Torsion Floor Panel - Glue Technique

[KCStudly]

Getting close to skinning and insulating my floor and I have a question on glue methods. I know this has been discussed before, because I have read about it, but let's have a refresher, shall we?

Floor frame consists of 2x2 and 1x2 (on edge) cedar stringers and xmbrs. Skins are 5 mm marine okoume top and bottom. 1-1/2 thick XPS foam board fit into void spaces.

Many people mention using a different glue on the floor frame to ply than they use on the foam to ply. Such as PL or TB2 for the frame and contact adhesive for the foam. I have 3M 30NF for the spray adhesive and TB2 (but I could be convinced to use PL) for the frame.

So if I used TB2 to glue the upper skin to the frame and then spray the cavities and foam pieces with contact adhesive, how careful do I need to be about avoiding getting adhesive on the second face (edges) of the frame? Should I use masking tape to keep the spray adhesive off of the frame then peel it off and add the PL or glue, or am I worrying about nothing? Just not sure if the adhesive and glue will play nice together. Any good reason not to just use the spray adhesive for all of it, skins and foam besides having to make sure everything is pretty level because the spray adhesive will not fill gaps like the PL? the cedar is running very true and any slight variation in the frame members sanded smooth very quickly.

Hey Linuxman, you've used the 30NF a bunch, what are your thoughts?

[Lgboro]

Used Gorilla Glue on my build and couldn't be more pleased with the results. You will probably hear a few chime in against Gorilla Glue but all my test pieces that were left in the weather have held as good as any glue could --the wood breaks before the glue joint (all you can ask a fastener of any kind to do). Just dampen like the directions say, cut you joints to fit and clamp and it is a super strong joint. I didn't use a mechanical fastener until I covered my tear with aluminum and wouldn't hesitate to take my tear anywhere on any road I've seen.

[aggie79]

I built my insulated floor using 1x2 on the flat with 6mm - 1/4" - Russian birch plywood on both sides. I used TB III to glue framing and plywood. I did not glue my insulation. You're using heavier framing materials and stronger orientation of the framing materials. The real strength is in the skins and not the insulation. I would not worry about trying to glue the insulation.

[KCStudly]

Aggie79, I want the added insurance of the extra strength. Where I am going is a bit rougher than most street rigs will see, and I already paid for the adhesive.

LgBoro, I know what you mean. Not a single permanent nail or screw in the floor yet.

[aggie79]

Aggie79, I want the added insurance of the extra strength. Where I am going is a bit rougher than most street rigs will see, and I already paid for the adhesive.

I think your point about not getting contact cement on the wood framing surfaces, that you intend to glue with TB, is very important and vice-versa. On my insulated floor I built the framing and then installed the bottom plywood. I assume you will be doing similar. Then I probably would use a roller to apply the contact cement to the plywood skin and one side of the insulation, rather than spray it, and only work a section or two at a time.

The real trick will be when you try to attach the second sheet of plywood. You'll need to apply the TB to the framing and contact cement to the insulation and somehow mirror and keep separate the two adhesives on the plywood while at the same time working against the clock with the short open time of the TB.
However you do this, you don't want to sacrifice the integrity of the framing to plywood join even if it means sacrficing some of the integrity/strength of the insulation to plywood join.

[Larry C]

I am currently in a similar situation, but with my walls. When I did my sandwich floor with 1/8" skins, I used thickened epoxy on the wood and on the foam insulation. For my walls, I used thickened epoxy to glue on my strip panel to the framing, and locktite foam insulation adhesive to attach the foam.
However, I now have to apply my outer 4mm Okoume skin. I have thought about using the same schedule for this skin, but trying to deal with 2 different adhesives at the same time would be difficult. So, I am going to just use thickened epoxy for the entire surface of the framing and foam. When figuring the cost, there really isn't much $ difference, and with epoxy, I will have plenty of time to apply it, and still be able to move the skin around if needed.

