Polystyrene adhesive

[BillConnerFASTC]

I'm working on a project - not theatre specific but I believe similar materials and processes to scenery - basically building a stressed skin panel with extruded polystyrene (XPX) cores and plywood skins. So far, it seems that 3Ms Fastbond 30NF is a good option and it's available from sources that I can order form and in quantities I can use. (I found some others that might be superior but they tend to be in drums of on pallets, and not set up to sell to a one project DIYer). It's basically a water based contact cement that won't dissolve the foamed plastic and provides a bond that is at least as strong as the "polystyrene tear strength", which I assume means it's strong enough. I wondered if anyone here had experience with this product and application.

 

[Colin]

I use 30NF frequently for laminating foam and attaching to a plywood substrate, although just for carving rather than something structural. It makes a very good bond in foam-to-foam situations, and with a little extra care it has bonded well to plywood too. Bonding to wood I usually need multiple coats on the wood side to seal the porosity and build up a smoother surface for contact. It seems like a size coat on the wood helps that aspect--paint usually, but I have done thin white glue and that worked too. Makes 1-2 coats work rather than 2-3. Not sure if the sizing maximizes the bond for a more critical application like stressed skin, or if it just makes it easier to get a merely adequate bond for carving, but it at least winds up strong enough to withstand being hacked at with all manner of hand and power tools we carve with.

I just pour and spread with a china brush because I can't stomach all the waste absorbed into a roller--stuff's expensive. I haven't gotten around to trying a squeegee, but I bet that could work well too. The type used for spreading poly on wood floors would be great for larger areas. If you get right to washing up, whatever you apply with can clean up and not turn into a brick. I've also seen people just submerge a brush or roller in a 5gal bucket of the stuff for preservation, but I don't like the inevitable gunk that introduces into a $300 bucket of glue. Drying time in my experience, even in a warm room at low humidity, is way longer than advertised. I've waited the better part of a day to make contact in cases where I may have been too liberal with the coating. A hair dryer works though.

 

[DRU]

When applying it to the foam, do 2-3 coats. The foam soaks up the adhesive pretty well. The adhesive also takes longer to dry on foam. The adhesive will go from light green to dark green as it dries.

I love the stuff; it just paints on with a brush or roller, so it is easy to apply. I've only used it for non-structural applications, such as foam moulding. I wanted to make a stressed skin with it, but I always felt that the adhesive never got stuck well together enough for me to try it.

 

[Colin]

The adhesive will go from light green to dark green as it dries

Oh yeah, that's another thing. Get the green version. Last time I ordered some they sent me the beige color by mistake and along with not being as fun to say as "green glue" it is also harder to judge coverage.

 

[BillConnerFASTC]

Good info. Thanks. I had sort of figured out I'd need to seal the plywood, or that it would help save glue. I'm doing some large areas, like 5' x 5' sections with 3/4" foam on 1/8 or 1/4" ply, so suspect I should figure out the roller thing - either a short roller that I can keep in the one gallon can or disposable rollers.

The green sees to be readily available. I was interested in the clear for the obvious reasons that some seams may show and the finished piece is varnished, not painted, but I get its very helpful to know where glue has been applied.

Many thanks.

 

[Van]

and don't rush it! let the stuff thoroughly set before adding the next coat. It forms a skin, it's essentially just a latex rubber in an ammonia/water medium, if you put it on too thick or if you try to rush it by using heaters it will skin over the puddles. this will lead to poor bonding once you go to mate the surfaces. We always used low nap rollers but if you be careful. If you roll too vigorously you can create a lot of little bubbles; this will lead to the same issue as above. I like to put the glue in a different container, preferably plastic, the stuff causes premature rusting on steel products even chip brush ferrells and roller handles and coffee cans, then push the chip brush through a slot cut into a matching plastic lid. This helps keep the glue from setting AND it acts as a drip guard to keep the runny glue off your fingers. Speaking of Fingers. If you happen to be hirsute be sure to wear gloves and or arm protectors. The glue is Latex based it will stick to hair instantly. I think the only reason they don't use it in Waxing studios is because the ammonia can really irritate skin. if it gets on you you have two options, wear it off or pull the hair out. Youch!

Happy Sticking!

 

[BillConnerFASTC]

Thanks, though not sure about advice from someone familiar with waxing salons.