3M is Broke!

So what was the answer that Nick gave you RE: lowered temperatures?

I’d have I just told you “You ask too many questions!” and hung up.

:W

:):)

afidel wrote:
So what was the answer that Nick gave you RE: lowered temperatures?

Below about 65F, the cure time is slowed. 50F (our overnight low) shouldn't be any danger of messing it up, but freezing temps during cure might.

Ruined! IMO but check with Nick.

Both of those adhesives cure mighty fast, even at low temps (55f -> 70f). I've used both and they are contact adhesives in a spray can.

I don't know what the RV mfgs are using for foam but it probably isn't high density extruded polystyrene, common in building applications. I have those sheets in my TT and they do a great job with heat transfer.

Those are contact adhesives as westend said, they bond instantly after you let both sides tack up. They have a high solvent content that flashes of very quickly that allows this quick curing. I am not sure what you are bonding but if you are bonding the exterior luan to the exterior FG skin that adhesive will soften at about 150 degrees F. So if your are siting in the sun for along time an epoxy would be a better choice. Epoxy adhesives are usually 300 or a little higher before they soften and begin to loose strength.

westend wrote:
Both of those adhesives cure mighty fast, even at low temps (55f -> 70f). I've used both and they are contact adhesives in a spray can.

I don't know what the RV mfgs are using for foam but it probably isn't high density extruded polystyrene, common in building applications. I have those sheets in my TT and they do a great job with heat transfer.

You're right on both points! In a past life, we used tons of Super 77 for a high density foam to make inserts in Pelican boxes for custom electronics. Well, I made prototypes. The bulk was used by others ;)

I chose to use the denser foam for strength and performance. The edges are sharper and cleaner and the surface is finer. I used a lot of it in our stick and bricks, remodeling an old farm house to keep out the air (or WIND, as it was pretty leaky, LOL).

I used a circular saw to cut it for a very precise fit (Traced the aluminum square tubing frame onto the foam, same as the luan). I figured this stuff is approved for up to 24in on center flooring support, so more than dense enough and significantly better than the original white stuff.

The weight difference is insignificant, maybe ounces. Even though we are just preparing it for sale, I want it to be nice for the next owners. I know cool bottoms of bunks are a comfort and moisture consideration (warm bodies, cold bunk floor), so this should help a bit with that.

I don't remember exactly, but I think the R-factor is something like 40-60% better with this stuff?

I spent about 3 hours prepping the back of the original fiberglass sheet, removing wood, paper, and adhesive with a machete first for the wood (light bits at a time, then as a scraper), then sprayed whatever was left with WD40 and let it soak in a bit, then used a razor blade windshield scraper to finish.

I wiped it down with acetone, though there didn't seem to be any WD40 left after the razor blade, always best to be 100% sure.

After church today the wife and I will lift the top sheet of OSB off the jig, wipe the primed surface of the Luan with a light bit of acetone and a quick wipe of the fiberglass, and make a 2-corner and long edge jig so we can easily align the fiberglass sheet squarely and accurately and "roll" it down onto the luan after coating both surfaces with 3M 90.

About 5 mins working time on the 90, both surfaces are tack immediately (unlike Super 77, which has some setup/tack time and even a light touch and separate to get best adhesion).

I'll then roll/press the fiberglass surface, put a shipping blanket over it to account for surface anomalies and replace the sheet of OSB on top and clamp it all down and add weight to the OSB again and wait about 24hrs.

Then we'll use a rubber mallet to reinstall the aluminum frame/trim all around and replace the screws.

I am still uncertain how I am going to attach the clips for the canvas bungees, though???

The originals were pop riveted. I would like to find something with a plastic dish that I can add a little Dicor under and then fasten to prevent any future repeats of a leaking fastener- which started this whole problem :(

Maybe something like a cup hook fastens, with a large plastic circle base? But low clearance and plastic to avoid snagging. Maybe plastic buttons with adhesive instead of drilling?

Any suggestions???

Gjac wrote:
Those are contact adhesives as westend said, they bond instantly after you let both sides tack up. They have a high solvent content that flashes of very quickly that allows this quick curing. I am not sure what you are bonding but if you are bonding the exterior luan to the exterior FG skin that adhesive will soften at about 150 degrees F. So if your are siting in the sun for along time an epoxy would be a better choice. Epoxy adhesives are usually 300 or a little higher before they soften and begin to loose strength.

Ditto - I used to use them a lot for laminating wood to foam for very large model airplanes. Learned my lesson when at a contest on a hot sunny day, and the wings bowed due to delamination. You would be very surprised as to what the "skin" temperature will get to on an RV sitting out in the sun. Use epoxy!

Good information about the epoxy, thanks!

For fastening systems, I'd look to the Marine industry as they make a lot of hardware for marine environments.

I primarily use contact adhesives for countertops and machine tables. We dispense it by brush rather than spray. A vacuum table is the shiz for a guy that is gluing a lot of surface on a continual basis. The vacuum puts a lot of force on the surfaces and does away with weighting and clamping. You can make a vacuum bag with plastic and a vacuum cleaner if you have the need.