Epoxying plywood together

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Tugboathunter
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Epoxying plywood together

Post by Tugboathunter »

what is the best way to epoxy two sheets of plywood together that will be the bottom of the boat? Do I went out both sides wait until tacky then put in more epoxy mixed with filler? Or just wet out both side and clamp together?

Thank you,

Stephen

Hercdrvr
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Re: Epoxying plywood together

Post by Hercdrvr »

First I would encapsulate both sheets with Poxy shield or Silver Tip, something thin, let dry and then join them with Poxy Grip. If you don’t have Poxy Grip then thicken up your epoxy a little.
I use a body filler spreader to apply Poxy Grip on large surfaces. Do not attempt on a cool day, it won’t spread!
One builders experience, others will differ,
Matt B

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Roberta
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Re: Epoxying plywood together

Post by Roberta »

I agree with Herc. Additionally, there are notched trowels and spreaders available to get an even layer of epoxy. Flat surfaces will tolerate thinner epoxy, but sloped or vertical surfaces will drain and starve the bond. Thicker epoxy better in these areas. Also, merely clamping edges could create voids and lack of contact in the middle. Staples or temporary screws may be needed to ensure full contact. On concave areas it is better to secure in the middle and work your way out to the edges.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

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chugalug
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Re: Epoxying plywood together

Post by chugalug »

I am far from an expert on this,but was reading "The New Cold-Molded Boatbuilding" from Reuel B.Parker and he states that epoxy doesn't cure correctly if glued to cured epoxy without sanding the cured stuff so it'll have a "bite" to hold onto.When I start my next build, I plan on gluing each layer(with Thickened epoxy) as it comes.First layer to battons,then second to first.I imagine that the epoxy would only penetrate the ply to first waterproof glue layer anyway if using ply.(I plan on using 1/4 inch thick fir running at opposing angles instead of ply.)Sorry I hijacked you just my 2 scents. :D
Working on regular-sized Bo-Jest


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Roberta
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Re: Epoxying plywood together

Post by Roberta »

With cured epoxy, it is necessary to clean off any amine blush and
rough sand for a mechanical bond. Epoxy that is still uncured, less than 24 hrs, you will still get the more desirable chemical bond without cleaning or sanding.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

TomB
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Re: Epoxying plywood together

Post by TomB »

I'll add my two cents too.

The original question...joining plywood on the bottom.

Encapsulating the first layer side facing the boat is ok but you may create a bonding problem between the layer and battens or the keel if the cured epoxy isn't scuffed up first. Better to wet the entire boat side of the sheet and apply it to the battens while wet, that will count as the first layer of encapsulation.

The plywood to plywood gluing...Don't wait for tacky! Wet one sheet, squeegee, roller, brush, whatever, go for speed and a uniform wetting (like painting). Then turn your attention to the other sheet. Apply slightly thickened epoxy, thick enough to stay but thin enough to sag if left for a while. Spread using a 1/8" notched trowel. The idea is to get a uniform thickened layer so you have a variegated surface, almost nothing and 1/8" thick. You don't want starved areas or areas with big puddles. Starving--->no bond Puddles-->humps on the boat bottom. Fasten the two sheets together in a way to push excess epoxy from between the sheets, center to the edge, edge across the sheet, not all edges and working to the center.

Works for me...your results may vary.

Tom

TomB
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Re: Epoxying plywood together

Post by TomB »

Roberta wrote:
Thu Mar 05, 2020 8:00 am
With cured epoxy, it is necessary to clean off any amine blush and
rough sand for a mechanical bond. Epoxy that is still uncured, less than 24 hrs, you will still get the more desirable chemical bond without cleaning or sanding.

Roberta
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Bill Edmundson
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Re: Epoxying plywood together

Post by Bill Edmundson »

I apply plain epoxy to the new layer. Then I thicken to about applesauce on the base layer then clamp or fasten as needed. I don't let it cure-out before joining.

Bill
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kens
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Re: Epoxying plywood together

Post by kens »

use a notched trowel,
in large areas you can get air bubble that may stay in the laminate, a notched trowel helps let air out
don't ask me how I know
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

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Bill Edmundson
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Re: Epoxying plywood together

Post by Bill Edmundson »

I agree with Ken. Use a notched trowel/spreader. Put down a uniform coat to help eliminate bubbles.

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

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