I bet when it happened you said 'oh dear me'.
However, I reckon you are doing the right thing in patching, rather than ripping it all off.
Now, the HeatnBond doesn't really bond to the Dacron, it is a meltable plastic which penetrates a fabric, then solidifies.
This seems fine for a longitudinal pull as you are using all of the surface - but a vertical pull stresses just one small part at a time, and the HeatnBond plastic gives way.
You do have a longitudinal bond, but when you shrink the Dacron, you will be using a hotter setting, and the HeatnBond will soften and give way. You might be able to work round it though,
by shrinking everywhere else. Tricky. There are usually small wrinkles left close to the gunwale which have to be sort of mopped up, although you could leave them if they were not too big.
Dacron is polyester and is funny stuff to glue as the surface is quite inert (doesn't form bonds). You need a specialist system like Loctite Super Glue, All Plastic, which does the trick. It has a priming pen (which presumably activates the surface), then you just superglue as normal with the other tube of glue. This seems to result in a really strong bond, which should be ok to heat - although I have not tried the heating/shrinking myself. Best try it out with a couple of scraps of Dacron first.
You should not need to overlap much - half an inch would be plenty and give lots of strength, then shrink as normal.
By the way, if your
iron was fluctuating, then you may also have already taken up some of the shrinkage in the Dacron - I certainly did, and only had limited capacity/leeway at the very end (just made it though).
I think all irons tend to cycle - heat up, then cool down, so it's best to try to be on the cautious side. Luckily, the iron I used ( also a cheap one) would not burn the Dacron even at it's highest setting.
Sent: Saturday, 28 May 2011, 21:08
Subject: [Airolite_Boats] Yikes
I bought a cheap iron to use on my 16 ft canoe. It had a heat surge just as I was finishing attaching the Dacron to gunwales. So, I now have a 2"x1/2" burn hole in the Dacron on the gunwale about 18 inches from the stem. I was planning on apply another layer of Heat N Bound and patch. But, I am afraid of what will happen when I shrink the Dacron. Should I patch it after I shrink?
I would really welcome any and all suggestions.