That older guy on this forum told me I was using firebrick wrong... he was right

I was laying firebrick in a boiler last month and this older guy named Pete commented on a picture I posted. He said I was buttering the whole brick instead of just the edges and it would crack by next winter. I blew him off at first (you know how it is). But after 3 weeks of heavy firing, two bricks in the back wall had hairline fractures. Next time I'm just doing the edges with a thin layer, leaving those air gaps. Has anyone else had their firebrick mortar fail because of too much material?

2 comments

2 Comments

the_sandra3d ago

Feel for you man, I really do. I did the same thing on my first fireplace rebuild, slathered that mortar on thick like peanut butter on a sandwich. Thought I was being thorough but ended up with a cracked mess by January. Pete sounds like one of those old timers who knows his stuff from watching it fail a hundred times. The air gap trick is the real deal, it lets everything expand and contract without fighting itself. You'll get it right next time, we all have to learn the hard way once.

ninah103d ago

Wait, you used to think a thick layer was the way to go too? I really used to believe more mortar meant a stronger hold, like you were just being extra careful. But after seeing my own chimney liner fail twice, I finally listened to an old mason and tried the air gap method. Man, what a difference it makes, everything just fits without fighting the heat. It totally changed how I look at fireplace work, I feel dumb for not figuring it out sooner. Did you have to redo your whole fireplace before you got it right?