looking for putty-like stuff that cures

Bondo

Dan

unk fired this volley in news:nieit1$mui$ snipped-for-privacy@gioia.aioe.org:

I presume you use the phrase "finishing a car" with some liberty!

If you don't know about Bondo (and/or other polyester body putty), then the words carry somewhat less meaning than they might, otherwise.

LLoyd

Everybody knows about bondo.

I want something

a) more flexible and stronger so I can

b) glue it to the bottom of the underlay, whaich can then be removed for cleaning/drying/other maintenance.

But since I posted, have found out about and decided to test a diy sugru recipe; could be just the thing.

The thing about finishing is it is like Zenos paradox, you never seem to get to the end.

There are oodles of different caulks nowadays. Go to your local home supply store and start reading what they say on the tubes. Or better yet just google them.

Off the top of my head you might try Polyurethane. It sets up kind of slow but works pretty good as both glue and filler. Commonly used in the roofing trade:

There's also body putty.

Mix up a small batch of silicone caulking and corn starch 1 to 1. It's a pain to mix at first, so do it in tall-sided container. For a sample batch the lid off a spray bomb will do nicely. The corn starch absorbs moisture from the air which makes the silicone dry in minutes, firm but flexible. Cheap and handy for many things. Haven't tried gluing it to anything but I expect it will be Ok.

No matter what he uses, the OP is going to have to use a release agent of some kind. Silicone is a terrible adhesive, but even that will stick in the grooves -- at least partly -- through some mechanical interlocking. The texture of that may even be too fine to see with the naked eye.

And no adhesive we're likely to encounter will stick to it very well, either, so running a bead of glue and then sticking on the underlay probably will create a mess.

As for flexibility, bondo doesn't have it. It's weak, it gets lousy adhesion, it will crumble if you flex it much, and, to get any adhestive to stick to it, you have to wash the top of the beads very well with acetone. Styrene floats to the top and has to be washed off. Sanding just spreads the styrene around, unless you used the acetone first.

I would try this: Get some polyvinyl alcohol release agent (PVA), which you can get at any boating supply store, and brush at least two layers into the gooves -- and on the flat spaces between the grooves. Lay in a bead of "zero shrink" (if you can find it) polyurethane adhesive. (The more expensive brands of polyurethane construction adhesive usually are low-shrink. They'll be *slightly* flexible after being cured.) Immediately lay the underlayment on top of it while it's still wet. Pray a lot. Let it cure really well Then try peeling it up.

It should come up if you don't have a lot of mechanical interlock. If you can spare a couple of days for a test, try it with a piece of underlayment around 6 inches square, first.

I would sink cling wrap into the groove, and tape it down on both sides. I know that will work because I sunk cling wrap into my ear, and then kneaded in that silicone/corn starch putty. Once it set up, it came right out. No, I did not make that up. :) I only did one ear at a time, so that in the worst case I could extract the plug with an easy-out connected to a slide hammer or a tow truck. :)

If the grooves are deep enough, a strip of something easily glueable could be imbedded into the putty. Short working time, but nicely kneadable.

If I were using PVA, I'd use more like ten coats. :)

Well, I've pulled 36-foot-long sailboats out of a mold with two coats, so that will be enough unless there is too much mechanical interlock

-- in which case, no number of coats will do it.

Just how much is that floorboard going to flex? Bondo should be perfect, especially with an overlay to stiffen it. Being a polyester resin, it flexes pretty well, too.

Let us know how it works. It sounds promising.

Remember, Grasshopper, a project is done when you say it is done. Ask any artist/painter.

Make a rod of it, say 1/2" diameter and 8 inches long. Let it cure. Now bend it with your fingers.

Snap.

Polyester can be moderately flexible, but not when you load it with calcium carbonate and other crap to make a filler, like Bondo.

Please report back on the DIY sugru results. That stuff is too handy and too expensive.

I've done a lot of glass work. On new molds which can stick even with a lot of carefully applied wax coats, we'd use two sprayed on coats of PVA for safety on the first pull, and still sometimes get some sticky spots. We had one large rough-finish project that we always ran unwaxed, and only ever used PVA. Never had any trouble with it. When the need for parts from it died down, the customer decided to do it himself. He had strict instructions on how to do the PVA, but his first part became one with the mold. Most likely he brushed on multiple coats. The stuff has a tendency to bead up and streak in some applications.

Anyway, getting back to the silicone putty, it's often used to make flexible casting molds. I don't think it would stick to even rough steel, and is flexible enough to overcome some undercut. At one to one it's a dry consistency. You can knead it and your fingers almost stay clean. At that density it will pick up about 3/4 of the detail of a coin's surface.

I agree. Bondo would be far from perfect for the job.

Ok, but what glue will stick to it? The "paintable" silicone window caulk is not much like tub caulk; even less like the clear silicone caulks.

If I were going to use silicone, I'd hope that the underlayment was coarse and fibrous enough to allow the caulk to embed and get a mechanical grip. Then I'd smear a layer into it, fill the grooves with the same stuff, and slap them together.

It's just silicone 1 with about 10-30% cornstarch mixed in, to speed up the cure.

Which is does, but it's way too damm sticky until it does cure. It does peel away from the foil backing on the sound-absorber stuff I put all over the floor, so that's a good point (means the underlay could be glued to the strips and the whole thing lifted off, assuming I don't get any glue where I shouldn't have.

Also it looks as though I would need about 20 tubes (calking gun tubes) of the silicone. That's a LOT of very sticky messy stuff.

So if there was a caulk that was not so messy, would NOT bond to shiny aluminum foil, and would stay somewhat flexible, and could be glued...

The grooves are shallow and gentle, about 1" across and 3/8" to 1/2" deep.

Sugru (the diy version) peeled right off the floor which is covered in the sound-absorbing stuff that has a aluminum foil top layer. If it wasn't so messy and expensive I might go for it, but I would like a better solution.

You may need to do some experimenting. Silicone will "peel right off" because it's a lousy adhesive, even when modified to make "paintable" caulk. I've used some that won't take latex paint; I had to use an oil-based primer. Two years so far. That's not a lot, but it is holding up.

It's not a surprise that it peels off of aluminum foil. The question is, how do you make it stick to the underlayment? If, as I mentioned, it's fibrous and coarse, you may get enough mechanical interlocking to do the job.

If you can try a little patch, you'll find out what works. I don't think that bondo is it.

I think Bondo wousld work. The floorboard in question is corrugated to s tiffen it. I doubt if one could bend the floorboard. But the original po ster wants a more flexible agent. Incidentally can you still buy Bondo wi th Calcium Carbonate? I thought it was all loaded with glass micro-bubbles now.

Dan