Styrofoam Coating Help

[willwoll100]

Hello everyone hope all is well :)

I've tried to search to find an answer and I found one thread but just got a bit lost reading it. Anyway I've got a Styrofoam wind tunnel model that I would like to coat so that the surface is relatively smooth. I initially tried to cover it in clay but obviously it cracked so has anyone got any ideas of what I could use.

By the way I'm based in the UK.

Regards

William Wallace

[EJB]

Dear Braveheart,

The trick is to find out what your 'styrofoam' is made of and what coatings will not eat it. Cheap and easy is to give it several coats of water based GESSO, the kind used for priming a canvas before painting. Sanding lightly between coats will help keep it smooth. You can then make the whole thing more durable by layering coats of resin, epoxy or auto body filler, again sanding between coats to shape and smooth. Generally speaking many thin coats are better than one thick one. Good luck!

[BMBourgoyne]

depends on what kind of surface you are looking for:
smoothness, durability, ease of application/shaping, and cost

assuming you taking about polystyrene foam (i.e., Styrofoam), it is easily dissolved by most solvent based materials (esp. polyester resins like fiberglass, Bondo, or fast dry spray paints), but a barrier coat of some kind (such as the gesso suggested above, or shellac, or glued-on paper or foil) will let you use any of these

for durability, fiberglass or a polyurethane plastic ranks best. see www.smooth-on.com for some sprayable plastics. these tend towards expensive, hard to apply, and toxic

for something relatively small, Bondo (automotive body filler) is a good option-- almost as strong as plastic or fiberglass but simple to apply (though still toxic)

plaster impregnated gauze ("plaster wrap") or cheesecloth is easy to apply and smooth, as well as relatively cheap, but brittle

joint compound (plaster paste used for covering the joints in gypsum wall board) over a glued-on paper (applied with wall paper paste) is even easy to apply and smooth, very cheap, but takes longer to set up and dry

a hard wax (such as parrafin) melted down and brushed over an aluminum foil barrier (applied with spray adhesive) is an option I have used frequently, as it is easiest of all, but least durable

and of course, simply gluing on a layer of paper using wall paper paste or aluminum foil using spray adhesive will give a pretty good surface, though not completely smooth.

good luck
Brad

[Merlion]

assuming you taking about polystyrene foam (i.e., Styrofoam), it is easily dissolved by most solvent based materials (esp. polyester resins like fiberglass, Bondo, or fast dry spray paints

I had some interesting (fortunately not nasty) experience relating to styroform being 'eaten' by polyester resin.

To reduce the weight of my clay model, I put some styroform blocks inside before adding on the clay. But the clay was a bit thin at some parts.

So when I finished modeling and casted my fibreglass polyester resin, this resin dissolves and 'eats' a few craters into the styrofoam backing blocks. Fortunately the result is a few bumps in the casted fibreglass resin, and they can be removed easily.

I suppose this is not the action of the polyester resin, but that of the solvent of the liquid resin.

[BMBourgoyne]

a barrier coat of some kind will prevent the styrofoam from dissolving-- such as gesso, shellac, or paper/foil.

as I use to tell students, ALWAYS TEST material compatability on scraps-- even when following the advice of others. Many a student has watched a project dissolve before their eyes the night before it was due because they did not heed this warning (or read the project instructions).

good luck
Brad

[Merlion]

I'll come back to this old thread. I was doing a test trying to apply the quick dry spray paint on polystyrene foam. This is the common EPS foam formed by small expanded beads.

The paint does not cover the surface completely. Instead it leaves an unusual texture, full or small craters, see attached. One side of the block is painted black while the other side is not.

Now I notice this comment below by BMBourgoune

assuming you taking about polystyrene foam (i.e., Styrofoam), it is easily dissolved by most solvent based materials (esp. polyester resins like fiberglass, Bondo, or fast dry spray paints),

But the paint does not seem to dissolve the PS. It just does not stick to the beads. It gathers on the edges around the beads, leaving small round cavities. It is an interesting texture.

[rberger54]

I was just doing some research & came across this old thread - so it may be kind of late. As we all know styrofoam is disolved by most non-water based solovents, fibergalss layup is impossible. Couple years ago I was experimenting with the problem. My solution was:

Mix 50% latex paint into 50% Hide Wood Glue - like elmers glue. Maybe 20% 80%. The paint - I used flat black - will tell you how thick your coating is. It will paint & kind of stick to the foam - 90% seemingly. You can pick it off - but you really have to try. The glue has some structural integrety. It does make a smooth surface, you can dip it for instance. But the trick is - it lasted long enough to paint the surface or do a gel coat in advance of fiber glass layup, or even a direct fiberglass layup. I found the wood glue is very similar to a standard parting - PVA (Poly Vinal Alchohol) - only much thicker. If you can completely seal the foam - the fiberglass resin will be prevented from affecting the foam.

After developing the method - I have not used it since - something I guess I need to go back to. Just throwing it out there if anybody else wants to play further with it.

[Merlion]

I've been told by my resin supplier that epoxy resin would not dissolve the beaded EPS (or expanded polystyrene).

Epoxy resin is suitable as a coating, or to lay in fiberglass matt, just like polyester resin. Actually it is superior, just more expensive.