Underlay the Right Way

In this special issue, we are emphasizing UNDERLAYMENT. The variations of product availability in this category are almost endless. You can pore it, trowel it, nail it, glue it, screw it and sometimes it's even tattooed for you. Regardless of what system you use, being familiar with the application, limitations and corresponding warrantees are what we need to understand. In the past we have had particle board, masonite, structurewood and let's not forget lauan as options for our board type underlayments. We have seen the plywood types (3 and 5 ply) come to the front of the pack and be the products most recommended by resilient manufacturers because of their non-staining qualities. I have talked until I was blue in the face about the lack of quality that lauan offers the end user, but for some reason it still has its place in the home centers and with some distributors. Some will argue that price is the underlaying factor for the decision to use it. I will argue that quality of the installation is compromised when a sub-par material is used. In some cases you void any and all warranty given by the manufacturer of the floorcovering when you use non-recommended products.

This would be all well and good if you had a warranty from the underlayment manufacturer to replace the job, but check the warranty for lauan; there is none! The terms "Interior Grade" and "Exterior Grade" also come into play; would it be a good idea to always use an exterior grade for all applications? Then if moisture is introduced, we would have covered our butt for the benefit of the end user. The following is a collection of how you should not do it.

The first example is a ceramic installation over old cushion backed vinyl floorcovering. A 1/4-inch backer board was used, but was it enough? Checking your ANSI specifications will help you with this one. Photo 1 shows the composite of materials used and Photo 2 shows the result. The total thickness of subfloor and backer board was only 1 inch!

There was too much movement in the underlayment for the ceramic, and cracks were everywhere.

In the next example, the fast track builder used masonite for all his underlayment needs. A low joist is the culprit. A check of subfloor levelness prior to installation would have told the machine that more prep work was needed. If masonite is recommended, then knowing how to install it and what adhesive can be used is most important. And let's not forget about open time on the adhesive (Photo 3). In this installation of solid vinyl over lauan, there is loss of bond at the glue line (perimeter). You can see that the product was laid in a timely manner; the trowel marks are not showing and the adhesive is a uniform layer (Photo 4).

But what happened to the transfer to the back of the flooring (Photo 5)? The lauan plasticized the adhesive and compromised the bond. Look down the center and you will see a 90 degree angle telegraphing in the middle of the tile pattern. You could measure the underlayment panel size as 4-by-8 foot.

This usually means lauan but not always. Do we butt and sand the joints or do we leave a gap and patch? That is the question. If you sand and don't vacuum, you will have problems due to the trapped dust on the surface of the underlayment affecting both your patch and adhesive bonds. If you over-water or don't use the proper additive (if the patch calls for one), then you may have telegraphing that looks like this (Photo 6).

Gypsum patch used to level the concrete before a solid vinyl tile was installed (Photo 7). Proper use of a trowel is one of the problems here. Because of a lack of levelness in the subfloor, the mechanic applied adhesive to the back of some tile (Photo 8). Due to a lack of surface contact, the tile popped off the patch.

Adhesive cannot be used to level out a subfloor. There is no bridging capability built into the product. We could argue about epoxies, but your soft set adhesives are not designed to overcome irregularities in a subfloor. Should a gypsum patch even be used for this?

"What you don't see can't hurt you" is no way to address your underlayment needs. Even your low grade floorcovering will look great if the proper prep work is done the way the manufacturer intended. So if you're not sure about how to install the underlayment or if you don't know what the floorcovering manufacturer recommends for underlayment, then "YOU MAKE THE CALL" and find out.