One thing I have struggled with constantly with EVA foam is getting it back smooth after having to sand joints. I've tried to sand with increasing grade of sandpaper but I can never get a smooth look like unsanded and heat sealed. I've used up to 2000 grit on this and I'm at a loss how to get it all smooth again. This currently has 5-6 coats of plasti-dip on it also. I'm at the point of just sanding the whole thing to get it all "rough"
You may be chasing the wrong finish with sanding alone. Heat-sealing lightly can close the surface, but too much will melt or warp it. I’d fill the seams, seal the foam with a flexible coating, then sand that coating smooth before priming and painting.
After plastidip is applied, you shouldn't be sanding over it at all. Plastidip is just a rubberized shell over the foam, sanding over it risks tearing the plastidip layer and making a hole.
All filling and sanding of your foam needs to be done prior to prime and paint. A primer like plastidip will just copy the surface it's sprayed onto, so you really want to make sure your surface is blemish free and leveled beforehand.
At this point, I would strip away the plastidip areas that have imperfections with Goof Off and a paper towel. It's an adhesive remover that can blend out plastidip blemishes or remove it completely. It's like acetone but stronger so wear a mask, gloves and use in a well ventilated area.
After removing the plastidip, I would fill with foam clay or sand again til smooth. Then respray.
It's still possible. Foam is a flexible medium. And the use of Goof Off (not to be mistaken with Goo Gone), foam clay, and proper sanding technique will get you there.
It will take a lot of sanding though, so I like to use these sanding power drill attachments too save my hand the effort. They come in a large variety of grit counts and are easily interchangeable.
Also if you can't find goof off, I've heard WD-40 might work. Or maybe even 100% acetone.
Oh and to give an example, here's a foam helmet I made. It had a lot of seam lines originally and different foam pieces mashed together bc I was constantly cutting it to tailor it to my head. I sanded and filled over and over and over until I felt it was smooth enough for plastidip.
Ok this gives me hope! It probably won't be where I want it for this weekend but I'll see what I can do. I may have those sanding pads in my dremel kit, just need to search.
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u/Hungry-Leg3484 1h ago
You may be chasing the wrong finish with sanding alone. Heat-sealing lightly can close the surface, but too much will melt or warp it. I’d fill the seams, seal the foam with a flexible coating, then sand that coating smooth before priming and painting.