What is a good glue for putting blocks of foam together, that will then be cut with a foam cutter? I suspect that the Poly. glues will be too hard to drag a wire through. I tried a new Elmer's spray on glue that does not hold very well. I was able to pull the blocks a part by hand.

Dave Brown's Southern sorghum rubber cement works pretty good. Hot wire cuts through it fine.

3M Super 77 spray adhesive. Just don't get it on too thick, or it will melt the foam. Just a light spray is all you need.

Why use something that is going to melt the foam if you get it on too thick? I swore off 3M #77 years ago when I switched to epoxy and Dave Browns contact adhesive. Now the only thing I use on foam is Pro Bond. It will not hurt the foam and achieves a far superior bond than any contact adhesive or epoxy. It hot wires well also, because it's a foam. Just don't inhale the vapors.

Vince

I used 3M Super 77 for a long time, in the past I purchased it from Lowe's or Home Depo, I just purchased some from Wal-Mart and something has changed. Use the last of my old spray can and didn't have any problem but I just used the new can and it attached the foam. Either 3M has changed the formula or what is sold at Wal-Mart is not the same, which is hard to believe. I do know you need to spray it about 6 - 8 inches from the foam, which I did, so in conclusion I'm will now use something different.

Mainly because it is inexpensive. Super 77 works fine for me.

I have/had a case of 3M 90 high strenght spray. It eats the foam on contact. I tried to come up with a way of using it. I found that if I thin Titebond to a mix of 50/50 with water it puts a skin on it and I can use the 3M 90 without damage to the foam.

On a 64 inch wing I had to glue up two pieces for each core. So I had to coat four sides and the weight increase was less then a 1/2 oz from the Titebond. The 3M 90 is some strong stuff, I tried it on some ply wood and the wood gave way before the glue.

Dru.

Tweet ip,
Go back about 4 pages and there is a bunch of posts
about glueing foam and 3m 77.

A $4 or $5 bottle of Pro Bond will sheet many foam wings.

Vince

there was a article in quiet flight international that warned us about a new 3m77 out there. it does eat the foam. the orginal is still available and will state on the can that it is foam friendly., but there is 2 types out there now, so to be sure always test on a scrap piece before u riun a good piece. ,,,,,,,,,,,,,also, i always use 3m to bond pieces when making foam plugs that are cut with a wire.

My understanding is the the 3M 77 is now marketed in an ORANGE can, which is NOT foam compatible. The original BLACK can is the same old formula.

If you like the old formula, purchase all of the black cans you can find. They are going, going, almost all gone.

R. C.

"Dave Brown's Southern sorghum rubber cement works pretty good. Hot wire cuts through it fine."


Ditto that remark... done that a number of times on wing cores... cuts perfect everytime with no ill effects in wing strength(no strength in foam anyway!). Good luck.


Dan

Using any glue that has to dry is not good on foam. There is no way for the moisture or gasses to escape and dry. you need to use a glue such as epoxy that chemically cures without having to have access to the outside environment.

3M 77 is not cheap. Elmers spray glue is about 1/3 the price. I've also heard stories about spray glues delaminating. I don't build with foam, but when I did I used Southern Sorgham. Is that the stuff Dave Brown markets?

If I were to build with foam again I would use polyurethane adhesive (gorilla glue, pro bond, etc.) but not spray glue. I just don't trust the stuff. I use it around the shop for non-critical type things and it tends to harden and crumble after a year or so.

On the other hand, if you're like me and your planes only last a couple months, then it's never really an issue.

The 3m-77 formulation has changed, it now contains acetone. Instant death for foam. Sorgum is still the best for laminating, for all out brute strength in high stress areas polyurethane is excellent. Weighs less than epoxy too.

Elmers makes a probond series one is a polyurethane gsidehe lue I have used for couple of years you damp wet one side with water the the glue on the other side it is allmost like the wall
foam but more adhesive very strong even glueing large picces of glass or balsa. CU