Large Lamination using Epoxy

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Large Lamination using Epoxy

Postby GaryS » Thu Apr 02, 2015 2:09 am

We are building the 22 foot 'Mai Tai' and implementing a plywood sheet double bottom. It is nearly at the stage where we need to epoxy the second lamination to complete the double bottom. The first lamination has already been epoxied to the frame (both sides).
We want advice/comments on the epoxy mix/mass to use when we fit this second 22 foot skin to each side. All surfaces have already been encapsulated and sanded ready for bonding.
Our approach at this stage is to use quite a thin mix of thickened epoxy and apply to both surfaces with a roller - keeping the amount of epoxy on each surface fairly thin. We do not want to have too much epoxy volume. Bear in mind that this is a substantial area, time is short and we want to prevent any void problems.
We have read about cases where unthickened epoxy (resin + hardener only) is put onto one side with a roller and a thin layer of thickened epoxy rolled on the other side - reducing the overall volume of epoxy in the lamination. Is this viable?
Any comments/suggestions would be appreciated.


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Re: Large Lamination using Epoxy

Postby Roberta » Thu Apr 02, 2015 4:56 am

I like using a notched trowel to spread thickened epoxy. Get or make one with 1/16th inch notches. Thin epoxy lams are OK for small surfaces, but voids would be hard to avoid over large surfaces. The trowel will help spread a nice even amount over one surface while the other is set on it. I purchased a really nice notched glue applicator trowel from Rockler that is made from silicon rubber and the epoxy pops off of it when cured.

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Re: Large Lamination using Epoxy

Postby chugalug » Thu Apr 02, 2015 7:32 pm

:roll: Could drill small holes through second skin here and there so that when the epoxy oozes through,you know that the second skin is on without voids
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Re: Large Lamination using Epoxy

Postby kens » Thu Apr 02, 2015 9:15 pm

your problem is not the thickness, nor the squeeze out.
Your problem will be the working time of that large a batch of resin.
I would get the slowest possible hardener, apply it in the coldest time of day, put it in flat containers like cookie sheets, and work as fast as possible.

I did the double bottom thing, and worked the second layer in sections, that is, I had scarf joints to make my 23' bottom, so I only applied 8' section at a time. the second layer and its scarfs joints all went down a section at a time. Pre-fit and pre-drill just enough screw holes to get a good location/position for the 2nd layers to go on without any fussing.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Re: Large Lamination using Epoxy

Postby GaryS » Thu Apr 02, 2015 11:43 pm

Thanks for all of your comments and advice - very helpful.

Roberta - we have looked at the Rockler Spreader and we hope to source them out here - they look good.

Chugalug - we have screw holes to see if the epoxy is oozing
Kens - we have two people ready to work real hard at this when it happens. Yes, it has to be quick and we normally approach this type of thing at night when the temperature drops to about 14C to 16C - we will be able to heat underneath the hull after the laminating has been completed to make sure it cures OK.

Our take on this at present is that we will initially roll the epoxy onto both surfaces, using a spreader to even out any overly thick areas. We think this approach will be the fastest way to get the epoxy on. We are well prepared to physically get the lamination on and positioned quickly - the screw-down process has also been well rehearsed. The initial lamination (to the frame) was a bigger job because of the extensive amount of clean-up required working under the hull - this second lamination will not have this amount of cleanup to cope with.


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Re: Large Lamination using Epoxy

Postby slug » Fri Apr 03, 2015 3:05 am

Gary. If you can get MAS epoxy I'd highly recommend it. You'll have lots (2 t0 3 hours?) open time. AND, little or no blushing, AND available with Lo Tox hardener. What's not to like?


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Re: Large Lamination using Epoxy

Postby Bill Edmundson » Fri Apr 03, 2015 5:17 am

When you get a panel in place, start in the middle and work out. This will kind of "iron" it out and give any air pockets a way out.

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