Subfloors and Finishes

Subfloor Types and Basic Installation Considerations

There are many different types of subfloors over which wood flooring can be installed. There are certain basic attributes that are critical for successful wood flooring installations done over all types of subfloors. The subfloors must be dry and will remain dry year round. The moisture content of wood subfloors must not exceed 12%, wood flooring moisture content must be within 3% of wood subfloor moisture content and concrete must not exceed 3 lbs. per a calcium chloride test, or 2 lbs. when installing over radiant heat. The subfloor material must be structurally sound. It also needs to be clean, thoroughly swept and free of all debris. For glue down installations, the subfloor must be free of wax, grease, paint, sealers, old adhesives, etc., which can be removed by sanding. Additionally the subfloor must be level or flat to 3/16” per 10-foot radius.
Wood Subfloors

Nail down installations are most common over wood subfloors, but glue down and floating installations are also possible. Wood subfloors must be well secured, by using a nail or screw every 6” along the joist to avoid squeaking. If the subfloor is not level, sand down high spots and fill low spots with a polymer-modified cementitious leveling compound such as Chemrex Self Leveling Underlayment from BASF. CDX plywood must be at least 5/8” thick for joist spacing up to 16” on center and a minimum of 3/4” thick for joist spacing greater than 16” on center (19.2” maximum). OSB should be at least 3/4” thick. Underlayment grade particleboard can only be used with the glue down method. If using an existing wood floor it must be smooth, level, well adhered and unfinished (if gluing down new flooring).
Concrete Subfloors

Concrete must be fully cured, at least 60 days old, and should have a minimum of 6-mil poly-film between the concrete and the ground. If it is necessary, grind high spots down and level low spots with a polymer-modified cementitious leveling compound or Ardex K-15 Leveling Compound. If gluing down onto concrete which is on or below grade, it is recommended to install sheet vinyl first and then glue the wood flooring on top of the vinyl, as this provides an effective permanent moisture barrier. An alternative to sheet vinyl is to use a concrete sealer approved by the manufacturer of the adhesive that you have chosen. If using EcoTimber HealthyBond Adhesive, the approved concrete sealer is Taylor Nu-Flor 500, which EcoTimber distributes. A concrete slab on/below grade that measures dry today may become moist tomorrow due to rising groundwater. Installing a moisture barrier may be viewed as an insurance policy against concrete becoming wet in the future, which can lead to subsequent floor failure.
Other Subfloors

Gypcrete can be used in floating installations only. Gypcrete, otherwise known as lightweight concrete, is not strong enough to hold together when a wood floor that is glued to it expands and contracts. If the flooring planks buckle and lift, they may pull pieces of gypcrete up with them.

Resilient tile and vinyl tile subfloors can be used with glue down or floating installations. Vinyl must be new and non-urethane coated. Ceramic tile, resilient tile and sheet vinyl must be well bonded to the subfloor, in good condition, clean and level. Do not try to sand existing vinyl floors, as they may contain asbestos, which are harmful to your health.
Installing Over Radiant Heat Subfloors

When installing over radiant heat subfloors it is good to know the facts. Most flooring is not warranted for installation over electric radiant heat systems, as these can heat up too quickly and damage the wood. However, many eco-friendly flooring products can be installed over radiant heat and arewarranted for such use by their manufacturers. It is important to check with the manufacturer because not all products are warranted for such use, and typically only hydronic (hot water) systems are approved. For many warranties, the system must be able to control the surface temperature of the subfloor so that it never exceeds 82°F. Also, it is essential that the subfloor be maintained at within 15°F of its normal operating temperature at all times.

Radiant heat systems keep the wood flooring very dry, so if the system is turned completely off (for example, during hot summer months), the flooring will absorb moisture. When the system is turned back on again it will dry the wood very quickly, which is the most common cause of damage. After the system has been off or not functioning, the floor should be brought back up to normal operating temperature very slowly, over the course of several days.
Eco Friendly Flooring Finishes: Factory Applied & Site Applied

Floor finishes can be applied prior to installation by the manufacturer of the flooring or on site by the floor installer. Each process has advantages and disadvantages:

The following are several advantages to having a factory finish. The factory finish is applied in a controlled environment with no air-borne dust or other impurities. Sub coats containing special additives like aluminum oxide can be added which will greatly increase the wear-resistance of the finish. Extra coats can be easily added by rollers, 9 coats of finish is not uncommon for a factory finish, while 2 to 3 coats is typical for a site applied finish. The finish tends to be much more durable than the best available site applied finishes (about twice as durable is a good rule of thumb). Shorter installation times and labor means a much lower overall installed cost. Factories apply finishes for much less than contractors. Improved indoor air quality - factory finishes are cured by ultraviolet rays in the factory and are completely inert by the time they are put in the box. There is no off gassing of solvents, VOCs, or other harmful chemicals.

There are also disadvantages of a UV-Cured factory finish. The seams between the planks are not sealed, potentially allowing spilled liquids to leak down and damage the wood. Also, the seams may require top coating to seal seams in areas where frequent spills are expected (restaurants, bathrooms, etc.). The end-user cannot change the wood’s color with stains without sanding off the factory finish.

The advantages of a site applied finish consist of creating a smooth, sealed surface over the entire floor. It allows the installer to customize colors with stains, bleaches and dyes. It also allows the installer to select gloss level and permits the use of spot-repairable oil finishes.

There are also disadvantages of a site applied finish. The wood must be sanded prior to coating, resulting in dust, longer installation times and substantially higher labor costs. The end user must wait for finish to dry completely, meaning they are forced out of their home for longer periods of time. Site applied finishes contain solvents and other drying agents that off-gas harmful chemicals into the air for days, weeks or even months after installation (depending on the type of finish). Even “natural” plant-based oil finishes off-gas harmful chemicals. Some “natural” oils have higher VOC contents than urethane finishes. Contractors often make errors that result in finish bubbles, applicator marks, sanding marks, dust in the finish, and poor adhesion. Expensive and highly inconvenient mistakes are common. The long-term durability is much lower than with factory applied finishes.