Houseboat Building or Repair - What plywood, exterior or marine grade?

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Houseboat Building or Repair - What plywood, exterior or marine grade?

by Don
(St. Paul, MN)

Houseboat Building or Deck Repairs<br> Use Exterior or Marine Grade plywood?

Houseboat Building or Deck Repairs
Use Exterior or Marine Grade plywood?

When it comes to houseboat building or a deck repair, what plywood do we use, interior, exterior, or marine grade plywood's?

Last September we purchased a 1969 34 foot Nautaline. It is what you would call a "fixer upper"! But we are looking at it as a fun project for this summer.

The question I have is I know it is recommended to use marine plywood, but I have read that a lot of people use a good exterior grade plywood and with the proper sealant, this works just as well, and alot cheaper !!

With all the other work that needs to be done on her, I want to do a good job, but I also have to be budget oriented.

We plan on keeping her for only a few years and then going to a larger boat, so I want to be able to get back the money I put in.

What are your thoughts on this, and do you have any helpful hints on making this as pain free as possible? Do you know of any books that cover this type of project?

Thanks Don.

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Reply - Answer
Well Don, welcome to the houseboat forums, and congratulations on buying a houseboat.

Now you happen to have the "million dollar" question. That's like asking what's better, the sunrise or sunset? We will get many opinions on which is best.

Now morally, I would suggest to use marine grade since it is a very different quality and construction grade of plywood. As the name implies it is for marine boating use.

I also understand you're dilemma of wanting to stay within a budget, and only wanting to keep the houseboat for a few years, then upgrading.

On a personal note, I have done some rebuilding and deck repairs on different boats, and have always used marine grade plywood. It hurts to pay more for the wood, yet you have to take into account your time.

When it would come to sell the boat, I always explained this to the prospective buyers so they would understand why the selling price was higher. The job was done right the first time, and didn't have to be redone later.

You mention if I could recommend any plywood boat building repair books. You will find explanation and information there on the different material, plans, and details.

Now back to using exterior grade plywood, you can use it, and use fiberglass epoxy to seal it up completely on all sides and surfaces. You just have to understand that exterior grade wood has many gaps and voids, especially when you cut it to size and shape. I also know of many people who use the lower priced exterior material.

Either way, I am sure that this post will stir up many different opinions, that I also am looking forward to hearing and reading them.

If you want to get some good instructional videos on doing fiberglass painting work and repairs, you will find some more information on our Houseboat video DVD page.

Lastly, hopefully some of our readers will share and post comments about their repair or houseboat building plywood grade techniques or experiences. Feel free to use the "Click here to post comments." link found near the bottom of this page.

Thanks again for sharing, IAN - from www.all-about-houseboats.com

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Houseboat Building or Repair - What plywood, exterior or marine grade?

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Plywood covering?
by: roy e

re: Mr. B's comments on canadian crezone.. .

Mr B. notes that the plywood has a paper like coating which takes finish well. I'm wondering if this coating whether paper or plastic, takes abrasion well? Show me a boater who hasn't scraped the hull, and I'll show you a boater who has never left the mooring.

In any event, it is good to learn of alternative materials.

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Tips on plywood choices.
by: 69 nautaline

Just a note on Plywood. The primary difference between exterior grade plywood and marine plywood is the fact the cores will have small voids in the inner veneers.

The same glues are used to assemble the plywoods. I have used exterior grade plywoods in all my boat projects as the marine plywood is just to expensive. (unless your building an airplane)

Be sure to stay away from interior plywood that have large numbers of plys for although these interior plywoods are very stable and straight, there are not assembled with waterproof glues and will delaminated in a moisture rich evironment.

Also do not use treated plywood if you are planing to use epoxy or fiberglass resin as the the chemicals that make the plywood "treated" prevent glues from sticking as well.

With all that said whether you choose marine or exterior it is of the upmost importance to keep water out of the wood for both types will rot in time given water and warmth. More so if you include freeze thaw cycles like we get here in Wisconsin.

The best way would be a treatment with a product like smith's Clear Penetrating Epoxy which I have used (but it is very expensive). For everyone else make sure the plywood on your boat is at least kept dry/sealed/coated/glassed especially on the edges with a good quality products and make sure that any penetrations into the plywood are sealed.

Screw and bolt holes through and around fittings "ESPECIALLY THROUGH HULL UNDERWATER FITTINGS/PENETRATIONS" are easy ways for water to get at the plywood especially on hulls, decks and horizontal surfaces.

In my Humble Opinion only...of course. From 69 Nautaline.

Reply - Answer
Well 69 Nautaline, I want to thank you for taking the time, and the excellent explanation about the differences and tips about plywood choices. It couldn't have been said any better.

IAN from www.all-about-houseboats.com

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Submitted by: 69 nautaline

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Just a note on Plywood. The primary difference between exterior grade plywood and marine plywood is the fact the cores will have small voids in the inner veneers. The same glues are used to assemble the plywoods. I have used exterior grade plywoods in all my boat projects as the marine plywood is just to expensive. (unless your building an airplane) Be sure to stay away from interior plywood that have large numbers of plys for although these interior plywoods are very stable and straight, there are not assembled with waterproof glues and will delaminated in a moisture rich evironment. Also do not use treated plywood if you are planing to use epoxy or fiberglass resin as the the chemicals that make the plywood "treated" prevent glues from sticking as well. With all that said whether you choose marine or exterior it is of the upmost importance to keep water out of the wood for both types will rot in time given water and warmth. More so if you include freeze thaw cycles like we get here in Wisconsin. The best way would be a treatment with a product like smith's Clear Penetrating Epoxy which I have used (but it is very expensive). For everyone else make sure the plywood on your boat is at least kept dry/sealed/coated/glassed especially on the edges with a good quality products and make sure that any penetrations into the plywood are sealed. Screw and bolt holes through and around fittings "ESPECIALLY THROUGH HULL UNDERWATER FITTINGS/PENETRATIONS" are easy ways for water to get at the plywood especially on hulls, decks and horizontal surfaces. In my Humble Opinion only...of course. From 69 Nautaline. <b>Reply - Answer</b> Well 69 Nautaline, I want to thank you for taking the time, and the excellent explanation about the differences and tips about plywood choices. It couldn't have been said any better. IAN from www.all-about-houseboats.com

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Which plywood?
by: Mr B

There is a 4' x 8' plywood called, Crezone, or Dura-ply available here in Canada, and surely in the States. It is marine quality, and holds a finish superbly.

One might see this material on the huge highway signs painted green? Made for being in the weather, and much cheaper than marine plywood.

The 1/2" thickness in Crezone, or Dura-ply has 5 layers of ply, and water resistant glue, and very few checks. Comes also with one or both sides bonded with a paper like substance that takes paint and finishes the best...

This is the product I used for my 22 ft scow hull with taped seams, and makes an excellent watertight hull.. Usually comes in 1/4, 1/2, 3/4, and 1" in thickness.

Just my 2 cents, Mr B.

Reply - Answer
Well Mr B, thanks for sharing that great info.
IAN from www.all-about-houseboats.com

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Houseboat Building or Repair - What plywood, exterior or marine grade?

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Houseboat Building or Repair - What plywood, exterior or marine grade?