sealing plywood end grain?

[patrick mitchel]

a stitch and glue kayak made from lauan ply (the cheap doorskin/non
waterproof). Kept under cover in the mild southern california coastal
climes. Showing delam in the areas where the ply has extensive exposure to
end grain (cockpit coaming, hatches). Also occasional splits on the sides
where impacts have occurred and allowed to open a bit. What's the best
strategy to keep splitting to a minimum (yeah, I know, marine grade ply.
Aint gonna happen- not in the budget.) When building the boat might the best
strategy have been a couple layers of thinned epoxy to penetrate the end
grain and flat surfaces given me a better chance of not having to deal with
this fairly minor problem (considering the age of the boat is approaching
10 yr old) It was fun to build the boats and the one that spent the majority
of it's life in a garage looks a lot better in the splitting dept (or the
lack of splits). Thanks Pat

[Brian Nystrom]

You've answered your own questions. Build the boat with the right
materials (marine grade ply) and seal it with epoxy. Is the boat
sheathed in fiberglass? If not, it should be.

The bottom line is that if you build a boat to last, it will. If you
build it cheap, you have to regard it as disposable and/or expect to
repair it frequently. You can't have it both ways.

[cavelamb himself]

You may also want to check the manufacturers data with regards to
thinning epoxy. Most of them say don't do it.

[brian...@gmail.com]

You did answer your own questions. Recognizing that marine ply is not
in the budget you will have to accept that the ply may not last as
long but 10 years ain't bad. I agree that it would be best to put a
layer of glass on, doesn't have to be heavy but it will give a lot of
increase in strength. System Three and I believe that West has a thin
penetrating epoxy. There is also a product out there I believe CPES
that is a thinned epoxy. In talking with the folks at System Three
their product has more solids and no solvents and still penetrates as
well. It is best to put a good coat or two of epoxy on any ply end
grain on a boat. Have fun.

Bria

[Brian Nystrom]

My understanding is that thinning epoxy just makes it porous when it
cures, as the evaporating solvent leaves behind passages in the epoxy.

[Brian Nystrom]

I have to wonder if someone who won't pay for decent wood will spring
for expensive marine epoxy?

[Mik]

Begs the question. Did you also glass the seams for strength? I don't
see it splitting on the edge if the edges are glassed.

[bellsouthnews]

Here's what "I" would do... I'd clean up the delam with my orbital sander
and round off the edges a bit (glass doesn't like sharp edges). I'd then
apply epoxy to the ends and let it set. Then, I'd sand it to rough it up and
then wrap the ends with fiberglass 'tape'. Doesn't have to be fancy. The
'bondo' CLOTH (not mat) from wal-mart will work fine. Cut it into strips
(It's actually one of my favorite glasses because it wets well and is very
strong.) Cut it into strips and wrap your delam areas. Then, after that
sets, build up the epoxy a bit on those areas with another coat or two so
it's good and sealed.

The strength of the glass should prevent minor dings and it will help keep
the area sealed. If you're trying to keep costs down, you can use the
'bondo' polyester resin that they also sell at wal-mart. I'm not sure about
it's UV resistance and from what I've heard, it's not good for structure
because it has a tendency to 'creep', but for sealing your end grain, it
should work just fine. (I'm sure I'll catch flak for that bit of advice, but
if you're wanting to do it on the cheap and you're not concerned about
appearance, that's the route I'd go.) Make sure you rough up the areas
you're gluing to so it holds. You can't get a chemical bond so you're going
to have to rely on a physical bond. Oh, and I agree with the other fellas.
I wouldn't try to thin the epoxy. I tried it once and it just came out bad.
If you want the epoxy thinner, warm it up. I use a heat lamp about 12" from
my epoxy jug. But if you heat it, be sure to use small batches because it'll
set up quicker. :)

Hope this helps.

Good luck.

Ron

[patrick]

Hi Guys; Yes, I did do the seams with glass. Matter of fact , the
hull had a layer of glass/epoxy, over a brushed on epoxy layer...I had
good luck with the paddle which was made the same way by laying a ply
with wax paper along the backside of the blade, then trowelled a bunch
of milled glass/epoxy to the edge, then sanded to shape. That has held
up famously . I wish I could same the same of the hatches that are of
lauan doorskin bent to shape over wood formers. They seem to have
occasional damage along the edges that allowed the water to wick
through the end grain and doing the damage. Am considering grinding to
a knife edge, then clamping the waxed ply backing to conform to the
edge, then doing the same epoxy/milled glass along the edge to toughen
and seal the edge concurrently. Yep, I'm on the cheap side. I thought
the the first couple boats I'd build were going to be trial horses
anyway so don't invest the bucks. Considering the lack of care I've
shown the oats, I'm considering building another using the same
(cheap) methods. Pat

[Pete C]

Hi,

When building with non-marine ply, try boiling an offcut to test for
delamination.

Also protect plywood end grain that's vulnerable to damage with a
strip of durable timber.

cheers,
Pete.

[Phil]

What if he used "Gorilla Glue " on the exposed edges ?

[cavelamb himself]

Phil wrote:

> What if he used "Gorilla Glue " on the exposed edges ?

It's hydroscopic - absorbs water.

Not exactly what you would want for a waterproofer.

Richard

--
(remove the X to email)

Now just why the HELL do I have to press 1 for English?
John Wayne

[Heikki]

Pete C wrote:

> When building with non-marine ply, try boiling an offcut to test for
> delamination.

I have seen this advice a few places, and I know that to qualify for marine
grade, plywood has to survive some heavy boiling tests. But I don't
understand what boiling has to do with endurance in marine environment.
Most of us don't sail in waters anywhere near boiling temperature.

-H

[Drew Dalgleish]

Boiling speeds up the breakdown process so you can find out quickly if
the ply is any good. A better test would be to make up samples and
leave them in the expected enviroment for a few years to see if it
will stand up but nobody wants to wait that long.

[Phil]

"cavelamb himself" <cave...@Xearthlink.net> wrote in message
news:u9SdnYyOaJ-PaqfV...@earthlink.com...

> Phil wrote:
>
>> What if he used "Gorilla Glue " on the exposed edges ?
>
> It's hydroscopic - absorbs water.

I understand that but doesn't it become waterproof when it's cured? I
haven't tried it but that stuff seems to go into porous surfaces very
easily.

[cavelamb himself]

No, over time exposure to water will destroy the strength of the bond.

[Boden]

I'd guess that you could thin epoxy with about 10% (max) solvent by
volume without much of a problem.

It wouldn't surprise me if the reason manufacturers don't advocate much
more than this is primarily because the environmental police would come
after them for releasing to much solvent vapor.

Boden

[doub...@hotmail.com]

I'd seal the end grain with acrylicexterior latex paint.

Best stuff.