wood?

[Larwyn]

There is no advice or solution in this post, just an interesting observation. I have found, totally by accident, and out of procrastination, rather than any scientific study that, that it seems as if the luan from the big box stores handles moisture okay if left uncoated. I know this makes no sense; a protective coating should protect the plywood.

The luan (from Home Depot) on my TD was left unpainted for 3 years with no problems, but soon after painting the luan began to delaminate in places. The problem seems to be confined to two sheets; one sheet on the curved roof is delaminating and also one on a flat side wall. I do not know whether the coating on my TD sealed water inside (it seemed plenty dry when I painted it) or the solvents in the oil based primer may have compromised the glue in the luan, probably something else that I have never thought of, but it appears that painting the luan actually contributed to the problem.

I threw together a small shed for my drill press and air compressor when I had that fancy "award winning" shop in a mud puddle out in the woods. It was skinned with unfinished box store luan (purchased at the same time and store as the stuff on my TD) for a good 3 years with no delaminating.

I also built a cabinet/closet out of box store luan on the outside of my present woodworking shop for storing my wife's gardening tools. It's going on two years now, no paint, and it is not delaminating. I would not be surprised to see it delaminate soon if she ever gets around to painting it as she has threatened to do......

I will repeat now, this is just an observation, nothing more.

[aggie79]

Like most, I purchased my plywood from a specialty sheet goods supplier. For other projects, I have used Arauco plywood (manufacturer - not species) from the big blue box. It has a premium price compared to their other plywood, but the Arauco plywood is much better quality.

There is no advice or solution in this post, just an interesting observation.

I do not know whether the coating on my TD sealed water inside (it seemed plenty dry when I painted it) or the solvents in the oil based primer may have compromised the glue in the luan, probably something else that I have never thought of, but it appears that painting the luan actually contributed to the problem.

I will repeat now, this is just an observation, nothing more.

I used both CPES and epoxy. Although I haven't experienced delamination in the Russian Birch plywood - my teardrop is still under construction - I have always wondered if the solvents in the CPES could be contributing to delamination. Perhaps the Rot Doctor will read this thread and could offer some thoughts on this.

[Arne]

I think what happened is by painting it, you trapped existing moisture inside and that is what caused the problem... maybe the wood was not completely dry.

[Larwyn]

I think what happened is by painting it, you trapped existing moisture inside and that is what caused the problem... maybe the wood was not completely dry.

That is a possibility, it had a couple of years to soak up moisture but it was stored inside an EZ-Up with walls and it was a hot, dry and windy year......

Also it was built in the shop pictured in the first shot below, but painted after a dry year in the Hill Country, current storage is in the second pic;

[frusteri4]

I am planning on welding together a frame out of 2x2 square tubing on a 3500# axle. don't really care what the wood looks like as long as it is strong and can hold together when glued/screwed, while cruising down some washboard roads, and possibly in some desert washes.

[afreegreek]

I think what happened is by painting it, you trapped existing moisture inside and that is what caused the problem... maybe the wood was not completely dry.

that and the fact you can not seal out moisture only water. moisture gets in and is trapped buy the finish so it doesn't dry out. this is why you must use marine grade plywood if you want it to last. no amount of goop is going to keep it out either. if you could there'd be no reason for long oil finishes like spar varnish and spar urethane. these finishes are designed to be flexible so the do not crack when the wood expands.

[dh]

I think what happened is by painting it, you trapped existing moisture inside and that is what caused the problem... maybe the wood was not completely dry.

that and the fact you can not seal out moisture only water. moisture gets in and is trapped buy the finish so it doesn't dry out. this is why you must use marine grade plywood if you want it to last. no amount of goop is going to keep it out either. if you could there'd be no reason for long oil finishes like spar varnish and spar urethane. these finishes are designed to be flexible so the do not crack when the wood expands.

AFG, I'm just curious, and figured with your boat building experience you might have an answer to this. Every "water resistant" wood glue I have come accross has a ANSI class for water resistance, What do the classes mean? What is more resistant, class I or class II? Also, they all say something like "not for use below water line" What do boat builders use below the water line?

[afreegreek]

I think what happened is by painting it, you trapped existing moisture inside and that is what caused the problem... maybe the wood was not completely dry.

that and the fact you can not seal out moisture only water. moisture gets in and is trapped buy the finish so it doesn't dry out. this is why you must use marine grade plywood if you want it to last. no amount of goop is going to keep it out either. if you could there'd be no reason for long oil finishes like spar varnish and spar urethane. these finishes are designed to be flexible so the do not crack when the wood expands.

