I think the fortifier makes the mixture stronger.
Paws

I am not familar with the specific products, but in general, a bonding compound is used where you are placing new concrete against old and helps the new concrete bond with the old. It's applied to the surfaces of the old concrete, not added to the mix.

The acrylic fortifier sounds like it is an admixture to improve the strength and/or workability of new concrete. It might improve bonding properties of new concrete, but check the label.

If it improves bonding and the concrete in hemispheres is still "green", the fortifier added to the mix to join the halfs may be all you need.

I have been adding bonding agent to my concrete mix since I started, and I think I must have read about using it here on the forum. I was curious too (when all else fails, read the label) so here is, verbatim, how the label on my bottle of Bonding Agent ("BA")reads:

"Lanco (brand name) Bonding Agent is a liquid admixture to cement that enhances the bonding characteristics when it's used to bond plaster, stucco, stone, wood, concrete, glass, brick and tile. Lanco Bonding Agent adds resiliency and toughness when used as a additive (sic) for cememnt to cement, cement to wood, plaster, stucco, tile and plaster to plaster."

I find that it adds an elastic quality to my portland/sand/water mix. Especially helpful when casting leaves (gives you a bit more control over the flow) and when sculpting, as the items you want to form (facial features if making grots or creatures)will hold their shape and not be crumbly, will have a smoothness, like clay. This type of sculpting is building up rather than carving down.

I also add it to any paint I use. An old, experienced friend of mine told me "That Bonding Agent will make paint stick to ANYTHING!"

I usually add about 1 part BA to the first 4 parts of water when I am mixing the portland/sand mix, never exact. I add water a little at a time after that. When I mix it into paint, (I usually use an airbrush) and since the BA is about the same consistency as the paint, I use about 1/3 as much BA as there is paint and then thin to the desired consistency.

I have found both Blue BA and White, at Home Depot. Unless you want your finished piece to have a swimming pool blue color, get the white.

I have also found that the pieces I have used the BA in the mix on are definitely less brittle than those without. Reinforcement also is a factor, no matter how small the piece.

Hope this helps!

Amanda

When you add it to paint what ratio fortifier/paint

This was very helpful. Thanks for sharing this with us.