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Boat Forum / Building / June 2008sealing plywood end grain?
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 > a stitch and glue kayak made from lauan ply (the cheap doorskin/non > waterproof). Kept under cover in the mild southern california coastal [quoted text clipped - 9 lines] > of it's life in a garage looks a lot better in the splitting dept (or the > lack of splits). Thanks Pat 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. >> a stitch and glue kayak made from lauan ply (the cheap doorskin/non >> waterproof). Kept under cover in the mild southern california coastal [quoted text clipped - 18 lines] > build it cheap, you have to regard it as disposable and/or expect to > repair it frequently. You can't have it both ways. You may also want to check the manufacturers data with regards to thinning epoxy. Most of them say don't do it. >>> a stitch and glue kayak made from lauan ply (the cheap doorskin/non >>> waterproof). Kept under cover in the mild southern california coastal [quoted text clipped - 21 lines] > You may also want to check the manufacturers data with regards to > thinning epoxy. Most of them say don't do it. My understanding is that thinning epoxy just makes it porous when it cures, as the evaporating solvent leaves behind passages in the epoxy. >>>> a stitch and glue kayak made from lauan ply (the cheap doorskin/non >>>> waterproof). Kept under cover in the mild southern california [quoted text clipped - 24 lines] > My understanding is that thinning epoxy just makes it porous when it > cures, as the evaporating solvent leaves behind passages in the epoxy. 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 I'd seal the end grain with acrylicexterior latex paint. Best stuff. > >>>> a stitch and glue kayak made from lauan ply (the cheap doorskin/non > >>>> waterproof). Kept under cover in the mild southern california [quoted text clipped - 33 lines] > > Boden 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 > 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 [quoted text clipped - 8 lines] > > Bria I have to wonder if someone who won't pay for decent wood will spring for expensive marine epoxy? > a stitch and glue kayak made from lauan ply (the cheap doorskin/non > waterproof). Kept under cover in the mild southern california coastal [quoted text clipped - 9 lines] > of it's life in a garage looks a lot better in the splitting dept (or the > lack of splits). Thanks Pat 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. 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 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 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. > 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 >> When building with non-marine ply, try boiling an offcut to test for >> delamination. [quoted text clipped - 5 lines] > >-H 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. What if he used "Gorilla Glue " on the exposed edges ? > 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  Signature(remove the X to email) Now just why the HELL do I have to press 1 for English? John Wayne >> 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. >>> What if he used "Gorilla Glue " on the exposed edges ? >> [quoted text clipped - 3 lines] > haven't tried it but that stuff seems to go into porous surfaces very > easily. No, over time exposure to water will destroy the strength of the bond. Richard Signature(remove the X to email) Now just why the HELL do I have to press 1 for English? John Wayne |
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