Does Pourable Foam Seal Plywood?

[mstrader77]

I have a question/observation that I would like input on. If using pourable foam under a plywood deck, does the plywood need sealed (CSM/resin) on the bottom? I can see the benefit if under the deck was an open space, but doesn't the foam end up acting like a sealer when it sticks to the plywood? It seems that the only way the plywood would get wet is if the foam was compromised and therefore the deck and foam would need replaced. I am assuming that the top of the plywood would be completely covered/sealed with CSM. Thanks for any input.

 

[metriccrescentwrench]

Re: Does Pourable Foam Seal Plywood?

NO, pourable foam isn't an adequate sealer.

At a minimum I'd paint the bottom of your deck with epoxy resin (not polyester because over time it develops micro-cracks and allows water penetration). A layer of light glass or CSM with resin would be even better. It seems like overkill, but if your going to all the trouble to rebuild a boat you might as well take every possible precaution against future problems.

 

[Woodonglass]

Re: Does Pourable Foam Seal Plywood?

Ditto ^^^^. The Foam will not 100% coat the bottom of the deck and will leave cracks and crevices where condensation etc. can and will form. $60 bucks will coat the bottom of your deck with Poly Resin and CSM. I thinks it's well worth the cost.

 

[GA_Boater]

Re: Does Pourable Foam Seal Plywood?

Ditto X3. If pourable foam sealed the plywood, we wouldn't have rotted stringers in poured foam boats. Also when the foam expands it may or may not fill every nook and cranny. Looking at many resto boats here and all, as in every one, has voids in the expanded foam.

 

[Grub54891]

Re: Does Pourable Foam Seal Plywood?

Mine had plenty of gap's from the factory foam.

 

[NickMcCabe]

Re: Does Pourable Foam Seal Plywood?

I'm not an expert but I think you would majorly regret having any kind of raw plywood on your deck. I would expect some condensation to occur on the plywood even if no water made it below deck (and we know it will). For that reason alone I would epoxy or ask about doing a lacquer or polyurethane coat on it.

 

[Yacht Dr.]

Re: Does Pourable Foam Seal Plywood?

I have a question/observation that I would like input on. If using pourable foam under a plywood deck, does the plywood need sealed (CSM/resin) on the bottom? I can see the benefit if under the deck was an open space, but doesn't the foam end up acting like a sealer when it sticks to the plywood? It seems that the only way the plywood would get wet is if the foam was compromised and therefore the deck and foam would need replaced. I am assuming that the top of the plywood would be completely covered/sealed with CSM. Thanks for any input.

If your going to re-deck then just use some poly resin on the underside.

I dont know of many boat manufactures that Glass the underside of decks .. just the topside to complete the tabbings and other things.

Foam or not .. you should consider some kind of moisture to develop under your deck.

Im not saying that the moisture will affect your deck .. but it could over time. As far as I know there is very few production boats that seal the underside of the decking.

You could do this for 'protection' .. or you dont have to do it at all.

I would still consider coating the underside with at least a few coats of resin ( poly or epoxy ).

YD.

 

[zool]

Re: Does Pourable Foam Seal Plywood?

Mine is cored with 3/4 ply, with glass underneath, and glass/gel on top, no foam...lasted 25 years and still no rot.

 

[Yacht Dr.]

Re: Does Pourable Foam Seal Plywood?

Mine is cored with 3/4 ply, with glass underneath, and glass/gel on top, no foam...lasted 25 years and still no rot.

Um .. ok .. some of us dont have those conditions. This is a case by case issue.

YD.

 

[zool]

Re: Does Pourable Foam Seal Plywood?

Um .. ok .. some of us dont have those conditions. This is a case by case issue.

YD.

"I dont know of many boat manufactures that Glass the underside of decks .. just the topside to complete the tabbings and other things."

Umm, wut?

The fact is, may manufacturers glass underneath, your statement is just wrong.

maybe you should get help for the conditions you do have...just saying

 

[Yacht Dr.]

Re: Does Pourable Foam Seal Plywood?

"I dont know of many boat manufactures that Glass the underside of decks .. just the topside to complete the tabbings and other things."

Umm, wut?

The fact is, may manufacturers glass underneath, your statement is just wrong.

maybe you should get help for the conditions you do have...just saying

Actually I dont know of many boat builds that have the underside of the deck glassed and foamed.

Now Im not talking about hatches or Engine compartments .. just those little boats that have a foam floating floor/deck builds.

I have many o' core samples that do not show Any glass on the underside of a foam filled build. I have been in a few production lines that did not do this glassing the underside of a foamed deck.

However .. It has been a few years since I have been on the 'Build line' .. so things might have changed.

But I am still correct in my suggestion that in the Past Builds there was not a great deal of glassing the underside of a foam filled Dink.

