In the late summer of 2016, a Lexington, Massachusetts-based estate property client contacted my company and inquired about remediating a large curb at the entry of her garage door threshold. It was left as the result of a mismeasurement by a contractor who had recently completed some home renovations and an addition.

After consultation, we agreed to chamfer the edge by grinding followed by the installation of a chip floor. It was a fairly straightforward project — it turned into anything but that!

The Installation

The concrete was about six months from pour, and we chose intermediate #30 diamond tooling on a Werkmaster Raptor XT. Upon completion of grind prep and thorough vacuuming, a slow curing urethane primer was applied. Two and a half hours into cure and after lunch in perfect weather conditions, a polyaspartic urethane coating was applied followed by chip broadcast to rejection. Approximately one and a half hours into that cure, the excess broadcast was vacuumed and the floor was lightly scraped. A second vacuuming was performed, followed by the application of an ultraviolet (UV) stabilized epoxy topcoat in the body of the garage and application of clear polyaspartic urethane on the threshold.

Our procedure under these conditions is to pin the garage above the threshold to minimize contaminate blow-in on a calm day. We then tidied up and departed the site, leaving instructions with the owner to keep vehicles off the floor for three days.

A few days later, I was contacted by the client via email with a picture attachment. The client noted that the workers left a garage door imprint on the threshold and inquired about how it might be remedied.

As any business owner would be, I was quite upset with the crew. However, the guys were adamant that there was no way they would have left a job after having “dipped” a garage door into a coating. Not only have I worked closely with my team, but this is such an easy fix in the moment that I believed them. I called them into my office, and when we called the client to tell her that the team was quite upset about the accusation, she admitted that it was a member of her staff, the cook, who did not realize the floor was new and used the garage door the day after we departed.

Now any pro in this business knows that a polyaspartic urethane can’t be embossed by a light-weight garage door gasket three hours into the cure, not to mention the next day. It must have happened earlier, but in pursuit of excellent customer service, I said that we would touch up the cook’s mark at no charge.

Fixing the Problem

After setting a date with the client, the team arrived and lightly disk sanded the entire floor. It was then vacuumed and wiped with acetone. A clear UV stabilized topcoat epoxy was mixed, squeegeed, and backrolled. This was followed by a second batch with the same procedure and threshold recoating. The crew then departed after again pinning the garage door in place.

About a week later, I was again contacted by the client — this time via phone. She said “I didn’t drive on the floor for seven days. I put the car in reverse and it wouldn’t move. I gave it some gas and I heard a terrible tearing noise.” My immediate thought was could we have a faulty lot of material? Then I realized that this was the same lot of epoxy that we had used on a basement, her floor, and another garage without any issues. My second thought was the client’s previous actions, blaming my guys and then her cook for the door drop, could be coming into play again. Regardless, we still want to give exceptional customer service, so I said, “we will come out tomorrow and take a look.”

Sure enough, there were a bunch of tire adhesion marks; however, the floor was rock solid. This was not a floor that had been soft for seven days and then all of a sudden hard as a rock. My business partner and I combined have more than 50 years of coating experience, and this was the first time that either of us had a client glue her car to a floor. One must see the humor at this point.

The floor appeared to have good integrity. There did not seem to be any delamination, just what appeared to be cosmetic damage. So once again, we lightly sanded the floor, vacuumed, acetone wiped, and recoated. With contractors, staff, and family coming and going, we insisted again that the floor not be driven on for three days.

A week or so later, the call came. I received another message from the client that floor was making sticking noises (meaning, in this case, delamination). I asked to once again take a look at the floor but the client refused. She stated that she was looking elsewhere for service. Later we were sent a letter demanding a full refund due the failure of the coating. We were informed that two other companies looked at the failure and concluded that improper or no surface preparation was done. Most of us in the business would certainly have the same conclusion unless we knew the whole story, which was that both the client and I stood in the driveway watching the grinding operation on the day of preparation.

Investigation Station

Having spent most of my career as an engineer in industrial process development, focusing on adhesive processing, I decided to recreate the failure to determine what exactly happened. We replicated the chip floor under the same process and conditions as the original installation, although we used a Metabo hand grinder rather than the big machine for prep due to the size of the sample.

We hadn’t seen any footprints on the client’s floor, so we knew that unless an individual was sleeping in the car, it was unlikely that anyone had been on the floor within six hours of application. The car must have been parked later. After top-coating the test floor, we parked a vehicle on it eight hours into the cure. After 24 hours, the vehicle was moved and parked on a fresh spot. No tearing noise was heard, but there was a distinct imprint. The floor appeared to have good integrity; however, upon careful observation, when scratching the surface with a fingernail, a hollow noise was heard compared to adjacent areas. After another 24 hours, the vehicle was moved again. No imprint was visible 48 hours into the cure.

Considering the first test didn’t recreate the tearing noise, we prepared a second test patch. This time, at seven hours after application, we drove and parked a vehicle with tires more closely representing the client’s onto the surface. The next morning the vehicle was started and put into reverse. The vehicle would not move. Upon applying power, a tearing noise was heard and an imprint was imposed on the surface. The vehicle was then parked on a new spot. At 15 hours from application of the topcoat, the vehicle was once again moved. There was no sign of an indentation at 15 hours.

Although we have always advocated waiting three days from the crew’s departure prior to driving and parking on this particular coating system, the client insisted that she was told that she could drive on it 48 hours after it was coated. It appears that under these replicated conditions, even 48 hours is an acceptable cure window prior to return to service. Apparently, pushing the cure envelope to seven or eight hours was a bit ambitious.

Conclusion

After much experimentation, we concluded that a vehicle or vehicles were parked on the client’s garage floor approximately seven hours after the crew departed. (Given slab and air temperature variability, the time could be plus or minus about 1.5 hours.) Once the bond was disturbed by compression and shear — translation force applied to a bond line joint — in mid-cure, delamination was likely to occur with subsequent subjection to surface loads. Although not the norm, this client had tried to pass blame to others on multiple occasions. Looking forward and under these ideal curing conditions, we will continue to advocate waiting three days prior to imposing floor loads. Also, we will continue to use experimentation to determine why or what conditions lead to failure.

Thomas C. Schroeder is owner of Master Garage Corporation in Marlborough, Massachusetts. He has 31 years of experience in adhesive development, process development, research and development, manufacturing, machine design, and business development. For more information, contact: Thomas C. Schroeder, www.mastergarage.com