Waterproof exterior (but still lightweight)

[bobhenry]

Please promise not to laugh .......

I am going to do just that and with .........................















The vinyl from an old king size water bed cut to fit!



But it was free

[michaelwpayton]

... Anyone have any thoughts, or a suggestion of a good hydrophobic material...

Oak Ridge has exactly what you are looking for

http://www.associatedcontent.com/article/463669/new_superhydrophobic_material_could.html?cat=3

[TD Beej]

... Anyone have any thoughts, or a suggestion of a good hydrophobic material...

Oak Ridge has exactly what you are looking for

http://www.associatedcontent.com/article/463669/new_superhydrophobic_material_could.html?cat=3

Not exactly what I was looking for but very interesting idea. The under side of the aluminum and the outer side of the ply could be coated to keep water from sitting or condensation from being a problem.

[GPW]

A really inexpensive sealer we used to use to waterproof cardboard for airplanes (models) 75% Mineral Spirits , 25% Polyurethane ... You need several coats ,takes more time and effort , but it really does sink way in and protects the wood ... edge grains especially benefit from multiple applications ... Used it on my first TD and although it flooded a couple times , the wood showed no water intrusion ... it was just a giant "tank"...
Worked great on the planes too ...even in our WET climate...
A useful trick in our new economy...

[michaelwpayton]

A really inexpensive sealer we used to use to waterproof cardboard for airplanes (models) 75% Mineral Spirits , 25% Polyurethane ...

Interesting

[kennyrayandersen]

I've been pondering how to make a TD water tight for a while, the basic plan that I've been leaning towards is to fiberglass and epoxy the heck out (all sides, edges and holes) of plywood and then skinning the exterior in aluminum (protection in layers). And though I've been vacillating on this, not insulating.

Reading this thread my latest brainwave is to use a hydrophobic blanket under the aluminum so even if a weakness is found in the aluminum shell the water would quickly drain out and it would also add a smidge of insulation, and the aluminum would then be able to act as a radiant barrier. Anyone have any thoughts, or a suggestion of a good hydrophobic material (fleece?).

Thanks, Beej

I was going to chime in with the I don't think epoxy is enough mantra when I saw Beej beat me to it. the fiberglass keeps the epoxy matrix from developing cracks that let the water seep in.

[michaelwpayton]

I've been pondering how to make a TD water tight for a while, the basic plan that I've been leaning towards is to fiberglass and epoxy the heck out (all sides, edges and holes) of plywood and then skinning the exterior in aluminum (protection in layers). And though I've been vacillating on this, not insulating.

Reading this thread my latest brainwave is to use a hydrophobic blanket under the aluminum so even if a weakness is found in the aluminum shell the water would quickly drain out and it would also add a smidge of insulation, and the aluminum would then be able to act as a radiant barrier. Anyone have any thoughts, or a suggestion of a good hydrophobic material (fleece?).

Thanks, Beej

I was going to chime in with the I don't think epoxy is enough mantra when I saw Beej beat me to it. the fiberglass keeps the epoxy matrix from developing cracks that let the water seep in.

A layer of glass (properly wetted out with good epoxy) will certainly add strength to any build. But, good marine epoxies do not micro-fracture, i.e. their flexural numbers are very high. Pull the "technical data sheet" for your epoxy, "Flexural Strength" should be in excess of 300,000 lbs. Additionally, good epoxy is absorbed, somewhat, by good ply AND good epoxy is never brittle... it's elastic... it's chemistry. When you have seen/see cracks, it's very likely that polyester was used... not epoxy.

Again, a layer of glass is great... but, if you don't use the correct wood, epoxy and methods... you're wasting your time... moisture will find its way in.

[Edit: Don't forget... epoxy MUST be UV protected, or it will breakdown. Maybe that, and/or certain fastening methods being employed, is why some are having problems.]

[DesertSkies]

I favor the epoxy, two coats on plywood flat surfaces, and 3 or more on plywood end grain or until the end grain surface is full and smooth with epoxy.

I've been considering epoxy instead of CPES, but I'm getting a little confused. Steve, are you talking about a marine epoxy paint or some other type of product?

[michaelwpayton]

http://www.systemthree.com/store/pc/SilverTip-Laminating-Resin-Gallon-10p39.htm

[Larry C]

I've been pondering how to make a TD water tight for a while, the basic plan that I've been leaning towards is to fiberglass and epoxy the heck out (all sides, edges and holes) of plywood and then skinning the exterior in aluminum (protection in layers). And though I've been vacillating on this, not insulating.

Reading this thread my latest brainwave is to use a hydrophobic blanket under the aluminum so even if a weakness is found in the aluminum shell the water would quickly drain out and it would also add a smidge of insulation, and the aluminum would then be able to act as a radiant barrier. Anyone have any thoughts, or a suggestion of a good hydrophobic material (fleece?).

Thanks, Beej

I was going to chime in with the I don't think epoxy is enough mantra when I saw Beej beat me to it. the fiberglass keeps the epoxy matrix from developing cracks that let the water seep in.

A layer of glass (properly wetted out with good epoxy) will certainly add strength to any build. But, good marine epoxies do not micro-fracture, i.e. their flexural numbers are very high. Pull the "technical data sheet" for your epoxy, "Flexural Strength" should be in excess of 300,000 lbs. Additionally, good epoxy is absorbed, somewhat, by good ply AND good epoxy is never brittle... it's elastic... it's chemistry. When you have seen/see cracks, it's very likely that polyester was used... not epoxy.

