marine plywood vs regular plywood

[Deryk the Pirate]

Hello folks,

Well as lil vardo sold to a friend I'm nearing start of lil vardo 2. I found a source for some nice 3/8 5ply marine plywood and was wondering what the benefits of building a tiny travel trailer out of it vs out of regular stock plywood? Would it still need to be sealed in epoxy like plywood would be or just painting it with a good oil based paint suffice?

Thanks in advance...
Deryk the Vardo maker (lol)

[dh]

The main difference is that the inner plys are solid, and have voids repaired like an A side would, so there are no voids in the inner plys. I would still treat the outside as you would CDX ply.

[Shadow Catcher]

Marine is the Roll Royce of plywood
"Marine plywood is specially treated to resist rotting in a high-moisture environment. Its construction is such that it can be used in environments where it is exposed to moisture for long periods. Each wood veneer will have negligible core gap, limiting the chance of trapping water in the plywood and hence providing a solid and stable glue bond. It uses an exterior Water Boiled Proof (WBP) glue similar to most exterior plywoods. Marine plywood is frequently used in the construction of docks and boats. It is much more expensive than standard plywood: the cost for a typical 4-foot by 8-foot 1/2-inch thick board is roughly $75 to $100 US or around $2.5 per square foot, which is about three times as expensive as standard plywood. Marine plywood can be graded as being compliant with BS 1088, which is a British Standard for marine plywood. There are few international standards for grading marine plywood and most of the standards are voluntary. Some marine plywood has a Lloyd's of London stamp that certifies it to be BS 1088 compliant. Some plywood is also labeled based on the wood used to manufacture it. Examples of this are Okoume or Meranti"

[Deryk the Pirate]

Yeah I saw that blurb also on wikipedia... but I was hopeing to hear from people who worked with it.

If there are no voids inside of it to hold moisture but if the end grain will still wisk in water its still going to rot right? If you have to encapsulate it in epoxy then is it really worth the price from regular CDX?

Thanks
Deryk

[StandUpGuy]

Yeah I saw that blurb also on wikipedia... but I was hopeing to hear from people who worked with it.

If there are no voids inside of it to hold moisture but if the end grain will still wisk in water its still going to rot right? If you have to encapsulate it in epoxy then is it really worth the price from regular CDX?

Thanks
Deryk

The other big difference is that it is using waterproof glue to hold the plys together so it is not going to seperate like interior rated plywood will with moisture. This is also true for lesser quality exterior rated plywoods. They use the same adhesives as the marine plywood but as previously stated they have no voids and they also have lots of layers, which adds strength.

[Deryk the Pirate]

Thanks Standupguy...so the big difference between marine ply and exterior ply is no voids to hold moisture and more layers for increased strength... too bad it still needs to be encapsulated lol.

I'm on a tight schedule to get lv2 campable for the first week of august. I'm guessin leaning towards useing a mix of paulownia and red and white cedar.


I'm guessing paint alone isn't going to seal marine ply well enough?

[dh]

Depends, I built a quickie dog house out of OSB and painted it with house paint, 5 years later its still standing, and the "permanent" doghouse is still in the shop in pieces. I did put put shingles on the roof though.

[wagondude]

While you still need to coat it, it will take far less epoxy to seal it than cheaper plywood. Probably not enought less to offset the cost. But if by chance you had an area that didn't get treated, it might go a few years longer without showing damage. And when it did start to show, it would likely be a smaller, easier repair.

[StandUpGuy]

Thanks Standupguy...so the big difference between marine ply and exterior ply is no voids to hold moisture and more layers for increased strength... too bad it still needs to be encapsulated lol.

I'm on a tight schedule to get lv2 campable for the first week of august. I'm guessin leaning towards useing a mix of paulownia and red and white cedar.


I'm guessing paint alone isn't going to seal marine ply well enough?

Yes I think paint can do a fine job of it. There are lots of people here on this site with painted trailers. I think your real question you might consider posting is about how effective paint alone can be for protecting a trailer. Frankly if you think about it a trailer is not much different than a house. I think most consideration is for the top. Keeping the water out of the roof is most important. On your build you used a rubber membrane. That coupled with well sealed and painted sides should be pretty good in my opinion.

[StandUpGuy]

In my case I plan on always storing my trailer in a garage so most of the time it will be completely protected from the elements. So in my case the trailer is not like a house at all in that the house must endure much more weather than my trailer.

[angib]

Marine ply has two differences:
- no voids on the inner plies (better for resisting water intrusion);
- better quality face plies (for appearance, particularly for varnishing).

Marine plywood uses exactly the same glues as exterior plywood.

Not having voids in the inner plies does improve the plywood's resistance to water but mainly only when in contact with water, like in a boat. For a trailer, it is a small benefit, if at all.

[Deryk the Pirate]

Yeah I can see it has its pluses, but for a tiny travel trailer not enough to warrant the cost of $94 a sheet for it with still needing epoxy.

decisions decisions

[doug hodder]

What I've done for exterior walls on a woody is to buy up the thinnest marine grade ply I can and then laminate it to a piece of exterior grade ply. Gives me the nice exterior mahogany appearance, without the price of the thicker marine material. It's a better grade and thicker bunch of veneers rather than a sheet of the mahogany over typical paneling ply. I wanted a mahogany wood on the exterior though....I wouldn't mess with it if you want to leave it a fir, but then I wouldn't stain a fir on the exterior. Just what I've done. Doug

[NathanL]

Marine plywood in itself doesn't mean anything and pretty much anything be sold as such. True marine plywood will have a stamp certifying it like 1088 or some such.

I've seen some pretty crappy wood that has been labeled (but not stamped) marine plywood in the last few years. Just like regular ply a lot of ply is being imported now labeled "marine ply" with no stamps and nobody seems to know what it is or where it comes from.

The good news is you really don't need it. There are several species that can be marine plywood. Douglas fir - which is nice and the cheapest but the faces have a tendency to check if you only paint them and not glass them. Sepale is really nice but more expensive and can be more decorative. Meranti is another choice, which is probably half way between douglas fir and Sepale in price and availablity. Sometimes referred to as mahogony plywood. One brand is hydrotek.

Like everyone has said marine plywood normally has no voids in the inner plys, an A face on the outside (You can get marine play in AA, AB, and AC) with AB what you find more often, and glued with a water resistant glue. Good marine ply will normally have a higher ply count as well. Instead of say 5 plies in an exterior AC grade the same thickness of marine ply can/will often have 7 plies.

Marine plywood in a lot of sizes will come in oversize sheets (more $$) of up to 5'x10' in a single sheet or up to 5'x24' in pre scarfed sections in 2' multiples.


Another option if you are going to paint is MDO (Medium Density Overlay) which is a high quality plywood with an exterior glue, limited voids, and a resin impregnated paper face on one or both faces. Stuff is wonderful for outside exposure and it's normal use is outdoor signs. Even without painting the faces will last a long time in heavy exposure. The resin impregnated paper face is ready to paint and takes paint well and no chance of checking etc....Don't confuse it with MDF. It also can be bought in oversize sheets up to 5'x10'.

Just another idea.


If you decide on anything outside of plywood from a big box store this site can come in handy for finding places that handle wood stock and sheet stock.

http://www.woodfinder.com/

[glenpinpat]

do not know if much help but when I built my first boat I was on a tight budget so I just used regular grade plywood. It was coated in resin. 10 years later we know use this boat as outdoor shelving and the wood is as solid as when first purchased.