waterproof epoxy?

rebars1

Senior Chief Petty Officer
Joined
Feb 23, 2004
Messages
744
I'v finished glassing (three layers)the plywood tramson and was wondering if I should coat the inside surface with something else below the splashwell before closing it in. The epoxy resin (West System) says it is water resistant (not waterproof). I will be filling the void spaces with foam. The splashwell will get gelcoat.
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: waterproof epoxy?

There is no such thing as waterproof. All things pass water, some just more than others. Epoxy resin is a better barrier to water than polyester. Thicker is better than thinner (2 coats is better than one). Epoxy bonds to wood better than polyester. Pay particular attention to edges and holes. For what you are doing, epoxy laminating resins like WEST and others are your best bet. Even a glass of water will leak water, just really really really slowly. You have to think like a chemist, there aren't many absolutes just varying rates of diffusion. From a practical standpoint 2 or 3 layers of epoxy will seal wood from water about as good as its gonna get.<br /><br />PS coat the entire transom not just the bottom half or you will have a little bathtub at the bottom of the transom.
 

rebars1

Senior Chief Petty Officer
Joined
Feb 23, 2004
Messages
744
Re: waterproof epoxy?

Thanks jimd. I just was not sure of the intent terminology on the label. I've laminated the entire transom with three layers of glass and epoxy resin against the original exterior boat shell. There is a formed fiberglass closed bench that also is the top of the splash well. Theoretically, this chamber is supposed to be an air pocket, with no water access. I'm going to fill it with foam this time.
 

uncwillie

Seaman Apprentice
Joined
Oct 10, 2004
Messages
30
Re: waterproof epoxy?

if you mix some powdered aluminum flakes in the epoxy you can improve the water resistance, as they do with the better barrier coats that preceed anti fouling paints. The flakes are like overlapping shingles.
 

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
Re: waterproof epoxy?

jimd, my informational source for the epoxy is oposite of what you have listed. Epoxy is for use ABOVE the water-line due to the fact it becomes brittle when wet over time. Polyester is used for the lay-up of the hull and deck on our 50ft Valiant Yachts. Epoxy wouldn't have made them the world-class Yachts they are.<br />Ultra-violet rays also degrade epoxy quicker.<br />This is info from the owner of the Valiant Yacht manufacturing facility at the Marina I work for.<br />No arguement with you, just info I obtained in my own quest for answers. :)
 

G DANE

Commander
Joined
Nov 24, 2001
Messages
2,476
Re: waterproof epoxy?

Nice to hear, Kenny. I did all mine with poly, before I read all about epoxy here. Guess its good, though. If you want a better water barrier, paint your work, when finished with one of the epoxy based water blocking paints, or a similar ureathane paint. Hope my poly work is good enough. If I suddenly stop posting, you will know why!!
 

jim dozier

Lieutenant Commander
Joined
Jan 8, 2003
Messages
1,970
Re: waterproof epoxy?

Walleyehed, virtually all fiberglass boats use polyester resin for glass reinforced plastic (grp) because it is less expensive, adequately strong and water resistant, is easier to work with, less toxic, and bonds wells to glass and to itself. It is however, less effective than epoxy in bonding to wood, and acting as a barrier to water diffusion. Many of the older grp hulls that had problems with hull blister were treated with a sealing layer of epoxy (after the blisters were removed) to reduce water absorption and subsequent additional blisters. You are quite correct about epoxy resin being more sensitive to ultraviolet rays and it should always be painted with a blocking paint pigment if it is to be exposed to direct sunlight. If it is used internally like a transom repair it won't see sunlight and need not be painted. Cold molded wood boats' entire hull above and below the waterline are made with epoxy saturation techniques and would not work as well with polyester resin.<br /><br />I guess what I'm saying is if you are working with grp it is usually cheaper and easier and just as strong to fix it or modify it with polyester and glass. If you are working with wood and glass together or wood alone you are probably better off with epoxy.
 
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