Advanced Question Pool apron problem

[Doug Dahlke]

I went out today to look at a pool apron. The pool is new and the owner had a coating put on the concrete apron. Soon after the coating began to blister up in spots and come off. The contractor came out, power washed the entire apron and reapplied. The new coating is now coming off. The coating contractor is ready to give up and refund the customers money. Any idea what is causing this and how to fix it. The coating looks like epoxy but I would think that would be too slippery to put around a pool.

[We Wash Concrete]

Hey Doug, can you tell if the epoxy type stuff is peeling from only the concrete? In other words, is the new coating peeling from the previous coating? I wonder if the chemical mixture is a little off preventing proper adhesion.

[Palmetto Home and Deck]

I have about thirty five years in bridge and heavy foundation construction. I have poured hundreds of thousands of cubic yards of concrete. I can't be sure, but my guess would be that the contractor that poured the pool apron applied a curing compound to the freshly poured concrete to prevent the concrete from drying too fast and causing curing cracks.

Some curing compounds are silicone or waxed based. they form a film on top of and penetrate slightly into the concrete to hold the moisture in the concrete mix until curing has taken place. These curing compounds would eventually wear off in a long period of time, but we could not use them where we would be pouring against them again or applying any sort of concrete paint on top it. If we had done so the new concrete would not bond to the earlier poured concrete and any concrete paint coating would spall or flake off just like in your pictures.

I seriously doubt if pressure washing will remove one of these curing compound easily. Maybe repeated washing...I just can't say. If we accidentally used one of these curing compounds in the wrong place we had to sand blast the surface area.

See if you can find the contractor who poured the concrete and see if they used a silicone or waxed base curing compounds on the pool apron. At least you will know what you are up against.

[MMI Enterprises]

Possable curing compounds as Len mentions is something to consider for sure. One would think the concrete guys would know better since such areas usually always get some sort of coating treatment or other.
On those bare/chipped areas you would want to splash some water on to see if it penetrates. Generally if it darkens and soaks up the water then it should be porous enough for to apply a suitable coating. Besides that the surface profile should be rough enough to provide mechanical adhesion. 80-100 grit would be a rule of thumb.
That said, judging by how it looks, I think it likely coating failure by way of inferior product rather than prep. Seems to look like one of those new fandangled deck coatings that was just painted on to the crete...probably doesn't involve any kind of primer/bonding system or anything along the lines of being a penetrating staining system or 2-part catalyzed system. If ya color such areas ya really got to lock thing in with some mil thickness of good stuff.

[Beth n Rod]

I'm no expert but from what I have been led to understand, concrete needs to be etched before applying a coating to it otherwise it will not be able to adhere to the surface well.
Without knowing the prep involved I could not elaborate much further on the cause other than to say it looks like the concrete was either too hot during the application and failed to adhere or there was still moisture on it and that has heated up during the course of the day causing the blistering.

Rod!~