Troubleshooting Adhesive Show-Through
Trowel notch selection
The selection of the trowel notch is critical for two reasons: first is the depth of the notch. Pressure sensitive adhesives do not require the heavier film of adhesive as do the multi-purpose adhesives used for felt-backed materials. Applications of adhesive with too deep of a trowel notch leads to indentations and tracking. In a lot of situations an indentation is not in the material, but in the adhesive film. Second is the spacing of the notch. When the notch is too wide it allows the material to conform to the wider spacing of the trowel notch creating a vein-like show-through. Both of these problems are exacerbated by the failure to properly roll the material into the adhesive. Rolling with the proper weight roller is more important with a pressure sensitive adhesive than ever.
Once the proper trowel is selected, now the application of the adhesive becomes the next area of focus. Remember the adhesive is going to be allowed to dry-to-touch this means if there are any puddles, voids, or trowel chatter marks in the adhesive spread and the light source is just right you are apt to have a show through issue. Let’s take a trowel chatter issue:
Photo 1 Shows a trowel chatter likely caused from not carrying enough adhesive in front of the trowel, then allowing the adhesive to dry-to-touch and the adhesive firms up keeping the trowel chatter in place, followed by placing the material into the adhesive and rolling. Because the adhesive was allowed to dry-to-touch there is going to be no migration of the adhesive from the rolling to eliminate those irregularities.
Photo 2 Now expose the floor to traffic and maintenance procedures the polish the material’s surface to a high gloss and you have a show through issue.
These types of issues are difficult to deal with because it is an aesthetic issue and there is no fixing for this show through problem short of complete replacement of the material. The harder the adhesive sets the more a show-through issue will manifest its self.
Photo 3 Shows irregularities showing through the sheet material all over the place. While this looks like a substrate problem, the substrate was a self-leveling underlayment and according to the flooring contractor, was very smooth and free of irregularities.
Adhesive overlap show-through is equally as big of a problem. When a professional installer spreads a width of sheet vinyl, it is generally done in two spreads. The first half is either lapped or tubed back so the adhesive is applied to the substrate. After being applied, a pressure-sensitive adhesive is allowed to dry-to-touch, before the material is placed into the adhesive and rolled. The installer then pulls up the other half of the material and applies the adhesive to the other half of the material. In the process of the spreading the adhesive the installer overlaps the adhesive up onto the adhesive of the first spread.
Photo 4 The installer allows the adhesive to dry-to-touch and then places the material into the adhesive and rolls the material.
Photo 5 Then the maintenance personnel come in and apply several coats of high-gloss polish which tends to accentuate the overlap, which can lead to a complaint.
What has happened is as follows: The adhesive was spread with the proper trowel with a notch of 0.032” (1/32”) The adhesive is allowed to dry-to-touch in the process the adhesive film shrinks to about 0.023” The material is placed into the adhesive and rolled with a 100# roller leaving the adhesive film at about 0.018”
The material is then lifted out of the first spread of adhesive and the second spread of adhesive is allowed to lap up over the first spread which is about 0.018” plus an additional 0.032” and allowed to dry-to-touch the material placed into the adhesive and rolled with a steel roller. The adhesive film at the overlapped area is now twice the thickness of the rest of the adhesive film under the sheet material.
Photo 6 Along comes the foot traffic and the maintenance personnel with the high-gloss polish and you have trowel overlap show through.
How is this problem overcome? There are two options; the first option is not to overlap the adhesive spread. The second is to spread the adhesive and then back roll the adhesive with a short napped paint roller to knock the trowel notch ridges down and even out the adhesive film. While a lot of installers bulk at the idea of back rolling the adhesive it is becoming more popular with the installation community too overcome trowel notch show-through, especially in the installation of VCT tile.