Thread: Glueing with BoteCoat

Hi Arron,

It may not be able to be quantified in any published form. But taking best practice from the people who have done the most physical research in the area, and following the theory of composite fracture, the evidence is very much on the side of leaving it in.

If you can do superfine joinery with hairthickness fits, then other glues start to be quite useful if you want a thin glue line.

Other glues may in fact do a better job when the glue line is intended to be very fine. For example you have to be quite careful to not overclamp epoxy gluing setups, whereas other glues relish tight glue lines.

But the questions is, in the large sized and often complex shaped objects we put together it is often to be sure what is happening in the joint when we offer plywood up or staple down some veneer.

With some items it is really easy to control fits, like putting masts together or laminations, but when you start dealing with hulls and the way wood bends around them you often find surprising gaps in places you didn't expect.

Not shooting for that last 1/32" in average circumstances saves a lot of time for a professionals and amateurs.

If you don't really know where the gaps will be, then you need something that is gap filling ... and that comes down to only one reliable solution - epoxy with an appropriate filling powder.

With tight fits a different glue and lots of clamps might do a better job.

PAR has talked about the range of different glues he uses for different situations and takes me to task (gently) for being so epoxy focussed (his joinery is better than mine!).

MIK

Thanks for the info guys. Mik & PAR that all makes perfect sense. In case I didnt make it clear, I'm not actually glueing anything with zero gap - but was just trying to understand the nature of the product.

Epoxy is certainly very capable stuff, makes me wonder where it has been hiding all my life.

cheers
Arron

Originally Posted by Arron

Epoxy is certainly very capable stuff, makes me wonder where it has been hiding all my life.

cheers
Arron

If you're old enough to be building boats, it wasn't around for most of your life

Richard

Once you know it ... it doesn't hide anywhere, elbows, under the fingernails, in your hair, back of the knees. Not much of it because we are all pretty careful .. but it don't hide!

MIK

Michael is correct, I use my bald spot as a squeegee on over head work, for example, which saves on shop supplies.


Epoxy has been around since WWII, but didn't gain real popularity until the 60's. It's was really expensive back then, so the only folks that used it where those that could accept nothing less, like the aircraft industry and high end manufacturing. By the late 60's it was becoming reasonably common, partly because the jury was in on polyester and boats were delaminating like a snake sheds it's skin. I was introduced to it in the early 70's, which possibly explains the third hand growing out the center of my back. It does make for scratching my butt much easier, but is uncomfortable to sit on.

I was like Michael for many years, but now am finding it's being over used in some respects. I've found this in restoration work, where epoxy has been the cause of failures, not the cure. The reasons get complicated and aren't necessary to go into, but epoxy can be a cure all, but also can be the cause of boat building ills. So, now I'm developing techniques to remove much of it from design work intended for home building. I have a current design that has about 70% less "goo factor", which is a huge savings in time and materials.

To directly answer your question. I've never tested neat epoxy in a very tight glue line joint. I have tested "glue starved" joints, where you apply enough pressure to render the joint epoxy free or very nearly so. These joints fail easily. It would be reasonable to assume a neat epoxy glue line of miniscule dimensions would suffer the same results.

In situations where I need tight joints, I'll "back out" the contact surface, except along the edges where it will be visible. This leaves the interior of the joint with plenty of goo to grab the work, but you have a wood to wood interface along the edges, which can be mashed together, sanded and results in a hair line joint. The backing out process doesn't have to be especially neat, I use a gouge or chisel and just hack out a hollow. The epoxy doesn't care how pretty it is and in fact prefers it not to be.

Howdy PAR,

I would kinda like to agree. For example I have listened long and hard to your suggestions of alternative glues ... but the thing I REALLY like about epoxy is that I know that using the drywall/plasterboard temporary screw method I suggest that the clamping pressures are just about perfect for pox without the customer having to buy many clamps at all.

I have very much taken on board the use of the aliphatic glues for things that are tight fitting like masts, or gluing up centreboard and rudder blanks with any outdoor environment gluing solution (it is all going to be glassed after all) and am regularly mentioning those (so my glue vocabulary is increasing thanks to PAR.

So if my tools list on the plan and the skills set is not very great as well a quite forgiving, then I find I can sleep at night knowing that things are VERY unlikely to break and very unlikely to leak.

The great folk on the PDRacer site experiment with every other glue available ... and always there is someone asking how to fix leaks or rot or ....

This does not mean that you can't make a durable boat - I would estimate that alternative methods and glues come out at about 90% reliable in the hands of amateur builders. My standard would be no leaks and no breakages ever unless hit by something.

I would say epoxy is about 99 point something percent reliable because it will cover situations where the fit is not so good. The failures are almost always that some poor chap has not mixed the epoxy correctly or not measured it correctly or as recently happened used a brush that had been soaking in vinegar to lay off fresh epoxy on the bottom of his boat.

Or this could be a factor too .. that I have used epoxy so much .. largely from an amateur perspective myself so that now i can write about it in a clear way and reduce the variables because of detailed descriptions in my plans. But that might be giving me too much credit.

So as a designer, almost universally, for amateur builders it removes a lot of the worry for me ... and the builder doesn't even need to know about the potential for worry, which helps sell plans.

Hmm ... maybe it is all about my own confidence levels!

Best wishes.

I too always advocate epoxy for novices. As you've pointed out Michael, it's just much more likely, a rookie will manage to stumble through, make mistakes, etc. and still have a trustworthy result. Epoxy has so much going for it, that it's very difficult to not recommend it for just about everything.