Parallax ) writes:
All of this is probably well known to most ppl here but is new to me.
In making my two Mini-Cups, I have experimented with various glues. I
just cannot resist the temptation to do somethign a different way.
So, here is my opinion.

I did some research at the public library and in this newsgroup before
building my first small plywood boat in 1999. Any home repair book at the
public library will have a section on adhesives although they don't deal
specifically with boats. At that time I used screws and urea formaldehyde
adhesive, a water resistent plastic resin first used in the 1930's on
plywood motor torpedo boats and plywood airplanes in the war and still
used in the manufacture of plywood, predating epoxide resins (I used a
local Canadian brand but its sold in the USA as Weldwood dry powder marine
glue) Not gap filling on its own but sold in a compound suitable for
plywood lamiating, and needs 70 deg temp and clamping or screwing for 8
hrs to cure. My avoidance of epoxy caused a lot of noise among epoxy
promoters on this newsgroup, which like what kind of plywood to use on a
boat, is a constant source of mixed opinion, mostly because not all boats
are the same and therefore do not have the same materials requirements.


Gorilla Glue: fairly easy to use requiring no mixing. It has less
strength than epoxy and as been stated by others, no ability to bridge
gaps with any holding ability. It really needs a tight fit.

I've used Bulldog brand's PL Premuim, their "strongest" polyurehtane
construction adhesive. Comes in a tube. Squeeze out with a caulking gun
and spread with a putty knife. As you noted these glues stick to the hands
for days. I've used it on two small plywood boats along with screws, then
sealed the seams with small amounts unreinforced polyester or epoxy resin
painted over, for abraision resistence and to keep water away from the PL
Premuim. I don't use it to seal the edges of plywood, preferring
polyester or epxoy for that.


West Epoxy: Convenient with the little pumps for mixing, holds really
well and bridges gaps. Very expensive and no matter how much of the
colloidal thickener I use, it sags and starts to run before it sets.

Every couple of years I buy a $5 bubble pack of two small toothpaste tubes
of household epxoy adhesive (tube of resin, tube of hardener, mix in equal
amounts) at the discount store (Elmer brand) for repairs around the house
and boats, also for sealing edges of boat plywood, and for small rust
spots on the car.


MarineTex: Another epoxy formulation I think. This stuff I like most
of all because it bridges gaps, holds like hell and does not run.
Very expensive.

Bondo: As reccomended by the Mini-Cup plans. Seems to have little
strength and I wouldnt rely on it as a glue. It does fill gaps really
well (no strength though) without running. It sets VERY fast. Fairly
cheap.

Conventional Fibreglas resin (the stuff that stinks): Not too bad to
work with, not sure of its abilities as a glue, havent tried it as a
filler, reasonably inexpensive

Bondo and "conventional fibreglass" are both polyester resin. Polyester
occurs in many places, in fabric (eg Dacron/Tyrelene sail cloth) and as
tire cords. there is even a polyester drapery tape you can buy at fabric
stores which I and a few others have tried instead of fibreglass cloth for
unconventional fibreglass taping. Polyester resin adheres like paint and
plaster, probably better, but, like paint and plaster, is not good at
gluing things together. I sometimes help it adhere by drilling small holes
in the surface. Many boatbuilders will say not to use it on wooden boats.
I use it on my small wooden boats for abraision resistance and for filling
and in one case for taped seam butt joints which are still surprizingly
holding, just like I use it on rust repairs on the car. It requires more
careful surface prepartion than epoxy resin because epoxy will stick to
anything solid except plastic and maybe some other stuff I don't know
about. In small quantities polyester is a lot cheaper than epxoy. In
larger quantities polyester is still cheaper, not as much on a percentage
basis but then with large quatities we are talking large amounts of money
so in abolute terms it is still a lot cheaper. On large boats the
difference as a percentage of the total cost of the boat is not so great.
That is because small boats are mostly hull but big boat hulls are just
containers for a lot of expensive accomodations, electronics, sails,
motors, artwork and other stuff on which silly buggers waste money.

Most of my repair and pathing work is so small its not cost but amount
needed which determines whether I use polyester or epoxy. The least amount
of polyester I mix is 1/2 teaspoon because that uses 1 drop of hardener.
So if I need less than that to seal a spot on a boat I'll mix a drop or
two of epoxy instead of miximg more polyester than I need.

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