length. Use 1" if the flooring is laid over 3⁄4" plywood on a slab. Use 1" to 1.25" in wood joist construction or over screeds.
Your manufacturer may recommend face nailing in addition to other fastenings, or else leaving a slight expansion crack, about the thickness of a putty knife, between planks. Check your specific manufacturer installation instructions for details.
LAYING A NEW STRIP FLOOR OVER AN OLD HARDWOOD FLOOR
An existing hardwood floor can serve as a subfloor. This changes the hardwood floor installation process a bit, but not by much. To start, drive down any raised nails, re-nail any boards that are loose and replace any warped boards that can’t be made level. Sweep and clean the hardwood floor carefully, but don’t clean it with water.
Remove thresholds to allow the new hardwood flooring to run flush through doorways. You’ll also want to remove doors and baseboards. Lay asphalt felt or building paper over top of the old floor. Do not install the new hardwood flooring over the old floor in the same direction. Install boards at a right angle or on a diagonal. If your client prefers the direction of the wood to be in the same direction as the old floor, you’ll have to overlay the old floor with 3/8” to 1/2” plywood.
PARQUET, BLOCK, HERRINGBONE AND SIMILAR FLOORING
You cannot treat cherry flooring the same as maple flooring or oak flooring. In the same way that unique woods call for different care of the materials, these unique styles of flooring have different recommended procedures for application. Block and parquet flooring procedures should be confirmed with a manufacturer before you start. Detailed installation instructions are usually provided with the flooring, or you can get a copy of them from the manufacturer or distributor.
Important note: this section of the guide applies only to 3⁄4" tongue-and-groove parquet flooring where tongues and grooves are engaged. It does not apply to slat-type or fingerblock parquet hardwood flooring.
Start by laying both the blocks and the individual pieces of parquetry in mastic over a double layered wood subfloor or a concrete slab with a moisture retarder. Use a cold, cut-back asphalt mastic spread at the rate of 35-40 sq. ft. per gallon. Spread using the notched edge of the trowel. Allow the asphalt to firm (or “flash off”) overnight or as directed by the manufacturer. After 12 hours, the surface should be solid enough to allow you to snap working lines on it. Use blocks of the hardwood flooring as stepping stones to snap these lines and you will be ready to begin the hardwood flooring installation.
Remember, there are two ways to lay out parquet. The most common way is to align the edges of parquet units (and thus the lines they form) squarely with the walls of the room. The other way involves creating a diagonal pattern, with lines at a 45-degree angle to walls.
Making a square pattern for hardwood flooring
You should never use the walls as a starting line for laying your hardwood flooring because walls are almost never truly straight. Smart flooring contractors should know this based on experience completing hardwood floor installation!
Instead of aligning to the walls, a chalk line works better. To begin, snap a starting line about 3 ft. or so from the handiest entry door to the room, roughly parallel to the nearest wall. Place this line exactly equal to four or five of the parquet units from the center of the entry doorway. Next, find the center point of this base line, and snap another line at an exact 90-degree angle to it from wall to wall. From here on, you will use this as a test line to help keep your pattern straight as the installation proceeds. A quick test to ensure the design is square involves measuring four feet along one line from where they intersect, and three feet along the other. The distance between these two points will be five feet if the lines are true (see figure 8 to explain this).
Diagonal pattern on hardwood flooring.
To set up a diagonal pattern, measure equal distances from one corner of a room, along both walls, and snap a chalk line between these two points. This forms the base line. (This pattern need not be at a precise 45-degree angle to walls in order to appear perfect.) A test line should again intersect the center of the base line at an exact 90-degree angle (see figure 10 for details).
Fig. 8. This diagram shows the working lines for laying block in a square pattern for your hardwood flooring.
Fig. 9. This diagram shows use of cork blocking around edges of a block floor.
Fig. 10. Here is a diagram of working lines for laying block in a diagonal pattern.
Special patterns for hardwood flooring installation.
