Prevost subfloor

[BELMARR]

Hi. My early 80s Le Mirage has a 3/4" plywood subfloor. Is it a structural part of the bus frame and has anyone used other materials for a subfloor? If so what considerations are there as far as strength, coefficient of expansion and the amount of flexing you want or do not want as the case may be?

[windtrader]

I'm no design engineer but it seems impossible that wood would be structural.

[Dave5Cs]

Don there are a lot of different woods that indeed are very structural. On building they use 3/8's and 1/2 inch plywood for shear panels by code on walls for wind and earthquake areas. Plywood on floors for shear also and twisting etc. 3/4 inch marine ply is always structural on floors and roofs and around stairways in homes and buildings.

[freds]

Given that I have a 1980 Prevost LeMirage I rather dough that plywood figured into any of their calculations. Heck was there even a computer program that handled this?

Is your bus an over the road passenger bus in a second or third life or a motorhome shell?

Since you have a what I call classic Prevost there are a few like members that you can find by reading my posts and other early Prevost members on here.

Enjoy and hey tell us more!!!

[chessie4905]

If 3/4" and not thicker, Lowes, HD, etc sell thet in a multiply version for $$ . More plies than regular. Our store stocks it. Probably for furniture etc.
Bigger cities near water should have marine grade if you want to spend that.

[dtcerrato]

Wood is extremely structural. I sometimes stand next to a huge live oak tree and am bewildered how  a horizontal branch 100s of feet long can support itself of many tons of weight! There are antique wood framed homes in huricane prone areas that have stood against the stands of time. And yes marine plywood floors in monocoque buses ARE structural to keep the box square. Major bridges of the far NW are completely made of lumber due to the absence or termites!

[windtrader]

Yes, I understand there are woods that are classed as structural. The question was wood in an OTR bus acting as a structural component. According to some here, it appears that in some designs the wood is actually considered structural. I just think wood can get wet and weaken and it just surprises me that a commercial bus carrying dozens of humans would be at risk of failing due to structural wood issues. I think wood in vehicles and I think 50's British cars and some of the really old open tour buses used in the park system, etc. But nothing heavy and on the highways.

[dtcerrato]

The term marine plywood carries merit! It is impervious to decline, mold, mildew, rot at least in it's 20 year service life. Boats & ships are built with it. Consider the many antique commercial buses 70 years and older on the road with still totally in tact wood floors, yea there are those that have rotted but 70+ years will out last steel in a lot of instances. Not a thing wrong with wood and it's renewable Don!

[Jim Blackwood]

Properly certified marine grade plywood is made with a waterproof glue that is impervious to moisture. The plys are thin and the sheets are perfectly flat. It is very strong. Of course water can still attack the exposed wood so it needs to be sealed with a quality urethane, preferably also in marine grade like a good spar urethane. Do that and it's well nigh impervious to anything you can throw at it short of physical damage. It is very rigid in shear and makes an excellent structural material. In the floor of your bus it will contribute to long term rigidity of the entire body shell. Very likely far superior to what was put there on the assembly line.

Jim

[dtcerrato]

We have a wrap around porch on the house with a two foot high band of 5/8" pressure treated T-111 (reverse board & batten plywood) below the screened opening. It was bought at a lumber yard called Scotty's back in the day. It has been on the house over 30 years with the scraps still laying around the sub tropical subterranean termite infested forest. Its all still solid & rigid as the day purchase. Great stuff!

[luvrbus]

Don there are a lot of different woods that indeed are very structural. On building they use 3/8's and 1/2 inch plywood for shear panels by code on walls for wind and earthquake areas. Plywood on floors for shear also and twisting etc. 3/4 inch marine ply is always structural on floors and roofs and around stairways in homes and buildings.

I think you are right Dave some bus manufactures even tell you the direction to lay the plywood.I screwed up installing some slide outs in my bays once and they never worked with a load,  I complained to Walter the manufacture and he told me I had the plywood going in the wrong direction he helped me redo it and they never gave another problem

[Jim Blackwood]

Look for the good housekeeping seal of approval.

[Dave5Cs]

And being Clifford was also a contractor too would probably agree that it also matters how far apart the nails or screws are to what type of structure it cam be used for. IE, 3/8 ply 5 ply shear panel on a stairway in a building is edges 4 inch centers and 6 inches in the field. 1/2 exterior walls 4inches edges and 8 inches in the field. So it matters what you are using it for. Take the ply out of a bus floor and then push the one side hard enough it will be a trapezoid.

Now ask about the guy that took off all the side wall panels on an MCI way back and the belly of the bus was on the ground because he did not block the base of the bus up before removing them.

[robertglines1]

in my prevost coaches there were 2 layers on floor of approx. 3/4 inch plywood  with lead sheet between them the top layer was short of width about 2 inches from side wall...don't know why.....I was told the lead sheet was for sound proofing.  This is basic info fwiw.. I do believe there was allot of engineering devoted to this design. I do believe it was a birch based plywood do to markings.  I do know as old as it was it was in perfect shape.   Just general info from memory...Bob

[buswarrior]

The floor will play a role in bus structure, in varying degrees.

Significant in the GM coaches.

In the early MCI DL coaches, when they started sagging, the floors tore up, and not at the fasteners. To be well fastened that it didn't just tear at the edges/fasteners, suggests someone expected it to be contributing something?

Does the Prevost in question have a full structure or semi-monocoque?

happy coaching!
buswarior