I have become a big fan of using AquaStrip remover on fiberglass and wood. Paint it on and let it sit, warm weather is better. Possibly paint on a second coat. Then lift the old junk away. Can get expensive, and messy, but easy and the offset of saved labor and time seems to be a fair trade. Once the paint is gone, you can sand to prep for new paint, change non-skid, etc as desired.
Here it is in action stripping 25 years of Cetol over original varnish for lots of teak on my 22' Marshall Cat, and also did great removing years of Penetrol build-up left from the prior owner's use of that stuff to keep decks looking good,. (It's OK until you stop, and then it is black and peeling.)
So I took home my engine panel (cockpit floor) for refinishing. It looks particularly bad and I want it to be a test run for possible future deck painting.
It's mostly painted non-skid (of unknown type) So first I tried the heat gun and scraper with some success. It was able to cleanly lift off chunks of the non-skid right down to the old gelcoat, although it was slow going and required a lot of heat.
Next I tried Aqua Strip. On the edges which aren't non-skid this worked pretty well, however after two coats (4 hours, 20 hours) it hasn't penetrated the non-skid. And worse, now the nonskid can't be removed by scraping because it doesn't hold together.
As another test I attacked it with the random orbital sander with 80 grit. It resisted this pretty damn well. 10 minutes had produced almost no results, far worse than scraping.
Any suggestions? It appears the non-skid was best removed by the heat gun and scraping. Although I'm still hoping another coat or two of Aqua Strip will get down to the gelcoat.
So far this effort on roughly 4 square feet doesn't bode well for future painting of the entire deck...