Sealant for plain plywood

[eye4u]

Hi,

I am contemplating building a small boat out of ordinary plywood and boards you would find at a home center such as Home Depot. What I am unsure of is how to seal the wood so that it will not absorb water and deteriorate. It would be nice if a sealant is readily available in most major cities, low cost, and would only need to be applied once. Aesthetics, cosmetics, and visual appearance is of no concern what so ever.

Am I asking too much?
What are my options?

Thank you.

Sealants are available, of course. Low cost will certain be a no no.

But much depends on the lifetime you expect and the operation of the boat. (weekend on a calm lake, or cruising the pacific nortwest)

Epoxy is one way to encapsulate the ply and make it watertight for a long time, but not cheap. And it is wasted on cheap ply, that should be a marine grade ply.

Which sort of boat are you thinking about?

Regards
Richard

[dskira]

Originally Posted by eye4u

Hi,

I am contemplating building a small boat out of ordinary plywood and boards you would find at a home center such as Home Depot. What I am unsure of is how to seal the wood so that it will not absorb water and deteriorate. It would be nice if a sealant is readily available in most major cities, low cost, and would only need to be applied once. Aesthetics, cosmetics, and visual appearance is of no concern what so ever.

Am I asking too much?
What are my options?

Thank you.

If you can try to avoid Home Depot.
The ply they sell is the lowest quality you can find. The glue (the most important componant on plywood) used will not keep the ply together, and the layer in between the outside one is full of void and made of poor wood.
As for board, they are just cardboard.
For a small boat the difference on price between good quality and poor quality material is almost a mute point.
Go for the real stuff sailor, and let the big box for the suckers
Daniel

[lewisboats]

For a throw away boat you can use just plain paint...although a couple of coats of primer and 2 or 3 coats of paint will come out best. Don't expect a long life from crappy materials but if it only hits the water a few times a year and is protected from the weather while in storage and any damage is promptly fixed you could expect to see anywhere from 2-10 years out of it...depending on how you take care of it.

[sean-nós]

Have agree with the guys Don't buy the cheep ply if not marine ply go for WBP the kind you would use in a bathroom it has water resistant glue and coat in epoxy resin.But you can't beat marine ply, any boat you build is a vessel to keep you and your friends and family alive while on the water, don't cut corners on life for the sake of a few $$$

[mental_boy]

Here's a strong argument for 100% acrylic latex house paint:

http://www.simplicityboats.com/latexcarnel.html

As far as home depot plywood goes, I agree with apex1. Suitability depends on use and expected life. A Latex paint/home depot ply boat could outlive us all if used occasionally and stored indoors.

[ancient kayaker]

Originally Posted by mental_boy

... A Latex paint/home depot ply boat could outlive us all if used occasionally and stored indoors.

That's been my approach. Assuming a smooth surface to start with (normal with marine ply, needs work with hardware store ply) my boats first get a coat of sanding sealer to fix the fluff, which is easy to sand.

The hull exteriors get 2 coats of primer and 2 top coats of a good quality brand of exterior latex, sanded between coats using a random orbital sander, top coat left as is.

For floors I use porch paint, 3 coats, no primer.

For brightwork I have been used both marine varnish and the house kind (exterior), but here the marine varnish is incomparably better and no more expensive in the long run as it gives a respectable finish in 3 coats compared with about 6 or 7 for house quality. My boats won't win the concours d'elegance and I don't plan to leave them in the water for weeks on end. House paint works on houses that get exposed to rain and sun, just like a boat that's hauled out after each trip.

These boats go about 2 years between finish repair work, but I touch up scratches if they penetrate the finish down to the wood. generally they are stored indoors (unheated) but I have left some out for a Canadian winter without harm, except for one that got such a build-up of snow that it got squashed. Never store a boat downwind of a fence in a heavy snowfall area!

[eye4u]

Thank you all for the input, I appreciate it

apex1,
It is not as much a boat as I mentioned, but rather extra flotation for an existing floating platform. The platform is OK and safe as it is, but sets 6" or so lower in the water than would be aesthetically pleasing. Supposing that the plywood/board components fail, the worst that would happen is it will "sink" back to its current draft plus a bit more due to the weight of the wood; it would be an annoyance at worst.

[missinginaction]

Eye4u, I generally agree with apex, lewis and the other posters here. The issue is that even douglas fir marine ply is going for $85.00 for 1/2" sheets, a price you might not be willing to pay for your intended use.

There is one type of plywood that I have used extensively in the interior of my boat (cabin sole, cabinets, partitians, bunks, etc.), it's called Araucoply and is available at some (but not all) Loews.

Here is a link to a discussion that we had here about Aruacoply in 2007......

