Barrier coat or Epoxy for coating bare wood hull

[Ken Fry]

Originally Posted by ajay73

Ken Fry, since I'm sensitized to epoxy I've use a few gallons of vinyl ester in deck repairs on my Catalina 27 and the product works just fine. No failures, no health problems( I do use a respirator). From everything I read it's better than poly ester but not a good as epoxy. And it is good a preventing water absorption. My experience is that it adheres to plywood pretty good. And my reading says it has decent flexural strength. Boat flex but enough to break a vinyl ester bond? My experience is that it is not much different than working with poly ester.

Yes I agree vinylester is better than polyester but not as good as epoxy. My aversion to the stuff (both v and p) is mainly from the smell and the working qualities. But if I were sensitized to epoxy, I'd be considering it, but not for anything that would be finished bright.

I've been thinking about Jamestown's advice re I2000. I think an issue with applying it to wood is that the solvents get sucked into the wood, instead of the epoxy getting sucked in. The platelets (mica) would also impede penetration. The cure rate is also too fast to allow "saturation" (as in the WEST system). So I think that Jamestown is right -- it's probably not very good on bare wood.

A huge advantage of epoxy over painting, other resins, etc. is that it cures slowly and soaks into the wood for quite a while as it does so. For the same reason, epoxy (neat) is an unfriendly paint. You leave the shop in the evening, and come in the morning to see all sorts of sags and runs. (Even thickened, it can do this: You get something faired, and come in the next day to find sags. For fairing, Bondo is better to work with than most of the putties I have mixed up... except for the smell, and the fact that its weak and not very waterproof. It is good for temporary fixturing: you can glue something together with it and then pop it apart when you're done.

Applied to any impervious substrate, you don't need penetration, so the i2000 works well to increase water resistance even though it is sitting on the surface of a polyester boat.

But having said all that, varnish is great. There are plenty of wooden boat builders who say something like: I don't paint with glue, and I don't glue with paint. A boat like you will build can last for generations, using it as you will and giving it just a modicum of care.

Wow! enough verbal diarrhea from me.

[Scubaseas]

I can tell you from 50+ years in auto repair that Bondo is now where near waterproof. It has talc in it and will actually absorb and hold water. If you want an easy sanding compound use marine fairing compound or make your own using 3M micro spheres/balloons. Do not add silica to it as that makes it very hard to sand. There is no place for Bondo on a boat. You can get waterproof body filler but you can make your own which will work better, last longer and sand just as easy compared to Bondo.

If you go resin thin the first coat 10% or so per the manufacturer's instructions. Acetone for poly or vinyl and alcohol for epoxy. This allows the resin to sink in and gives you a barrier or primer coat so the subsequent coats won't sink in and disappear.

If you are looking to add strength or toughness use a cloth followed by a veil mat. You can varnish or paint on top of that if you want but varnish isn't as tough for pebbles or sand on the beach as a coat of resin cloth and veil mat would be. Fiberglast carries 0.1oz veil mat and 3.5oz glass cloth.

[Ken Fry]

Originally Posted by Scubaseas

I can tell you from 50+ years in auto repair that Bondo is now where near waterproof.

Definitely. I realize it might have seemed like I was endorsing Bondo for use on a boat. Near boats, I use it only for fixturing -- temporarily gluing something to the floor. Even then I try to avoid it, it because I don't like the styrene smell.

For fairing on boats, I use microballoons in epoxy with just enough wood floor to prevent sagging. For fairing a fender on a car, I will use Bondo -- its' quick and easy, and cures super fast, so you can do three coats in no time: one to get it close, another to get is closer, eventually test painting it with gloss, only to find out that it needs more work.

(I've given up on painting my own cars -- I was never all that great at getting surfaces right, and I'm not all that great at painting either. Nitrocellulose lacquer and buffing was the only reason I could get something to look ok. Usually, with things that have to go on as a wet coat to be glossy, I find the sweet spot by chance: I am no stranger to runs. Bad eyesight, not enough light... probably contribute. )

[Scubaseas]

Definitely. I realize it might have seemed like I was endorsing Bondo for use on a boat. Near boats, I use it only for fixturing -- temporarily gluing something to the floor. Even then I try to avoid it, it because I don't like the styrene smell.

Paintless dent repair uses a hot melt glue that can be debonded with Alcohol. Might work better for you than Bondo.

[Ken Fry]

Originally Posted by Scubaseas

Paintless dent repair uses a hot melt glue that can be debonded with Alcohol. Might work better for you than Bondo.

