Fiberglass Sandwich Problem

[JustMrWill]

Here is what I did:

-Cut 3 pieces of exterior grade A-C plywood to fit my transom.
-Sanded.
-Wiped down with acetone (could not find styrene anywhere).
-Applied polyester resin on once side of first piece.
-Layed mat and added more resin (wetted out mat completely).
-Applied polyester resin to one side of next piece.
-Layed that one on top of first.
-Repeated etc. to get plywood-resin-mat-resin-plywood-resin-mat-resin-plywood sandwich.
-I clamped the crap out of it and let it cure for about 2 weeks.

I removed the clamps yesturday and I noticed that today the edges are separating.

I have read the whole epoxy/polyester debate so please dont go there...

What did I do wrong? Not enough resin? Improper prep etc?
How can I fix it? Can I just add resin to where it is separating and re-clamp or do I need ot start over?

-JMW

 

[i386]

Re: Fiberglass Sandwich Problem

I'll be doing the same at some point so I'm interested to see the answer to your question.

My understanding is to first seal the pieces and let them cure.

Sanding not necessary since the resin will fill the gaps.

Don't clamp too tight or you'll squeeze out too much resin.

Please set me straight if I'm wrong.

 

[Bob_VT]

Re: Fiberglass Sandwich Problem

I used multiple pieces of plywood and used gorilla glue between them. I also used stainless steel screws to help the clamping action accross the pieces. I left the screws in there.

You could "add" resin and reclamp but IMO it would just act as a filler. When you are laminating plywood your bond will only be as strong as the bond between the other wood layers. The resin and fiberglass does not penetrate beyond the first layer of wood.

 

[Mark42]

Re: Fiberglass Sandwich Problem

Was the plywood allowed to fully dry before being assembled?

 

[JustMrWill]

Re: Fiberglass Sandwich Problem

I am thinking that I may have over tightened the clamps and squeezed out too much resin. The wood was completely dry before I started. I used non-waxed polyester so adding more shouldn't be a problem. I think I will try to pull the layers apart and if they give...then I will add resin and re-clamp and hope. If they don't come apart...I am going to try to pour some resin into the gaps, reclamp and hope. I was trying not to use screws but I may end up using them in the end.

I have a couple pictures of my progress...I'll try to upload them and post them today.

-JMW

 

[JustMrWill]

Re: Fiberglass Sandwich Problem

Here is how I had it clamped...looking at the picture...it does look like alot of resin squeezed out....

-JMW

 

[klos]

Re: Fiberglass Sandwich Problem

First I mate the pieces of plywood together to dry fit everything, run only two stainless wood screws into the wood then take them back out, (only use the screws for keeping the wood aligned during clamping and curing.

Next I only laminate two pieces of plywood at a time, Wet out one side of wood then one layer of 1.5 oz mat, and the same for the other piece of wood so when they get sandwiched together you will have two layers of mat in the sandwich.
Then do the third after the first two have cured, (takes a little more time but in my oppinion its easier that doing all three at the same time.

After the resin is almost completly cured I pull out the screws and fill holes with cabosil/resin putty. I don't realy like the idea of leaving srews in there.

I have made some test pieces this way and the wood failed long before the fiberglass did, there is no way it will come apart.

One more thing, clamp it just enough so you can see the resin bubble out a little, you don't want to squeeze out all the resin & use 6" to 8" blocks of wood between the wood and clamps to spread the load a bit.

Hope this helps.

 

[asianbandit]

Re: Fiberglass Sandwich Problem

I think i know where you went wrong..You needed to resin soak the plywood a couple of times before sandwiching between fiberglass.. The resin needs time to soak into the plywood, you can thin this out with acetone to make sure it goes through the wood all the way. I would let the resin coated plywood set for a day or two then begin with sandwiching the fiberglass in between

 

[JustMrWill]

Re: Fiberglass Sandwich Problem

Sorry for not updating this thread....

I was able to pull apart one side "easily" but the other side bonded. I re-applied resin and another piece of mat...then applied even more resin and re-clamped (not as tight). After a day or so, I removed clamps and it is not coming apart.

-JMW