How to build a perfectly flat floor?

[TheHubbardBus]

Originally Posted by gs1949

I don't think vinyl is technically a solid. I think it's considered a supercooled liquid, like ice, and therefore would not act like a solid during temperature changes.

Kind of getting off topic here, but solid is a physical state of matter, not a chemical property of matter itself. So vinyl or any other solid would be a solid, until it melted (or subliminated into a gas, to get waaaaaay off topic ).

From what I've learned so far from my e-research, 'vinyl' is too generic a term to characterize the performance of vinyl plank flooring. There are multiple distinct categories of vinyl plank floor... 'original' LVP, rigid-core SPC (stone polymer composite), rigid-core WPC (wood-polymer composite), etc. And within each category the construction and materials differs across manufacturers.

We chose SPC because, as a broad category, it's supposed to be the most dimensionally-stable vinyl-plank-type product across temperature changes. And we chose COREtec because they make SPC, their warranty rates it up to 140-degrees even w/ a floating install, and some guy on the internet who sounded like he knew what he was talking about recommended it for non-temp-controlled spaces (with the admonition that doing so would still likely void the warranty ). I guess we'll see.

[TheHubbardBus]

Originally Posted by musigenesis

Think of it like a jigsaw puzzle. You could bend it pretty considerably along either axis, but you couldn't get it to sit down in a bowl-shaped depression. I think it's just easier for the manufacturer to explain it as "gotta be flat".

Perhaps. But each edge of these puzzle pieces is one heck of a lot more complicated than my 1000-piece recreation of Martha's Vineyard. I have two samples sitting on my desk in front of me. You lock them together and then even start to pull them down into a contour like you're describing and you can feel they don't want to bend that way. There's stress on the joint as soon as you pull any curve on them at all. Stress on an engineered joint formed of composite materials that all have the potential to expand & contract at different rates.

I'm not saying you're wrong. But I don't see the point in not doing it the way the manufacturer suggests when it wouldn't cost me much more than a few extra hours and petty materials (if that).

[Jolly Roger bus 223]

a pic of your floor would help us help you.
how bad does it sag?
are there rivet or screw heads sticking up?
are the old seat bolt holes pulled up?
lots of options but i dont know that normal store bought lumber for a subfloor or furring strips is the best option even if you can plane it?
i have other ideas if you are interested.
requires a 4 to 8 foot straight edge cause a level isnt going to do any good unless your bus is perfectly level before you start.
best option for leveling a bus subfloor would require leveling the bus chassis frame in all directions look to see if your bus has rubber mounts in between the body and chassis and fix any that are wore out and then take a look to see how bad or not the bus body floor is.
still several options at this point.
or just paint/seal the metal
i recommend some type of foam board insulation and thickness is you and your floors choice and then again your choice of marine grade plywood thickness ran width wise to eliminate the waste from trying to stagger the joint in a length wise run unless you get the measurement to work out for you to get to use two cuts out of one sheet.
still several options and ideas.
i would want to check with both the marine plywood manufacturer and the vinyl plank glue manufacturer to guarantee that the glue will actually stick and hold on the treated marine grade plywood?
it is treated to be resistant to water intrusion so how/why would a glue stick to it?
still other options?
good luck!

[TheHubbardBus]

Originally Posted by Jolly Roger bus 223

a pic of your floor would help us help you.
how bad does it sag?
are there rivet or screw heads sticking up?
are the old seat bolt holes pulled up?

No sag, and anything that was sticking up sticks up no longer, but a couple rough areas where the rust was worse than elsewhere (mainly, where the condensers screwed through the floor), and yes, a handful of bolt holes are kind of 'pulled up' a bit

Originally Posted by Jolly Roger bus 223

best option for leveling a bus subfloor would require leveling the bus chassis frame in all directions look to see if your bus has rubber mounts in between the body and chassis and fix any that are wore out and then take a look to see how bad or not the bus body floor is.

I don't care if it's level, unless level is a prerequisite for making it flat. And I'd prefer to use a method to flatten it that didn't require the floor to be level.

Originally Posted by Jolly Roger bus 223

i recommend some type of foam board insulation and thickness is you and your floors choice and then again your choice of marine grade plywood thickness ran width wise to eliminate the waste from trying to stagger the joint in a length wise run unless you get the measurement to work out for you to get to use two cuts out of one sheet.
still several options and ideas.
i would want to check with both the marine plywood manufacturer and the vinyl plank glue manufacturer to guarantee that the glue will actually stick and hold on the treated marine grade plywood?
it is treated to be resistant to water intrusion so how/why would a glue stick to it?
still other options?
good luck!

We plan to use either foam board or spray foam.. I'm still deciding between the two. We're spray-foaming everything else, so I figured since I'm using joists, and they're going to be in there anyway, spray foaming everything might be the way to go (as much a question as a statement ). Our short-bus is such a small job there's no price difference between having the entire bus spray foamed vs just the walls/ceiling. So unless there's a really compelling reason not to spray foam, that's the direction I'm leaning. I'm OK with doing the trimming afterwards.

Never thought about glue adhesion to the plywood... great info. I'll make sure to do that! And yes, width-wise alignment. Good stuff.

[CMORGANSKOOL]

I'm going to put down a layer of 1" rigid foam board on the steel before putting the floor in. May I suggest that as an option rather than plywood. It's a great option for it's insulation and flatness properties and compresses very well.


https://youtu.be/zNY7RFuSgmQ

[TheHubbardBus]

Originally Posted by CMORGANSKOOL

I'm going to put down a layer of 1" rigid foam board on the steel before putting the floor in. May I suggest that as an option rather than plywood. It's a great option for it's insulation and flatness properties and compresses very well.
https://youtu.be/zNY7RFuSgmQ

Much appreciated, CMORGAN . I hadn't even considered alternative materials. I'll look into it!