Smooth-on delam problem?

[Apex Predator]

The longbow that I am currently working on went crack this morning while I was stringing it up for the first time this morning.  The riser overlay was coming loose from the back of the bow.  I sanded the bubinga off of the black fiberglass accent, and then was able to pull off the fiberglass pretty easily.  I put the overlay on yesterday morning and it cooked for 4 hours at 140 deg.  The smooth-on is new to me, since I have only had it a couple of weeks.  I bought it from Threerivers, which has a lot of stock turn over, I'm sure.  I sanded both surfaces with 80 grit and cleaned everything with acetone.  The only thing I'm questioning is the ambient temp.  My garage was 50-55 deg when I laminated the overlays to the bow.  Maybe bad smooth-on?  I've been using smooth-on exclusively for the last 9 bows, and have had absolutely no problems.  Any ideas?

[Pat B]

Maybe reheating that section caused the glue to release. Try using a glue that doesn't require heat or at least much heat to cure. Gel superglue should work for it, especially for the handle overlay but the tips also.     Pat

[Apex Predator]

Nope.  It released on the newly cured joint.  The previously laminated joints were fine.  That is the reason I try to keep any add-on lams at least 15-20 degrees cooler during cureing.

[Pat B]

Did it come off the tips too. If not, maybe the area was accidentally contaminated.  I have never used smooth-on so these are only guesses.  Pat

[Apex Predator]

The tips are ok so far, but all I have done is strung the bow.  There was just the slightest flexing around the fades that started the riser overlay de-lam.  The tips are under very little stress until shooting.  I'm not sure I trust to shoot her.  I plan to re-do them as well.

[Pat B]

If the handle area is flexing, your overlay will need to flex also.

[snapper1d]

Here's something I have found.This will probably stir up arguments but here is what I found.SmoothOn tech sheet says on it to sand clean and when using it on metals to sand and ruff up the surface.I have seen bows where the lams were ran thru a sander using 60 grit that there can be many tiny bubbles under the glass because the epoxy just cant get into.I have had limbs delam because of it also.Now I sand my lams down smooth with 220 grit to get rid of the deep grooves and sanding marks left by the 60 grit.With clear .040 glass you can still see score marks in the lams from using 60 grit in a sander.I may be a perfectionist now but I dont have problems now either.I have read where some people recommend scoring up the wood with hacksaw blades and thing trying to get a better glue surface but if so you will still get those little pockets where glue cant get down into and there will be voids there.Well let the worm in that can I have opened out and lets go fishing.

[Apex Predator]

I think I have narrowed this down to several problems after reading the respsonses here and on another fourm, and some reflection.

1. It was too cool in my shop. I need to either pre-heat my materials, or heat my shop.

2. The overlay was about an inch longer than I normally make them. I think that it just extended into the bending part of the limb. I will go back to the normal length.

3. The overlay was unfinished and too thick to start bending. I will thin it close to final thickness before stressing next time.

Thanks for the help folks.

[snapper1d]

Too cool will definitely do it.

[BenBow]

also you have to be sure to stir it together for at least a couple of minutes. I've had trouble when I've gotten in a hurry or didn't think the joint was a high stress one and not taken the time for proper mixing.

[BigJim]

I use 36 grit on all of my lambs and I make all of my own lams without any problems. I Know when I was making lams for another big company and sanding with 50 grit, they weren't happy with the 50. They requested coarser.

I see no sign of lines under glass caused by rough wood. I do see some lines in glass itself ocasionally and can get bubbles from too much moisture in wood.

Just my experience, BigJim

[Ken E.]

I had similar problems in the past while glueing up bows during the cold months in my basement(about 55 degrees).  I had bows delaminating.  I contacted smooth-on and they said it must be 70 degrees for the epoxy parts to mix and work properly. I now heat the basement during glue-ups and have had no problems.

Ken