Adhesive Failure - What did I do wrong?

[Toytaco2]

I originally joined the forum in 2007. I could never have built my TD without the resources I found here. I haven’t posted in a while and now I’m passing on the TD to my sons and working on a van conversion. The advice and knowledge here has always served me well and so I’m more confident asking the folks here their thoughts instead of the van life guys.

I recently started putting in a subfloor, and knowing condensation to be mostly unavoidable in a van I treated the subfloor framing with Kilz Mold and Mildew primer. Lots of van builders suggest anti mold/mildew coatings for the subfloor. I glued the Kilz primed framing to the floor using Sikaflex 221 which is supposed to be an excellent product used in RV construction and weighted down the framing to cure for a few days. Today, when I expected to screw down the plywood framing I noticed a few framing members were loose and then discovered all of them could be fairly easily removed from the floor. The polyurethane Sikaflex 221 was not removable and securely stuck to the floor, but not holding to the primed framing. In fact, the framing had a sticky sort of film on it, but no cured adhesive.

I’d love to hear your thoughts on what happened and, more importantly, recommendations on how you would attach subfloor framing to a van floor.

Thanks for your help,

Mike


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[tony.latham]

I’d love to hear your thoughts on what happened...

Well... the primer and the adhesive aren't compatible. But I guess you know that now.

What it is, I don't know. Probably something chemical. But trying to glue to a painted surface isn't a good idea since you'll only get the adhesive strength of the paint at best.

Can you glue bare wood to bare wood and then paint and get the same effect?

Tony

[Toytaco2]

Well, the van floor is primed and painted sheet metal with some raised areas, like a pickup truck bed. Most people are gluing framing to the floor, then insulating the voids, and finally screwing down the plywood subfloor. Most of the raised sections now have the old adhesive on them and it’s pretty much un removable now. So I’m going to have to rip framing to fit in the valleys. Definitely will not prime them with that Kilz this time.

Is there any consensus now on a good adhesive for bare wood to the van floor.


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[tony.latham]

Is there any consensus now on a good adhesive for bare wood to the van floor.

PL3 will work fine for that. You might scuff the paint with a 3M pad.

Tony

[twisted lines]

I have not used that sikaflex but have used 252.
I changed to the posted that comes in several colors, Sands and rebonds excellent to itself after roughing,
Then Cleaning with MEK (wipe on wipe off) Re Apply as needed.
Both Polyurethane, My results have been stellar
I have used "High Gloss" polyurethane sealer on plywood as in the mix, and cover over with the caulking sealing it, always cleaning with MEK prior to moving on; that part is nasty.

Sorry to read about your experience, your results may be different, different product but I sure would try it.

[bdosborn]

Is there any consensus now on a good adhesive for bare wood to the van floor.

https://faroutride.com/floor-installation/

These guys have a good guide on van floors and are often quoted on the van building forums. I don't plan to use any adhesive on my van floor, I've got a bedrug down and will lay insulation and flooring over that. From their site:

Believe it or not, there’s no need to secure anything; the floor isn’t going anywhere! The large plywood sheets, combined with the weight of the cabinets (and others) will ensure the floor stays where it belongs. Doubt it? We completed our conversion in 2017 and our floor hasn’t moved at all. And many people have used this technique with the same results.

Bruce

[Toytaco2]

Thank you all for the recommendations. And Bruce, that link is extremely interesting. It has me totally rethinking my floor construction method. Thanks for the link.

Mike


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[Toytaco2]

I have not used that sikaflex but have used 252.
I changed to the posted that comes in several colors, Sands and rebonds excellent to itself after roughing,
Then Cleaning with MEK (wipe on wipe off) Re Apply as needed.

Now thinking about how to fix this mess. I hadn’t considered the possibility that additional Sikaflex could adhere to itself after curing. I'll do nothing without testing, but, could I reasonably expect that to be true for polyurethane adhesives in general. Also is MEK any better than acetone for preparing its surface?


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[twisted lines]

I have not used that sikaflex but have used 252.
I changed to the posted that comes in several colors, Sands and rebonds excellent to itself after roughing,
Then Cleaning with MEK (wipe on wipe off) Re Apply as needed.

Now thinking about how to fix this mess. I hadn’t considered the possibility that additional Sikaflex could adhere to itself after curing. I'll do nothing without testing, but, could I reasonably expect that to be true for polyurethane adhesives in general. Also is MEK any better than acetone for preparing its surface?


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They are both great product's but spendy, I wouldn't hesitate to test.
My sikaflex only took seconds and I knew it stuck
MEK was hard to find and expensive Sherman had it here. Scratch and clean everything.
The MEK was recommended buy the paint manufacture; it's pootent. I was using and it makes the thing's I used sticky again just before another application, The grinding didn't make a huge mess and for the most part it isn't dusty.

[JasenC]

Always glue to raw wood otherwise your bond is only has good as the primers bound, which isn't designed to be structural.
It's also vary likely you had an incomparability issue between the adhesive and primer, many of these newer building adhesives are a lot more finiky then the old liquid nails, but their big advantage is the Poly adhesive don't harden, dry out and become brittle like the old school stuff did/does.

[MickinOz]

Sika 221 is listed as an adhesive/sealer with 1.8 MPa tensile strength.
Sika 252 is listed as an adhesive with 3 Mpa tensile strength.

My take is that Sika 221 is great for reinforcing and sealing screwed joints, 252 is the one for glued only joints.
But while the 252 data sheet says that it will stick to paints and primers, it qualifies that with (two component) i.e super strong paints and primers.
252 failed under my hurricane hinge, but has worked perfectly sealing joins in my roof sheets and seating my doors in the walls.

Screw the floor down would be my recommendation.