Again, a layer of glass is great... but, if you don't use the correct wood, epoxy and methods... you're wasting your time... moisture will find its way in.

[Edit: Don't forget... epoxy MUST be UV protected, or it will breakdown. Maybe that, and/or certain fastening methods being employed, is why some are having problems.]

I am no expert, but I have been using epoxy and fiberglass for 20+ years building canoes and kayaks. Fisrt let me say.... In all the years I have carried epoxy/fiberglass over wood boats, on the roof of vehicles, and on the water, for hours and hours, in all kinds of weather, from hot hot sun to torential rain, and even snow, I have NEVER NEVER NEVER had water get through the epoxy glass lay-up.

I am just talking about soft wood strips glued with carpenters glue, a single layer of glass on each side with epoxy and several coats of marine varnish. Also, some of my marine plywood boats are built with glass on the outside only, with just epoxy coating the inside.

I have tried and experimented with literally dozens of techniques and materials in the last 20 years. Some are really great, and some are lousy.... the cost of a good non blushing epoxy and fiberglass is minimul compared to total cost of rebuilding a water damaged unit.

I would never ever think of using CPES, polyester resin or bondo on wood. Epoxy is all I ever use. There are techniques to apply epoxy and glass that have to be learned over time that can make or break a good lay-up.

You would be well served visiting boat building forums to learn a lot more about using epoxy/glass over wood.

I think the exterior of a tear should be glassed, especially the edges but it doesn't need 6 ounce cloth. 3 oz is plenty . However, edges must have a radius. Glass doesn't work well over sharp edge.

If the plywood skin is only coated with epoxy the top and sides will expand and contract at different rates in the sun. The edges can seperate. If the edges, that have a radius, are covered with fiberglass/epoxy, the chance of joints opening are greatly reduced. Again, proper lay-up techniques work best.

I really feel for all those that have spent so much time and effort in their build and have it leak, ruining there beautiful cabinet work. There are a certainly a lot of real crafts men and women building tears, I only hope to build something near the quality of so many I have seen here. But, what I will concentrate on is keeping out the elements at all costs........

Larry C.

[michaelwpayton]

Again, a layer of glass is great... but, if you don't use the correct wood, epoxy and methods... you're wasting your time... moisture will find its way in.

[Edit: Don't forget... epoxy MUST be UV protected, or it will breakdown. Maybe that, and/or certain fastening methods being employed, is why some are having problems.]

Larry C... as you can see from my comments above... and other posts of mine in other threads... I agree with you. That's why I mention, above, "methods" and "fastening methods" and why in other posts I have mentioned/recommended "taped seams, epoxy fillets," etc. Having already said all of that... my primary point above was to highlight the fact that epoxy, properly applied and protected, does not crack. By the way... I too have experience with plywood core composite boat building and have never had ANY moisture intrusion related problems.

[DesertSkies]

Thanks for the link, Michael.

Larry C (and others contributing to the epoxy topic), I plan to have all exteriors covered with trim which I planned to seal with silicone or something similar to keep moisture out and protect them because I can't get a radius on them. Would it be worth glassing edges if I use aluminum trim?

Otherwise I'm gathering it would be better to apply the resin Michael suggested over bare wood on the walls, roof, inside doors, etc. instead of CPES.

Am I finally getting a clue?

[Cliffmeister2000]

Looking at Barrie's (bgordon) build has me thinking seriously about a core-less Fiberglas trailer. Or rather, a cardboard core that is glassed on both the inside and the outside. I've never done Fiberglas, but I really like the looks of his trailer. Looks like it would last forever!

http://tnttt.com/viewto ... sc&start=0

[michaelwpayton]

Thanks for the link, Michael.

Larry C (and others contributing to the epoxy topic), I plan to have all exteriors covered with trim which I planned to seal with silicone or something similar to keep moisture out and protect them because I can't get a radius on them.

Otherwise I'm gathering it would be better to apply the resin Michael suggested over bare wood on the walls, roof, inside doors, etc.

Am I finally getting a clue?

Here's how I plan to build mine:

1) I will be using Meranti Hydrotech plywood, which meets the BS1088 standard.

2) All plywood will be coated with epoxy resin.

3) All epoxy coated surfaces will be UV protected with spar varnish... because I plan to have a woody finish.

4) For the most part, panels will be joined using "fiberglass taped seams," "epoxy fillets" and other methods which eliminate the need to screw into the epoxy coated ply.

5) If any "screws" are "required," (e.g. if I get a little lazy )... I will over-drill the hole, fill the hole with thickened epoxy and then screw into the epoxy.

[michaelwpayton]

Looking at Barrie's (bgordon) build has me thinking seriously about a core-less Fiberglas trailer. Or rather, a cardboard core that is glassed on both the inside and the outside. I've never done Fiberglas, but I really like the looks of his trailer. Looks like it would last forever!

http://tnttt.com/viewto ... sc&start=0

That is a very cool build. Lots of different options for core material. I've used foam (Divinycell) instead of plywood for some parts of boats. BUT... I really want a "woody finish"