Pictured is MAPEI’s Ultrabond G19 two-part urethane flooring adhesive in a sheet vinyl flooring installation. Before installing flooring over concrete, ensure the slab is warm enough.


This month’s mailbag brings up some important questions about installing resilient flooring. Make sure to read each question and answer so these situations do not become big problems for your store or installers.

Question:Do you feel wire brushing or hand sanding the concrete surface is adequate for conducting a calcium chloride test?

Answer:No, I do not feel it is adequate. To measure Moisture Vapor Emissions Rate (MVER), only grinding the surface of the concrete will open the capillaries of the concrete surface. Sealers, curing compounds, adhesives and other residues penetrate into the concrete’s surface, and will restrict the moisture vapor flow. A restricted moisture vapor flow will create a low moisture reading and false positives. False positives mean moisture is most likely in the concrete; it will just take a little longer for it to get to your material and adhesive -- but it will occur. 


Question:Can you tell me what may have caused an epoxy adhesive to fail on a vinyl-backed sheet vinyl job over hard trowel finished concrete?

Answer:A hard trowel finish (burnished) is a result of over-troweling the concrete during the slab placement and finishing. Burnished concrete is a difficult surface to achieve a good mechanical bond. The epoxy adhesive needs to be able to get a bite into the pores and capillaries on the slab’s surface. When the concrete surface is too smooth, the epoxy cannot get a very good mechanical bond. Many resilient installations and floor preparation patches are placed in jeopardy due to this condition. Concrete surfaces need to have the texture of fine sandpaper and if this does not exist, then it needs to be abraded to achieve a bondable surface. 


Question:Are moisture mitigation coatings reliable to control moisture in concrete slabs?

Answer:Most of them are reliable providing the preparation is done following the moisture mitigation manufacturer’s instructions for preparation and application. In instances where the coating has failed, the concrete surface was not prepared properly.  The coating (which is going to be subjected to much more stress) was unable to get a good mechanical bond. Keep in mind these coatings are not able to withstand an acidic slab, but they work well in an alkaline slab environment.


Question:Is there a simple way to determine if a slab is porous or non-porous?

Answer:Knowing whether the slab surface is porous or non-porous is extremely important. Test by sprinkling some water droplets on the concrete and watch to see if they soak into the slab or bead up on the concrete surface and remain. If the surface is non-porous and will not absorb the water droplets, you must determine why the slab is non-porous. If it is due to a curing compound or sealer, it should be removed.  If the concrete slab is non-porous due to a moisture treatment, then a dry-to-touch adhesive designed for non-porous substrates must be used.


Question:Can you explain the importance of proper concrete slab temperatures?

Answer:A general contractor will tell you the heating/air has been on for a week or more. The installers arrive at the jobsite and the ambient temperature is 65°F (18.3°C) and the slab temperature is 57°F (13.9°C) or less. It is obvious the slab is nowhere near warm enough to install and the general contractor says, “Show me in the specs where it states what the slab temperature should be.”

When you are dealing with a cold slab, you are allowing many problems to present themselves. A cold slab could cause the moisture testing results to be inaccurate. Many times moisture will migrate back into a cold slab. Next, cracks and control joint problems are almost a given problem, because the slab is going to expand when it warms up to its scheduled maintained environment.


Question:I have tried several different meters with a variety of results for the ASTM F-2170 RH (in-situ) probe test. Can you give me an idea why this is occurring?

Answer:There are several things you must look at. 1) Are the meters you are using calibrated and up to date? 2) Did you acclimate the probe in the hole? The probe should be allowed to stay in the sleeve until the meter stops any drifting. 3) Is the meter measuring the bottom of the hole at the 40% depth requirement or measuring the entire gradient of hole? Measuring the gradient will give you lower readings. The purpose of the in-situ test is to measure the slab at the 40% thickness on a slab drying from one side or 20% on a slab drying from both sides.


Question:Can you explain why my installers have problems installing vinyl-backed sheet vinyl with a full spread of epoxy adhesive?

Answer:Installing vinyl-backed with a full spread of epoxy is one of the most difficult installations in the flooring industry. Too many times an epoxy adhesive is specified because it is looked upon as a cure all. If an epoxy is necessary there are several factors to be aware of: 

The installer must be well versed in the characteristics of epoxy; not just any installer will do. 

Temperatures must be taken into consideration. Epoxies are thermoplastics and very temperature sensitive.

When mixing, be sure to check the instructions. Some are to be hand-mixed, while others are recommended to be power-mixed.  It is extremely important to mix the two components thoroughly.

When applying the adhesive use a properly notched trowel, combing the adhesive from side-to-side. This allows any trapped air to escape during the rolling process or trowel and flatten the trowel ridges down with a short napped paint roller.

After the prescribed open time, do not trap any air beneath the material when placing the material into the epoxy.

Finally, and most important, is using the proper weighted roller. Most installations require the material to be rolled a minimum of three times: immediately after, one hour after and at two to three hours.

As epoxy starts to develop a little tack as it allows trapped air to be compressed. After a short time the pressure from the trapped, compressed air forces the material out of the adhesive. Be mindful of this problem.


Question:Why are linoleum seams so much more difficult to weld compared to vinyl?

Answer:Linoleum seams are not heat welded like vinyl seams. The rod used for linoleum is thermo-plastic. Vinyl seams use a vinyl rod that uses a thermo-fusion process. A linoleum seam is really a thermo bond, like colored hot melt plastic. For linoleum seams, the first pass skive should be done immediately followed by the second pass while the rod is still warm. Failure to do so will allow the rod to solidify and makes it easier to “zipper out” of the seam. The bond of a linoleum seam takes a while to develop.


Question:Why does a heat weld seam appear to become dirty after installation?

Answer:Most of the flooring materials on the market have a urethane finish to ease maintenance. Unfortunately, the weld rods do not have this same coating. When heated, the weld rod plasticizers are active and leave an oil-like residue on the surface of the finished rod. This residue is very prone to attract soil. A way to prevent this is to apply floor polish to the finished weld rod. 


Question:What are the causes of wood underlayment joint show-through?

Answer:There are several factors that cause underlayment joint show-through. 1) The fastening not following manufacturer recommendations. Fastening should be done within 3/8” from the panel joints and spaced along the joint, per the underlayment manufacturer’s recommendations. 2) Using wrong fasteners. Use the proper length fasteners with proper spacing of the fasteners along the panel edges and in the field. 3) Gaps between underlayment panels. The panels should be butted up lightly and fastened from the joint to the outside edges, so no fullness is fasten into the panels. 4) Wrong patching material. The joints should be sanded smooth and not filled using floor patch. This allows a slight expansion from the moisture in the adhesive without pushing up the floor patch.

Do you have questions for me that weren’t covered here?  Please feel free to email me atrthompson@cablespeed.com.