Best way to encapsulate plywood

[tubenewb]

I am replacing some 1/2" Plywood pieces in my boat..I plan on using poly,1.5 csm and 6oz cloth ..
Is there a certain pattern to follow ? Should I come around and over lap with the csm in one direction, then come around and overlap with the cloth in the other direction?
My my concern is how do you glass all the edges?
I guess you could slit the corners and fold over but I was guessing there needs to be overlap .
I am definately using the csm/6oz on the top side , doe anyone think I should continue with the 6oz on bottom side as well?
Thanks in advance

 

[BWT]

Re: Best way to encapsulate plywood

As a general rule, I always start and finish with CSM. Start because it's a pliable, sticky laminate that holds resin (think of it link a bonding layer), and finish because it sands smooth for finishing (if you paint ,there's no print through of the glass in the paint). Make sure to wet out the ply FIRST before laying down the initial layer of csm (personally I like to keep rolling it on until it stops soaking in and starts to gel).

More than likely for this application laminate orientation is not important (what pieces are you replacing?) What alot of people here on the forum like to do is use epoxy (either regular or quick set) to seal the plywood edges AFTER all of the glass is laid up. If you're able to round over the edges of the ply then it's possible to wrap the csm over the edges. If the ply itself is stiff enough for it's application then there is no reason to use the cloth on the bottom; BUT do make sure to have a layer or two of CSM for waterproofing.

 

[parrisw]

Re: Best way to encapsulate plywood

1/2" is a Royal Pain in the Butt to wrap with CSM, I just did it with mine, I went with 1/2" for weight savings, and I didn't need 3/4", however next time I may just go with 3/4 for ease of wrapping with CSM.

 

[tubenewb]

Re: Best way to encapsulate plywood

As a general rule, I always start and finish with CSM. Start because it's a pliable, sticky laminate that holds resin (think of it link a bonding layer), and finish because it sands smooth for finishing (if you paint ,there's no print through of the glass in the paint). Make sure to wet out the ply FIRST before laying down the initial layer of csm (personally I like to keep rolling it on until it stops soaking in and starts to gel).

More than likely for this application laminate orientation is not important (what pieces are you replacing?) What alot of people here on the forum like to do is use epoxy (either regular or quick set) to seal the plywood edges AFTER all of the glass is laid up. If you're able to round over the edges of the ply then it's possible to wrap the csm over the edges. If the ply itself is stiff enough for it's application then there is no reason to use the cloth on the bottom; BUT do make sure to have a layer or two of CSM for waterproofing.

I am doing a deck patch apx 11"x48" and rebuilding a foam floatation box apx 33"x24"x12". I know many seal with epoxy on the edges but I am going with poly. I am to understand that's th way to go with existing glass work on a 80's vintage boat. Other wisw the epoxy sounds great.
I guess using poly I am wondering how to tackle the edges if I won't be able to wrap. Hmmm

1/2" is a Royal Pain in the Butt to wrap with CSM, I just did it with mine, I went with 1/2" for weight savings, and I didn't need 3/4", however next time I may just go with 3/4 for ease of wrapping with CSM.

Thanks for the input didn't think of the weight. I was basing more onthe structual build up not really knowing how pliable it would be. Hmmm.

 

[Chris's CVX16]

Re: Best way to encapsulate plywood

I did mine a few weeks ago and skipped the plain old CSM and went for 1708 instead. I used 1/2" marine plywood and used 3 layers. I wet the face of the transom and then draped the 1708 over it and got it nice and flat. I overlapped onto the bottom a few inches and then laid the first pre-cut piece of plywood in after I wet the bottom and side edges as well as the rear face. I repeated this 3 times. Between the 2nd and third layer I ran screws in from both sides to get a proper clamping force. Then on the third layer put in a few screws from the front only. After about an hour of cure I trimmed the edges all nice and neat then glassed in the sides to the stern along the edges and then glassed in my knee wall and the foot of missing floor section .

