This from Jim Michalak's April, 2002 newsletter
http://homepages.apci.net/~michalak/
I hear Jim is about to publish a book. Judging by the quality of information
in his newsletters, I say, buy it!
I BOIL WOOD
Blame it all on the late Pete Culler. He was talking about making boats and
boating things with Weldwood glue, which is a powdered glue that you mix with
water. Very easy to use but the manufacturer says it is water resistant, not
waterproof. The usual way to test glue quickly for waterproof is to boil it for
an hour. Culler said something like "If you're going to boil your boat,
don't use Weldwood" and was widely quoted thusly, including by Harold
Payson who has done more to educate us about plywood boats than anyone.
So I made several boats using Weldwood and still have several around and
don't worry about it. But one of them, a Bolger Jinni that was my second
homemade boat, had to sit outside for several years and it often filled somewhat
with rainwater in storage. After a few years of this treatment I noticed the
internal chine logs were getting spongy where they were constantly wet and
little leaved plants were growing out of them at times. One year I chopped out
the bad parts and noticed there was no sign of any glue in those joints, they
were held only by nails and the external fiberglass tapes. I gave it little
thought thinking that I didn't get enough glue in the joints during assembly. I
repaired the chines with fiberglass/epoxy taped seams and made a cover for the
boat and improved the drainage. But a year or two later the mainmast, which was
laminated from two pieces of wood, came apart at the base where it stuck out
from under the cover. The Weldwood there was also gone.
And I came to the conclusion that Weldwood, indeed, was not totally
waterproof. And the boil test was perhaps not a lot of hooey after all!
PLYWOOD...
Plywood glue has always caused worries and since it varies so much from load
to load I began to advise that builders boil a piece if they were at all
suspicious. I got a letter from one builder who had boiled some "good
buy" plywood and it delaminated after 20 minutes in the boil pot. Was that
good enough?
I didn't really know since I had never boiled anything!
So I rounded up some different plywoods that I had out in the shop, all of
which were supposed to have "exterior" glue. I put them in a pot and,
when my wife was away, boiled them on the stove.
My first sample was a piece of cheap 3/8" BC pine. After an hour in the
boil it showed no sign of delamination.
My second sample was a piece of 3/8" (actually slightly less) exterior
plywood that I had used for the bottom of my AF4 which I built four years ago.
This had two thick crude looking plies of fir (I think) with a thin skin facing
of a flawless mystery wood. After an hour in the boil it showed no sign of
delamination.
My third sample was a piece of cheap 1/4" lauan underlayment which was
sold at a real lumberyard, not a depot type of store. The sheet was unmarked but
the yard said it had waterproof glue. After an hour in the boil it showed no
sign of delamination.
So the builder's plywood that was delaminating after 20 minutes in the boil
was clearly not the same stuff I had.
And now more than ever I think the boil test is a good quick way of checking
glue.
GLUED JOINTS IN LUMBER...
With the plywood testing done I thought to test in the same way some glues
that have been used in cheap boatbuilding. Here are my results.
Weldwood. A few years back I cut a small section off the edge of my
Birdwatcher's centerboard and I tested that piece. The board is laminated from
layers of 1/4" plywood using Weldwood water mix glue. After an hour in the
boil pot it was still quite together which is interesting since this is the glue
that caused all the furor in the first place. I was able to pry it apart with a
knife but I'm still not sure what that means.
Tightbond2, it says "not for use below waterline" right on
the bottle. Guess what? After an hour in the boil it held up as well as any glue
tried.
PL Premium is a construction glue that you use in a caulking gun. Very
handy and thick so exact fits or lots of pressure aren't needed. I had a piece
of an old project, about 3 years old, that had a 2x2 glued to 3/8" plywood
with this glue and it had been outside the entire time with no sign of failure.
After an hour in the boil pot it looked quite solid but when I gave the glue
line a pry with a knife it popped apart cleanly where the glue met the wood.
Strictly speaking I suppose that is a failure. But here is another test result
from a recent email I got:
" First, I am using PL premium for the glue. I tested the strength by
gluing up two small 2 X2's, letting it dry and I soaked it in water for a
week(submerged). I then took a 5 lb sledge and commenced on beating it soundly.
It held. I was impressed. I did the same with a liquid nails product and it
broke apart with handstrength."
Epoxy, in this case a bit of "DC7" which is an epoxy paste
in a little can from the hardware store. I've used it with total success to stop
rust holes in old fuel tanks. After an hour in the boil it held well but clearly
was getting very soft, as did the PL Premium. Epoxy is well know to have
strength problems at higher temperatures.
WHAT IT ALL MEANS..
Like Pete Culler I think all the glue are sufficient for a boat that is
stored under cover. As for the long term effect of water on the glues, I'm not
sure the test proves anything. The idea of " I soaked it for a few
weeks" may not be good enough for a boat that will sit in the water (or
fill with rainwater) for months at a time.
I would not use any plywood that didn't pass the one hour boil test. After
all, the pieces I used passed and they were from very cheap sheets. And just
because the plywood passes the boil test, it may delaminate in places where not
enough glue was used. The lauan I tested was like that - bubbles and peels at
edges where there isn't enough glue.
A Final Thought..... I saw this posted by Dave Carnell on
news:rec.boats.building
"....the real advantageof interior glue is that it is a cold press
operation vs. the hot press operation required for exterior glues.
The durability of the interior glues is surprising in some ways. I once
tested lauan underlayment by soaking in water until it sank, drying at 150°F.
in an oven, resoaking, and redrying. It didn't delaminate. I also tried freezing
it while wet and it held together. When I bent it for boat planking on a hull
being built outdoors, it came apart as soon as it got rained on. Once it is
stressed, the whole game changes.
I have seen people talk about testing in a dishwasher, but that isn't good
enough. Boil it for an hour or two. If it doesn't hold together, it is no
good."