Most of the time, you can lay out two working lines to work on existing parquet patterns. Herringbone requires two test lines, and one will be at 90-degrees. The other crosses the same intersection of lines, but at a 45-degree angle to both of them. Intricate and breathtaking wood flooring requires careful preliminary layout preparation. Taking the time to complete this alignment of each piece of wood will ensure a smooth hardwood floor installation and will help you build a reputation as a remarkable hardwood flooring installer.
Keep in mind that you will always have to accommodate small variations in size of wood pieces as the hardwood floor installation takes place, since each piece of wood is naturally unique. Be careful to keep the overall pattern squared up. Once a “creeping” pattern has begun to develop, it is very hard (if not impossible) to correct. The more carefully you lay out a floor before beginning hardwood floor installation, the less problems there will be during field work. Wood parquet must always be installed in a pyramid, or stair-step sequence. Avoid using rows during parquet hardwood floor installation. Again, this prevents small inaccuracies of size consistency in the wood pieces from being obvious; as “creeping” occurs, the size differences become magnified and give an even worse appearance of misalignment.
Process for parquet wood flooring.
Start by placing the first parquet unit where the base and test lines intersect. Then lay the next units ahead and to the right of the first one, using the lines as a guide. Continue the stair step sequence, keeping a close eye on the corner alignment of new units with those that are already in place. Work in this manner until you have installed a quadrant of the room, leaving trimming at the walls for later. Then return to the base and test lines and lay another quadrant, repeating the stair-step sequence. Install the last quadrant from the base line to the door, keeping in mind that you may need to use a reducer strip at the doorway. If your flooring company has hired expert floor contractors, you will be left with a finished product that you and your client are both very proud of.
Don’t forget that tiles for most hardwood floor mastics can still slip or skid if sideways pressure is applied even after some open time has gone by. You can avoid the potential threat of this sideways pressure by working from “knee boards” or plywood panels laid on top of the installed area of hardwood flooring.
Additionally, do not place any heavy furniture or allow any foot traffic over the finished parquet wood flooring for at least 24 hours. You don’t want slipping or skidding of the boards to occur. Keep in mind that some mastics also require rolling over the flooring after installation, and you’ll want to be sure you know whether yours requires this step or not. If so, cut blocks or parquetry pieces to fit at each of the walls, allowing 3⁄4" expansion space on all sides. Use cork blocking in 3" lengths between the wood flooring edge and the wall so you allow for the wood flooring to expand and contract. If you are using blocks, we recommend also using a diagonal pattern in corridors and in rooms where the length is more than 1.5 times the width. This diagonal placement minimizes expansion under high humidity conditions, such as the Chicago area in summertime.
SPECIAL CONSTRUCTION SITUATIONS FOR FLOORING COMPANIES
Hardwood flooring over a radiant heated concrete slab.
Hardwood flooring insulates heat and may require higher water temperatures for a radiant heat system. Keep an outside thermometer on the job site where your flooring contractors are working so that you can monitor rapid temperature changes.
The temperature of a home’s boiler water should not exceed 125 degrees. This will keep a concrete slab from reaching any temperature over 85 degrees, which is an acceptable level for most mastics. The wood flooring should be installed using the same process as any other slab project, except plywood should not be fastened to concrete with nails or powder-actuated fasteners.
Four to five days prior to delivering your materials for the hardwood floor installation, turn on the heating system at the job site. This heat will remove any extra or excess moisture so that the slab is ready to use.
Note: It is also essential to check hardwood flooring and mastic manufacturers’ specifications for suitability of use over radiant heat. Some cannot be used in a heavy heat environment.
Strip wood flooring in a wood plenum system.
When constructing a wood floor using this method, the hardwood flooring installer utilizes a crawl space which is completely sealed off from the outside as a plenum to which air from the heating/cooling system is supplied. Warm air can then enter each room through floor registers, so a ground cover of polyethylene film must be used. You also need to operate the heating system for 4-5 days prior to delivering hardwood flooring materials to the job site. This will stabilize the moisture in the location and help acclimate the materials to the environment. In all other respects, you’ll proceed with the hardwood flooring installation as you would in any other case. Your flooring contractors can refer to the previously stated recommendations, procedures, and time tables.
