Laminating 3/4" Coosa to make 1.5" transom

[bakerjw]

Planning ahead here. Unfortunately, my rebuild of 12 years ago had some water intrusion into a section of deck requiring me to revisit the upper portion of the rebuild. Pulling the cap will not be a big deal so I am pulling it and the wood deck and redoing it with nidacore.

With the cap pulled and deck reworked, I am opting to go ahead and replace the wood transom with 2 sheets of 3/4" Coosa 26. I am again using epoxy as I did for the original rebuild.
So, between the 2 sheets of Coosa, what is the best to use between the 2 sheets?
- 1708 with a layer of CSM on the stitched side?
- Just 1708?
- A few layers of CSM?

One sheet of Coosa will be laid flat on my vacuum form and wetted down with epoxy and the CSM/1708 or just CSM. The top side will be wetted with epoxy and laid down on top in a kind of rolling manner to minimize air pockets. The sandwich will then be vacuum sealed. When it is all under vacuum, will the air bubbles work their way out from the middle? I had considered perhaps a few 3/16" holes in the top Coosa board with some cups over the top to catch the escaping epoxy and to allow air an easier pathway to escape.

Still a few weeks away from doing this but as always, doing research and make sure I have things clear in my head before running

 

[MikeSchinlaub]

If I was doing it, I would do a layer of csm on both halves and the side that will contact the hull. Let it cure, scuff it up, dry fit together with a couple screws, use resin putty to bond, and finally screw the two together working from one end out.

This is what we did to a few of the floor sections that had to be doubled up. Assuming a fiberglass hull, you're leaving the outward facing side bare because it will be glassed in anyway.

Coosa is very porous, and really drinks up the resin. Plan on more resin than if you were doing wood. Wet the coosa generously before laying the glass.

 

[matt167]

Unless things or processes have changed, CSM is Not compatible with epoxy resin due to the styrene. So the answer would be just biaxial cloth if using epoxy.

 

[redneck joe]

I want to follow this one, there will be a few experts along shortly. Not me, im the peanut gallery...

 

[Scott Danforth]

1708 and CSM are not compatible with Epoxy

They need the styrene in poly resin to break down the binders

You can use 1700 with epoxy

 

[Pmt133]

1708 and CSM are not compatible with Epoxy

They need the styrene in poly resin to break down the binders

You can use 1700 with epoxy

Scott, you sure about the 1708? The ones I've seen and used are stitched meaning its good to go for epoxy. No styrene needed. (This would be us composites and whatever my local place sells....)

 

[Scott Danforth]

The CSM that is stitched needs the styrene to break down the binders. It's not the stitching, it's what is stitched to the 1700 to make it 1708.... The CSM

 

[Pmt133]

us composites lists their 1708 as epoxy compatible. (No binder/coating just glass fibers) Not the regular csm though as it uses a binder to hold the fibers together. Or am I missing something and my side project is going to come apart?

 

[MikeSchinlaub]

My bad guys. I spaced on the epoxy resin.

 

[bakerjw]

Merritt says that their 1708 is epoxy compatible.

1708 Double Bias +/-45 50″ Roll 110lbs – Merritt Supply Wholesale Marine Industry

merrittsupply.com

FWIW. they were outstanding on freight shipping for 2 3/4" Coosa panels, 5 Nidacore panels, a bunch of epoxy and a few other things.