It sticks just fine, but you need a wetter mix and I find that throwing handfuls at the foam sticks better than trying to smear it on. I've got some grocery boxes I did in 2001 with cement and subsoil that are still looking fine.

Sometimes it helps to mix plain portland cement and water (half and half proportions I think) and use an old paintbrush to paint on a real quick, very thin, coating. This dries in minutes. You could do a search on "slurry" and find more references to it here on the forum. Adding some bonding agent liquid to this slurry couldn't hurt either.
This dry slurry layer makes it easier for the tufa or concrete to stick to slippery styrofoam.
Mixing some bonding agent into your hypertufa mix might also be enough to help it stick without doing the slurry step.
Try it different ways and see which you like best.
Good luck! - sounds like a great project
Laura
one other helpful thought.... be sure you have figured out how you will join all these parts and support them so they won't fall over, etc, etc, BEFORE you start. I sure wish I would follow this great advice more often!

Hi,

I followed the instructions that I found on a web page for constructing hypertufa-on-foam troughs. Their technique used a coat of carpenter's glue on the foam. Seems to work well. It would be easy to compare the results for glue to non-glue sample chunks if you were really curious; I didn't bother,

s_d

I wouldn't use PVA, I fear it would delaminate due to water sensitivity, maybe the cross linking stuff would work.

From what I've read about PVA fibers, PVA and cement form a chemical bond - the cement should be mixed with plain water as latex & acrylic admixes could interfere with that bond.

Hey Erv!

What are you using to keep your stacked coolers together? You might think about applying some (not alot) of drywall tape to help hold together your coolers and also give your tufa something to stick to, in addition to painting on any of the previously suggested sticky substances.

Jo