PL and Epoxy on the same project?

[Russ Kaiser]

I have made two Stitch and Glue boats loosely based on Gavin Atkins mouse boat for my kids. Since I have four children and the boats have become a great source of enjoyment, I would like to whip out two more so they can all get out on the lake at one time.

The first two boats were all epoxy construction with the sides and bottoms fully covered with cloth. I would like to minimize cost and speed up construction by doing the initial inside construction with PL Premium.

Not having worked with this product before I had a couple of questions.

1. Can it be spread easily to form fillets and if so how much time do I have to work with it, minutes... seconds?

2. Assuming the above is possible, is it also possible to bed fiberglass tape into the PL before it sets and does that make sense?

3. Is cured PL sand-able?

4. Is there a compatibility issue with epoxy? I would still like to use epoxy and cloth on the outside of the boat.

I looked through a bunch of postings that referenced PL Premium, but it didn't find the specific answers to these questions. If this is viable, any tricks of the trade you can pass on would be appreciated.

Thanks,

[FAST FRED]

I have become allergic to Epoxy so use PL when I can.

IT is fine if you can assemble the parts fairly quickly.

It foams up helping looser joints.

I would not use it as a laminating glue with taper , but haven't tried.

FF

[Russ Kaiser]

Hey Fred, Thanks.

I knew that Gorilla Glue foamed and tended to spread joints if they weren't clamped, but I had no idea that PL did the same thing. That alone probably eliminates it. You can't neatly fillet something that is going to spread.

[Russ Kaiser]

I assume everyone knew that I was specifically talking about the Polyurethane type of PL product. If that is unsuitable, are any of the other Caulk Gun applied adhesives non-expanding and compatible with epoxy?

[Deering]

You can get epoxy in a caulk gun arrangement. It premixes the resin and hardener before it squirts out. Have never used one myself but they look pretty slick. That would probably speed things up, but doubt that you'll save money.

[Russ Kaiser]

I was looking for something cheaper and quicker. Loctite markets a paneling construction cement. Here is a link:

Power Grab Molding and Paneling Construction Adhesive

It is not for water immersion but these boats come out of the water between uses and I was only looking for something to do the internal construction; the initial cementing of the sides, frames and seat.

On the first boats those pieces took a few days because I only worked on seams that were horizontal so I did the bottom, then flipped the boat on one side the next night, the opposite side the next, etc.

It would be great to do all those steps in one evening. I finished the inside of the first boats with multiple coats for Polyurethane finish followed with paint so I would want something that I could polyurethane over.

[rwatson]

You could try something like Purbond

eg http://boatcraft.com.au/Shop/index.p...96126fabb3d480

it is foamy enough to be gap filling, and you need to hold the parts in a jig to avoid distortion, but its waterproof and epoxy compatible.

[Russ Kaiser]

Thanks RW - Purbond looks a lot (spec wise) like Gorilla Glue. I was really looking for something that cured quickly and did not foam.

[Steve W]

You could use polyester products, such as bondo for the fillets and polyester resin for the tapeing,dont glass the whole outside, just paint it, ive used Benjamin Moore Impervo and Retardo enamels with good results. Now im not recomending this approach for anything other than cost savings and before folks start saying polyester doesnt stick to wood please bear in mind that most of the fiberglass boats we all sail have their bulkheads tabbed in with polyester.
Steve.

[GTO]

I used PL premium building a boat with chines. (Bolger windsprint)

Sanding it gums up the sandpaper very quickly. Not what you want to be doing.

PL doesn't foam like Gorilla, which I also tried. It does expand some and does develop bubbles in it.

When used to glue things together, I would let it cure and then use a wood chisel to slice the excess off - strips 10 feet long at times.

Search the web. Somewhere/sometime ago, I ran across a page where a guy tried various glues with fiberglass to make fillets. Based on my experience, the cleanup would take too long to justify PL's use.

If you would like to lose the expense of the epoxy, maybe you could try one of bolger's chined designs.

Elegant Punt

Just a suggestion...

[philSweet]

I'm in Steve's camp-

My family had a 14' mac dinghy (they made 5 14'ers, my dad had a knack for finding weird boats.) It was built of 4mm ply, polyester bedded taped seams, and red paint. It only lasted 35 years, though.

BM Impervo/Impervex should be used over Ironclad as a primer. Ironclad requires no topcoat, but its gloss retention is not real good. Done this way and having already built a pair, you should be able to splash a pair of mice in a three day weekend.

[DCockey]

I've heard that polyurethane glues loose a major portion of their strength if the gaps are large enough that the glue foams.

[rwatson]

Originally Posted by DCockey

I've heard that polyurethane glues loose a major portion of their strength if the gaps are large enough that the glue foams.

The glue foams whether there are gaps or not - either in the gap, or oozes out around it.

I wouldn't say the glue is designed for long term strength - I would never rely on it unless epoxy/cloth went over it.

What this country really needs is a hi performance hot melt glue - quick, and easy to apply.

[DCockey]

Originally Posted by rwatson

The glue foams whether there are gaps or not - either in the gap, or oozes out around it.

I wouldn't say the glue is designed for long term strength - I would never rely on it unless epoxy/cloth went over it.

What this country really needs is a hi performance hot melt glue - quick, and easy to apply.

The glue in the joint is what matters, not the glue which oozes out. If joint has a gap large enough that the glue in the joint foams then the joint will have reduced strength; that's my understanding. So polyuretheane glue is not gap filling IF full strength is important. It works best with tight joints.

Epoxy on the other hand retains full strength irregardless of the size of the gap.

The glue which oozes out doesn't usually contribute to the strength of the joint.

[rwatson]

Originally Posted by DCockey

The glue in the joint is what matters, ...
The glue which oozes out doesn't usually contribute to the strength of the joint.

True, and most of the stuff that oozes, gets scraped off as well. When the epoxy is applied, it does its own 'oozing' into any gaps. thereby filling the voids at the joins.

But really, in joining end grain plywood sheets, no glue, even epoxy, will provide adequate strength, as evidenced by the epoxy and glass along, and over all joins in the deceptively named 'stitch and glue' process.

It should be called, 'stitch, temporary tab , then re-inforce with glass and epoxy'

In fact when I think about it, I don't know where the plywood gluing comes into it. Most processes don't say anything about gluing the plywood edges - you just put in the wire, apply some epoxy tabbing, and then cover the join with glass and epoxy strips once you can remove the wire.

For my next kayaks - I am tempted to just use instant setting hot-melt glue in place of the epoxy tabbing every 6 inches, and then just run the fibreglass covering over it. That should be plenty of strength. I guess the biggest risk is the epoxy delaminating from the small blobs of glue, leaving tiny voids - and that should be a non-problem for the overall craft.