YD.

 

[saginawbayboater]

Re: Does Pourable Foam Seal Plywood?

freudian slip :laugh:

 

[NSBCraig]

Re: Does Pourable Foam Seal Plywood?

I've never seen a deck that wasn't glassed underneath. Where the floatation foam is doesn't matter to the basics of boat building.

I have seen them stop the glass going up boxes that contain the foam, but never no glass under a deck.

 

[Woodonglass]

Re: Does Pourable Foam Seal Plywood?

My 1961 Lonestar, 1972 Chysler BassRunner, and my BIL's 1984 Glastron, ALL had Glass on the bottom side of the deck. And even if they didn't I'd still advice everyone to put a minimum of 1 layer of 1.5oz csm down with their resin, cuz resin without glass when flexed enuf will crack and allow moisture to penetrate into the wood. Poly has no binders like epoxy. It needs the fibers in the CSM to keep it from breaking and cracking.

 

[saginawbayboater]

Re: Does Pourable Foam Seal Plywood?

old aerocrap, oh sorry aerocraft, no glass under deck. A little slip of my own! :laugh:

 

[chconger]

Re: Does Pourable Foam Seal Plywood?

My 1961 Lonestar, 1972 Chysler BassRunner, and my BIL's 1984 Glastron, ALL had Glass on the bottom side of the deck. And even if they didn't I'd still advice everyone to put a minimum of 1 layer of 1.5oz csm down with their resin, cuz resin without glass when flexed enuf will crack and allow moisture to penetrate into the wood. Poly has no binders like epoxy. It needs the fibers in the CSM to keep it from breaking and cracking.

My '88 Glastron had no glass under the deck. In the bow area it was painted red. But even that minor protection ended around the front seats and there was nothing at all moving to the stern.

 

[ondarvr]

Re: Does Pourable Foam Seal Plywood?

Most boat builders now use treated wood, so there is less need for it to be glassed, old school was build it fast and cheap because it will last 10 years or so no matter how its done, sometimes the top of the floor isn't even glassed, just carpeted. This doesn't mean not coating the bottom side is the correct way to do it, only that it will last for a while being left bare.

Coating the bottom side with just poly resin will be of little value, more like a waste of money, it typically develops many small cracks rather soon and becomes useless as a water barrier, epoxy can do a good job though. Using a layer of glass can create a very good barrier, but attention to detail is important, if any holes or screws are left unsealed all the money and hard work in other areas is wasted because water will migrate into the wood and it will rot. It makes no difference whether you use epoxy or polyester, leaks will cause the wood to rot.

 

[jigngrub]

Re: Does Pourable Foam Seal Plywood?

I have a question/observation that I would like input on. If using pourable foam under a plywood deck, does the plywood need sealed (CSM/resin) on the bottom? I can see the benefit if under the deck was an open space, but doesn't the foam end up acting like a sealer when it sticks to the plywood? It seems that the only way the plywood would get wet is if the foam was compromised and therefore the deck and foam would need replaced. I am assuming that the top of the plywood would be completely covered/sealed with CSM. Thanks for any input.

IF:

1. your below deck is poured solid with foam, and:

2. your hull is watertight, and:

3. your deck is completely sealed and watertight, and:

4. You keep your boat covered and dry when not in use:

... you have nothing to worry about by not sealing the bottom of your decking, and might even be considered a waste of money if you do seal it.

A watertight hull filled with foam will be impervious to water, and should your hull be breached the foam will seal off the hull preventing water from entering.

A well glassed in deck top with NO PENETRATIONS and a water shedding finish like GEL COAT or any other finish that aids in the draining of water (unlike carpet the absorbs and retains water) will/should keep you decking and below deck structure bone dry.

Just remember, the first time you put a screw through your completely sealed new decking... you might as well have shot your boat through the heart with a .44 magnum.:mad-new:

... and laying carpeting in your boat is like strapping a suicide vest to it with a delayed timer on it.:facepalm:

 

[Yacht Dr.]

Re: Does Pourable Foam Seal Plywood?

Most boat builders now use treated wood,

I would like to verify that .. could you please post or PM me of what you consider 'Most boat builders' that currently use PT wood

I know that some do use the PT wood .. but cut to the chase and tell me the Main builds that actually use this on a production line build.

That way I can verify this.

I have called up a few .. and I cant verify this myself as a Golden Rule of build.

Im not talking about Pontoon builds .. im talking about run of the mill production boats that use PT instead of MG.

I understand that if you put holes in your boat without proper sealant will compromise the substrate .. but that is a given.

YD.

 

[ondarvr]

Re: Does Pourable Foam Seal Plywood?

For builders that still use wood the list would be shorter for those that don't use PT than those that do.