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Old 09-30-2019, 08:59 AM   #1
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Flooring Questions

I know there are plenty of other threads about flooring, but they also seemed pretty old.


The recommendations I read were to use Marine Quality Plywood and Foam board. Can people confirm if these are the proper kind of products that are being referenced:


Marine Grade Plywood:

https://www.lowes.com/pd/3-4-CAT-PS1...4-x-8/50254845


(is $76 a sheet about the price I should expect to pay)





EPS Foamboard:
https://www.homedepot.com/p/R-Tech-1...0821/202532854





So my assumption is to clean/sand any rust of the metal bus flooring, apply a rust-preventive primer (Kilz, Rust-oleoum, etc), lay down the foam board, and then lay down the plywood on top of the foam board. Does this sound correct? Any other suggestions?
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Old 09-30-2019, 10:09 AM   #2
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I ended up using AdvanTech 3/4" tongue and groove flooring. Check it out online - there's a lot of info from people comparing it to traditional 3/4" plywood. It was about $50 a sheet for me.

I don't know how well it compares to marine plywood.

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Old 09-30-2019, 10:12 AM   #3
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I'm questioning the value of even using plywood over XPS foam.
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Old 09-30-2019, 10:26 AM   #4
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I put the AdvanTech over my foam boards since I wasn't laying any other flooring yet, and so I would have a solid foundation to attach everything else to. If you're not attaching anything to the floor directly, you may be able to get away with just your final floor, but make sure there's no buckling or anything that will smoosh your foam, or you'll end up with a very uneven mess.
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Old 09-30-2019, 10:29 AM   #5
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I'm questioning the value of even using plywood over XPS foam.
I think you should. The foam wonít hold up
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Old 09-30-2019, 11:40 AM   #6
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Marine plywood is made to resist water. If your bus does not leak, Marine plywood would be waste of money as it is expensive. I used no plywood. 1-1/2" foam, vapor barrier and finish flooring.
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Old 09-30-2019, 11:41 AM   #7
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I think you should. The foam wonít hold up
Trying to understand why ply wood under is the only way for the foam to hold up?
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Old 09-30-2019, 11:59 AM   #8
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Trying to understand why ply wood under is the only way for the foam to hold up?
I think they meant plywood over the foam.

I see folks here placing foam sheet and cover it with plywood with no framing and seem to be doing fine.

I have some reservations. I have installed a couple of shower pans that were constructed with fiberglass or abs over foam.

All of them developed a depression where you stand while showering. I'm almost 150 lbs. I think that the foam should have held up..... It didn't...

Just to be safe, I am going to use some 2x framing under high traffic areas.
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Old 09-30-2019, 12:01 PM   #9
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I dunno that marine plywood is required. If you have some sort of "water event" (burst pipes and whatnot) I suppose it would be useful. I think normal plywood should suffice.....if you want a sort of ghetto-marine plywood, you could paint it with Drylok on both sides, which is what people use to build plywood aquariums (lots of videos of this on Youtube)
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Old 09-30-2019, 12:08 PM   #10
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I dunno that marine plywood is required. If you have some sort of "water event" (burst pipes and whatnot) I suppose it would be useful. I think normal plywood should suffice.....if you want a sort of ghetto-marine plywood, you could paint it with Drylok on both sides, which is what people use to build plywood aquariums (lots of videos of this on Youtube)
I used exterior plywood on my first bus. Flooded it three times....

We opened windows and used a fan on the carpet to help it dry. When we replaced the carpet the plywood underneath was undamaged.

I agree with Drew. Marine plywood is overkill.
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Old 09-30-2019, 12:39 PM   #11
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Originally Posted by PNW_Steve View Post
I think they meant plywood over the foam.

I see folks here placing foam sheet and cover it with plywood with no framing and seem to be doing fine.

I have some reservations. I have installed a couple of shower pans that were constructed with fiberglass or abs over foam.

All of them developed a depression where you stand while showering. I'm almost 150 lbs. I think that the foam should have held up..... It didn't...

