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Boat Forum / Building / June 2008Best glue for plywood in damp environment?
Hi: I need to build a base plate (25x25") out of regular exterior plywood that will be a total of 3" in thickness. It will be in a damp (not wet) and dark environment, under the center of a gazebo, about 1 foot off the ground. I simply cannot afford marine plywood. I plan to glue either 6 layers of 1/2" or maybe 4 layers of 3/4" exterior. It needs to be relatively permanent. Once in place it will be almost impossible to get at. It will sit on concrete (30" diameter) and will bear much of the weight of the gazebo. What would be the best glue or sealant I should use? Any tips? I've never done this before. Thanks very much. John (at home now, but soon to be at the cottage) > I need to build a base plate (25x25") out of regular exterior > plywood that will be a total of 3" in thickness. > It will be in a damp (not wet) and dark environment, under the > center of a gazebo, about 1 foot off the ground. I'd use 6 layers of 1/2", 4 ply, CDX plywood, epoxy and microballoons. Use fairing putty(epoxy & micro-balloons) to fill the surface voids in the ply proud. When cured, sand smooth. Epoxy 3 ply pieces together, let cure, then do a final glue up to get a 6 piece fabrication. Glass over the plywood with a couple layers of 17 OZ, +/- 45 glass and epoxy. Allow to cure about 10 days, and you're finished. BTDT Lew >> I need to build a base plate (25x25") out of regular exterior >> plywood that will be a total of 3" in thickness. [quoted text clipped - 19 lines] > >Lew Hi Lew, Thanks for all your suggestions. What are microballoons? John >Hi: > I need to build a base plate (25x25") out of regular exterior [quoted text clipped - 16 lines] > > (at home now, but soon to be at the cottage) Is this basically some sort of "spacer pad"? If so, why not either use some lengths of PT landscape timbers, or build a form and pour a little concrete. Plywood isn't going to be at all permanent in that application from the sounds of it. >>Hi: >> I need to build a base plate (25x25") out of regular exterior [quoted text clipped - 21 lines] >little concrete. Plywood isn't going to be at all permanent in that >application from the sounds of it. The plate is bolted to a 30" diameter concrete footing (3 ' into the ground).. All the main beams meet at the center on top of the plate, and bolt to it. The plate then transfers the weight to the concrete. This is what the plans call for, and I'm relatively new at building, so I wanted to follow the plans exactly. It calls for a 3" wood plate. I thought plywood would be best. (The plans didn't specify the diameter of the footing, but I wanted it to be bigger than the plate, so I made it 30" A couple people have told me the 30" was "overkill" but its in now and aged since last fall. john > On Wed, 14 May 2008 13:08:20 -0400, salty@dog.com wrote:. > [quoted text clipped - 11 lines] > > john I might suggest using a glue like PL Premium. It will expand to fill voids as it cures and is waterproof. It does however degrade when exposed to UV but I don't think that will be an issue here. Apply the glue with a notched glue knife and don't use too much clamping pressure - in a similar project I just nailed the pieces together rather than trying to clamp them. AndrewB I have a decent amount of experience building structures and using plywood as a structural material in an area tha could get damp makes absolutely no sense to me. Pressure treated is the only way to go and I'm not talking pressure treated plywood. Like already suggested, use PT 2X's ON EDGE for support over the concrete. > <j...@thecottage.com> wrote in message > [quoted text clipped - 25 lines] > > AndrewB >The plate is bolted to a 30" diameter concrete footing (3 ' into the >ground).. All the main beams meet at the center on top of the plate, [quoted text clipped - 9 lines] > > john I suspect they call for 3" thick because that's 2 layers of 2"x ?? dimensional lumber laid at right angles and nailed together. I'd use pressure treated 2x8's without any glue just enough nails to keep it from moving. The weight of the gazebo is straight downwithout any movement. I think that's the cheapest and quickest solution although you've had lots of suggestions that will all work well. Whatever you decide to do you need to put a moisture barier between the wood and the concrete a piece of tar paper would work best. What structural function does the plate serve??? Unless a plate is on top of a continous concrete run a plate is useless. If you are connecting piers of concrete with wood , PT 2X's on edge is the only correct solution. On May 14, 9:41 pm, idontwantanys...@thankyou.com (Drew Dalgleish) wrote: > >The plate is bolted to a 30" diameter concrete footing (3 ' into the > >ground).. All the main beams meet at the center on top of the plate, [quoted text clipped - 18 lines] > decide to do you need to put a moisture barier between the wood and > the concrete a piece of tar paper would work best. Having recently joined the construction industry from the boat repair industry, I am constantly fascinated by the way architects design stuff. To paraphrase "Bud" Macintosh in his book, we often wonder how such a small head can hold so much stuff! I understand that you want to follow the plans but here's how I would do it..... So the concrete footing is in place; I would build up the concerete to the correct level with dry "deck mud" (assuming that the eventual loading of the joists is within tolerances. Then I would hammer 3 inch nails into the underside of the joists where they meet the deck mud. The nails are left sticking out of the underside of the joists about an inch or slightly more. The joists are then tapped into the still wet deck mud and levelled to the final level. Let deck mud dry and viola, done. 2 hours, next job please! Arnold > Hi: > I need to build a base plate (25x25") out of regular exterior [quoted text clipped - 16 lines] > > (at home now, but soon to be at the cottage) I agree with Ystay and Drew D. KISS as they say. >The joists are then tapped into the still wet deck mud and levelled to the >final level. Let deck mud dry and viola, done. 2 hours, next job please! Recipe for rot. You should be sure and use the arsenic treated lumber. Casady (snip my original message) Thanks, everyone, for the many replies and suggestions. I'm going to think about them all for a few days before I decide which option/s to take. I appreciate all of your imput. John (still at home) |
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