Hardwood flooring expanses measuring 20 feet and wider.
You should consider alternative hardwood flooring installation techniques when working in large rooms. You may also want to consider these options when working across diagonals and/or where hardwood flooring runs through doorways to produce an expanse over 20’ wide. Start with a line-out near the center of the space. For example, you would set up a line across the center of the room with diagonal installation or start near the center line of the total expanse of the room. Next, the flooring company should insert and glue a slip tongue in the starter strip groove, and proceed with the hardwood flooring installation in the two opposite directions. Remember to include field expansion spaces in the wide expanse.
TIPS FOR EASIER AND SMOOTHER HARDWOOD FLOORING INSTALLATIONS
“In-use” Moisture Content.
You may experience problems such as cupping with a hardwood floor installation. This is likely to happen if there is a difference of 4 percent or higher between the expected in-use average moisture content of the hardwood flooring materials and the in-use average moisture content of the under-floor construction. All hardwood flooring contractors should be careful to take these measurements accurately at the start of a hardwood flooring installation project. The greater the difference between these two measurements, the more severe and visually significant the problems will be. Cupping is a problem that could easily ruin an otherwise-beautiful mahogany, oak or walnut floor, so don’t let this ruin your flooring company’s reputation. Remember: finishing should proceed only after one to three weeks has passed since the hardwood floor was installed. If you wait longer, job site conditions can result in more problems. You don’t want a floor to sit exposed to the elements for too long. However, if you complete hardwood finishing immediately after installation, the wood flooring will not have had enough time to adjust to its new environment. You must balance between the risk of exposure and the need for wood to adapt to its surrounding. This balance is something learned only by an advanced, expert hardwood flooring company.
Work from left to right during the hardwood flooring installation.
You’ll find that it’s easier to work in the same order you’re used to reading in – left to right – when laying down wood flooring in strips. The left measurement is established when you have your back to the wall where the starting course has been laid. If you find you must cut a strip to fit to the right wall, use a strip long enough so that the cut-off piece is 8" or longer and start the next course on the left wall with this piece.
Utilize both long and short pieces to create an elegant look for hardwood flooring.
Always use long flooring strips at entrances and doorways in order to achieve the best appearance possible. Incorporate as many short pieces as possible at random in the floor, however. If you group them in one area, this will not look good. Consult with the most experienced floor contractor from your flooring company in order to find the best design possible.
Put a “frame” around obstructions in the hardwood flooring.
If you “frame” hearths and other obstructions, using mitered joints at the corners, you can produce a much more professional and finished look to a strip flooring installation. Ask other members of your flooring company for photographs of this style of hardwood flooring if you have not seen it before.
How to reverse direction of strip flooring.
You may find it’s necessary to reverse the direction of the flooring to extend it into a closet or hallway for your hardwood flooring installation. To reverse the direction, join groove edge to groove edge, using a slip tongue available from flooring distributors. Glue the slip tongue in place, then blind nail along that edge. Proceed in the opposite direction, continuing to nail in the conventional manner.
Use only sound, straight boards for subfloors.
The final quality of the finished hardwood flooring is determined by the subflooring. Use only square edge 3⁄4" dressed boards no wider than 6" and remember, boards which have been used for concrete form work should often be cast out. Generally these boards, regardless of their type (oak, cherry, bamboo, walnut) are warped and damp.
Don’t pour concrete after hardwood flooring is installed.
It is a common misconception that it’s a good idea to pour a concrete basement floor after a hardwood flooring installation is complete. However, by doing this, a flooring company introduces many gallons of evaporating water from the drying concrete into the air of the house. This moisture may be absorbed by the hardwood flooring and you don’t want it to soak into the wood elements. This building practice is not recommended. You will allow excessive moisture into the vicinity of your beautiful hardwood flooring and you can damage woodwork to the point of irreparability. Hardwood flooring installation should wait until all concrete and plaster work is complete and dry.
