By Ray Thompson, Jr.
It is amazing how many times I go to look at a flooring issue at a hospital and hear the same concerns expressed by the staff. The selected flooring material is relatively smooth with multiple coats of high-gloss polish and when selecting the flooring or determining a care program, they have no idea how much a high-gloss finish will accentuate the slightest irregularities in the material, adhesive or substrate. Their only concern: how shiny is the floor’s surface? Unfortunately, the low light levels at most hospitals only exacerbates the whole issue.
End users/specifiers are hung up on static load capabilities of a piece of material. Their thinking, which is incorrect, is the higher the number the better the material. They do not consider the impact of foot traffic, equipment, rolling loads and stationary loads.
All materials indent; the question is to what degree? The industry standard is that an indentation up to 0.005″ is acceptable. However, if you look at a 0.005″ indentation, it is extremely visible in a high-gloss, low-level light environment.
Where is the indentation taking place? Is it in the material, the adhesive or in the substrate? What is causing the resilient floor indentations? Heavy equipment, hospital beds, static or dynamic loads, or foot traffic?
Let’s look at each of these items to see how each affect’s the material’s performance:
It’s hard to determine why this high-gloss, mirror-like appearance got its start, but I have seen floors with up to 15 coats of a high-gloss polish buffed to a mirror-like finish. In one instance, I encountered a floor with a thick buildup of polish and the hospital staff was complaining that the chairs were indenting the material. After applying a strong floor stripper to remove this buildup of polish, the staff realized the indentation was in the floor finish and not the material. Also, after removing the high-gloss polish, the material’s surface had a reduced gloss level. Maintenance personnel need to understand that two or three thin coats are better than one heavy coat of polish.
Many of the hospital chains are realizing that some of their indentation problems can be eliminated by selecting a lower gloss polish system.
It takes a lot to indent a piece of homogeneous or heterogeneous material. When a piece of material is sent to the lab to be tested for static load capability, they rarely fail to pass the testing. The reason is the indentation is not occurring in the material, but in the adhesive line or the substrate. Fact: When an indentation is close to the maximum, it looks extreme. If you were to compare the difference in the depths of indentations, you would find that a 0.001″ indentation is not very noticeable, but a 0.005″ indentation looks like a crater.
Indentations most often occur in adhesives. In a fine-notch trowel application, the adhesive film is about 1/32” deep when applied, allowed to dry-to-touch, the material is placed into the adhesive and rolled with a 100-lb. roller. The remaining adhesive film, depending upon the adhesive, still measures between 0.018″ – 0.022″. Meaning, that an indentation appearing in the adhesive line is very likely – especially if the adhesive is not cured.
Finding an adhesive that fulfills this need is difficult. If an adhesive is too hard, the installer needs to be very careful on the use of the trowel because the trowel notch or any irregularities in the adhesive spread will show through the finished material. If the adhesive is too soft, then the possibility of an indentation is severe. The same is true of the trowel notch. Trowels that are not properly notched will make the material prone to indentations. Indentations can also be caused by the depth of the trowel notch, as well the notch spacing. Flooring and adhesive manufacturers have tried several methods to stop this problem from occurring.
Back rolling the adhesive with a short-napped paint roller, after the adhesive has been troweled, works well in knocking down the trowel ridge. With a hard-setting adhesive trowel notch, show-through is kept to a minimum because the notch is essentially gone. However, because the adhesive was troweled, the adhesive film is relatively uniform.
Rolling the adhesive with a paint roller alone does not work well because it’s difficult to maintain a uniform adhesive film. This would allow indentations to be in the areas where the adhesive film was too heavy.
Spraying the adhesive is one of the newer methods in attempting to eliminate the indentation problem. The spray can be applied in a very thin film to keep indentations from developing. Unfortunately, a thorough cleaning of the substrate is necessary prior to spraying the adhesive and is sometimes difficult to achieve. Dust and fine dirt, either on the back of the material or on the floor, can work as a bond breaker and result in other problems. The sprayer can also kick up debris and get beneath the material, creating a show-through of the material. The application of the spray must be uniform. If it’s heavily applied, it can result in either an indentation problem and/or a lumpy show-through.
Applying an adhesive film to the back of the material is the latest attempt to overcome the indentation problem. It’s believed that a film of adhesive less than 5-mils will eliminate the indenting at the adhesive line. In these cases, the adhesive would have to be pre-applied to the materials back and covered with a release paper. Like the spraying method, dust on the substrate would have to be controlled with the use of a primer.
Marginal moisture conditions are also a concern. For example, an installation is started when the moisture is on the upper limit of the moisture specification. The adhesive will remain soft and not totally cured. Soft adhesive film and indentations go together.
Hospital equipment manufacturers have no concerns for the flooring industry. The casters on some hospital beds are rounded instead of flat and leave a very small footprint (static load pattern). This footprint, coupled with the weight of the bed and the patient, is enormous. Attempting to pivot a locked down caster increases the possibility of an indentation.
Stiletto heels are probably the most destructive thing to all types of flooring. These small heels create unbelievable force to the surface of the flooring. For instance, a 100-lb. person wearing a stiletto-type heel will create a pressure of about one ton. The formula for figuring the load bearing from a stiletto heel with the cap in place (which is 1/20“) is to multiply the person’s weight by 20. If the cap on the heel is gone and the spike is exposed (which is 1/80“), then multiply the person’s weight times 80.
The real solution to resilient floor indentations is to control the amount of adhesive applied to the substrate, and to use a low-gloss or matte finish. The hospital bed problem will remain until we get some cooperation from bed manufacturers. The use of epoxy adhesives is not the answer to indentations in resilient flooring.