Thompson's water sealer over acrylic paint didn't work for me, at all ...
I bought 2 concrete benches (with 4 bench supports that have lots of scrolls and other architectural detailing) on clearance at Home Depot, with the intention of removing the hideous white paint/yellowed antiquing already on them -- and painting them faux stone. (There was a "plasticized" acrylic/poly finish over the paint.) After first trying sanding, and then resorting to laquer thinner to remove the existing finish down to the original concrete in all the intricate recesses, I put many hours into repainting them, using artist acrylic paints. I applied Thompson's "all-surface" spray sealer, which is rated for exterior masonry, stone, etc. (maybe using the spray was one of the problems, but I didn't want to buy a gallon of regular Thompson's, when I didn't need that much). Even after a couple days of drying time, the finish was distinctly oily -- to the point that you would not want to sit on the bench and risk ruining your clothing. Hoping the oilyness would wear off with some weathering, I set one of the benches and the 4 supports outside. The next day, it rained, pretty steadily, all day. I checked the bench mid-day, and to my horror, the Thompson's had completely washed off, and the acrylic paint (which is water-based) was "thinning away" as well (i.e., the top coats of black antiquing I applied into the recesses was completely gone, and the base coat was visible under a more-and-more transparent top, faux paint job.) I brought the bench and the supports back into the garage, let them thoroughly dry, and put more hours into touching them up, while I did some additional research on what I could use to seal them. I did not want to strip my acrylic paint off and start over with a different kind of paint.
I am in Minnesota, so the seal/finish has to be very durable, due to extreme weather -- and, in MN, it is not practical to pick everything up outside in the fall and bring it indoors for the very long winter. I found the following MN statuary's web site very helpful -- and they also sell jars of the concrete sealer that they use:
http://www.svjcreativedesigns.com/info/care.php. (See their recommendations for the type of paint to use.) Before ordering sealer from them, I continued looking for something that specifically could be used as a sealer over my existing acrylic paint. I stumbled upon Patio Paint by Deco Art -- which is an acrylic paint, but specifically formulated for outdoor use on concrete, terra cotta, wood, etc.:
http://www.decoart.com/products/product_home/patiopaint_only.html.
These paints are available at Michael's Craft stores (limited color selection available in the stores -- but the full range of over 60 colors and specialty textured versions are sold through Deco Art's web site in 2 oz. bottles ... at less than $2 each, with a few colors available in larger sizes.) Since Patio Paint also comes in "clear," I decided to try to use it to seal my existing acrylic paint job (to prevent a final, over-the-top concrete sealer from causing my acrylic paint to soften or run), and then use a concrete or other sealer over the clear-coat of Patio Paint. I was concerned that I'd go through a lot of the clear Patio Paint, but 2-1/2 bottles was all it took to put 2 coats on everything -- about 15 square feet of paintable surface. It looks like white glue when applied, but dries totally clear -- having a somewhat glossy finish. It leaves a flexible, "plastic" coating over the painted surface (similar to what was on these benches when I purchased them, although the factory finish seemed a whole lot thicker). While it's drying, be careful; if scratched with your fingernail or abraided in some way, it will "tear" and tend to peel if you try to rub out your scratch. If you scratch it, rub it gently with a paper towel to smooth the tear back down, and then apply more Patio Paint over it. To avoid visible brush strokes, use a very soft bristled, flat artists brush.
DecoArt claims that Patio Paint does not need a sealer over it -- that it is flexible and weather-proof. Based upon the way the clear-coat application that I applied "feels" after drying, I sense this to be true; however, considering the hours I have invested into this project and the fact that winter is approaching soon, I want to make sure. So, while at Michael's, I also discovered a matte-finish, multi-surface (wood, painted surfaces, plaster, etc.) polyurethane varnish also made by DecoArt, which is rated for exterior use (also availabe in satin and gloss). Many sealers that I have looked at indicate that they are not suitable for outdoor applications. So, instead of using a "concrete sealer" (as I am afraid it might degrade my acrylic paint job), I am going to apply this varnish over the Patio Paint clear-coat. As was the case with another person who posted a question, my focus at this point is sealing/protecting the PAINT, not the concrete.
Based upon my experience with this project, if anyone is painting a statue or fountain one solid color -- I think tinted masonry paint (such as UGL masonry waterproofer) or those referenced on the Minnesota statuary company's website are perfectly fine. But, if you are doing a detailed painting job, whereby you need a number of different colors (thus, it's not practical to buy quarts/gallons), I'd go with Patio Paint. While I have only used the clear-coat at this point, in the spring, I am going to experiment using the colored Patio Paint on other smaller, unpainted concrete statuary and bird baths that I have, as well as terra cotta pots -- and see how it hold up without sealing. I will try to remember to add a post regarding the durabiltiy of the exterior varnish that I have yet to apply.