Best adhesive to glue subfloor framing to primed metal floor?

[Nord]

Hi,

Here's what I've got going on. 40' 1989 Bluebird. I've prepped and painted the floor. I'm going to use 1-1.5" of closed cell spray foam for the floor walls and ceiling. I'm about to start framing the subfloor....

Can I get some opinions on which adhesive is best to glue down the 2x4 framing to the already Rust-Oleum primed metal floor? I bought the liquid nails subfloor but want your ideas before I move forward. I'm hesitant to screw the framing through the floor and make new holes.

Am I overthinking this? What haven't I thought of?

Thanks,
Matt
@elchanchoamarillo on Instagram

[sproutroot]

Looks like you've got a great start!
I also hate puncturing the shell. Almost everything in my bus is glued together with Great Stuff or offbrand spray foam adhesives. Back before rusty vehicles were so frowned upon, I used to resort to painted spray foam to get vehicles through annual inspections, so I know the stuff doesn't rattle loose.
There will be things in the bus that absolutely have to be bolted to the floor. If you plan ahead you can use these items to help keep your glued subfloor fairly stable.

[waxman]

I used Loctite pl premium to glue a layer of 3/4 ply to the floor then screwed 2x3 studs into that with 1.5 foam board friction fit in-between studs then 1/2 ply on top. wall studs will attach to the ribs and have pocket holes that screw into the subfloor. probably overkill but its solid as hell and should last the life of the bus with no issue. some adhesives don't like to bond to metal so just verify on the packaging but once you get further along and have some weight on it i think most heavy duty construction adhesives would be adequate

[farok]

Originally Posted by waxman

I used Loctite pl premium to glue a layer of 3/4 ply to the floor then screwed 2x3 studs into that with 1.5 foam board friction fit in-between studs then 1/2 ply on top. wall studs will attach to the ribs and have pocket holes that screw into the subfloor. probably overkill but its solid as hell and should last the life of the bus with no issue. some adhesives don't like to bond to metal so just verify on the packaging but once you get further along and have some weight on it i think most heavy duty construction adhesives would be adequate

Another vote for PL Premium! Worked well on foam and plywood in my bus, overtop the rusty metal primer covered floor.

Chris

[YankeeDespot]

I prepped my deck like you, then laid down 1/2” rigid insulation then glued 3/4” oak planks to that. The wood warped in spots, and I ended up drilling about 100 holes and power pro One screws the sock them puppies down. It’s still not ideal as the oak planks haven’t stabilized. I found that using a good (I used dewalt) still bits and cutting oil made the drilling easy. Easy-ish. So if you find you need to screw some of the subfloor, with a good bit it doesn’t take too long, and I got probably 30 holes with each bit. I used cheap liquid nails adhesive and the was a mistake. I concur with other posters that hi end adhesive is the way to go.

[Nord]

Thanks for the ideas everybody. I'll probably return the liquid nails and get the loctite premium. I'm now thinking of using 1x2"s for framing of the subfloor instead of 2x4s just to maximize headroom. So I'll glue those down and put cinder blocks on them and wedge 2x4s between them and ceiling to keep downward force as the glue dries. Then I'll spray foam and screw the OSB to the 1x2s. ��

[musigenesis]

I'm attaching my subfloor by welding bolts to the steel floor and screwing short pieces of dowel rod down onto them through the XPS foam board, then screwing the plywood onto the dowels. This provides a mechanical connection between the plywood and the sheet metal layer (which in the case of my bus is as much to hold up the sheet metal as it is to hold down the plywood) without piercing the metal floor (also allowing me to disassemble it if necessary).

Glue seems fine in normal circumstances, however. A lot of people use it and not many people seem to report its failing catastrophically. I imagine that even if it does fail in places gravity will keep everything where it should be anyway.

[Nord]

Originally Posted by musigenesis

I'm attaching my subfloor by welding bolts to the steel floor and screwing short pieces of dowel rod down onto them through the XPS foam board, then screwing the plywood onto the dowels. This provides a mechanical connection between the plywood and the sheet metal layer (which in the case of my bus is as much to hold up the sheet metal as it is to hold down the plywood) without piercing the metal floor (also allowing me to disassemble it if necessary).

Glue seems fine in normal circumstances, however. A lot of people use it and not many people seem to report its failing catastrophically. I imagine that even if it does fail in places gravity will keep everything where it should be anyway.

That's a good idea! Probably won't do it cuz my welding skills are sub par at the moment but I like the idea alot.

[musigenesis]

Originally Posted by Nord

That's a good idea! Probably won't do it cuz my welding skills are sub par at the moment but I like the idea alot.

Trust me: if I can do it, anybody can.

[Nord]

So I ended up exchanging the Liquid Nails for Loctite PL Premium 3x. Instead of screwing down to the floor I cut 2x2 wedges and jammed them between the ceiling and subfloor framing in order to keep pressure until the glue dries. I'll know tomorrow how well it worked when I remove the wedges.

[Gdog 5651]

you folks are over working it I used foamular 1.5 " foam glued to treated floor ospho clone glued with pl put down drimax osb 500 day water resistant sub floor no sub framing did this 2 years ago and built interior on it the 1.5 foamular could be subbed for any thickness foam you desire and you could shoot pool on my floor any time any where in my schoolie after 2 years no squeaks no waves no problems and after you build it you don't have to worry about hitting framing to support your construction. Gene

[WIbluebird]

I didn't even bother with glue or adhesive. If you cut the insulation tight to fit it won't budge. Once you build out walls and furniture then the stuff won't be going anywhere.

[atthebeginning]

Loctite pl premium for sure. Skip the firring strips. Glue your dense foam directly to the floor. Use sandbags or some other weights on each panel. Glue your 3/4” plywood subfloor to the foam with weights again. Screw whatever you need to to the plywood. DON’T penetrate the metal bus floor.

[Crookedgarage]

We choose not to use any glues or adhesives of any sort in the whole build, because once you use it then change your mind for any reason or make a mistake your into demo mode and that's destructive. We strategically let the floor and what ever else float within limits. We used screws, nuts and bolts where we deemed needed. So far nothings come apart or loosened, no issues. It gives the ship some room to flex on down the road because it will do that, Letting the new structure find it's place. Sometimes the more ridged the harder it breaks.

[ahibbert]

t looks like you're doing a great job on the floor. But I have to warn you that you need to put a finish coat of paint over top of the primer. Most primers other than epoxy primers are hydroscopic in other words they absorb moisture and they will make your metal rust quicker than if you did nothing. Other than that good luck you're doing a great job.