Keep an eye out for doorways, stair treads, and high traffic areas within the hardwood floor.
Always use slip tongues or engage the flooring end matching into groove side of flooring if the hardwood flooring direction changes. This will prevent movement or misalignment of the boards to and give a solid transition in the wood flooring.
Utilize voids between screeds, or avoid them.
To give additional protection from moisture and to deaden the drumming sound that sometimes occurs from foot traffic on hardwood flooring, masonry insulation fill, normally used in hollow concrete blocks, can be poured between the screeds of a slab installation. Work with your flooring company’s contractors to determine the best masonry insulation to use.
Multi-story building installations may require sound deadening.
You can reduce noise transmission from an upper to a lower floor by nailing the subfloor to the joists in the normal manner and then covering this with 1⁄2" or thicker cork or insulation board laid in mastic. Next, cover this layer with another 3⁄4" plywood subfloor also laid in mastic. Nail the finish strip or plank floor to the plywood, or lay block or parquetry floors in mastic on the plywood. In the case of parquet, you can use the 1⁄2" tongue and grooved type for the second subfloor plywood. Note that specifications for some high-rise apartment buildings in large cities call for other types of sound-deadening construction. A highly-populated area such as Chicago may require that you build according to other specific rules and regulations. Be sure your flooring company educates your flooring contractors on these specifications prior to planning hardwood floor installation at any job site.
Mastics and trowels.
Several types of mastics are available for use in laying hardwood floors. Generally you’ll only use hot asphaltfor laying screeds on concrete. In these cases, the screeds must be positioned immediately on pouring the mastic because it dries quickly. Cutback asphalt, chlorinated solvent and petroleum-based solvent mastics, on the other hand, are all applied cold and are used for laying tongue and grooved block and parquet floors. Cut back asphalt mastic can be used to hold a vapor retarder and/or to glue a plywood subfloor to the slab. Check the specific manufacturers’ instructions on coverage, drying time and ventilation to ensure a successful hardwood floor installation. Usually, trowels have both straight and notched edges which are used in different circumstances. The notched edge comes in handy when a correct mastic thickness is specified. Flooring manufacturers and distributors may both sell mastic and trowels. Check with your flooring company to see if there is a preferred type for most of your hardwood floor installation clients.
Different Manufacturers Products.
Avoid randomly mixing different manufacturers’ products. Transition areas such as doorways offer a convenient way to separate hardwood flooring products bought from different manufacturers.
STRIP FLOORING ON WALLS AND CEILINGS
Because of its beauty and decorative quality, strip wood flooring is being used more and more often for interior wall and ceiling applications. Not only can majestic oak, white oak, walnut, cherry, bamboo and Brasilian wood be used to create hardwood floors, but these materials can also produce incredible wall and ceiling designs. Storage and handling practices for walls and ceilings are the same as those for any regular hardwood flooring installation. Remember to observe precautions concerning moisture conditions to avoid ruining hardwood materials. In particular, the job site should be closed in with all doors and windows in place and all concrete, masonry and plaster thoroughly dry. Install a vapor retarder within the wall system on exterior walls, checking with an HVAC engineer to ensure proper placement. The flooring can be nailed direct to the studs for a horizontal application.
For vertical or diagonal application to a stud wall, nail 1.5" thick furring strips (2 x 4s) to the studs at 12" spacing and nail the hardwood flooring to these strips. For masonry walls, fasten lengths of 2 x 4s on 12" centers to the walls with concrete fasteners designed for the expected load. Nail size and schedule are the same as for flooring applications.
INSTALLATION OF GYMNASIUM HARDWOOD FLOORING OVER A CONCRETE SLAB
Gymnasium hardwood flooring offered by NOFMA mills are most often made of 3⁄4" oak, pecan or maple. Occasionally, NOFMA mills make 25⁄32" maple. Beech and birch are also utilized. It is most important to have some resiliency built into these floors, but in most respects hardwood flooring installation closely follows the screeds-in-mastic method recommended for conventional use, with a plywood or board subfloor installed over the screeds.
