BYYB Forums

hi members my question is,if you are going to glass a canoe is there any reason why you can't use a p.v.a. glue ? when i say glass i mean inside and out ....

If you are going to glass the outside of the hull you will have a superior adhesive already on hand.  In the words of the designer of my project, "you have epoxy, use epoxy".

The only suitable PVA for a sheathing is TiteBond III which is very marginal in regard to elongation, peel strength and modulus of elasticity. Compared to epoxy it's not even a close race, epoxy crushes PVA's in every physical attribute category you which to compare them. Even polyester is superior in many of the physical properties departments. Lastly, the only good way for a PVA sheathing to work, would be vacuum bagged on in an autoclave. Given this, the logical choice is epoxy, unless you just happen to have access to at least a two full atmosphere autoclave, big enough to stuff your boat into.

thanks paul & chris i don't know what i was thinking if you are going to epoxy a boat why would i use pva for strip planking when i will have epoxy for the glass  ???

Just mix some epoxy, add wood flour and if you have it a bit of silica until it is the consistency you want, then either brush it on each strip as you plank or put it in a good quality zip lock bag with one of the bottom corners cut and squeeze it on like a cake decorator.  Scrape the ooze out off every strip or so and add it back to the bag.

Epoxy doesn't stick well to PVA so consider this when making a decision.

Are you saying that Titebond III should not be used for assembly if you are planning to glass the boat at a later date? Would there be issues with the glass sticking to areas where Titebond residue might be exposed?

If you use a PVA (like TiteBond III) on a surface, then 'glass over it, you will have a delamination problem later. Many strip planked boats with PVA glued strips and epoxy/fabric sheathing have proven the issue, though a large amount of these strip builds also have had no troubles (yet).

The point is, testing has shown, epoxy doesn't stick well to PVA'd surfaces, even if the surface is wiped clean with a damp towel before it cures. In most cases, this means a localized delamination along a glue line, depending on how neat you were with the PVA. If the glue line is located well back from the edge of a sheathing, then you'll probably be okay, unless some impact or flexing in the area forces delamination around the PVA joint. This is probably why many strip builders that have used PVA, haven't seen issues with delamination (the joints were relatively neat).

Testing strained test pieces to modulus elongation limits, looking for premature failure. Naturally the PVA surfaces failed long before the raw wood/epoxy surfaces, which is the point.

So, if you want to build with PVA, you can, but be really neat, possably with taped off seams so any ooze out can be mopped up before it touches the outer surfaces. A pencil line thick, PVA glued joint will not matter much in the big picture, unless it's close to the edge of the sheathing, receives an impact or other sheathing strain (like twisting, flexing, etc.) or (most importantly) if you haven't smeared PVA on the surfaces to be sheathed.

hi fella's i think i have started something here about the glue, the only reason i asked was' Guillemot' the greatest kayak builder in the world uses builders wood glue on all his projects,but then again he doesn't build weekenders which no doubt would have to be epoxy for the extra stress's put on the boat..

It's no big deal Gary, there are lots of well respected folks that are miss informed about adhesives. Larry Pardey has many books to his credit and is well respected, but he thinks epoxy is a "fad". I'm not sure if he thinks we'll revert back to resorcinol or not, but this is clearly a ridiculous point of view on his part, which shows his bias.

I'm not saying you can use PVA's, but just that if sheathing with epoxy, you need to work especially neat, as to not contaminate surfaces, so the epoxy will stick.