Flooring help

[Piper]

Hi guys, this is my first post on here so bare with me. My bus is a 2001 Chevy Express shuttle bus. Like some people, we were surprised to find that there was no metal underneath the previous plywood flooring. After reading through the forums on here, I was unable to find a consistent response on how to proceed with new flooring. I think the best solution would be to just replace the previous wood with 3/4”marine grade plywood and insulating/building on top of that. I seriously have no idea what I’m doing or any experience in this area so it is very stressful and overwhelming. What should I treat the new marine grade plywood with? Is my bus going to be okay without any metal underneath? The previous plywood was 3/4” as well and lasted almost 20 years in good condition while operating in Ohio. The plywood seemed to have a very thin layer of metal glued on to it that faced the road. It was pretty thin and I have not been able to find anything like that online. Because of that, I’m afraid on how the new wood would hold up without the metal. Any help is greatly appreciated. I am just stuck and unsure how to proceed with so many options.

[Danjo]

I think I’d get FRP, a bucket of adhesive and some plywood. Glue the FRP to the plywood and use that face down. Get some wood to metal screws to attach it

Use urethane sealant on the wood to metal interface and between plywood joints. Make plywood seams land on metal frame

[BeNimble]

My shuttle bus has no metal, not even painted the wood. don't bother doing anything, put in some plain plywood and your flooring. move on to the other 477 things left to do.

[novice]

Whoa, I didn't know this was a thing? Definitely making me reconsider whether or not a shuttle is the way I'll wanna go, since I was hoping to build out this winter, but know cold weather large scale projects tend to initiate a panic-freeze response.


You could certainly call a metal supply shop about prices on plate steel or aluminum panels and weld or bolt those in over the joists before laying down a thick ply.



There are certainly ways to treat an otherwise bare wood panel from below your rig as well-- you could, in fact, use roofer's asphalt tar which is generally pretty weather resistant, though nasty stuff to work with. As long as the board material is thick enough and feels supportive, anything else you do will be an added bonus, I'd just concentrate on sealing everything well and not worry about going to "overboard" in terms of sealants, though considering weight will be of the utmost.


Don't feel hesitant to call up a shuttle bus mechanic and ask how they'd approach the problem! Best of luck!

[musigenesis]

One property of plywood is that it can get wet but if it is allowed to dry out afterwards, it will not rot and its ability to dry out in the future will not be impaired (OSB, by contrast, is less able to dry out in humid conditions, and soaking it permanently impairs its ability to dry out even more). If you just lay down untreated plywood and move on as BeNimble suggests, the underside of the plywood will occasionally get wet when you drive in wet conditions, but it will dry out afterwards (unless you park in a snowbank or a river or something) and be fine. You would want to use some sort of seam sealer between the metal frame and the plywood, to prevent water from working between the seams and getting trapped somewhere it can't dry out.

[Danjo]

I’ve worked with a lot of cheap plywood that had layers delaminates and warp after leaving it out in the rain just one day. So if you go with straight plywood, be sure to get marine grade board, that is, the kind made with waterproof glue.

Do your research

[Rwnielsen]

(unless you park in a snowbank or a river or something)

Note to self....

[Piper]

I really appreciate the insight and advice. I’ve purchased some 3/4” marine grade plywood and have applied 2 coats of the KILZ weatherproof sealant on each. What additional steps should I take to ensure my wood is protected such as the tar mentioned? I was told I would only need to seal the side of the wood that is facing the road, that doesn’t sound right to me though, is that true? I don’t want to skip on anything needed so I’m more than willing to take precautions, but I don’t want to use more material/work than required. I think the use of FRP under the wood is a very interesting one and I’m curious to what others think? It seems there’s only one post about it on here and the guy decided to go with sheet metal instead because it was free.

[novice]

As musigenesis mentioned, allowing wood that does get wet to air out is pretty important. I think sometimes I've gone a little overboard trying to make wood something it's not-- impenetrable.

If I'm not mistaken, I think a good amount of polyeurethane brands allow for breathability so that something like a deck, for instance, can dry properly if somehow some moisture made it inside the coating. I would look for such a coating for your interior floor perhaps? Though I would like to hear if other folks have experience with the stuff I'm talking about first.

[Foamenter]

Originally Posted by Piper

... no metal underneath the previous plywood flooring...

Originally Posted by Piper

plywood seemed to have a very thin layer of metal glued on to it that faced the road....

Why not just replicate what was there already? Find some suitable sheet metal and glue it to the plywood, then coat that in whatever undercoat you want.

It sounds like there was a layer of metal to protect the wood from the elements, and the metal would also be impervious to any high temperatures (exhaust pipes get hot). Plastic (FRP) close to the exhaust sytem =

From the G/M upfitter guides (most years have this in the section regarding exhaust):

Exhaust gas temperatures can exceed 1600ºF under extreme operating conditions, with pipe surface temperatures slightly less than this.
Extreme care must be used when placing body components in the proximity of the exhaust system so as not to exceed the rated
temperature limits of the components. Due to variants in underbody configurations of the vehicles, General Motors is not in a position to
make recommendations on how to insulate or design components in the proximity of the exhaust system.

Disclaimer: I have no experience or expertise.

[Foamenter]

BTW: if you want some info about that chassis - https://www.gmupfitter.com/pdflists/view/6

Look for your year of G/H van. I've seen that some years don't have the full PDF, but others do. YMMV

[Daledorm]

I think if you live in a fairly dry region I’d just use marine grade plywood and caulk the seams. If you live in a wet climate I’d do the same but look into having an undercoating applied to your vehicle once you are finished with the build.

[Sharee100]

I have a 2001 Chevy Express. The bottom plywood was painted with weatherproofing. I added another layer of plywood, then 1 1/2 inch foam insulation with 2 x 3 studs between pieces, then another layer of plywood, and finally vinyl flooring. I have had no additional deterioration of bottom layer and all the layers I added inside add stability, insulation, and keep some of the road noise outside. I did add a floor runner carpet in the winter so I could walk around barefoot. I have heard that some people replace the plywood with metal supports and sheet metal (which is supposed to be standard on school buses).

[jmiraglia]

Possible that the metal was the thin metal used in roofing flashing?