Epoxy Floor Coating Peeling When It Rains

I received the following email over the weekend:

Hello I have had my garage floors coated by a contractor twice. The first time it started peeling whenever it rained and the tires were wet when I parked on it. The second time he came back to redo the floor, he said he used a different coating (supposedly more durable). He made me wait 10 days before parking on it, so it rained again yesterday and guess what happened. Can you give me an idea of what could be going wrong, because I’m sick that I had to pay for this and can’t even get the floors right.

Since the problem is tied to rainy weather my first guess would be that the concrete floor has a ground water issue. Most people think that concrete is impermeable (water can not go through it), on a large scale this is true as you can see from dams and other concrete structures that hold water. But on a microscopic scale concrete will actually allow water to seep from one side of the structure to another unless it is sealed.
Water problems in a concrete slab such as a garage floor are usually caused by ground water that is seeping up through the slab due to hydrostatic pressure. This means there is water pressure building up under the slab and the pressure is forcing the moisture through. This is called hydrostatic pressure. A moisture barrier is used to stop the majority of this flow when a new slab is poured. Usually a very heavy plastic is laid down before the concrete is spread out. This sheet stops the flow of water into the slab and instead helps to channel it away from the underside of the concrete.

Epoxies are designed to be used on dry concrete which are not susceptible to hydrostatic pressure. An epoxy is not breathable which means if there is any water being forced through the slab it will be collected under the epoxy coating. This can cause the epoxy to de-bond from the concrete and flake or peel.

To check for this problem, take a clear plastic sheet and lay it over the section where the epoxy has peeled up. The sheet should be about 6 inches bigger on all sides than the area that is peeling. Next, tape the sheet down all the way around with tape. The next time it rains check to see if any moisture has accumulated on the bottom side of the plastic. We use clear plastic because you can see the water beads forming. If this hydrostatic pressure text shows that you have moisture coming up from the slab then this is most likely your problem. My bet is this is what you will find.

Solutions For Hydrostatic Pressure Under A Concrete Slab

If your test proves that you have a moisture problem then your only option is to try to get the water away from the slab before it has a chance to percolate up to the surface. There are several fairly easy things to check.

Are your gutters and downspouts in good shape? You should have no leaks and the water should be channeled 10 feet way from the side of the garage.

Does the soil slope away from the foundation. Over the years the grade around a foundation can settle and rain water from the yard can actually flow toward the house and garage instead of away from it. This water can build up under the slab and cause problems.

These are fairly easy fixes to check out. If neither one of these issues is the problem then a more extensive fix will be needed. The first thing I would do is install a drain system around the entire garage foundation. You will have to dig a trench down below the gravel sub-grade which was laid down before the concrete was poured. This should allow the majority of the water to flow out from under the slab and then you can channel it away. Use perforated plastic pipe and back fill it with drain rock (clean gravel that has had all the fines removed). Be sure the water is channeled at least 10 feet away from the structure.

After each one of these fixes you can check to see it you have solved your moisture problem by redoing the hydrostatic text with the sheet of clear plastic. If you still have moisture problems then you may have an Artesian well. This is a place where underground water is actually forced to the surface. If this the situation then removing the excess water causing the hydrostatic pressure will be even more trouble. You will need to cut a hole in your slab and install a sump pump. You also need to cut trenches and install French drains. These allow the water to flow to the sump where it can be pumped.

If you have no other moisture problems other than your epoxy de-bonding then you may want to consider stripping the epoxy coating and just leaving your garage floor the way it was.
I hope this helped.

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