It’s important to understand each step involved in preparing a substrate. Should one step be overlooked, it could compromise the entire floor installation.


When the floor is properly treated and leveled, installation of wood flooring is much easier and a more successful process.
"Before application of adhesives, always check the subfloor for surface contaminants! All subfloors must be smooth, dry, clean, flat and free of dirt, grease, wax, old adhesives, paint oil, or anything that would hinder a good physical bond."



A good physical bond can only be achieved with an adhesive once the subfloor has been prepared properly.
After being in the flooring business for more than thirty years, I am still amazed by installers who ignore these notices, similar to the one above, on adhesives and substrate coatings. You cannot underestimate the importance of proper floor preparation. I teach and I preach that correct and complete subfloor preparation is the most important part of any glue-down wood flooring installation. Yet, over the years I have heard many excuses for not correctly prepping a substrate and none make the least bit of sense to me. The most common excuses are, "I do not have the time," or "They are not paying me enough to do floor prep." I often wonder where they find the time and/or money, for expensive wood floor covering repairs and replacements. What wood flooring installers need to realize is that more flooring installations fail because of improper prep work than any other cause.



Proper substrate preparation is essential before applying adhesives for wood floors.
There are specific steps to properly prepare a substrate. Should one be overlooked, the entire floor installation could be compromised. When working on a project such as this, it is important to understand the technical details involved in preparing the substrate. These specific guidelines should be followed for a properly installed wood floor.

Step 1: Clean your subfloor The first step in preparing a substrate is cleaning. Before installing the wood flooring, prepare the substrate by removing existing floor coverings, adhesives, patch residue as well as the curing compounds and slab conditioners on the surface of the subfloor.

Hint: Scraping a concrete substrate with a 4-inch scraper and sweeping with a broom is not floor prep! The substrate should be sanded with a floor buffer and (20) grit or 3 1/2 coarse sand paper. After it is sanded, the subfloor should be swept, vacuumed and mopped with clean water, or tacked with wet towels beneath a push broom.



Step 2: Inspect the subfloor for moisture, cracks, and unevenness
Once the subfloor is cleaned, the next step is to inspect it. Look for unevenness of the substrate, cracks and visible signs of moisture and/or contaminates.

If there are cracks, they should be identified and treated. When filling the cracks, be sure to adhere to manufacturers' specifications regarding installation of the crack filler or crack isolation membrane.

Moisture is another important thing to consider while preparing the substrate. If the subfloor is damp, or shows visible signs of moisture, it should be allowed to dry before the wood flooring installation. Excessive moisture can cause adhesive bond release, discoloration, cracks or checks in the finish and curling or buckling of the wood flooring. Prevent these problems during installation preparation and you will save yourself a lot of time and money.

Step 3: Do proper moisture and pH testing
When preparing to install wood flooring over a concrete substrate, it is important to remember one thing: pre-installation surface preparation and moisture testing is a must for all moisture control systems. It is important to remember that all test sites should be cleaned at least 24 hours prior to setting the tests.

Test for moisture using an approved moisture meter. The moisture meter will detect the presence of moisture in the top 1/2 inch of the concrete slab. If the meter reading is high, a calcium chloride dome test must be conducted to determine the amount of vapor transmission and if the wood flooring can be installed without the application of a moisture vapor sealer. The only moisture tests recognized for testing moisture vapor transmission is the Calcium Chloride Test (ASTM F-1869). This will measure the vapor emissions over the substrate. Be sure that this test is done in an acclimated environment that is between 60-80°F and between 40-60 percent relative humidity.

A total of three tests must be used in the first 1,000 square feet. One additional test must be administered for each additional 1,000 square feet (or the remainder of the substrate if under that size).

When preparing the substrate, a ph test is used to determine how much carbonation occurs near the surface of the substrate. A ph level of nine or less is important for maintaining adhesive bond. Hint: Keep an organized documentation of the installation All tests should be well documented and kept on file. Also, take photographs of the test sites during the installation process and keep them with the test data. This will show a clear picture of the installation progress.

Step 4: Level the substrate if it is uneven
To avoid having to redo the installation, it is better to make sure you're working with an even substrate. Industry standards for the levelness of concrete when installing wood flooring are 3/16 of an inch in 10 ft and 1/8 of an inch in 6 feet. This can be verified using a strait edge, a level, or a laser. If the substrate is not within industry requirements, a floor-leveling compound must be used to bring the substrate to acceptable tolerances. One way of doing this is by filling low areas of the concrete with an approved Portland cement leveling compound. For the high areas, try grinding them with a grinder or corundum blade.

After the subfloor has been properly cleaned, checked for moisture, treated or sealed if necessary and leveled, installation of the wood flooring is a much easier and more successful process.

So the next time you have an excuse for not having a properly prepared substrate prior to installing wood flooring, remember; you're only wasting your time and money for expensive repairs and replacements. Excuses will not assist you with this painful lesson.