......I finished with 1500, and polished it after that, but there seems to be a slight bluish/white cast to the finish. It didn't get back to the actual glass-like look that it had before I sanded it down.........it seems that it marks very easily in the state that it's in. Should I let it sit for another week or so before using it? Will the polycrylic get harder over time? It just seems soft......
Lets start off with sanding. Always start with a grit that will actually flatten your surface and keep it lubricated. Water should work just fine for that. Some people use mineral oil, but I dont know what will or will not react with Polycrylic. Once your surface looks flat and level, move up about 2 notches on the grit scale and remove ALL the previous sanding marks. keep doing that untill you get to about 5,000 or 6,000 grit. Then use any automobile rubbing compound to remove the scratches you cant even see from the 6,000 grit. This should give you a low luster. For a deep mirror shine, step up to a good automotive polish. The mirror finish is dependant on all of the stages of sanding. That is, if you started with 400 grit and next jump to 1,000 grit, the 1,000 may not get out all of the 400 grit scratches.
Ok, now for problem solving. Lets start with the bluish/white cast. Since you put on the Polycrylic too thick it is probably still somewhat soft. It is conceivably possible that the surface absorbed some of the wet/dry sandpaper backing dye or maybe reacted with the rubbing compound. The softness, again, is attributed to the heavy coating. As stated earlier, part of the drying process of the first coat is evaporation of solvents. The solvents in the finish are trying to work their way out so the finish could dry and it has a lot of layers to penetrate.
let me state that I am not familiar with Polycrylic so anything I say is just an educated guess. I looked briefly on the Minwax site and didnt get much info on the Polycrylic as to what it is so I am guessing that it has a high acrylic base. Acrylics are relatively soft compared to most varnishes and lacquers but should still be OK. Next.......Min-wax is a fa cocta brand of finish. Ask someone who speaks Yiddish to translate although you can probably figure that out yourself. If a product is sold in Walmart or Home Depot, youcan bet it is bottom of the line.
Back to your finish...... let it harden another week or so and then start with the sanding procedure all over again and I think you will be just fine.