My home inspector told me about an easy, inexpensive and nearly permanent repair: Loose brick repair with epoxy. It works really well if you need to fix a loose brick in something like a fireplace or a retaining wall. Epoxy is a effective loose brick adhesive.
Epoxy works because it’s stronger than cement. And while it’s not economical to use epoxy for mortar instead of cement, in small quantities it’s cheap enough, and much quicker.
An ideal loose brick adhesive
For small repairs, ordinary liquid epoxy is perfect. You can find it in the adhesives aisle of your local hardware store or home improvement center.
Repairing the loose brick
If the brick is loose enough that you can remove it, remove the brick. Squirt some epoxy on all joining surfaces. Mix it up with a toothpick. Then set the brick back in place.
For repairs where there’s a larger gap that epoxy glue can’t bridge, use epoxy putty. If you’re buying in person, you’ll probably find that in the adhesives aisle as well, but look in the plumbing section too. The epoxy putty from the plumbing section is usually cheaper than the big-brand epoxy putty in the adhesives aisle, even though it works just as well. Wear disposable rubber gloves when working with epoxy putty, because it can be nasty stuff. Break off a small piece. Knead and roll it until it’s completely consistent in color. Then press it into the gap. Start out with less than you need and mix up more, because once it’s mixed, it starts to set up in minutes.
When fully mixed, it’s sticky, and once fully cured, it’s very strong.
I have a short brick retaining wall in my front yard with a couple of loose bricks in it that I fixed with epoxy and putty. I’ve also fixed a corner brick in my fireplace with it. You can use a combination too, if some of the mortar has broken away. Use the liquid where it reaches with a gap. Then press the putty into large gaps. This approach gives a stronger, more weather-resistant and longer-lasting repair.