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Epoxy Strength

Posted: Mon Apr 24, 2017 4:42 am
by curt1893
So I've always heard that epoxy would be stronger than the wood when properly done, so I'm assuming that I'm doing something wrong. When I glued together my sheer and chine boards using a scarf joint, I put on West Marine epoxy and slow hardener (don't remember the exact numbers) and let it cure for over 24 hours. I followed the 5:1 ratio and mixed well, but for some reason my joints keep popping apart.

My question is, has anyone else had problems with West Marine as far as the strength when gluing, or is this mainly for encapsulation. I'm about to try some Loctite Marine epoxy if this latest glue up doesn't hold.

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 6:02 am
by vupilot
You didnt say anything about adding any filler? Are you not adding a powder filler like West Marine 400 series fillers?
Read the discription when choosing one.
https://www.westmarine.com/buy/west-sys ... ecordNum=3

Those thin finishing resins need additive for structural bonding. GlenL poxy grip is the only epoxy i know of that is meant to be used structurally straight from the cans. Most others require additive.

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 6:06 am
by Roberta
Post pictures of the failed joint, what product was used (West has different formulas), and what were the conditions were when curing. 24 hrs may not be enough time for full cure. That often takes several days, or more, for a fully cured joint using epoxy. Are you using an 8:1 ratio on the scarf joint, meaning, is the joining surface 8 time the thickness of the material? Was the surface of the joint like? you want some roughness for the epoxy to soak in and bite into. Glen L has Poxy Grip for joinery and Poxy Shield for encapsulation. Great products and easy to use.

Roberta

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 7:29 am
by JaTro
What about temperature required for curing, although Atlanta should be warm enough:-)

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 7:43 am
by Roberta
Temperature below 70 degrees require more curing times.

Roberta

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 8:31 am
by Bill Edmundson
JaTro

Temperature is important. Epoxy will eventually cure in a freezer. There are a couple of brands come in two-part caulking tubes. They are a little expensive. They're very easy to use.

Bill

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 9:28 am
by JimmY
Also, what type of wood are the sheer and chine? White Oak needs to be roughed up for bonding with epoxy, and you don't want the clamping pressure to be too high that you squeeze out all of the epoxy.

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 5:36 pm
by curt1893
Thank you all for all of the comments. Pretty sure Vupilot hit it on the head, probably. For some reason, possibly assuming all epoxies are the same, I failed to notice any mentioning of fillers to create an adhesive. I just assumed that was for when you wanted to fill holes/gaps (something like wood flour).

For others reading this, I'm using red oak, and I believe the temp is constant around 65 - 75 degrees while it sits in the garage. I've been trying to get atlas a 6:1 scarf ratio. I'm build a can-yak, so the bend isn't too bad. Hopefully soon I'll have some pictures.

Thanks again.

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 6:00 pm
by Roberta
Oak will need to be roughed up a bit to get the epoxy to soak into the pores of the wood. Also, red oak is easily rotted in boats. Make sure you encapsulate and keep that wood as dry as possible or the boat will be very short lived. I would recommend soaking everything that is red oak with CPES and then epoxy coating over that. Hate to see all your work fail due to rotting wood.

Roberta

Re: Epoxy Strength

Posted: Mon Apr 24, 2017 6:12 pm
by curt1893
Yeah, that's the plan. So, before I read everyone's replies, I purchased a small tube of Loctite Epoxy glue. Now I have a much better understanding of what the consistency of adhesive should look like. It's like night and day to the smooth liquid epoxy+hardener.

Re: Epoxy Strength

Posted: Tue Apr 25, 2017 8:02 am
by Scot2640
I don't think its the case here but I read it in the comments forum of an epoxy producers website when individuals were claiming that the epoxy would not kick off or set up. It sounded like they were confused by the 5 to 1 ratio thing and they were unaware that the pumps were already calibrated with the 5 to 1 metered pump. Those with the complaints seemed like they were literally pumping 5 pumps of resin and one pump of the hardener.

Re: Epoxy Strength

Posted: Tue Apr 25, 2017 8:10 am
by Bill Edmundson
Scott

My wife did that to me one time. Most of it eventually went off. The rest was a gummy mess to get off. What a PITA!

Bill

Re: Epoxy Strength

Posted: Tue Apr 25, 2017 3:06 pm
by curt1893
See, I first thought I was getting the ratio wrong, but double checked that it was weight or volume 5:1. I didn't spring for the pumps but rather a digital kitchen scale.