Gorilla was mentioned when I posted this question on the Home Improvement forum. I've never used Gorilla, it must be something. The application isn't very critical eye-sight wise. The broken brick, when reparied will be mostly covered by the (new) mantel resting on it and extending several inches beyond it. I will also add a face board to the mantel, making it look much thicker (maybe some molding) and that too will block seeing the undelying brick bracket.

no you should not glue over cutback adhesive. it may not hold a bond well. plywood is a great solution. So is surface prep to remove the cutback, but cutback can seep into the porous concrete, which can also effect the bond of the new adhesive and it have less strength, and they might not be able to get it all up wich means less bonding strength. Plywood curcumvents the needed adhesive removal and does away with the unknowns. The installer that saysd he did this dozens of time without issue it taking a risk with your floors because adhesives specifically state that they can not be installed over old adhesive. He is also a corner cutter and probably a lower price. Whereas the other isntaller is giving you a realistic proven porofessional solution. Why take the risk ? If it fails it will cost you more. Remember the isntaller only has to guarantee the installation for a year or two. What happens in one year if it starts losening and popping up ? You live with it or pay to have it fixed or replaced. Go with the plywood.

I was just looking for adhesive yesterday to bond wood panels....in the house without blowing my self up having a furnace on. I'm still not sure how safe I am with what was bought, they will mention flammable, but nothing is said about not being flammable. And tech sheets are for some scientist I haven't met yet. Branding doesn't help. It just adds confusion as to what the actual adhesive is meant for. There were more types than one would want to count. Glues are as interesting as paint to me. Both can have properties for use beyond their specified application. And branded for doing so allows them to increase cost of material significantly over what they would normally be used for. I remember 20 years ago seeing a crackle finish. A recipe combination of acrylic paint and hide glue. The guy at the hardware store said he had never heard of hide glue. When found, it was a couple of dollars for a quart. Now twice that for a very small bottle. Hide glue is the centuries first glue. It is now used for fine furniture inlays, old manuscripts/books/art restoration and wood musical instruments. One has to be a skilled craftsman to use this. Although still used by many woodworkers too. Not clear if it is the same formula as once was. Just a glue history lesson... Glue for the normal user can be very confusing. And due to regulations is not what we once knew. One of the things I have found is a good contractor may use the same type for an application, but their adhesives are far superior to what we are offered. If you want the best in various construction needs, even beyond adhesives, head for the contractor's options. Thank NASA for our selections and gluing a plane's tail. A positive as they have given us hundreds of every day life products than we could list here.

E6000 would be my glue of choice. It will glue everything to anything and it works great on terra cotta. (For future use it's also weatherproof so it's great for gluing outdoor hard-to-glue surfaces) For starters I would have glued the knob on before painting. The problem you might encounter depending on the amount of paint you used is that the knob will not be glued directly to the terra cotta but to the paint layer that you covered it with. There is a possibility after constant lifting up on the knob that the paint could peel off the terra cotta surface causing the knob to come off. The E6000 will still work but next time you might want to leave a small unpainted area where you are going to glue the knob to make sure it will be secure when dry. If you can I would try to either sand the paint down or at least rough up that area where you are going to glue the knob and touch up around it when it's dry. The E6000 is paintable.