Chris,
My son and I did an experiment with a variety of glues for a project he was doing. Probond is a good product, and you have to be aware that it expands slightly during the cure and dry process.
I am not so sure what process you plan to use the glue in. If it is to adhere more mix to an already existing piece, or to glue it to something. If you are planning to adhere new mix to already cured mix you will need to dampen the cured piece, brush it liberally with your bonding agent,(if using probond I would let it sit for at least 10 minutes) then apply your damp new mix that has some bonding agent incorporated into the actual mix. You can enhance the 'grab' ower of your probond by patting a little dry sand into/onto the damp probond :)then letting it sit for 10 minutes.
I am not sure that I would use probond only because it expands, but if you factor that in you will probably be ok.
Always enjoy seeing the pictures of others creations.
Happy casting, lucky you to still be able to work on your projects.
Dena

Thanks for the advice Dena! It is to attach new tufa/concrete to an existing piece. I didn't know of the expansion quality of this, but it should still be ok - as long as it glues well! :)

Had some recent success with Gorilla glue.This stuff is the meanest ,toughest glue I've ever used.I spoke to someone over the weekend who is using this stuff in his house construction.If it's good enough for that...
Good luck
Cheers from here

The first thing to do is decide which Elmers ProBond Glue you are discussing. There are several different ones from contractors to poly.
I suspect Chris and Dena are not talking about the same glue although I could be wrong.

Gorilla & Elmers both make a 100% waterproof Urethane glue. Either of these expand and require clamping to achieve full bond strength. The Urethanes are about the only true "waterproof" glues commonly available (they are both rated for marine use below the waterline) and are capable of bonding just about anything to anything. The strength of either brand is generally greater than most of the materials being glued with about the only exception being steel. For steel, there are some Sika Brand industrial adhesives available that are even stronger than welding in most applications. There are some serious "glues" out there these days. One note regarding Urethane glues...use rubber gloves. If you get any of it on you and don't get it off within mere seconds...it turns your skin black and it stays that way until new skin replaces it. And there ain't no scrubbing it off. Forget it. Please...don't ask how I know this. Use your imagination...then use gloves.

The Elmers Probond that I am using is a white glue product. I guess expansion won't be much of an issue as I'm slapping new tufa concrete mix on to an existing piece. The way the calendar is romping on, these won't be ready for Christmas, oh well, still a good winter project, and there's always b-days :)

I forgot to add...

Thank you all for your replies, it's all knowledge and appreciated! :)

Elmers Probond is a complete LINE of glues, at least a dozen different types.
I believe Dena was talking about Elmer's Probond Polyurethane Adhesive (but I'm not sure)which is a completely different animal than what you have Chris.

You can use what you have as a concrete bonder and/or admix either straight up or diluted with water.

Chris,
I used ProBond a "contractor's grade Elmer's" product. Comes in a white cylinder squeeze bottle with an orange capper for the tip. Says the following on the bottle, The Ultimate Adhesive, Polyurethane Glue,
Waterproof, Bonds Virtually Anything, Super strong. Of course along with all the other warnings......The color is an icky varnish color. (icky in my opinion).
Chris do not just put it away......
Stick to it and hope you will show a picture of your project either in process or completed.
Dena

David you are correct! The stuff I have is "premium polymer glue". It also gives instructions for using it as a bonder and fortifier - I'm always leary of claims made on the label, so it's good to have the input of the group:)

Tango it's always good to get your advice from experience, and don't ask you how you know, the comment on lime in another post curled my toes - yikes!!!!

I'll be taking pics, and if it doesn't work, well it'll be a tutorial on what not to do :) I couldn't just set them aside, they stare at me every time I walk thru the kitchen - I *knew* there was a reason I like lots of counter space! lol