Ron Magen wrote:
Andy,

I'm sorry if 'we' wasted your time. Especially if you already knew the
answer !!

The entire discourse could have either been avoided, or taken a different
tack, if you had mentioned this fact . . . up front.

snip


Sorry about the confusion. I had thought that my question was about
whether a coated 1/4" panel could be safely curved around the hull or
whether it would be too stiff or brittle. I didn't think that my
choice of resin was part of the question although I did mention it
because it was pertinent. I did sort of get an answer in that with the
poorer adhesive qualities and higher brittleness of polyester that
there was a risk of it cracking.

Andrew Butchart

On 25 Jul 2006 06:54:42 -0700, wrote:

Thank you everyone for your input. I will probably ignore the advise
to throw away my remaining resin and spend 3 times as much for epoxy
and run the chances of developing an alergic reaction. PLEASE - the
whole polyester vs epoxy controversy has been done to death. I know -
I've been part of it on this forum for years. I had hoped that this
thread wouldn't re-ignite it but it seems that it has. I went into the
project fully aware of the impact of my materials choices.

I will however plan on putting the panels in place before coating them
- reducing the chances of resin failure.

Hi,

You could use a bonding agent to go between the resin and wood to
improve the bond.

Someone here in the UK recommended Bondaglass G4 which is a moisture
curing polyurethane pond sealer. I'd have thought the nearest thing in
the US is POR-15, another moisture curing polyurethane coating.

It would be worth trying a few samples with a small amount of POR and
seeing how much better it is than without.

If you need a lot of it, an industrial coatings supplier might be able
to find something similar at a reasonable price.

cheers,
Pete.

Andrew Butchart wrote:
[SNIP]
My concern is whether the resin will be able to take the bending after it
sets up, or will it crack? Has anyone else tried to do things this way?
[SNIP]

Dear Andrew,

Whether the resin will crack depends on how thick of a coat you decide
to apply, and how much you're bending the panels. If I were you, I'd
coat the inside of each panel before putting it on during the "tacky"
phase of curing. If it does crack, you'll have to seal those cracks
while crawling inside the boat. Hey, at least you won't be doing the
whole job from the inside.

Mind you, if you're building a boat that'll spend most of its time out
of the water, I wouldn't bother coating the inside with poly. I've seen
many interior poly coatings (especially the thicker ones) unstick from
the plywood, yet stay in place, retaining dampness between it and the
wood. If I were you, I'd just bed my frames properly with either a
plastic adhesive sealant (like 5200) or something else that'll prevent
moisture from finding its way between frames and hull skin. Exterior
house paint would be fine for the interior coating, and you can just
slap on another coat when you've scratched the inside.

I've seen you on the group for a few years, so I assume you know how to
build a "cadillac" boat. The above is how I'd do things if I were
building a dinghy on a tight budget. I wouldn't listen to the doomsday
prophets, either. Your little boat ain't gonna disintegrate or
spontaneously explode into a cloud of wood chips and sawdust, while
you're out a-fishing, just because you didn't use top-quality
materials.

Regards,
-Max

wrote in message
ps.com...
Thank you everyone for your input. I will probably ignore the advise
to throw away my remaining resin and spend 3 times as much for epoxy

And what percentage is that compared to the entire boat?

and run the chances of developing an alergic reaction.

Mmm.... allergic vs whatever you get from inhaling styrene (carcinogenic)
fumes.....

PLEASE - the
whole polyester vs epoxy controversy has been done to death. I know -

It is then all the more surprising to see you went for poly..... :-)

Meindert

May I call to your attention an earlier post, from the original poster?




I had hoped that this
thread wouldn't re-ignite it but it seems that it has. I went into the
project fully aware of the impact of my materials choices.



Those of us who choose to build with poly do so knowing full well the
potential consequences of our actions. We have heard the arguments,
perhaps more of them than we care to hear, and will proceed on our
decided course, regardless. You are welcome to sit back and smugly
think, "Those a$$(#*$* are going to get themselves killed, and I'll be
right there to say I told you so", but quit trying to convince us otherwise.

FWIW, I use epoxy and poly both, depending on what I'm building.

Chuck

I'd advise against applying a resin coating before bending.
1. It might reduce the bending radius for the plywood which might not
then bend to the curvature of the hull. It will increase the effort in
bending, how much I do not know.
2. Bending will put many tiny cracks in the resin letting in water.
I've seen a nice wooden kayak with a thin interior coat of epoxy which
was left out all winter. Water worked it's way into the wood under the
epoxy. That's extreme.

I don't see any problem painting or oiling the inside surfaces. I don't
think bending would crack latex paint or linseed oil. I use linseed oil
on the intror of my small boats but white paint would lighten up the
interior of a Weekender's cabin.

Waterproofing might not be much of an issue. It's doubtfull the
interior of the boat would be immersed for any length of time. Maybe
water lying in the bilges. It would be pretty easy to maintin a finish
on the inside bottom of the boat.

I don't see any problem with polyester resin. The plywood needs to be
clean, and lauan (RONA sells a nice meranti underlayment now instead of
the wormy lauan they used to have) is porous and tends to soak up resin
nicely. Adhesion should not be a problem. I use polyester to seal the
chines on my underlayment lauan and virola (now there's a *really*
crappy plywood) boats.

Andrew Butchart wrote:
For my current project - a Stevenson's Weekender - I'm very close to being
able to put on the sides. To avoid crawling around inside the boat coating
and painting, I'm wondering about doing that before I put the sides on.
I'll mask off where the glue joints will be during a trial fit. The sides
will be 1/4" luan coated with polyester resin (no fiberglass on the inside).
I'll fiberglass the outside after assembly.

My concern is whether the resin will be able to take the bending after it
sets up, or will it crack? Has anyone else tried to do things this way? I
don't really want to crawl around inside the cabin breathing in fumes trying
to do the coating.

--
Andrew Butchart

Wm Watt wrote:
I don't see any problem with polyester resin. The plywood needs to be
clean, and lauan (RONA sells a nice meranti underlayment now instead of
the wormy lauan they used to have) is porous and tends to soak up resin
nicely. Adhesion should not be a problem. I use polyester to seal the
chines on my underlayment lauan and virola (now there's a *really*
crappy plywood) boats.


I should clarify. I think polyester coatings on plywood are most likely
to succeed under three condtions
1. new (clean, dry, etc.)
2. porous
3. rigid
I forgot to mention "rigid" in my previous post. I think if the plywood
flexes the polyester is more likely to become detached from the hull.