Just to be safe, I am going to use some 2x framing under high traffic areas.
Yes, plywood over foam and then a finished floor on top. I don't see how removing the layer of plywood is going to effect the durability of the rigid foam board under it all.
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Old 09-30-2019, 03:45 PM   #12
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For a point of reference the pink Owens Corning Foamular 150 foam board found on shelves at The Orange Home Center is specified to have a minimum compressive strength of 15 psi "at yield or 10% deflection, whichever occurs first." The weight of a 150 pound individual standing directly on this foam, if spread perfectly evenly over 10 square inches, could cause a 1" foam board to crush almost 1/8".

People's feet are larger than 10 square inches, though they don't strike the floor exactly evenly and don't spread weight perfectly evenly either so dents in the foam would still happen.

What it comes down to is this: how rigid is the finished floor covering, in other words how well does it spread load? A roll product like linoleum will do little. Laminate flooring will do much better, but I wouldn't be surprised if the small bit of flexion below the joints made the flooring fail early. Of course if the bus isn't a full-time residence then "fail early" is still very far down the road!

A layer of 3/4" plywood is going to spread load very well and prevent any damage to the foam from concentrated loading. It's probably overkill, and it does deduct from the ceiling height that several of us are sensitive about.. but it's also easy and relatively cheap insurance. It also provides an anchor for relatively light-weight things to be secured to the floor.

Personally, I'm not going to put plywood over my foam. Instead I'm thinking aluminum plate somewhere between 0.060" and 0.120" thickness (it'll double as a heat spreader for in-floor radiant heat, but that's another story!).
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Old 09-30-2019, 07:18 PM   #13
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I ended up using AdvanTech 3/4" tongue and groove flooring. Check it out online - there's a lot of info from people comparing it to traditional 3/4" plywood. It was about $50 a sheet for me.

I don't know how well it compares to marine plywood.

Chris
I will second the recommendation of 3/4" Advantec T&G Subfloor panels. I have used them in traditional construction, and more recently as the subfloor on the bus. They are super solid, and fully impregnated with waterproof resin. I paid about $30/sheet at a local Riverhead. Can't get them at Lowes or Home Depot locally here in RI.
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Old 09-30-2019, 09:13 PM   #14
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I just got done with my floor. I used the 1" Pink XPS because it has more compressive strength and less ability to hold water than the white EPS styrofoam. I used 1/2 A/C ply over it because I'm trying to save every 1/8" of height. The ply over the foam over the metal floor should be rigid enough. I did go with wood supports under the plywood seams so the joints don't get uneven. Going to lay cork for the finish floor.
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Old 10-01-2019, 12:51 AM   #15
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I will second the recommendation of 3/4" Advantec T&G Subfloor panels. I have used them in traditional construction, and more recently as the subfloor on the bus. They are super solid, and fully impregnated with waterproof resin. I paid about $30/sheet at a local Riverhead. Can't get them at Lowes or Home Depot locally here in RI.

3rd, this is what I did also. Prob would have gone 1/2 inch looking back at it.
I was going to go straight rigid foam, but was afraid the laminate i put over the top would separate over time without something harder underneath
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Old 10-01-2019, 06:42 AM   #16
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Thanks for all the feedback

Thanks to everyone's advice. This helped me narrow down what approach I'm going to take.



I'm tearing up the current bus floor now. I'm hoping to be ready to lay down the floor in about 2 weeks, but I want to order the materials I need now so I have what I need when I'm ready to start.
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Old 10-01-2019, 08:02 AM   #17
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So how do people feel about vapor barriers? Where do they go? in between the metal and the foam board? or between the finish floor and ply?

ya know for waterproofing and such
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Old 10-01-2019, 09:18 AM   #18
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very insightful thread! Lots of great discussions and examples
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Old 10-01-2019, 09:51 AM   #19
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if the primary purpose of the plywood underlayment is to spread weight over the foam, it seems like using slightly thicker flooring could be just as sturdy for typical floor traffic.
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Old 10-01-2019, 10:02 AM   #20
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if the primary purpose of the plywood underlayment is to spread weight over the foam, it seems like using slightly thicker flooring could be just as sturdy for typical floor traffic.

I imagine the regular 5mm underlayment at Home Depot would work just fine, especially if you weren't looking to use it to secure furniture and cabinets to. I don't think you could go wrong with a grid of furring strips though just the same.
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