APMM Community Forum : Fiberglass & Composites
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 Subject : Re:Polyester Resin over EPS.. 09/18/2018 03:43:00 PM 
Posts: 7
Location: Ebensburg, PA
At the shop I worked at eons ago, we had to make a lot of "rock wall" shapes (non structural, decorative only) for a science center exhibit. We mad a basic paper mache covering using diluted white glue and newspaper. After it dried, we went ahead with the fiberglass layers over top. Seemed like the cheapest, easiest choice at the time.
Scale Model Studios
 Subject : Re:Polyester Resin over EPS "Styrofoam".. 09/17/2018 01:49:35 PM 
Posts: 208
Location: Overland Park, KS
So I did some online research and acted upon my findings this weekend. Turns out, acrylic gesso makes a passable resist for saving EPS foam from the ravages of polyester resin during fiberglass lay-up. The source said to use multiple thin coats, rather than one or two thicker ones. Due to the size of the part I was working on (and the fact that I wasn't overly concerned if I got some surface distortion), I went ahead and used two thicker coats anyway. Having done that, my surface held up with no problems over about 98% of the surface. I had a few areas where the foam beneath got pitted out a bit (I'm guessing either the gesso just wasn't thick enough there, or some deeper pits in the EPS had never gotten gesso in them in the first place).

If you attempt to use this method yourself, I'd recommend using at least three coats of gesso, making sure to leave no EPS exposed.

Ultimately, I'm sure the high-tech primers listed above are a far better choice, if money is no object, or your surfaces are critical. Gesso has the advantages of being readily available at any art supply or craft store, cheap, and obtainable in quantities large or small right off the shelf.
 Subject : Re:Polyester Resin over EPS.. 09/12/2018 05:17:59 PM 
Posts: 208
Location: Overland Park, KS
(Reply to MILE from Mark Ferri)

Hi Michael,

Good questions. Our shop has used various hard coatings over large EPS forms. You can brush on a couple coats of Styroprime from Industrial Polymers before laying up polyester resin.
Another idea you can use just to create a structure is a product called Aqua-Resin. The two part water based liquid and powder components when mixed can be brushed on or sprayed through a standard paint gun. The 10 mil Aqua veil when applied does well “melting” into the surface and is very easy to sand smooth. It is also non-toxic.
There are other stronger, sprayable polyurethane and polyurea coatings offered by a Chemline in St Louis, but they are considerably more expensive and harder to work with. If anyone on the MILE is familiar, I would also appreciate advice on best practices for this product. Thanks!


Mark Ferri
3D Production Manager
 Subject : Polyester Resin over EPS "Styrofoam".. 09/11/2018 06:03:25 PM 
Posts: 208
Location: Overland Park, KS
Does anyone have experience applying polyester resin over EPS “Styrofoam”? I’m building a rather large sculptural object (6’ diameter hemisphere) using EPS as the core, and planning to put a layer of fiberglass over the exterior to give it a bit of structure. I’ve read that polyester resin will attack the EPS though, so I’m curious if anybody knows of an inexpensive resist that can be applied to create a barrier between the two? I know there are products like Styroshield made for this purpose, but the price on such products is high enough that I’d be money ahead switching to epoxy resin for the fiberglass lay-up before using those.

Any suggestions would be appreciated.
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