Hello

I have begun building my DAW Extra 300S, and after doing a lot of glue test (we do not have "Goop" in Denmark), I ended up using Polyurethane glue for the gluing the spars into the wing.

Is this the proper way to work with wood/EPP joins? I am also going to do some EPP/EPP (e.g. wing to fuselage) in the future, and will the Polyurethane (the kind that foams up) work here?

I was not totally happy with the test I made, since I could break the EPP/EPP join apart at the Polyurethane glue join.

JJ

I always thought It is impossible to break a foam-foam joint in the glue line. That is, you see glue on both sides of the break. Did you see the glue on both pieces of foam at the break? If you did, I can't explain it, PU is much stronger than the foam. Good polyurethane glue is very strong. I use PU on EPP/EPP joints with only one problem....that is, the darn stuff foams out of the joint and is VERY hard to remove after it dries. Taping over the joints helps keep the glue foaming to a minimum.
hoppy

Hoppy



I just read your post about poly glue foaming out of the joint and causing problems. I have done some extensive testing on various amounts of water added to the glue to promote curing. only very, very small amounts are needed for proper curing. Adding larger quanities of water causes more and more foaming almost to the point of the glue looking like 2 part insulation foam.
This result can be used to help fill spaces and such as it's harder and stronger then insulation foam. When proper amounts of water are used for curing foaming is very minimal with no loss of strength.

Stef

Stef,
I don't add any water. Here in Florida, the humidity is always high enough to cause "good" foaming. The Elmers ProBond Polyurethane may also be a high foamer for all I know. In any regards, it can be a mess.....probably the biggest mistake is using TOO much glue!
hoppy

yeah it's not the heat it's the hummdidity! Our humidity always seems a little low to insure good cure and a little foaming. That's why I started experimenting. Pretty tough to lower so you could control the foam. Just mixing up alittle right now elmers haven't tried any other brand.


Stef

This may help.On a butt joint I poke holes in both sides of the foam about 1/2 inch deep and about 3/32 dia.I let the water/poly mix start to foam then spread it very thin on one side,the holes will soak up almost all of the foam expansion and will give a very strong joint with all of those noodles,sort of like small spars.

Interesting ideas on the holes... I've been using poly for a while... Great stuff when you don't use too much... Too bad it can't be thinned....

Thanks for the tip!

Depending what you are going to use it on you can thin poly glue. A little acetone will thin it out and as long as the surface isn't attacked by the solvent it works fine.


Stef

Aurgh (/&#¤(/&#¤/(=#&¤(/&

Used PU to glue spars into wings (EPP) and now IU have noodles of hardened PU along the spars. Very hard to remove ")(#&/#)&"/#/()"#/)("/#)("&/#)(&/")?(&#)?/(#&

JJ

I have built a couple of the DAW EPP foamies and have had good success with just plain 5min epoxy for the spars. EPP/EPP have used goop but since you don't have that try bathtub silicone adhesive. It might work.. I have not tryed this but have considered it. Also look for a marina, they usually have some kind of silicone adhesives for marine type applications.

I think regular hot glue also works. EPP has a very high melting temp. Dave uses it on some of his combats. Watch the weight though.

Hope this helps
Killer