Arauco plywood good or bad

[66mstgfsbk]

i searched and cant find much. can i use this for my transom? i was told it is glued with waterproof glue, i think its a ACX type. if not what type of ply should i use

 

[fishrdan]

Re: Arauco plywood good or bad

Radiata pine used in Arauco plywood is susceptible to rot, more so than other pines, so it's not good for use in a boat,,, or at least that was the info I found while researching it for my project. The inexpensive, nice looking plywood was tempting, but I didn't use it, didn't want to be the guinea pig and have plywood failures on a big project. If it was a small project I would have gone for it...

Exterior plywood and marine plywood is commonly used for the transom, but in all honesty, if you fiberglass the transom I don't see why the Arauco plywood wouldn't work out well.

 

[erikgreen]

Re: Arauco plywood good or bad

I'm using Arauco ply for my new boat build.

The stuff is susceptible to rot, but not significantly more or less than any other boatbuilding wood. Unless you're going to use mahogany or teak plywood or use PT plywood, when wood gets wet it's going to rot eventually, and on the off chance it doesn't it's still holding water that will rot nearby non treated or lesser quality wood and weight down your boat.

Arauco is also more ecologically sound than a lot of other ply.. it's plantation grown, not wild harvested, so it's a renewable plywood. Due to the manufacturing process and the fact that the source wood is plantation grown there are a very limited number of knots and almost no voids at all - I found just a couple small ones I could stick a fingernail into in a couple full sheets I cut up.

It's also five ply layers where other plywood the same thickness is three, and both sides are sanded well beyond what you'd expect in anything but furniture grade ply. It's really pretty stuff. See my thread on a winter/spring build for some pics.

One final note - I did a boil test on the stuff (an hour boil to check for delamination) and nothing happened. I know a real boil test repeatedly boils the stuff over time to simulate aging, but I know the glue is waterproof at least.

I don't believe Arauco is yet rated -X... I think it's AC or AB but it hasn't been officially cleared for exterior use yet since it's relatively new, so it isn't officially sold as "exterior grade".

It's good stuff though.

Erik

 

[66mstgfsbk]

Re: Arauco plywood good or bad

if i use this type of ply is there anything else i should do to it besides soaking it in resin? the only holes that will be cut/drilled are for the omc stinger outdrive, swim steps, and drain, i plan on sealing those with 5200. also what/how should i use to "glue" it to the outer skin, can i use 4 inch wide strips of biaxle on the inside or does it have to be a solid sheet of cloth? i am using poly for resin. thanks

 

[erikgreen]

Re: Arauco plywood good or bad

Edit: Short answer - nothing different from installing any other plywood. It's not super rot susceptible or anything, it won't rot faster than 95% of the other plywood you might get, including marine plywood.

You don't need to soak it in resin. For poly, what you want to do is coat it with a thin layer of resin and glass... maybe 6 oz. woven or .75 oz mat if you're just waterproofing. If you're using biax with mat that works too, but using that for waterproofing is overkill. Just glassing it so that all wood is covered would be good, including the part where it gets glued to the existing fiberglass skin.

For attaching to the existing skin, I'd use either poly glue or thickened resin for lamination... resin mixed with chopped fibers and cabosil, or wood flour. Basically you make a thick resin that won't dribble out the bottom of the joint. Clamp together using through holes or biiiig clamps.

Or if you're talking about mating the edges of the transom with the hull sides and bottom, that's different. For that, fill any gaps along the sides and bottom with glue as above, then use two layers of 17 oz. 4 inch tape, offset by at least an inch side to side (for wider coverage) along the seam, making sure you get all the bubbles out. Once that's done you can cover the whole transom with thinner glass if you like to protect it, or not if you've already done that to waterproof it.

I'm assuming you've done this the standard way, by removing the inner skin of the transom and then the rotten wood.

Finally, for waterproofing penetrations the 5200 is good, but here's what's best: Overdrill each hole by about a quarter inch using a bigger drill bit, then plug the entire hole with a mix of resin, cabosil, and fine chopped fibers. If you're concerned about appearance then fill the outside skin with gelcoat and smooth it, or else drill a pilot hole from the outside then counter-drill from the inside to get the oversize hole without penetrating the outside fiberglass skin. Then fill the hole from the inside.

Once it's hardened, re-drill the hole the appropriate size for your attachment/bolt. That way even if the 5200 or whatever leaks, all water will get to is the hardened resin and not the wood.

Erik