Q: Is it better to remove cutback adhesive, or use a cementitious skim-coat over it?
A: My inclination is to remove the cutback adhesive with a removal product formulated specifically for the job. However, if an adhesive remover is used improperly or not thoroughly cleaned up, it can create a subsequent bonding problem. Any adhesive remover residue on the surface of the substrate will attack the new adhesive.

A skim-coat, consisting of a cementitious smoothing compound, is sometimes used in in lieu of total cutback removal. The cutback adhesive should be scraped down to a thin residue, with all of the trowel ridges removed, before the skim-coat is applied. A skim-coat should not be used in areas subject to heavy traffic. Note: the potential for bond failure increases in proportion to the number of layers of existing residuals left on the substrate.

Q: What are your thoughts about applying a multi-purpose adhesive over an existing layer of multi-purpose adhesive?
A: Compatibility is the main concern when one applies a new adhesive over an existing adhesive. Failures are common when old existing adhesives, which were high in solvents and low in plasticizer content, have been covered with a new adhesive that is low in solvent content and high in plasticizers. This situation results in a phenomenon called “reverse plasticizer migration.”

Q: How profoundly does temperature affect resilient installations?
A: Low temperatures have the greatest and most damaging effects. With lower temperatures comes higher humidity. In combination, they can exert a huge impact upon the overall installation. Low temperature causes material handling and cutting problems, adhesive bonding problems, setting and hardening concerns with patching compounds, and dampness in the substrates.

Even more harmful to an installation is the fluctuation of temperature and humidity. Resilient installations performed under such conditions have a brief longevity, especially where the adhesive’s bond is concerned.

Q: I performed a vinyl composition tile (VCT) installation that shrank uniformly at each of the tile joints. What caused this?
A: Several possible causes could be at the root of your problem. These include:

Improper storage of the VCT (usually under abnormal environmental conditions).

VCT subjected to a damp environment prior to installation.

The substrate was too wet to install over at the time of installation.

There was no temperature control on the job site at the time of installation, or immediately afterward (before the tile adhesive had set).

Floor maintenance procedures were undertaken before the tile adhesive was set.

Q: What do you consider to be the best wood underlayments for use with today’s installations?
A: Many good underlayments are available today. In general, I find that the more expensive that they are, the better they perform. Personally, I prefer the hardwood veneered type of underlayments. But even the best underlayments are useless unless they are acclimated, and properly installed and fastened over a structurally sound, dry substrate.

Q: You wrote in a recent article (Aug. 1999, NFT) that a VCT installation should not be stripped. How do you feel about the use of a sealer instead of a stripper?
A: I think use of a sealer is a great idea. A floor sealer is a polish that’s resistant to high alkalinity. Once a VCT installation is completed and the adhesive cured (approximately five days), application of a coat of floor sealer will help protect the tile and adhesive from the ill effects of alkaline-based cleaners and strippers. Many installations are compromised by improper maintenance procedures.

Q: I’ve experienced adhesive bonding problems when I install resilient materials over gypsum underlayments. How can this be overcome?
A: Gypsum underlayments, while not recommended by resilient manufacturers, are used in large quantities on many construction projects. In almost all cases, the underlayment is pumped on to the subfloor and it’s often over-watered. Over-watering creates a soft, dusty surface that undermines the bond of adhesives and patching compounds to the underlayment surface.

To overcome this problem, many manufacturers of gypsum underlayments recommend the use of a primer applied to the underlayment surface approximately two hours prior to the start of the installation. The primer will stop the dusting effect and inhibit the absorbency of the underlayment’s surface.

Q: Why is it necessary to roll epoxy adhesives multiple times?
A: Epoxy adhesives have a high solids content and no initial tack. Their high solids content produce little or no shrinkage when the adhesive sets. This means the adhesive just goes from a liquid state to a solid. Because there is no tack nor adhesive shrinkage to draw the material down into close contact with the substrate, the material must be rolled into the adhesive.

Because of roll curl and substrate undulation, the resilient material will resist staying put in the adhesive. So, the need for re-rolling the material is extremely important. Failure to re-roll an area that has come loose results in a bubble that will be difficult to repair because the epoxy adhesive cannot be reactivated.

The accepted epoxy adhesive rolling procedure is to do so immediately after the material is placed into the adhesive, again in 30 minutes to 1 hour and again a final time after about 3 hours. Many installers place masking tape on the floor to indicate the times that they rolled each area.

Q: What method do you use to put new notches in a worn trowel?
A: I am not aware of a good trowel-notching device on the market. I prefer to use a replaceable blade trowel and keep a good supply of new blades. Many complaints arise from use of trowels that have been irregularly notched with a file. Typically, one or two deep notches telegraph through the surface of the finished floor. The depth and the spacing of the trowel notch are critical to the success of a resilient installation.

Q: It seems that floor covering installers are forced to install their materials much too soon — usually before the job site is ready. What are your thoughts?
A: No doubt about it, the construction industry is in too big of a rush. Today’s job superintendents seem to have less knowledge than those of previous generations about the construction process, and they often are paid a bonus if the job is completed on or ahead of schedule. As a result, the only thing the superintendents are interested in is job completion. Unfortunately, the floor industry is either too afraid to say “no” to superintendents that rush flooring installation, or it simply doesn’t know better.

Q: We’ve had problems with patching compounds de-bonding after they’re placed in the cold joints of a concrete slab. What causes this de-bonding?
A: De-bonding can occur for several reasons. It’s possible that the cold joint was not cleaned out thoroughly, or that some type of residue on the concrete (or down into the joint) is preventing a bond from taking place. Another possibility is a moisture problem with the slab. Moisture migrates along the path of least resistance and usually appears first at the cold joints.

Finally, it’s possible that the slab temperature was not stabilized prior to the installation of the floor. A concrete slab will expand at a rate of 1/8 inch per 100 lineal feet of concrete for every 5º F increase in the slab temperature.

Q: It seems that new slabs are more prone to cracking than those of the past. What are the causes of concrete cracking?
A: The primary causes of concrete cracking are as follows:

Over-watering of the concrete mix. One gallon of extra water in a cubic yard of concrete will increase its shrinkage by 10%.

Improper spacing of the control joints. Control joints are cut into the concrete to control the cracking of the slab. If the joints are too far apart, the slab will create its own cracks.

The slab was dried too quickly. When this occurs, a spider web cracking pattern will develop on the slab surface.

Surface tension cracking is caused by the presence of excessive bleed water on the surface of the slab.

Ray welcomes your questions and comments about this or any other article he’s written. You can contact him in care of NFT or e-mail him at www.rayt-fci@cleelum.com.