Rick, Are you talking joint compound for sheetrock (drywall)? If that's the case, it's sort of a plaster that you cover nailheads and joints in sheetrock. What are you thinking of using this for, texturing walls? I thought this was for indoor use. Billie

As far as I can tell,it's for drywalling(or sheetrocking as you south of the line call it).As to indoor /outdoor use,I'm not sure.Obviously,indoors,and maybe that's where it stops.Hopefully,someone might have some history with it.As I said,it's just been sitting there,doing nothing!
Cheers from here.

Well it's drywall mud, indoor use only.
But that doesn't mean it can't be modified.
The very popular and expensive Gardencast is just a small amount of POP added to Portland and some admixes.
It would be interesting to see what you would get adding joint compound to Portland.

I have yet to try it but I saw it on the Carol Duval Show and Christopher lowe where you could carve something in styrofoam and then cover it with joint compound after it dries you can sand it and smooth the rough looking edges and paint it or stain it and then if you plan on putting it outside you can put a varnish or a sealer on it.You must make sure every bit of the styrofoam is covered tho because I believe the varnish will melt it if you leave a hole or a gap someplace where it can make contact with the styrofaom.To try and find the directions I'd go to HGTV.com and try and find the direction under carol duval show

A couple of weeks ago my DW and I did a venetian plaster faux finish on our livingroom wall, using Durabond90 mixed with latex paint.
The Durabond looks a bit like portland cement, but doesn't act like it. It's a bit like the drywall compound too, but is too hard to sand (according to the instructions on the side of the bag). Cost in Ontario is about $15CDN for 15kg - should be about $12US for 30lb, more or less.
There was some left over, and I had some perlite handy too, so I mixed equal amounts of Durabond & perlite, added enough water to make a squishy mix (note the scientific term denoting a tufa-like consistency), and pressed it into a small yoghurt container. I then pressed a glass oil lamp bulb into the mix, and let it set overnight.
The result looks like a portland/perlite/peatmoss mix, but is a bit heavier and a bit stickier - I had to cut the mold open, which I don't usually have to do when I make tufa.
It was well set by morning, and hardened nicely during the next week.
It occurred to me that this might give some relief to tufaneers who suffer from withdrawal symptoms during the cold weather. I know it's not real tufa (no portland cement and no peatmoss), but it might make a winter substitute.
Another possible use is as a quick prototyping material - sets a lot faster than tufa.
And the way I used it originally, it mixes nicely with latex paint - just dulls the colour a bit.
I'll try to post some pictures later this week.

Durabond90 is mostly POP with additives giving it a hard finish. It would probably make a terrific mold making material, better than POP alone.
Has anyone tried it for leaves?

Just remember that plaster (gypsum) won't take the weather. Probably be fine indoors though.

Why not use a light concrete layer to cover it and waterproof it. It couldn't be less soluble than cardboard, which we sometimes use as a way to thicken a PVC pipe or piece of heavy wire, knowing full well that it will uptimately dissolve, but the cement or hypertufa remains. I have one piece that is still tougher than nails six years later. You just have to make sure that it's completely covered--and that the chemicals don't dissolve the joint compound in the initial stages.