Refractory Mix Cracking

[Westozchoppers]

Hi Can Anyone Tell Me Why ? The Refactory Sila Mix Im Using In Perth W.A
Is Cracking, Im Weting The Bricks And The Mix Im Making maybe A Little to moist

Cheers Pat

[CSWolffe]

Did you use the premixed refractory mortar? Im building a small scale prototype(cant afford the real one yet, but want to practice with the materials), and here in Salt Lake the premixed product is much easier to get ahold of. It comes mixed VERY wet, and from my experience, wet cements are more likely to crack. More water in the mix means more volume, and when the mix dries(even though it is a chemical reaction, not just drying), water is forced out of the cement, and this means a loss of volume. this causes shrinking.
I think. Anyone more experienced here wana back me up?

[Westozchoppers]

Cheers for your input!
I,m not using a premix with water, rather a dry - premix. But what I've since learned in the forums , The're suggesting not to use an air-dry, mortar, for exactly the reasons I'm encountering !

Cheers
Pat

[Neil2]

All refractory mortars I know of will shrink somewhat. If you are spanning a joint of more than 1/4 inch or so expect cracks. If you want to span a larger joint - extend the mortar with a sharp sand (mortar sand or silica sand). For 1/2 inch span, go with a 1 to 1 ratio, 1 inch span try a 3 sand to 1 mortar mix ratio. If you have tapered joints, try having two mortars - "neat" for the tight part and "extended" for the wider part.

[Westozchoppers]

Cheers for the info Neil, ended up going with the fireclay , lime,sand and cement mix recomended by Forno Bravo, and now have completed the oven. Now been sitting for two weeks and about to start firing. Will post photo's from start to finish in the next week.

Cheers
Pat

[Nokka]

Hi Mark here from NSW Australia. I hope this is a suitable place to ask this question but...
I've gotten hold of some high temperature raku clay and intend to mix it with lime and sand for a dome mortar - what do you guys reckon??
ta