Waterproofing, please read

Me and my friend have built a ten foot sailboat. In order to waterproof it we are planning on puting silicon or auto body waterproof hardener in the seams. Then we are planning on painting the entire boat with exterior waterproof and UV protected paint. The boat is made of mainly plywood. Do you think this would waterproof our boat? Any other suggestions on how to waterproof our plywood sailboat would be very helpful.

 

Well, I guess by the way you asked the question you haven't used marine plywood either, but for a 10' starter there are solutions.. First forget the auto stuff, and the silicon. You need to encapsulate the plywood in epoxy, and use epoxy fillers in the seams. A single layer of "glass would be helpful too. You can use a fine finishing cloth then heavy primer, sand, primer, sand, and then marine paint, and you'll end up with a professional looking little boat. Good luck.

 

We were just planning on doing what it says at the pdracer website (pdracer.com) At first we were gonna fiberglass it but since we aren't going to use it more than 4 years we figured it would be cheaper to just fill the cracks in and the seal the wood with exterior wood paint. Here I'll quote this from www.pdracer.com from the miscellaneous questions section

Should I completely cover the outside of the hull with resin?
Epoxy or polyester resin coating will help increase the life of a boat, but a boat that is just painted will last for atleast 10 years with the right care. The most important factor is preventing standing water in the boat.

Would you guys agree? As long as we keep it off the ground, cover it and store it upside down too should it last? Oh btw this is his friend, the other kid thats making the boat too.

I guess we could always cover it in epoxy resin just without the fiberglass, what do you guys think?

 

Thanks steve. yeah i looked at the website and i think the exterior UV protected and waterproof paint will work really well but i think we are going to have to find something else to use besides silicone. On that website it said the silicone is useless. Epoxy seems like it will work really well. The jolly roger will be awesome

 

use poly resin, paint it on in 2 layers,,only 35 bucks a gallon and that might be enough. it will last way longer then marine plywood alone

 

I have built skiffs with regular siding plywood and sealed the seams with mat and polyester. They last about three years if left outside in the weather.

 

thats because you sealed it with mat, the fiberglass on top of the wood traps moisture under it which saturates the wood eventually, just try the resin, not the glass.

 

If the boat itself isn't anything fancy, it seems the seams are what need to be addressed, and as said, silicone (while being very waterproof by itself) has very poor adhesion properties. Good way to make a fish lure, bad way to seal a crack in water.
Epoxy/tape is great for sealing seams. A ten footer might only use a quart of resin and one 50 ft roll of tape.
Any complete encapsulation with or without glass is going to cost money and increase the weight of a trailered boat. If the boat is worthy of such an expense, this would not be a bad idea, as it offers abrasion resistence and waterproofing, but any open boat with an epoxy-sealed outer hull should also be sealed inside (with plywood, no glass is required inside). Otherwise, there is nothing to prevent water being absorbed through the inner skin except paint (a couple of days of rain will add enough water to the structure to become problematic).
Still, it all amounts to expense and extra time. It will also weigh a few pounds more. At over one hundred dollars US per gallon, and cloth expense as well, epoxy/cloth could double the cost of a simple dinghy built with non-marine ply. It also will challenge the novice to work with materials that he is unfamiliar with, and that alone might end up as an added cost in terms of mistakes such as would require redoing a botched area.

Alan

 

Just painting on polyester resin won't do much, polyester has very little strength on it's own and doesn't sick all that well to wood, unless you don't want it to. It normally cracks and starts to peel off when the wood expands and contracts, good paint would be a better bet if you want to go cheap.

 

One advantage to an epoxy encapsulation prior to painting plywood is that fir plywood is not as pricey as the mahoganies or other more paintable species, so by using fir ply, which has the kind of grain that telegraphs right through paint, an epoxy coat will solve that problem for the most part. The savings compared to using a more paint-friendly expensive ply might just pay for the epoxy. The side benefit is a moisture barrier that will increase the life of the boat.

 

he didnt say anything about strength, he jus wanted water proofing, and i've never seen polyester resin peel from my floors, but of course i cover them up with rug after lol, if i just paint it on and let it soak into the wood, it has always stayed and is like a really long lasting thomson water seal to me lol. i didnt think that if he just painted it, and was using the paint barrier to keep the water from coming in that paint would leak before the resin would, but then again ive never done it for the whole boat jus floors

 

The strength I'm talking about is it's lack of ability to not crack when applied like a paint over wood without any glass to reinforce it. Polyester is a poor choise for this type of application, epoxy is far better and if you want it to last for a long time then glass needs to be used.

 

Polysulfide (3M 101 or similar) the seams if you plan on extended amounts of time on the water (more then a few days at a time). Polyurethane (3M 4200 or similar) the seams if she'll be trailer born the majority of the time.

You have three real choices to seal the wood - all need a fabric sheathing to be effective. Polyester, vinylester and epoxy are the choices, with polyester being the cheapest and least able to stay stuck to the wood and epoxy being the most costly, but the strongest, most waterproof and best stick-um available.

Thompson's Water Seal is useless on a boat, don't even think about it. Hell, it doesn't even keep the moisture out of the deck, hanging off the back of your house.

If you elect to use a polymer to seal the wood, you have two choices. The first is to just coat and sheath the exterior. This will save some money at first, but will cause a host of problems down the road, as it will trap moisture under the plastic skin and this will rot the wood in time. The other is the recommended method, which is to encapsulate, embalm or generally entomb the wood in plastic then skin it with fabric in the areas that need abrasion protection (all of the exterior for example).

The choice of encapsulation must be carefully considered as it can add substantially to the cost of a small boat, possibly doubling or tripling materials cost and surly dramatically increasing building efforts.

You don't need these polymer coatings in many small craft designs. On the other hand, there are also plenty of designs that can't exist without the goo's and 'glass fabrics. Knowing what you have is important in this consideration. A stitch and glue or taped seam design, pretty much marries you to the heavy use of these embalmed boatbuilding methods. A plank on frame design can happily live without the goo in a can syndrome and lessen the building costs and effort.

The decision is dependant on the builder's wishes, skills, willingness to perform maintaince on her, where and how it will be kept, etc. If you are willing to provide reasonable care, keep it covered and in good order, you don't need the 'glass and goo treatment (unless the design requires it). If you think you'll not be as attentive with the boat as you should be (honest answers folks) then you may be better off with the added protection of an encapsulated and sheathed craft.