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"What's a good coating material for making styrofoam planets?" Topic

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Gearhead21 Mar 2020 4:19 p.m. PST

I've got a lot of spheres of varying sizes, and I want to start making planets. Trouble is, I don't know what the best material to prepare their surface is. In the past, I've tried gesso and a product called Mod Podge, but each has its own problems. I've heard someone recommend PVA, but I'm not at all sure. What about plaster of Paris?

Any ideas, preferences, or advice?

Personal logo Dentatus Sponsoring Member of TMP Fezian21 Mar 2020 5:00 p.m. PST

Don't know about planets but I always seal foam structures with a mixture of latex house paint and white glue before I do anything.

Gearhead21 Mar 2020 5:11 p.m. PST

Hmm. The biggest challenge is the fact that there's so much filling to do, not just sealing.

tima113 Supporting Member of TMP21 Mar 2020 5:40 p.m. PST

There's a product called foamcoat that can be smoothed with a wet sponge before it dries. Saw it at a model RR show sometime ago.

Gearhead21 Mar 2020 6:08 p.m. PST

Thanks, I'll take a look!

Chimpy21 Mar 2020 6:52 p.m. PST

I just painted mine directly with acrylic blues and greens. The beading in the polystyrene adds a textured effect. I bought a model of the solar system and just cut the planets in half before painting.They make great looking ice planets or moons although that may be not the effect you're looking for.

Gearhead21 Mar 2020 7:01 p.m. PST

The ones I have aren't expanded beads, and their surfaces are pretty rough. They really do need a lot of prep and filling. The Mod Podge stuff was a lot like PVA, and it took countless layers and sanding to get a nice smooth surface. Way too much work, and it actually started to bubble (trapped air forcing itself up) after a few months!

dampfpanzerwagon Fezian22 Mar 2020 2:39 a.m. PST

I second Mod Podge.


Gearhead22 Mar 2020 6:38 a.m. PST

Rosco brand FoamCoat looks awesome, but it's professional-grade stuff, sold by the gallon and a bit too pricey for my needs. If I was doing more projects and would actually use it up before it went bad or hardened in the bucket, it'd probably be perfect.

I do see some alternatives from other manufacturers that might be okay, and are sold in smaller amounts.

Thresher0122 Mar 2020 8:56 a.m. PST

You could just buy wooden, plastic, or rubber balls.

I like the inexpensive, latter ones, that are filled with air, and you used to be able to purchase for $1.00 USD or so. They can be partially deflated, come in various swirled colors, and make great planets of various sizes (I like mine big and imposing). Orange ones make great suns/stars too.

Gearhead22 Mar 2020 9:12 a.m. PST

Well, I already have a bunch, so I'd rather use them up; it's what I got them for anyway.

BuckeyeBob22 Mar 2020 4:33 p.m. PST

this video mentions a large number of sealants for foam. Perhaps it may help you.

Personal logo Sgt Slag Supporting Member of TMP23 Mar 2020 7:50 a.m. PST

I've heard of people using spackling/dry-wall patch compound, with a wet sponge to smooth it out, before it dries. Then lightly sand, as needed. The spackling will take any paint, as it seals the foam, if it covers it… Otherwise, use a first layer of latex paint, ensuring complete coverage. Follow that with any type of paint you desire, water-based, or solvent-based. Cheers!

Personal logo javelin98 Supporting Member of TMP23 Mar 2020 11:19 a.m. PST

Both of these work fine, although you might need multiple coats to get a smooth surface. I think you could use gesso to paint on your land masses and then use one of these foam-friendly paints to give the whole globe a base coat, which should then help lock the gesso down and prevent it from flaking off.


EDIT: Krylon used to make a latex line called H2O, but I think it's been discontinued. That's a shame, because it was great stuff for use with styrofoam.

billclo23 Dec 2021 11:02 a.m. PST

Make paper-mache planets, inflating them with a balloon, then puncture it after the outside dries?

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