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Epoxy questions

Posted by Hansen 
Epoxy questions
June 01, 2017 10:35PM
I'm building custom "captain's box" coolers for my inflatable boat in order to gain a little experience with epoxy and fiberglass before starting a restoration / decking project of a wooden boat. I laid up my first test yesterday and ran into the following issues - any advice for solving these would be most appreciated. I'm using Raka UV inhibited epoxy and will call them for advice as well.
1st - The glass seemed to "float" to the surface of the resin in all but a couple of spots where it was really thick, exposing the weave on the top. Am I "starving" it, or (other than vacuum bagging) is there something I can do to get it to lay down flatter and stay under the top coat when I wet it out? I also couldn't get it to stick down when I bent it around a corner. It is only 7oz glass so this surprised me.
2nd - the epoxy didn't really bond to the foam. I'm using "polyiso" foam which comes with an aluminum face that I peeled off. This left the surface pretty rough so I thought the epoxy would penetrate or at least get a good mechanical bond - it did neither. I was able to peel it right off without damaging the foam.
I did a 2nd test using "fast" hardener and scuff sanding the surface before applying the epoxy. It doesn't look like it will turn out differently but I'll re-post if there is a change after it cures fully.
Thanks for any light that anybody can shed on the subject for me.
Cheers,
Elliott
Re: Epoxy questions
June 01, 2017 11:18PM
I hope others have other perspectives. I've used blue and pink foundation foam in the past and that's all.

Foundation foam has a slick surface resin will not adhere to so I roughed the surface up gently with 220 paper on a lightly applied random orbit sander. Then I made a few deeper scratches with 100 grit paper by hand, using a drywall sanding pad, with a handle.

Spread resin with a drywall trowel. Lay down the fabric. Stroke the fabric with the same trowel from the center out to the edges. You want a pebbly surface, showing the weave. Trying to get a smooth surface all at once requires too much resin which will float the fabric.

After it's hard wash with acetone, rough it up gently and trowel out some finish coats........if you do want to achieve a smooth finish. But do that on top of the pebbly surface you made the first time.

On foam how much fabric do you need? For a cooler? This is the black magic part. Are you working with ten ounce fabric or three oz fabric?

I'd say two layers.
Re: Epoxy questions
June 02, 2017 03:11AM
Knowing to expect two coats is a big help... I've heard of "starving" the fabric (not applying enough resin) and I was trying to avoid that... good thing it was a test.
I was planning one layer of 7oz, maybe 2 on the lid since I'll probably stand on it from time to time. I'll get one layer on and see how it feels...
Still hoping to hear more on the adhesion issue.
Thanks for the help!
Re: Epoxy questions
June 05, 2017 07:25PM
Send us a photo when you're done
Re: Epoxy questions
June 06, 2017 04:43AM
Will do.
Any advice or techniques for getting the glass to stay folded around a corner? I was thinking I could oversize the fabric and clamp the dry edges to hold it taught while the epoxy dries. Then when the corner is stuck down but still green, go back and wet that edge. Would that work or would it just create a bubble?
Also, any guess on how much thickness fiberglass plus epoxy should add? I know you can build it up indefinitely but I'm talking about just one coat of 7oz to waterproof and provide a little strength, not the bottom of a boat... just trying to figure out how much space to allow for the parts to grow so they will still align when I reassemble after glassing.
Thanks
Re: Epoxy questions
June 06, 2017 05:59PM
RE> glass around a corner

Round off the edge to start. You can often get a corner layup to stay put, without bubbles, by baby sitting the layup, and by stroking a drywall trowel (keep it in solvent in between strokes) from next to the corner down and away.

Another way is to use duct tape and Visqueen. Tape some Visqueen to an already cured part of the object on one side. Make the wet layup. Pull the Visqueen tight over the corner and somehow tape the other edge so the Visqueen keeps tension tight over the rounded corner.
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