Warning: that new forge refractory might crack on you in 3 months

I switched to a premixed refractory from the big box store last January. Looked fine at first, smooth finish, held up through about 40 heats. Then last Tuesday I fired it up and found a hairline crack running from the firepot to the shell. Six inches long. By Friday it was wide enough to stick a quarter in. The old mix I used for years never did that. Anyone else see these new batches fail faster?

3 comments

3 Comments

rowanellis1mo ago

Started helping a buddy reline his forge back in March and he used that same box store mix. Did maybe 50 heats with it, looked solid. Then he texted me a photo a few weeks ago and the whole lining looked like a dried up riverbed, cracks everywhere including one big split right down the middle. He pulled it all out and went back to his old recipe with the fireclay and sand mix he's used for years. Never seen a commercial batch go that bad that fast.

patb121mo ago

Did he let it dry out long enough before the first fire? I've seen that mix crack up bad when people rush the cure, especially if they fired it too hot too fast. A slow ramp up over a few days and keeping it from getting to full welding heat for the first dozen or so heats makes a big difference. Still, if it's already that cracked, he's better off just ripping it out and going back to what he knows works.

susana661mo ago

That box store mix might have some portland cement in it. I've run into that before with a batch I grabbed in a pinch. Portland can make a forge lining look fine for a while then just crumble when it gets cycled hot and cold enough times. The old timers knew to keep lime and cement out of forge linings for that reason. Rowanellis's buddy might have hit that exact problem. The big crack down the middle sounds like the whole thing shrunk and gave up at once.