Floor insulation and rust.

[Clayton]

I had a fair amount of rust on my floor and I am working on that. Next step is to add insulation and plywood. I am going to use 1/2 inch r3 foam insulation then 1/2 plywood on top. I would go thicker but am trying to maximize the little headspace I have. Originally in this bus the plywood sat directly on the steel floor which held water and created rust. I was thinking of putting a layer of poly down directly on top of the steel floor before my insulation or plywood. Has anyone done this? Any suggestions?

[Tango]

Personally, I am going to thoroughly clean the floor then use a rust converter that forms a poly coating...then several coats of of good quality rust fighting paint. Over that I am going to try something a little different. Since there will always be the possibility of moisture getting in (all skoolie windows leak, plus there will almost always be some condensation)...leaving a small airspace between the ply and the metal so it can breathe. I will be using the open web liner material normally applied to tool chest drawers. I discovered that it is 100% water proof as well as mold & mildew resistant. Should also function as a bit of a thermal break.

[GreyCoyote]

Originally Posted by Tango

Personally, I am going to thoroughly clean the floor then use a rust converter that forms a poly coating...then several coats of of good quality rust fighting paint. Over that I am going to try something a little different. Since there will always be the possibility of moisture getting in (all skoolie windows leak, plus there will almost always be some condensation)...leaving a small airspace between the ply and the metal so it can breathe. I will be using the open web liner material normally applied to tool chest drawers. I discovered that it is 100% water proof as well as mold & mildew resistant. Should also function as a bit of a thermal break.

"Strong is the noggin' on him, yes!" (paraphrasing Master Yoda)

On a serious note, this is worth a thread of its own. I'd be VERY interested in your journey in this direction and the results of it!

This type of lateral thinking is almost always a good thing.

[Phatman]

Originally Posted by Tango

Personally, I am going to thoroughly clean the floor then use a rust converter that forms a poly coating...then several coats of of good quality rust fighting paint. Over that I am going to try something a little different. Since there will always be the possibility of moisture getting in (all skoolie windows leak, plus there will almost always be some condensation)...leaving a small airspace between the ply and the metal so it can breathe. I will be using the open web liner material normally applied to tool chest drawers. I discovered that it is 100% water proof as well as mold & mildew resistant. Should also function as a bit of a thermal break.

I like the sound of that Tango. I'm always interested in trying new things that kinda turns the conventional upside down.

[jazty]

Originally Posted by Clayton

I am going to use 1/2 inch r3 foam insulation then 1/2 plywood on top. I would go thicker but am trying to maximize the little headspace I have. ... I was thinking of putting a layer of poly down directly on top of the steel floor before my insulation or plywood.

Since you asked, I have two recommendations for you:

First, use thicker plywood. At least 5/8", 3/4" even better. 1/2" does not distribute the load as well as thicker variants and you may end up feeling some floor flex. This isn't based on engineering, it's just from my own testing. I had planned on using 1/2" to save money on my floor, but it didn't feel substantial enough in the end.

Second, the metal floor in your bus is already a moisture barrier, though you can't be 100% sure that water or humidity will not infiltrate through seams. Placing poly directly over top of the metal will likely trap water instead of keeping it out. Once you get a tiny bit of water between those layers it will travel all over due to capillary action and stay there indefinitely.

In my opinion, unfaced XPS rigid foam is as good as it gets for placing directly over top of a metal floor. If there is water between the metal and the foam it will be wicked up (slowly) and evaporate on the other side (assuming average relative humidity on the top side is lower than on the metal side; as in your vehicle is above the water line). Likewise, if there is constantly a puddle sitting on top of the foam it will work its way through, but that's a more obvious and fixable situation. Like in any building envelope you only want ONE moisture barrier. All the other material must be able to breathe to some extent. Foam+wood does.

Even putting vinyl flooring over top of the plywood shouldn't affect it's ability to absorb and release moisture completely unless its installed over the entirety of the bus floor, wall to wall. Most people will only have the flooring in the aisles once the cabinetry and walls are built. The plywood and foam can still wick in this situation. I think this was the big problem with most stock floors. They were built with vinyl flooring wall-to-wall and plywood. There was no means for the water to wick through the wood and back out once it finally made it through the seams.

[WhiteWhale]

I agree with Jazzty. Use 3/4 structural Plywood, unfaced foam board, and no additional vapor barrier. I sealed up all holes in the metal floor, then used construction adhesive to lay down foam and plywood. Then I used 2x2 strips screwed into walls along floor edges to help hold everything down. For plywood I used a product from Lowes called "DryPly". Which is a T&G water resistant structural plywood. Its a little expensive but far better than any MDF.

Good luck!

[Scooternj]

Originally Posted by WhiteWhale

I agree with Jazzty. Use 3/4 structural Plywood, unfaced foam board, and no additional vapor barrier. I sealed up all holes in the metal floor, then used construction adhesive to lay down foam and plywood. Then I used 2x2 strips screwed into walls along floor edges to help hold everything down. For plywood I used a product from Lowes called "DryPly". Which is a T&G water resistant structural plywood. Its a little expensive but far better than any MDF.

Good luck!

I like that idea. Especially since I've been planning on not having any OSB onboard.

[Tango]

One nice thing about the size of my Shorty...I can afford to use only Marine ply.

[prof.fate]

moisture gets into school buses from rain, snow on kids boots, open windows and ot thomas saf t liners leaky roofs. We have a bus with a leaky roof hatch (gasket issues).

So once cleaned up a converted bus should stay much dryer.

But you'll still get some moisture in there - spills, condensation, a peeing puppy perhaps. With no place for the moisture to get out it will rust or mold/mildew.

Don't know the absolute answer - the Jeep guys love bedliner materials, a hi-tech house next door being built used a liquid vapor barrier (paint it one). I"m thinking of covering the inside in one of those materials.

[EastCoastCB]

Originally Posted by WhiteWhale

I agree with Jazzty. Use 3/4 structural Plywood, unfaced foam board, and no additional vapor barrier. I sealed up all holes in the metal floor, then used construction adhesive to lay down foam and plywood. Then I used 2x2 strips screwed into walls along floor edges to help hold everything down. For plywood I used a product from Lowes called "DryPly". Which is a T&G water resistant structural plywood. Its a little expensive but far better than any MDF.

Good luck!

This is the method I've been planning to use.

Although, I'll be using marine grade ply, the expensive stuff. One of the few things I plan to really splurge on.

[superdave]

i used 3/4 t&g advantec. its supposed to handle moisture well, its mostly glue. over 1" foam board screwed down with self drilling stainless steel screws