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New deck plwood

PostPosted: Mon Apr 10, 2006 1:45 pm
by txcaptdan
I have just finished cutting out new deck plywood for my 20' Cruisers inc. Seacamper. i have used 1/2" 5ply marine fir plywood. I am planning on covering deck with original style vinyl or a mahogany strip.
My question to those who have done this before is what should I treat surfaces with before final assembly. Plywood removed didn't seem to be treated with anything top or bottom. These where the original decks as they had hull # written on them.
In my boat you can see under front deck when assembled. Topside will be fared over screws and glued vinyl.
Is it neccesary or even needed to epoxy seal or varnish either side?
I am contemplating painting lower surface that would be visible under bow, if you laid down in bunk.
What are your thoughts or past experiences?

deck photos

PostPosted: Mon Apr 10, 2006 2:01 pm
by txcaptdan
Here are a couple of shots of deck
Thanks Dan

Deck Seal

PostPosted: Mon Apr 10, 2006 3:49 pm
by Rodney Syverson
Dan; I have read in Danenberg's book I believe or somewhere that putting down CPES or any sealer is beneficial for adhesion of top coats of varnish or whatever. I think the logic is to create a barrier so that less film will be absorbed into the pores of the wood and lost on the surface. On varnish this necessitates more varnishing but on an adhesive it merely preserves your bonding material on the surface where it is required. An epoxy sealant that sets up might not have any compatibility issues but it wouldn't hurt to check. On the underside of the hull it might not be so important other than any untreated wood will absorb moisture which can contribute to premature wood decay. My vote would be to seal both surfaces. Rod

PostPosted: Tue Apr 11, 2006 4:21 am
by a j r
I definately recommend a sealer coat on all sides of the plywood (even the edges). This is a great application for Smith's CPES.

As for the underside of the deck, a coat of CPES followed by several coats of varnish is my recommondation.


PostPosted: Tue Apr 11, 2006 12:25 pm
by txcaptdan
I have had some serious thoughts about the wisdom of sealing everything we replace in these boats with epoxy. Isn't that the definition of fiberglass boats and look what happens to wood encased in resin, I would be willing to bet you have seen a few soft core glass boats lately?
Original manufacturers did not seal all wood - was that to allow wood to absorb then dry out, as opposed to water getting into sealed wood and never drying out? Their methods lasted far beyond their own expectations. As I disasembled my boat I have found very little sealed wood beyond being marine plywood that has seemed to hold up well. Even original laps were not sealed, just raw plywood to raw plywood.
I would like to do as an original restoration as possible and make it so the next boater that gets my boat 50 years from now could do a restoration and not have to rip the boat apart because of my or others over use of epoxy.

Sealers versus epoxies

PostPosted: Tue Apr 11, 2006 5:03 pm
by Rodney Syverson
Your concern with utilizing epoxies is valid. Usually encapsulation of wood with epoxies is the kiss of death for a wooden boat, even though it is touted to be an acceptable procedure for salvaging wood boats by some boat restorers. The term epoxy is a general term applied to any two part component where the combination creates a solid or semi solid product, weather it is paint, primers, sealers or adhesives. People call anything they have to mix together an epoxy.

CPES appears to be unlike any other epoxy in that it does not get hard and it supposedly breathes, which you might guess allows the migration of moisture into the wood. The key is, water molecules are larger than gas molecules. Hence a greater barrier for water to get in and gas to get out. A hard epoxy like a polyester resin or epoxy resin will offer a permanent barrier that will not allow passage of water until it cracks. And on a boat or anything that flexes it will crack. Then the water molecules have clear passage to wick into the wood which will eventually become saturated and the uncracked areas are sealing perfectly and will not allow the moisture to gas out. Eventually the wood turns to punk.

I had the same questions you have until I started reading Danenberg's articles in Classic Boating magazine and his two books. Everything he says appears to be spot on in my book. He bristles at the thought of encapsulating wood with epoxies, even though it is done by big buck restoration shops, but he stands by CPES and has had enormous experience and success with it.

The original manufactures did not have the products available to them that we have now. We just need to decide what is best with the information we have. I firmly believe Danenberg is right and have followed his recomendations.
The underside of your deck no doubt could get by with out sealers as that is high and dry but any area exposed to serious moisture really needs to be sealed. The original manufactures I firmly believe did not go overboard on this as it no doubt was a significant factor in manufacturing, schedules and costs for a boat not expected to have more than a 6 year life span. I often wonder how many years more I would have gotten out of my 62 Sea Lancer ribs had the backside of the ribs had they been properly sealed. There was virtually no sealant on the back sides and with out exception they all exhibited some signs of deterioration. Sure they gave probably 30 years of useful life but I have to believe they would have gone further if they had not been wicking moisture out of the bottom of the boat.

PostPosted: Wed Apr 12, 2006 4:27 am
by a j r
Ditto to what Rod wrote. CPES is NOT a hard epoxy. It is a SEALER that does allow the migration of moisture in and out of the wood.

PostPosted: Wed Apr 12, 2006 4:28 am
by a j r
If you want to read TONS of information about CPES look at the discussion forums at

Do not lump CPES in the same basket as West, MAS, etc...

PostPosted: Wed Apr 12, 2006 9:13 am
by txcaptdan
I agree that a sealer should be used, but I am not a flag waver for CPES. It is thinned epoxy that anyone can make from a high quality epoxy thinned with Exylene or acetone. I have added thinner at a 25% mix to epoxy and gotten great results.
Check out for a discussion on the subject.
I guess I just refuse to pay the per ounce price for CPES when the bulk of it is thinner - a cheap ingredient.
The thinned epoxy that I have applied seems to set up an excellant surface for adheasion of other materials, it doesn't set up a hard glossy surface like straight epoxy but a dull tacky matte surface.
I have read that CPES has a 3 part epoxy to 7part thinner ratio - thats pretty thin. True the more thinner the better penetration but the less epoxy solids.

PostPosted: Sun Apr 23, 2006 4:08 pm
by mengelmar
I echo Txcaptdan's experiences with thinned epoxy. I bought one kit of CPES before finding the page. Now I thin epoxy to varying degrees to custom fit the immediate purpose (ie. stabilization of minor rot, sealing of new wood, primer for paint or varnish)