I finished doing an attached spillway spa to my pool with Sider-Proof FF-PR roll on plaster. Here is what I learned:
First, for a spa project and small areas, mixing an entire bag was too much to work in the allotted time (about an hour at 70 degrees). Mixing 1/4 bags and 1/8 bags by weight, e.g. 10 lbs of powder to 42 ounces of resin, worked great for me and I had no problems blending the edges of adjacent work areas. Second, I switched to a 4" roller instead of a full size paint roller. Third, a spray bottle with water was THE KEY to getting a smoother finish for me. Roll it on kinda of thick, clean the magic trowel with a sponge in a rectangular bucket to keep the trowel in, hit the area with a few mists of water from the bottle, and then trowel it smooth. You can get too much water on the surface, but that comes off with a grout sponge way easier and looked better than having it too dry and creating bumps/humps. Fourth, 6" sanding discs, 80 grit medium and 120 grit fine, with my air orbital sander worked better than manual labor and the sanding sponge option. Fifth, get a 2 gallon bucket and use a smaller mixing attachment for your drill for smaller quantities. Sixth, for bullnose corners on steps/seats, I took a 6" plastic trowel and heated it with a heat gun, then folded/rounded it down the center in line with the handle into a 90 degree bullnose trowel. Worked perfect for applying a thick amount of product to the edge.
Overall, after day one, I thought I was in big trouble. Did an entire bag, product became too firm by the time I got to the end of the spa (80" diameter and about 48" deep with a bench seat and jets, tile insets, drains, etc). For the second and third days, I broke it down into smaller, more manageable areas, and had more time to smooth. Project now goes from a 4 out of 10 after day one to a 9 out of 10 after day five. Getting the finish as smooth as a professional (mainly because my delivery method is a roller instead of spraying it on - thickness varies during application) is not a problem with the product, but with me as my lack of experience showed early on. By then end of the project, I was able to apply and smooth the product that would rival the pros. I feel the ideal "team" would be three people: One to apply the product and keep about 4 square feet ahead of the second person who smooths the finish, with the third person mixing ahead if you are doing large areas and making sure you have clean water for your tools.
In summary, I'm very pleased. Color is white and uniform. To do a "skin-coat" from the plaster guy was going to be $1,000 and this ran about $300 and I now have total control over being able to work on/fix any future plaster issues. I would recommend this product but would also say that this borders on a 10 of 10 on the difficulty scale (for a spa anyway).