The cured 1708 is as thick as one ply of the 5 ply 1/2" plywood. It was a tiny bit thicker than the old transom but I had splashwell repairs to do so that didn't matter much. I used nearly 6 yards of CSM on the floor and in places I needed easy to work with material and it is decent but after going thru 7 yards of 1708 I think I'd use more of that on my next project boat. Ya it is $10 a yard more expensive but you don't need to be doing this again any time soon. Figure the extra $70 I spent on 1708 is cheaper than going out and getting even 1 sheet of marine plywood let alone several more gallons of resin.

 

[BWT]

Re: Best way to encapsulate plywood

the older boats (and most of the new ones today) were built with poly resin. However, as far as adhesion and bonding there is no advantage in sticking solely with poly; epoxy will bond just as well or better. As long as you're only using the epoxy to seal the edges, there will be no issues with tabbing the surface of the patch onto the surrounding floor (you'll still be bonding poly with poly on the surface). If there are any gaps around the perimeter of your patch either use some thickened poly resin or epoxy.. It will be just fine and you won't have the hassle of trying to edge wrap relatively thin ply (especially since the edges won't be rounded over).

 

[tubenewb]

Re: Best way to encapsulate plywood

the older boats (and most of the new ones today) were built with poly resin. However, as far as adhesion and bonding there is no advantage in sticking solely with poly; epoxy will bond just as well or better. As long as you're only using the epoxy to seal the edges, there will be no issues with tabbing the surface of the patch onto the surrounding floor (you'll still be bonding poly with poly on the surface). If there are any gaps around the perimeter of your patch either use some thickened poly resin or epoxy.. It will be just fine and you won't have the hassle of trying to edge wrap relatively thin ply (especially since the edges won't be rounded over).

Ok I was under the impresion there was some kind of incompatability...Are you sugesting use some resin just for waterproofing the sides and back to poly for tabbing things in ??
Thanks so much

 

[Cadwelder]

Re: Best way to encapsulate plywood

Ok I was under the impresion there was some kind of incompatability...Are you sugesting use some resin just for waterproofing the sides and back to poly for tabbing things in ??
Thanks so much

I don't want to speak for someone else, but I think what he's saying is as long as you're not applying the polyester over areas of epoxy you're okay. The issue is say you have one layer of epoxy over your deck and tabbing in with polyester....that would not be good.

But since edges won't interfere with the rest of the tabbing your fine.

 

[BWT]

Re: Best way to encapsulate plywood

yup, what Cad said. Edges are not the bonding surface; the tops are what is tabbed for the structural bond. As long as there is no epoxy used on the top face, there will be no issues. Use Epoxy for sealing the edges only unless you plan to do the whole repair in epoxy (which would be fine too)...

The general rule is:
Epoxy over poly or vinylester = Good to go..
Poly or vinylester over Epoxy = no good...

 

[tubenewb]

Re: Best way to encapsulate plywood

Thanks for the info guys . So does this sound safe? Hit the clean wood with some epoxy on the edges. Then hit the boards with my csm/cloth combo on top , csm on th bottom.
What do you think, little epoxy creeping past the edge ok or sand sqaure off first and let a little poly go over? Guess its like picking the lesser of two evils..if I am carefull we are talking about what a 16th of epoxy..good stuff guys. .thanks for taking the time

 

[BWT]

Re: Best way to encapsulate plywood

I would layup the glass first with poly, then give the edges a light sanding, tape off the top face and layup the epoxy on the edges (probably 2-3 coats or until it stops soaking in; use a fast set and layup each successive coat after the previous has tacked but not cured). Pull tape and your good to go.

 

[tubenewb]

Re: Best way to encapsulate plywood

This will work out nicely. I can use the rest of the epoxy resin for waterproofing my standalone interior pieces..ex. removable seats, engine box that surounds the bilge where the covers rest on... great stuff.. thanks so much btw. I re read. Looks like you pretty much said this in your 1st reply..got it now