This is a surface of a concrete pool after an acid wash. I first thought it is plaster covered with paint, but then, by the feel and look of it, it does not seem to be paint. Hence I have several questions in one:

  • What can this white(r) layer be?
  • What can be under it? (the actual concrete base is yellow, and it is deeper)
  • If the gray stuff is plaster, why is it not white?

pool surface

that's the actual concrete under the gray surface:

pool concrete


I don't see any white in the pic, just the gloss gray surface surrounded by the etched surface.

The pool surface looks like it was etch with muriatic acid (as you already mentioned) in order to prep the surface for new plaster. This is what I understand that is done to remove loose scale on pool surfaces. It needs to be flushed thoroughly to cancel the etching.

Plaster can be colored as with any masonry cement or product.

The gunite or shotcrete base (concrete) will be under it about a 1/2" to 3/4" under it depending on how much the acid took off. I would be surprised to see that is yellow. It should be at least a light gray.


The added picture helps me a bit, it confirms what I know what should be in place, regardless of the colors that present themselves. On my end I see gray plaster, if it is white, it really does not matter, it is a matter of esthetics. Bottom line it is plaster. The added picture also shows the concrete base, whether it be yellow in color, or not. Again I do not see the yellow if that is what you are referring to, but I do see the concrete base. The texture (albeit the picture could be a little more clear) and color on my ends says it is concrete base, which is usually applied with either of 2 methods which are sprayed in place. Gunite is one method, shotcrete is the other, although there are hand applied ways to do this too.

What I did not detail in my first post, was the first picture shows the original surface that was not removed by the acid for some reason. When the plaster is applied it is troweled in place to create a smooth surface. This portion may have been troweled to the point that is became harder than the surrounding plaster, or maybe other conditions created this.

  • added a "concrete" visual. the white stuff is white, the shot has no sun, hence it looks gray. everything I read about acid washing a plaster is that it brings that "white" clean/new plaster under it, but in this case I am confused, what are these layers? – tolitius Jun 5 '14 at 22:53
  • I added a little more to my answer above. It sounds as though you need to have the pool replastered – Jack Jun 6 '14 at 12:24
  • thank you Jack. I took these pictures almost at sunset, hence the coloring does not exactly relay, but the bottom is yellowish, and yes, it looks and feels as concrete. great to know that the gray stuff is plaster. what I still don't understand is what is this white(r) stuff? It is another layer of plaster? (too thin) But it is also not paint. – tolitius Jun 6 '14 at 13:18
  • If you mean the triangular patch of different looking material that appears to be on top of the other gray stuff, I believe that is the same plaster, laid at the same time. It, for what ever reason received a harder finish, less prone to etching, and since it has a different texture (hard and smooth) versus the etched surface (coarse and rougher) the light will refract off each surface differently, even though the color is the same. Concrete when troweled, if one area is treated slightly different than another (more water added, less water) that can change the color too. – Jack Jun 6 '14 at 23:59

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