Arauco ply?

Along with using it in my boat I've built some bird houses and roosting boxes that stand out in the yard all year round. These I only varnish and they have held up very well over the past 3 to 4 years.

Consider Araucoply sealed (3 coats all 6 sides) with epoxy and covered with a layer of 4 oz fiberglass cloth where is will get any wear. Paint the epoxied plywood to protect it from UV degradation, take reasonable care to fix any dings that might develop and you'll get many years of good service out of your project.

BTW the gentleman refered to as guest20100203 in the link is a very knowledgeable contributor to this forum who unfortunately doesn't participate any longer.

Good Luck,

MIA

[ancient kayaker]

Originally Posted by eye4u

Thank you all for the input, I appreciate it

apex1,
It is not as much a boat as I mentioned, but rather extra flotation for an existing floating platform. The platform is OK and safe as it is, but sets 6" or so lower in the water than would be aesthetically pleasing. Supposing that the plywood/board components fail, the worst that would happen is it will "sink" back to its current draft plus a bit more due to the weight of the wood; it would be an annoyance at worst.

The requirements for a floating platform such as a dock or diving platform are quire different from a boat. Plywood is a bad choice of material for that application. The extra floatation that comes from the air enclosed in the plywood space will leak out in a few months unless the build standard is extraordinary. There are cheaper and better materials sold specifically for the purpose, plastic barrels, closed cell foam, even oil drums, it's all out there.

[troy2000]

I just dropped into a Home Depot in Beaumont today (California, not Texas) to do some price checking, and was amazed by what they didn't have on the shelves. For example, the only 3/8" plywood they had besides textured siding was some CDX garbage labeled as 'sheathing.'

I assume they meant 'shear paneling' instead; that's all it would be good for. I counted six voids along just one edge of the top sheet on the stack.

If that's typical of Home Depot stores nowadays, I won't be going there to buy wood. I'll have to go find a real lumber store instead. What I originally went in to look at were prices for 1 x 12 x16' nr 2 pine, to plane down and use in building a flat-bottomed canoe. The longest pine boards they had were 12', and that's when I decided to look at the plywood and some 1 x 2's instead.

[eye4u]

Hi,

I said boat originally in an attempt to be non-specific. I'm sorry for the confusion.

I had considered using 55 gallon plastic barrels, a place near me has them for $10/ea. I ruled those out because of dimensional constraints.
Currently my plan is to use wood because I can build it into the shape of any rectangular solid I chose to make best use of available space.
I am aware of the air leaking out problem, which is why I was looking for a good sealer; to keep the air in, and to keep my from having to re-apply in a year or so.
My current plan is to apply hot asphalt roofing tar. Like I said; cheap and robust are important, not looks. Two or three coats liberally applied boiling hot should soak into the wood and seal it up very well. I like whatever is the most difficult to apply and toxic to health; as these tend to be the most robust in the application; as opposed to the consumer garbage that's almost safe to ingest.

I gave Home Depot as an example because they're more well known than the actual lumber yard/home center I go to. Almost every time I go to 'depot, I walk out mad for one reason or another, usually because I wasted my time and should have known better. It's amazing how they have so much stuff, but nothing that ever suits what I need.

[mental_boy]

You could stuff it with 2 liter bottles/styrofoam chunks etc. to minimize sinkage if the box leaks.

Originally Posted by eye4u

Hi,

I said boat originally in an attempt to be non-specific. I'm sorry for the confusion.

I had considered using 55 gallon plastic barrels, a place near me has them for $10/ea. I ruled those out because of dimensional constraints.
Currently my plan is to use wood because I can build it into the shape of any rectangular solid I chose to make best use of available space.
I am aware of the air leaking out problem, which is why I was looking for a good sealer; to keep the air in, and to keep my from having to re-apply in a year or so.
My current plan is to apply hot asphalt roofing tar. Like I said; cheap and robust are important, not looks. Two or three coats liberally applied boiling hot should soak into the wood and seal it up very well. I like whatever is the most difficult to apply and toxic to health; as these tend to be the most robust in the application; as opposed to the consumer garbage that's almost safe to ingest.

I gave Home Depot as an example because they're more well known than the actual lumber yard/home center I go to. Almost every time I go to 'depot, I walk out mad for one reason or another, usually because I wasted my time and should have known better. It's amazing how they have so much stuff, but nothing that ever suits what I need.

[eye4u]

LOL
I like that idea

[Petros]

You might consider closed cell foam insulation board, that would float good and will not get water logged. If you want protection you could "sheath" it in pressure treated lumber (not plywood), and than also cover it in your tar bath. It would float better and hold up pretty good.