Also, two layers of 1/2” plywood cushioned and laid on a 45-degree angle to each other may be used as a subfloor. Well in advance of beginning the hardwood floor installation, allow all of the floor materials to acclimate to the established environment. Regardless of the wood type, whether you are using oak, pecan, maple, beech or birch, the wood will need to settle in to its new surroundings and adapt to any moisture or temperature changes.
Check that the slab is dry, level, and that it has been maintained with a good float finish. For best results on your hardwood flooring, don’t allow surface variations greater than 1⁄4" in 10'. If necessary, you can fill low areas with concrete leveling compound and grind down high areas to create a smooth surface. Sweep the slab so it is pristine; then, prime it using asphalt primer.
Allow this to dry completely before you coat it with asphalt mastic, using a notched trowel designed to apply at a rate of 50 sq. ft. per gallon. Embed a layer of 15 lb. asphalt felt or building paper, starting at a wall with a half sheet. Lap the seams. Cover this with another layer of mastic and embed a second layer of asphalt felt or building paper, starting at the same wall with a full sheet to cover the seams of the first layer. Both hot or cold mastics can be used. If the cold type is used be sure to allow time (at least two hours) for solvents to evaporate before applying the building paper.
Fig. 11. Here is a diagram of working lines for laying block in a diagonal pattern.
Alternately, you could embed a 4 to 6 mil polyethylene film inside a cold mastic to create a surface vapor retarder. Be careful to lap the film edges at 6". No surface vapor retarder is needed for a suspended concrete slab with a controlled environment, but a suspended slab over exposed earth or an uncontrolled environment requires a proper vapor retarder over the slab. In this case cross ventilation below the slab is essential so that no excess moisture can creep in. If the slab lies over exposed earth, a ground covering of 6 mil polyethylene should be used.
Screeds used and their application are identical to that previously described, but be sure to note these exceptions. Place them on 12" centers, (9" centers with 3rd grade flooring) unless a subfloor is to be used, then 16" centers are allowed. Leave 2" of space between the ends of the screeds and the base plate on all walls to allow for expansion. The strip wood flooring may be nailed directly to properly spaced screeds, but a much more sound and satisfactory hardwood floor can be achieved by installing a subfloor of 3⁄4" minimum plywood or 3⁄4" dressed square-edged boards no wider than 6". Follow arrangement and nailing schedules described previously. If boards are used, leave 1⁄2" space between them.
Start laying the finish flooring in the middle of the room and work toward the walls. Engage the first two courses groove-to-groove with a slip tongue glued into one groove. Join the strips and face nail as well as blind nail both courses. Proceed with succeeding courses in the conventional manner, using either 7d or 8d flooring nails, 2" flooring cleats or 2" 15 gauge staples with 1⁄2" crown. After an area 3' or 4' wide has been laid across the room, leave a 1⁄16" expansion space between the last course laid and the next course. Repeat this expansion space evenly at 3' to 4' intervals across the room. Different area environmental conditions may require more or less field expansion. Nailing is most important. Nail to all screeds and to both screeds when a strip passes over a lapped screed joint. All end joints do not need to meet over screeds but adjacent strips should not break over the same screed space.
For hardwood installation where a subfloor is used, keep nails no more than 10" to 12" apart with a minimum of two nails per board near the ends (1"-3") along the length of strips. Along all walls and at doorways, allow 2" of expansion space. This can be covered at the walls with an angle iron bolted to the wall or a special wood molding, and at doorways by a metal plate designed for such use. After hardwood flooring installation and through the dustless sanding and hardwood floor finishing process, the interior environment should be maintained near to an occupied condition. Extended times with no HVAC in operation should be avoided. This can promote a static “green house” effect. These conditions can allow an abnormal increase in moisture which may adversely affect flooring.
If problems occur during hardwood flooring installation, contact the distributor immediately. If problems arise before hardwood flooring installation or you have questions, call the NOFMA office 901/526-5016 between 8:30 a.m. - 4:30 p.m. Central Time.