Cool. I'll look into it.

Paintless dent repair: magic. Had some hail damage once -- maybe 50-100 small dents. They fixed it all -- looked brand new. It would be fun to learn how to do it... When I've taken dents out, I had a vague understanding of how to use a shrinking hammer, etc, but never got to the point that my pounding away did much more than just reduce the amount of bondo required.

There is a Cobra replica, with the body made in Poland, hand hammered out of aluminum. Might as well be magic.

[Flagfish]

Originally Posted by Spot

I hope all goes well. There was talk about building El Toro dinghies the other day and I almost started moving furniture- that'll fit in the living room, right?

Oh yes, it should definitely fit in the living room... but the new house you'll have to buy for your wife might be expensive :-)

[Spot]

Originally Posted by Flagfish

Oh yes, it should definitely fit in the living room... but the new house you'll have to buy for your wife might be expensive :-)

Ajay73, how is that boat coming along?

[geoleo]

Seal up wood and rot is assured

[ajay73]

Spot, won't start it until end of February to mid March.

[tomtriad]

You might like to join the Duckworks Facebook group - lots of small boat builders there with tons of experience. I have a 1982 42' cold molded wood trimaran; all the wood is clear coated with epoxy and the exterior is covered with 8 oz 'glass cloth laid up with epoxy. Lots of plywood. Make sure the edges of all plywood are epoxy coated to prevent delamination. Thicken with a bit of silica so some stays on the edge, then paint it to protect from sun. Even marine plywood is made with non waterproof glue - go figure. Whatever you coat with make sure its compatible with the epoxy. I like Awlgrip 545 as a primer over epoxy.

[Ken Fry]

Originally Posted by tomtriad

Even marine plywood is made with non waterproof glue - go figure.

That's not true. Waterproof glue, (usually even boiling water proof) is the one characteristic that all "marine plywood" has. Some marine plywood is made from woods that are not classified as "durable" species. (Okume in not durable, for example) but the glue is always waterproof.

Even exterior grade plywood uses waterproof glue.

[tomtriad]

Originally Posted by Ken Fry

That's not true. Waterproof glue, (usually even boiling water proof) is the one characteristic that all "marine plywood" has. Some marine plywood is made from woods that are not classified as "durable" species. (Okume in not durable, for example) but the glue is always waterproof.

Even exterior grade plywood uses waterproof glue.

Even if the plywood is made with "waterproof" glue it will delaminate due to water absorption if the edges are not sealed.

[Ken Fry]

Originally Posted by tomtriad

Even if the plywood is made with "waterproof" glue it will delaminate due to water absorption if the edges are not sealed.

Of course. Everyone seals plywood edges. Unsealed marine plywood delaminates because the wood can soak up water and expand so much that the interlamination stresses are high enough to cause failure. The same can happen if the faces are not sealed. (That's one reason so many polyester/glass covered wooden boats failed.)

Per The Gougeon Brothers on Boat Construction (pg. 76):
"When you buy plywood, consider the quality and
species of internal veneers and the suitability of the
adhesive used in the laminate. Voids within the
plywood may cause failure, and the glues used in
marine applications must be waterproof. A strict
grading system, outlined in Figure 9-3, describes
the quality of surface veneers in domestic plywood,
but other markings are used to identify adhesives
and to grade interior plies."

The BS 1088 standard plywoods use glue that is not just waterproof, but also boil proof, steam proof and able to withstand wet/dry cycling.

[pbmaise]

Originally Posted by Tupaia

Sounds like a small open traditional boat. Consider using Tung Oil - should stress "pure" Tung Oil. This is a hard multilayer surface used on traditional Chinese craft for centuries. Is easy to top up from season to season. Just a suggestion.

Along these lines I favor synthetic linseed oil. Synthetic linseed oil takes a rather long time to fully polymerize however, is a harder product than natural tung oil and natural linseed. I recommend application early in the morning on a very dry surface on a day with full sun. Then let it cure in the hot afternoon full sun.

I purchased large amounts of the synthetic linseed oil to protect all my galvanized wire and galvanized fittings. I found I got several years of use in between coats.

[ajay73]

Along the lines of what Tupaia says on page 1, I'm now considering Pettit EZ Wood sealer 218 and then painting with a polyurethane like EZ Poxy. Doing this both inside and outside. The big concern, as everyone knows, is avoiding moisture seeping into the wood enough to loosen the epoxy bond of the lap joints. The EZ Wood Sealer is a tung oil combined(polamerized) with a phenolic resin. Any thoughts?