Should I use epoxy to join two pieces together, perhaps epoxy reinforced with screws or is waterproof wood glue efficient? Basically I’m joining two three-quarter inch pieces together to make a single one and a half inch thick piece of wood to work with.
Best adhesive for joining two pieces of marine grade plywood together to make a rudder
- Thread starter Chuck_FLA
- Start date
You are planning to wrap the finished rudder in fiberglass, yes? Screws will be redundant extra weight and high-speed paths for any incoming water, so should be avoided. Waterproof glue should be what holds the plywood itself together, so that should hopefully be sufficient. Epoxy will also work. Since you're fiberglassing the whole thing anyway a layer of straight epoxy over the wood would be useful for creating a water-impervious layer around the whole finished blade before adding the fiberglass outside layer.
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,435
I like @PaulK ’s ideas.
A layer of epoxy between two pieces of plywood. Let rest till cured (think at least 48 hours, but consult the product manufacturer).
Now you have a raw blank to shape into the desired foil.
Shaping finished, soak in some thin epoxy to seal the wood. Maybe two coats.
When cured, fiberglass with a couple of glass layers for toughness. If you use a clear redo product you may have an interesting wood grain look to the final result. I would then cover with several layers of varnish to provide UV resistance. Without the varnish expect the fiberglass/epoxy to yellow within 18 months of exposure.
A layer of epoxy between two pieces of plywood. Let rest till cured (think at least 48 hours, but consult the product manufacturer).
Now you have a raw blank to shape into the desired foil.
Shaping finished, soak in some thin epoxy to seal the wood. Maybe two coats.
When cured, fiberglass with a couple of glass layers for toughness. If you use a clear redo product you may have an interesting wood grain look to the final result. I would then cover with several layers of varnish to provide UV resistance. Without the varnish expect the fiberglass/epoxy to yellow within 18 months of exposure.
or sooner. We had clear epoxy filler on our deck turn brown and opaque in about five weeks. We ended up having to paint the whole deck.
Slow cure epoxy if you really want to make it impervious to water
If you really want to make the rudder 101% waterproof, check in the System Three Book. For saturating the surface of the wood, you want to use an epoxy mix of 10% lacquer thinner. Straight epoxy is too thick to soak in. Use two thinned coats for starters.
Better still, read the book.
Better still, read the book.
Straight epoxy will not work well, it needs to be thickened with colloidal silica.
To get the best bond, warm the surfaces of the plywood to be bonded, this will drive out any moisture and as the wood cools cause a vacuum drawing the epoxy further into the wood. Use neat expoxy, i.e, without thickener. Slightly warmed, around room temp, epoxy will work better than cold thick epoxy, allowing it to soak in better.
Before this first layer of epoxy sets up, cover the surface of one panel with thickened epoxy and set the other panel on top of it and clamp. The epoxy will lubricate the panels so they will slip and misalign easily.
Epoxy does not need a high clamping pressure. Align the panels and place some weight on top. In a couple of areas that will be cut of put a screw to maintain the alignment. There should be good squeeze out around the edges.
The West System manual, available on their website is a good resource as is the System Three manual.
To get the best bond, warm the surfaces of the plywood to be bonded, this will drive out any moisture and as the wood cools cause a vacuum drawing the epoxy further into the wood. Use neat expoxy, i.e, without thickener. Slightly warmed, around room temp, epoxy will work better than cold thick epoxy, allowing it to soak in better.
Before this first layer of epoxy sets up, cover the surface of one panel with thickened epoxy and set the other panel on top of it and clamp. The epoxy will lubricate the panels so they will slip and misalign easily.
Epoxy does not need a high clamping pressure. Align the panels and place some weight on top. In a couple of areas that will be cut of put a screw to maintain the alignment. There should be good squeeze out around the edges.
The West System manual, available on their website is a good resource as is the System Three manual.
West system has other fillers than Colloidial silica for this purpose. The have other fillers for adhesive purposes such as 404, which is better recommended for your application. As mentioned above, Epoxy is strong, resilient and adheres to a number of various materials, but it does not hold up to UV sun. So, if you want a wood like finish, then you must use a varnish with UV inhibitors. Not all varnishes are compatible with epoxy either. Captain's varnish by Z-spar is compatible. Also, you don't want to use a linear polyurethane varnish for long exposure to underwater applications as it will blister. Polyurethane varnishes and paints are great above the waterline.
Either 404 or 406 (colloidal silica) can be used for bonding. For this application either one will work. The important factor is to avoid using low density fillers like 407 and 410.
406 is just fumed silica and useful for thickening. 404 is wollastonite, which is an abestos-like mineral whose needle-like form gets harder than fumed silica and can take higher loads. 404 isn't very good as a general glue for wood. 406 somewhat better.
But the best thing for laminating or gluing wood is finely milled fibers thickened with fumed silica. If one wants to stay in the West Systems world, this would be 403 thickened with 406.
Mark
But the best thing for laminating or gluing wood is finely milled fibers thickened with fumed silica. If one wants to stay in the West Systems world, this would be 403 thickened with 406.
Mark