gaps between joints?

Problems, how to use. Also see: "EPOXY", in the left-hand column of the Home page.

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john mac
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gaps between joints?

Post by john mac » Mon Apr 23, 2012 2:21 am

Hi everyone, i've been reading up the use of epoxy in boat building. I'm about to start my plywood on Douglas fir cabin cruiser but have a few questions. I'd always been told that joints need to be very tight for epoxy, but some people say to use thickener and don't over clamp the joints? Also would westsystems 105 and 205 do for the project, bearing in mind i'm not an expert joiner so the joints won't be as tight as i'd like.

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tsmitherman
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Re: gaps between joints?

Post by tsmitherman » Mon Apr 23, 2012 5:32 am

John Mac,
Epoxy is very forgiving and most people believe it actually holds better with a small gap(s) in the joint. You certainly want to be sure you don't over-clamp the joint. Light pressure is enough.

Good luck on your build.
Tom
------------------------------
36' 1969 Willard Aft-Pilothouse Trawler
Blog: www.genesisboat.blogspot.com


Knot-So-Fast (BoJest) SOLD

"It's amazing what one can do when one doesn't know what one can't do." - Garfield

john mac
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Re: gaps between joints?

Post by john mac » Mon Apr 23, 2012 11:50 am

cheers tsmitherson, have you any experience with west systems?

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Bill Edmundson
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Re: gaps between joints?

Post by Bill Edmundson » Mon Apr 23, 2012 12:53 pm

West is considered the standard by many people. But, Poxy Shield and System 3 are equals.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

neel thompson
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Re: gaps between joints?

Post by neel thompson » Mon Apr 23, 2012 1:01 pm

Hi John,,,,,, I used West System Epoxy Resin 105 and used the slow hardener 206 for my entire build. Coat both surfaces with the clear epoxy mix and then thicken with a West System filler. I used 404 high density filler. I also mix in some mahogany sawdust to help thicken and give it that darker color. Get it to the consistancy of Mayo or Peanut Butter. Then coat only one of the surfaces to be glued together with the thickened Epoxy mix and clamp the pieces gently together. Using the slow hardener gives you more time than you need to get things together and it takes about 24 hours to cure enough to remove the clamps. I also used drywall screws in many places when glueing. Make sure you remove them within about 30 hours or the heads may break off. When using epoxy, you do have a little forgiveness in your joints, but I found that everything seems to go together better and look better in the end if you spend a little extra time getting things right before you glue....Good Luck,,,,,,Neel

john mac
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Re: gaps between joints?

Post by john mac » Mon Apr 23, 2012 2:05 pm

cheers guys, i've just ordered 1.2kg of 105 and 206 west system and 150g of 407 low density filler, i'll give it a go and if alls well then buy enough to build the boat. Its ok to fiberglass over this stuff?

upspirate

Re: gaps between joints?

Post by upspirate » Mon Apr 23, 2012 2:20 pm

407 shouldn't be used for gap filling....not strong enough.

407 is a fairing filler(micro balloons)

use 406 or if big gaps, use 403

john mac
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Re: gaps between joints?

Post by john mac » Tue Apr 24, 2012 12:59 am

cheers guys, i just amended the order for the filler, whats the best type of screws to use, silicon bronze?

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jprice
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Re: gaps between joints?

Post by jprice » Tue Apr 24, 2012 6:34 am

I didn't know it was possible to not have gaps between the joints! :lol:

Anyway, as far as screws are concerned, some people like stainless, some (like myself) prefer silicon bronze.
I think either would be fine.

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Iggy
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Re: gaps between joints?

Post by Iggy » Tue Apr 24, 2012 7:49 am

Any screw I am leaving behind (embedded) I used silicone bronze. Screws that I have exposed are stainless (mostly hardware stuff).

As far as epoxy and gaps, its not an issue. What you need to watch for is having the epoxy 'soak' into the wood and then starving the joint if clamped crazy-tight. I always put an unthickened layer of epoxy on both surfaces first, then thickened the batch and put a generous layer on. Don't mix really big batches, go in small steps and you should have no trouble doing both steps before the epoxy sets up. Thicked epoxy seemed to set up a lot faster than unthicked.. and smaller batches also tended to set up slower than bigger batches... mostly due to heat. Bigger volume adds heat from the chemical process. Thickeners add insulation to the mix, which also adds heat.

And yes, you can fiberglass over thickened epoxy. My deck lines are tinted white, thickened epoxy under a layer of fiberglass cloth.
Ian (aka Iggy)
My Malahini Build

john mac
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Re: gaps between joints?

Post by john mac » Tue Apr 24, 2012 1:35 pm

cheers guys, another tip is keep a bucket of water outside your workshop, and pour any epoxy that you don't use into it. There have been incidents of fiberglass factories burning down due to staff leaving tubs of epoxy lying around. Believe it or not the heat generated by curing epoxy can become deadly, especially if left beside a barrel of acetone, so i've been told!

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