Extruded Polystyrene: High-load 60 type

Hi all,

I have a potential line on some sheets of extruded polystyrene foam that look somewhat interesting. The supplier calls it high-load 60.

8’ x 2’ x 3" sheets, 2lb. density, 60 psi crushing stength (at least I think that’s the right term), blue.

Does anybody have experience shaping this exact stuff? I couldn’t tell for sure, but it felt like it might tend to come off in chunks when shaping, and/or not sand very well. Those would be my only reservations. Any advice appreciated!

Ive shaped some boards out of blue styrofoam the density was 28kg per cubic metre not sure what that is in imperial,

Shapes easy with no problems, but delames easy if its just glass and resin over it. It really needs a pvc sandwich to cover it then no problems with delam.


There is a lot of info in the archives on this material. Type in blue foam, blue dow foam…or something similar. I made one board with 1-1/2 lb density home depot EPS, 3x6oz deck and 2x6oz bottom, glass it heavy and it should last a while. Mine is almost 6months old and still goin strong, I thought it would have fallen apart by now. The shaping should go fine, be prepared to fill small rips or places where small beads fall out, I used watered down spackling. Have fun and look in the archives…peace and waves…

Sean W.

Yep, I did a board with that stuff…It sounds like Dow brand Styrofoam (the white beaded stuff is NOT Styrofoam, Dow has the trademark on that brand name, it’s their extruded foam, which does not have beads) It does tear easily, but usually a gentle touch remedies that…80 grit sandpaper works really well, use a gentle touch when surforming…

This is not the beaded stuff, so don’t spackle the surface, you will just get a weak bond. One of the biggest draws is that it does not take in water whatsoever.

Don’t forget, you have to use epoxy. Poly will melt the foam…

The stuff has really good physicals–good dent resistance, strong, stiff and light. I made my board stringerless, with 3x4 oz bottom and 3x4 oz deck, with a 6 oz deck patch, and it’s a little lighter and WAY stronger than a PU / polyester board I have that’s a similar size.

The other problem with the stuff is that nothing sticks to it very well, and since it doesn’t take in water or any liquid, epoxy will not seep into the foam at all. The usual solution is to leave the blank rough sanded, and baste it before glassing it, really squeegeeing the epoxy into the foam, hard. I went an extra step, and cut shallow parallel razor cuts into the foam. the resin went into these grooves, creating a physical bond with the foam. I did some peel tests before glassing, and this produced the best result, big hunks of foam were coming up with my test strips.

I would not reccomend this stuff if you are going to be in a hot area. Apparently it gasses out when heated, and will delam. I live in San Francisco, so no problems—I’ve been surfing my dow board HARD for about three months now and it’s doing fine.

There’s plenty of discussion about it’s utility as a foam in the archives, with advocates and foes, and what I took from it all is that it’s great for backyard boards, but not reliable enough for production. I think the production guys would love to use it because it has the best physicals and does not take in at all, but the delam issue has not been solved.

BTW, I managed to get a four inch sheet, and cut the rocker in six slices, then glued them up sideways to make my blank. (as if I had five stringers, but they are just glue-lines) I clamped a rocker jig on either side of the 4" block, and used wound guitar string in a sawing motion, running along my rocker templates. The friction with the foam heats up the wire just enough to cut, and no nasty fumes. (if you hotwire, USE A RESPIRATOR! AND VENTILATION! the stuff gives off nasty fumes. basically if you can smell it at all, it’s too much. I think there is cyanide there, as well as other stuff!)

hope this helps…

Thanks, all.

You’re right, it is Dow brand Styrofoam. It had a different feel to it than the stuff I’ve seen at Home Despot, which I guess is due to its higher density and toughness. I’ll look at that as a good thing.

Wells, I like your guitar string pseudo hotwire trick. A friend of mine laminates his blanks in the same way you describe, with good results as well.

Thanks also for the tip on using a respirator if hotwiring that stuff for real. When I was a kid, I used to burn scraps of blue foam just because I thought it looked cool and smelled good. Guess I wasn’t doing myself any favors. Hm, maybe that explains a thing or two …

Wells - Sounds good. What type of glue do you use and did it cause any problem with shaping ridges along the glue lines? Photos please.

Hi John,

I just used a thin coat of RR epoxy.

Before I cut the rocker segments, I rough sanded the block, so all the bonding sections would take the epoxy. While gluing up, I squeegeed the resin into the foam HARD, going over it several times to really get it in there, and scrape any excess out. I probably used less than 4 oz. for all 5 joints. I wanted something that would stick the segments together, but not impede shaping much. My reasoning went that when bonding foam, the bond need be only as strong as the foam itself–anything more, and it’s just overkill. I did some tests, and with this method, chunks of foam were tearing right across the seam, meaning the seam was generally about as strong as the foam, no more, no less.

I did have a bit of a problem shaping the glue lines, but only during the veery fine work at the end, and it was no problem to just plane down the ridges, and chip out little flakes of epoxy where the line crossed the rail curve. I think in the future, I will attempt to tape off where I think I will be shaping the rails, and put no epoxy there while gluing up the blank.

Gluing up the blue foam is a breeze, it’s so stiff and resilient, that there is no worry of it flexing out of shape. I basically made a rack with two level bars for the sections to rest on, rocker-cut side down, put each piece beside the previous as I was squeegeeing each side, and then wrapped the whole stack in saran wrap to hold it together. Just stretch that stuff out tight each wrap, and many wraps really add up to a lot of pressure. Also, when you cut it off the blank, it makes a good drop-cloth! Two rolls is more than enough. It lined up so well that a quick rough sand was all it took to get a smooth perfectly flat bottom. contours were added later.

I’ve been meaning to do a write up on the board for the resources section, it’s my third board, and was done entirely by hand, in an apartment and back yard in san francisco. Some of the strange solutions I came up with might be of use to the limited resource backyard builder…I have pics of the board, just too lazy/busy/out of funds to run the film over to the walgreens and type up some description. Speaking of out of funds, anyone need an inexpensive architectural and interior design photographer in the bay area heh heh?