AFG, I'm just curious, and figured with your boat building experience you might have an answer to this. Every "water resistant" wood glue I have come accross has a ANSI class for water resistance, What do the classes mean? What is more resistant, class I or class II? Also, they all say something like "not for use below water line" What do boat builders use below the water line?

most PVA glues sold as waterproof meet certain specs that allow them to be labeled as such but they are not water proof, only water resistant. that's why the 'no under waterline use' label.. the whole thing is a bit of a wash as far as standards in labeling goes.

here's some good reading..

http://www.glen-l.com/weblettr/weblette ... ywood.html

[dh]

The luan (from Home Depot) on my TD was left unpainted for 3 years with no problems, but soon after painting the luan began to delaminate in places. The problem seems to be confined to two sheets; one sheet on the curved roof is delaminating and also one on a flat side wall. I do not know whether the coating on my TD sealed water inside (it seemed plenty dry when I painted it) or the solvents in the oil based primer may have compromised the glue in the luan, probably something else that I have never thought of, but it appears that painting the luan actually contributed to the problem.

3 years ago the guy over the lawn and garden department at our Lowe's was a Sr. horticulture major at ASU. This year its a guy we call crack because he walks around with his ass hanging out, recomending whatever fertalizer hapens to be moving the slowest at the time.

The box stores are quickly spiraling down, and looks like they are pushing themselves lower and lower. I long for the days when competition pushed business to higher and higher standards. I'm rather disgusted at the thought that my grand children will sit in a class room that used to me a shop, and hear rumors of how they used to teach people how to make stuff with thier hands there back in the day.

[dh]

I always thought you where joking about that mud puddle

[Larwyn]

I always thought you where joking about that mud puddle

Nope, for a couple of years there, I was dropping a sump pump in that hole and pumping all that water to a low spot 150 feet away. Other times it was hot dusty and dry. Those were my "good ole days".......

[greekspeedoman]

frusteri4,

I build an offroad teardrop using a mix of luan & baltic berch. I used the luan to skin the outsides of my plywood walls & the birch on the roof for the flex stuff. Purchases were made at a local lumber yard (not just because they're better, bla bla bla but also because I like to support the local guy). I am very happy with both plywoods. I don't know if my luan was a better quality than the "box stores" but I have had no problems with my finish or with leaking (fingers crossed).

If you're curious, you can see my build process at: http://www.overlandtrailer.com/body-external/

[frusteri4]

what is the difference between "exterior grade plywood" and "marine grade plywood"

[doug hodder]

Veneers used, glues, moisture content and a whole lot of money.....

At the risk of catching a lot of flak, I'll go out on a limb and say that for a tear, marine grade isn't necessary and I'd be willing to bet that very few do use it. I've used it as a overlay on top of my exterior grade ply sides, just because I wanted the mahogany. Living in Dayton, your humidity isn't so high that it is required for a build. Precautions should be taken to seal all the edges, whether it's marine grade or otherwise. I've used it on 4 of my tears for the sub floor and the walls, but used MDO on the last tear. Medium Density Overlay....takes on an epoxy coat great if you are doing a painted tear.

There are plenty of tears built from exterior grade that are doing just fine. I had a '49 Kit that I'm sure wasn't built from marine grade or exterior grade for all I know, and was in great shape after 40 years. It too was in a drier climate. Doug

[afreegreek]

Veneers used, glues, moisture content and a whole lot of money.....

At the risk of catching a lot of flak, I'll go out on a limb and say that for a tear, marine grade isn't necessary and I'd be willing to bet that very few do use it. I've used it as a overlay on top of my exterior grade ply sides, just because I wanted the mahogany. Living in Dayton, your humidity isn't so high that it is required for a build. Precautions should be taken to seal all the edges, whether it's marine grade or otherwise. I've used it on 4 of my tears for the sub floor and the walls, but used MDO on the last tear. Medium Density Overlay....takes on an epoxy coat great if you are doing a painted tear.

There are plenty of tears built from exterior grade that are doing just fine. I had a '49 Kit that I'm sure wasn't built from marine grade or exterior grade for all I know, and was in great shape after 40 years. It too was in a drier climate. Doug

marine grade ply is not necessary but for the few extra dollar you get a lot more than just waterproof adhesive. real marine grade is tested and certified. it has high grade core veneers and face veneers as thick as the core veneers. it's a much higher quality product all the way around whereas exterior grade is generally a lower quality product with a better glue.. the other factor is it's finish quality, hit it with 220 and your ready to go.. both faces too.

all things considered it's the best bang for the buck there is.. you get all the attributes of baltic birch with a real waterproof glue. can be had in many species, some that are half the weight of baltic birch and it comes in 4x8 and 4x10. you can also get it with the grain running across the panel if you want it.