Has the subfloor been prepared properly? Has all dirt and debris been cleared? Has the adhesive been given adequate open time? Installers, like this one participating in a training class, need to focus on details large and small.


Like so many jobs requiring a specific technical skill, installing a floor involves a series of little details. And I don’t have to tell you there is very little room for error. All too often, when a job goes sour it is due to some small detail that was not adequately addressed. Often it is a matter of not understanding the specific requirements of the environment or the materials used. So, this month let’s look at some of the questions that readers have sent in, as well as some I have heard in the field. I purposely focused on small, often overlooked elements involved in installation work-like trying to keep the nozzle on your caulk gun from clogging up. If there is something you’d like me to address I encourage you to send me an email at the address included on this page.

What is the cause of seam contamination and how can it be avoided?

Seam contamination is usually caused from adhesive migrating up into the seam. This can be minimized by allowing adequate open time of the adhesive. Open time allows the adhesive to develop body and helps prevent migration when rolling the floor. Once a seam has become contaminated it is very difficult to obtain a thermo-fusion effect from the seam sealer.

What is the best way to clean your trowel when using epoxy adhesives?

Whenever I use epoxy adhesives I coat all of the tools that will come in contact with the epoxy adhesive, with a carnauba based floor wax. Either that or rub them down with a paraffin or beeswax. This will prevent the epoxy from achieving a good mechanical bond to your tool. The treatments you use can also be easily scraped off. You can also tape your trowel with Duct Tape, leaving just the trowel notches exposed. When the epoxy is dry just peal the tape off.

Why do most underlayment manufacturers recommend ring shank nails? Also, what are your thoughts on stapling?

I have found that either ring or spiral-shanked nails do an excellent job of fastening an underlayment to the subfloor, provided that they are not too long. Manufacturers of underlayment recommend a 3d nail (1-1/4”) for underlayments less than 1/2” thick. As for stapling, I feel the mallet driven staple is a great substitute for hand nailing. I have a tendency to use a stapling pattern closer than what is typically recommended. My advice is to staple in a diagonal fan pattern and work from the seam sides of the underlayment to the open sides of the panel. A word of caution: The problem with pneumatic stapling is the staples tend to be driven too deep into the underlayment.

Please explain what they mean by "pounds of moisture" in a calcium chloride test?

Moisture Vapor Emissions Rate (MVER) is measured by the amount of moisture gained to the anhydrous calcium chloride crystals used during the moisture test. The figure enables installers to use a standard measurement tool at any job site. Water weighs 8.3 pounds per gallon so a MVER of 8.3 pounds would represent one gallon of water per 1,000 square feet per 24 hours. Remember, each pound is equal to one pint of water.

What is the difference between seam sealing and seam coating?

They may sound similar, but they are very different. Seam sealing is a method of thermo-fusing the two edges of a piece of material together. This requires that temperatures be above 55º F (12.8º C) when sealing and no contamination to the seam edges. Seam coating is a topical coating of a high tensile strength coating material using a mechanical bond to hold the two edges of the material together.

When I use heat welding I find there is a tendency for the areas where I start to pull loose. Can anything be done to prevent this?

Don’t start the heat weld process until you are sure your heat weld gun has warmed to its required temperature. Then, just before you insert the rod, preheat the groove so the material is hot enough to receive the rod.

What are your feelings on mixing the Portland cement based patches for floor preparation?

Over the last decade the flooring industry has gone almost exclusively to Portland-based patches. During the mixing process, care must be taken to stay within the manufacturer’s recommendation for powder to water ratio. Failure to do so will compromise the quality of the mix, yielding a softer patch, when set. I am also a strong believer in power mixing the water and powder. This will break the surface tension water allowing the mix to be more fluid and easier to work.

I notice that if I round the corners of my smooth edge trowel I can get a smoother trowel application of my embossing leveler. Any thoughts?

I agree. Rounding the corners of a smoothing trowel used for skim-coating or embossing leveling prevents ridges that must be scraped down later. What I have done is to round the edges on one side of the trowel about 1/2” radius and then leave the other side square for instances where I need a square edge.

It seems I am always throwing away tubes of caulking before they are empty because the nozzle is clogged with hardened caulk. Do you have any ideas on preventing this?

Yes. To prevent this type of waste, simply take a piece of heavy surgical tubing, clamp off one end and fill with petroleum jelly. Slide it over the open end of the caulking tube. This will prevent the air from drying out the caulking. When you are ready to use the caulking again, remove the piece of tubing, clean the nozzle and it is ready to use.

When installing underlayment under toekicks of a cabinet what is the best way to fasten the edges down?

There is no easy way to nail under a toekick of a cabinet. What I do is use a high grade multi-purpose adhesive and put a band of adhesive under the toekick just before I put the underlayment into position. Then I will either weight or wedge the underlayment until the adhesive dries. Caution, do not use solvent-based construction adhesives.

Can mixing floor patch in the middle of a floor lead to underlayment joint show-through?

Yes, and that is why this is a very poor habit to get into. When you mix your material this way, a portion of the water put onto the floor is invariably absorbed into the underlayment. Always mix your floor patch in a plastic bucket using a power mix with a drill motor.

What causes the concave effect to the vinyl heat weld rod when the skiving is done?

There are two factors that cause this concave effect; skiving when the rod is still too warm or trying to skive in a single pass. Vinyl rod takes a while to cool. If you try to rush the skiving process, the knife will stretch the center of the rod when cutting, the warmer the rod the more stretch and the deeper the concave. When done properly there will always be a very slight concave effect.