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Discussion Starter · #1 ·
As I begin the subfloor install, including layers of 1/2" Polyiso and 3/4" birch plywood, I'm interested in opinions on attaching the plywood to the van floor.
I've seen where people use plusnuts and bolt in from the top, and others using t-nuts and bolt through the bottom.

My preference, unless I'm convinced otherwise, is plusnuts. It allows me to use bolts slightly longer than necessary and not have to cut off the excess. The only reason I see for one over the other is strength, and maybe that is where t-nuts win out???

In either case, I'll use 3M undercarriage spray to seal things up at the end.
 

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I glued 1/2" thick plywood pieces with T-Nuts pre-installed here and there with 3M 4200.. then just screwed the floor panels to the t-nuts.
no drilling (not that it really matters after you've cut a hole for the roof fan...), and it's easy to remove the floor if needed (to add power cables for example)..
My floor is made out of 3 planks of plywood, tongue and groove between them for a "flat" fit.
 

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as flooring options are attached to subflooring keep in mind that many adhesives for fiberglass-backed sheet vinyl, heterogeneous sheet vinyl, vinyl tile and carpet are intended to be used in heated occupancies with a minimum year round temperature that might be above the temperatures your van will experience. it's always good to contact the adhesive supplier and ask if thier product is suitable for your proposed use.
 

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Some folks have used aluminum angle to bolt the subfloor to unused D-Ring anchors and have avoided putting holes in the floor altogether.

I had a few existing holes from upfitter shelf and partition installation by the previous owner. After removing these, the bolts and holes were used for my floor mostly because they were already there and I wanted to fill them with something.

All the other modules that sit on the floor (fridge, bench/bed, galley, storage) are securely bolted to L-track low on the walls, and existing OEM anchors on the upper walls. Those modules hold the floor in place quite securely.

If I hadn't already had some holes in the floor I would have not made new ones. The existing holes used plus-nuts and there was evidence of rust at each hole which I had to clean up. (to be fair, the upfitter had obviously not applied anything to them during their installation)
 

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I used an high grade outdoor construction adhesive and glued down 1 1/2" batons, filled the voids with polyiso, and 7/16" ply on top. No holes is a very, very, good thing. I went 1 1/2" batons due to needing water and electrical raceways under the floor. You could do 3/4" batons and a 1/2" floor.

Whatever you decide, a 3/4" subfloor is way overkill. The polyiso will support a 1/2" floor no problem.
 

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No fasteners here. 1/2” sheet foam in the valleys glued down with contact cement. Sparing application of expanding foam in gaps then quickly slap down the subfloor plywood. Weigh down evenly across the subfloor, I used 35 lb boxes of catalogs from work. Let cure overnight.

Made for a very solid and quiet floor with no potential for rust. See my build post for details.
 

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If I hadn't already had some holes in the floor I would have not made new ones. The existing holes used plus-nuts and there was evidence of rust at each hole which I had to clean up. (to be fair, the upfitter had obviously not applied anything to them during their installation)
I "wet set" rivet nuts with POR-15 Rust Preventive Paint. It prevents rust and helps reduce spinning.
 

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Discussion Starter · #10 ·
Thanks for the responses one and all.
Has me thinking I can use the D-Ring bolt holes around the edges and plusnuts in the middle areas, with undercarriage spray on those spots. I'll overlap at the plywood seams with rabbits, perhaps glued, so I should be able to minimize floor holes with strategically placed plusnuts.
 

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Discussion Starter · #12 ·

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Thanks for the link, I'm convinced. I'll glue and screw, no holes in the van floor to attach the sub floor.

Everybody like the 3M 4200 Adhesive/Sealant for gluing down the plywood strips?
I used 3M 5200 and hardwood strips. The 5200 is stronger than 4200 (which is formulated to resist UV exposure).

The weak point here though is probably the plywood strips (which may delaminate over time due to moisture) so the issue of which adhesive to use may be moot. I would carefully seal the plywood strips with a non oil based polyurethane. These sealants don't like oil.
 

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Discussion Starter · #14 ·
One final question, to sand/rough-up the paint I'm gluing to or not?
I've seen it both ways, preference is not to sand, I expect sufficient adhesion anyway.
 

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Suggest expanded PVC furring strips attached with VHB tape. The floor can then be attached to the PVC strips with screws. We prefer holding the floor down with the D-ring attachment points and letting it float on the insulation as much as possible to reduce noise transmission.

All the best,
Hein
DIYvan
541 490 5098

Furring strips with VHB


Furring strips around perimeter with Thinsulate AU4002-5 acoustic/thermal insulation.
 

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One way to build a floor:

https://www.ortontransit.info/floor

1/2" closed cell foam between the corrugations. Actual height is about 7/16" so 1/2" foam is slightly compressed.

The primary method of attaching the floor to the van was done using the D-ring tapped bolt holes. How I did the D-ring attachment was tedious and not the best way. If I did another I would change by using a 1/2" x 1 1/2" aluminum block bolted to the D-ring tapped holes. One through hole for the D-ring flathead screw and a second tapped hole above the D-ring bolt to be used to bolt the floor to the van with an angle. The location of the D-ring holes are not the same elevation above the steel floor. By using the aluminum block the tapped holes for the floor can all be at the same elevation and high enough that attachment angle can be above the plywood. Simply bolt an angle to the aluminum block and then bolt the angle to the floor plywood.

The 2015 high roof 147.6" wheelbase van had three existing holes through the floor at the edge of the slider step. The only new floor holes added were 3 close to the van centerline between the rear wheel housings. Spare tire was temporarily removed to tighten the 3 nuts.

The 80/20 floor frame work slots were then used to bolt the cabinets to the floor. The 80/20 cabinets were also bolted to the van walls in numerous places. The end result was one large 80/20 framework.

I would not want the floor permanently glued to the van. Want to be able to remove the floor if necessary in the future.
 

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Discussion Starter · #20 ·
Lots of techniques and methods.
I've been browsing this forum for over 3 years now, even thought I've only had my van for a couple of months, and if you can't find multiple ways to do something, your just not looking.
Went with the glue, 4200, curing right now, using birch plywood because it is better quality than standard plywood. I'll bolt all the cabinets to the walls as well, I feel good about the technique and process.
 
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