Larry

[KCStudly]

Thanks, LarryC. The epoxy probably would have been a good choice, too. I was attracted to the 30NF because it is water cleanup, one part, and has a 30 minute working time to get things right (IIRC). Not that you can move things around for 30 minutes, but that the window of opportunity to get the two surfaces together is about 30 minutes after the tack time.

Aggie79, did you get a different result from Linuxman? Over on my build thread, where I asked more or less the same question as OP, he has indicated that he has seen no problem with applying TB3 directly over the sprayed on adhesive. Best I can tell he has the most experience here with the 30NF (not sure how long his first build has been in test mode, though). You mind me asking what leads you to believe it would be bad? That was my initial thought, too. It seems like it could go horribly wrong in the "chemical soup", so I am looking for valid input, real world experience from both schools of thought. It’s kind of hard to argue with firsthand experience, though, and from what I can tell he has used the same method for at least a few builds.

As of right now my plan is to:
1. Finish adding the centerline blocking.
2. Use TB2, a few brads or staples for alignment, glue the bottom skins on, and weigh it down with heavy stuff to cure.
3. Trim the excess ply from the edges.
4. Flip it right side up.
5. Pre-fit foam.
6. Template the mounting hole locations from the trailer frame.
7. Drill and install the blind thread inserts (counter sinking slightly as required).
8. Spray the adhesive being careful to concentrate on the inside face of the bottom ply (avoiding the frame top and insides as much as possible without going to the trouble of masking).
9. Apply TB2 to the tops of the floor frame.
10. Use leftover slats as "stickers" to assist in placing the top floor skins, running a screw in here or there to keep the skins from shifting while I pull the stickers out.
11. A few brads or staples and weight to cure.
12. Trim excess top skin.

Thanks everyone for the input. I'd still like to hear more on the subject if it's out there.

[KCStudly]

Spray the adhesive being careful to concentrate on the inside face of the bottom ply (avoiding the frame top and insides as much as possible without going to the trouble of masking).

I can also use a piece of cardboard or poster board as a masking tool as I spray to avoid getting overspray where I don't want it.

I also forgot to mention that my floor skin is in several pieces, so I can bite off smaller sections one at a time without being rushed by the cure times.

[aggie79]

My thoughts/concerns are not with a chemical incompatibility with the two adhesives but with a possible weakening of the bond. TB is a PVA glue. PVA glues work in part by bonding porous materials and in part by bonding with cellulose. If the contact cement coats one side of the framing there could be a lesser bond. I have experienced this situation with epoxy and sanding sealer interfering with the PVA bond of a wood to wood joint but can't say if this would apply to the contact cement. It sounds like you will be minimizing the overspray so it shouldn't be an issue.

[KCStudly]

Tom, Your input and second opinion on my intended method are greatly appreciated. Thanks.

[linuxmanxxx]

KC the dry time is 30 min (much shorter in high heat and the bond time is up to 2 hrs for the 30nf. I apply the tb3 while the 30nf is still tacking so it goes thru to the wood and the wood to wood bond is much stronger than just using the contact cement. The 30nf sticks to the foam so good there's just no way I can stop using it. I'm using GG for some things like the double layer of foam in the roof I'm using GG to bond together instead of the 30nf because it's cheaper and not overly critical bonding area. My newest gem is a discovery I've made for inner trim that looks so much sleeker and easy to setup and use and inexpensive as well.

[KCStudly]

My newest gem is a discovery I've made for inner trim that looks so much sleeker and easy to setup and use and inexpensive as well.

Oh? Do tell. Do you mean that you are using the 30NF for trim, or is it something else?

Inquiring minds want to know.

[linuxmanxxx]

I'm using gg and short nails to secure but the trim is the find. Its flat 3/4 plastic and clear so just paint it with spray paint to match interior gg the corner edge and bam done. I used moulding before and just looks tacky to me. This gives clean sleek lines.

[KCStudly]

Hmm, clear trim. have you tried painting just the back? Wonder if it would have a gemstone appearance.

[linuxmanxxx]

I did but can't remember why I didn't do the back of it. Only home depot has it in paint dept its corner protector moulding. I'm sold on it after first piece went in. it's what are in my build pics I've ben posting.