Screeds (also known as sleepers) are dimensional lumber boards that are laid over, or embedded in, a substrate. They are laid perpendicular to the finished floor, either laid on-end or laid flat-side-down, providing a nailing surface for the wood flooring.
The tar and screeds installation method is very unique, and regional in where it is implemented. This installation method is most common in the Gulf Coast states, specifically from Houston, Texas, over to the Baton Rouge and New Orleans areas in Louisiana.
The hot tar adhesive and screed method of hardwood floor installation became popular in 1945 when builders started building homes on- and below-grade with concrete slab foundations after World War II. The high moisture levels in these areas needed a system that would stop the ground moisture from getting into the home.
Over the years, we have discovered many advantages of using hot tar adhesive for hardwood floor installation. It provides a permanent bond to concrete, it has excellent waterproofing qualities protecting against vapor intrusion, it absorbs noise for sound control, and it remains flexible, allowing the flooring to expand and contract during seasonal humidity changes. Another big advantage to this system is that the tar and screed installation method for hardwood floors has a proven track record.
Hot tar and screed installation is easy and safe when installed by installers who have been trained properly. The hot tar used in this installation method is a blend of selected asphaltic materials that contain non-chlorinated solvents, specifically designed for this application (not roofing tar), and manufactured in Houston, Texas. The NWFA Wood Flooring Installation Guidelines also acknowledge the use of any elastomeric wood flooring adhesive in place of hot tar, but for the purposes of writing about what we’re accustomed to in the Houston area, I will be referring only to hot tar.
The application of the hot tar adhesive requires surfaces to be clean and dry. The tar should be heated in an open and well-ventilated area until it turns to a liquid (approximately 325-360°F/163-177°C). This hot tar then is poured onto the slab and spread out at an approximate coverage rate of 20 square feet per gallon using a notched rake or squeegee with teeth approximately 1” wide and ¼” apart.
The screeds should be clean, straight, and dry. Screed material laid flat typically is 2” x 4” or 1” x 4” lumber made of pine, Douglas fir, high-performance 23/32 OSB or plywood ripped to 3 ½” widths. Screeds must be kiln-dried. If using pressure-treated material, only use material that has been kiln-dried after treatment (KDAT). The screed material should be conditioned to the expected in-use conditions and should coincide with the temperature and humidity (EMC) requirements of the flooring being installed over them. The screeds should be cut to approximately 24” lengths and laid flat 15 to 20 minutes after applying the hot tar.
The screed material should be laid at a 90° angle to the flooring. Screeds should be parallel to each other, and joints should be staggered, which is easily accomplished by alternating full and half pieces on the starter wall. Screeds/sleepers and subfloor must have a minimum 3/4” expansion space at all vertical obstructions.
The moisture content of any screed/sleeper material should be no more than 2 percent MC difference from plank flooring (greater than 3” widths) and no more than 4 percent difference from strip flooring (3″ or less widths). Check the moisture of the screeds/sleepers with a wood moisture meter set to the appropriate species setting for the wood being tested.
The tar and screeds installation method is most common in the Gulf Coast States.
Photos courtesy of NWFA
Check the screeds for flatness by using an 8’ – 10’ straight edge. All screeds should come into contact with the straight edge. Sand or plane the high areas of the screeds/sleepers to achieve flatness tolerance where the straight edge comes into full contact with all screeds/sleepers. Replace low screeds/sleepers or shim the low areas of the screed/sleepers with a shimming material that will not affect the penetration of the flooring fastener into
the screed/sleeper.
Only 3/4” solid or engineered tongue-and-groove material may be installed directly to screeds. Installing ¾” flooring up to 3 ¼” width screeds should be placed an average of 3 ½” apart, to provide approximately 50 percent coverage of the subfloor. Installing ¾” flooring greater than 3 ¼” up to 5” in width screeds should be placed an average 1” apart to provide approximately 90 percent coverage of the subfloor. We call this 90 percent coverage a solid screed installation. Only use floorboard lengths that span two or more screed/sleepers.
Wide plank flooring greater than 5” widths should not be installed directly over screeds/sleepers. Wide plank flooring will require a minimum 23/32” wood panel subfloor to be installed over the screeds/sleepers.
“Why is the hot tar and screed system only popular in the Houston area…I guess it’s just a regional thing.”
The hot tar and screed method of hardwood floor installation is almost exclusively used in the Houston and surrounding areas of southern Texas and southern Louisiana. Our extremely humid climates and high groundwater table makes this system very effective.
We installed a white oak floor using the hot tar and screed/sleeper system for a friend of mine in San Antonio, Texas, which is about 200 miles from Houston. His builder, architect, and designer had no idea what we were doing, as they have never seen this system before. After we completed the project, they asked, “Why is the hot tar and screed system only popular in the Houston area?” My answer was, “I don’t know!” There is really no reason why the hot tar and screed system couldn’t be used over concrete slabs in many regions of the country; I guess it’s just a regional thing.
Gary Zak is the owner of All Brite Floors Inc. in Houston, Texas. He began in the wood flooring industry in 1973 and started All Brite Floors in 1990. He also is an NWFA Certified Hardwood Flooring Inspector. He can be reached a gzak@allbritefloors.com or 713.461.7060.