Old 02-15-2010, 05:32 AM
Join Date: Feb 2010
Location: Australia
Posts: 5
Default Refractory Motar Cracking

Hi Guys,

I am currently in the process of starting the second course of my oven.

I noticed that when I was constructing the opening that the motar was cracking after approximately 1 hour of setting.

I have tried soaking the bricks in water prior to laying, adding more water to the mix, but neither seem to work. The brick work in some instances does not stick at all.

I don't want to risk anything colapsing, so I would greatly appreciate any help regarding this.

Also, how long should I wait until removing the form I have used to construct the opening. Considering that the average temp here at the moment is 32 degrees celcius.


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Old 02-15-2010, 01:50 PM
3G_ 3G_ is offline
Join Date: Aug 2009
Location: Adelaide
Posts: 86
Default Re: Refractory Motar Cracking

Hi Ric

Try adding less water to the mortar, not more. I found a tiny hairline crack would develop during drying if the mortar is too moist. Also I kept the area that was drying damp with a wet towell during warm days to slow the drying down.
I found brickies sand shrinks alot compared to plastering sand, i wonder if a mix of 50/50 would shrink less. I didnt want to risk it on my dome but could be a good experiment if anyone has some firebricks left over!
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Old 02-15-2010, 02:39 PM
Tscarborough's Avatar
Il Pizzaiolo
Join Date: Oct 2009
Location: Ausitn
Posts: 3,291
Default Re: Refractory Motar Cracking

The larger the aggregate (and better graded), the less shrinkage cracks.
The dryer the mix, the less shrinkage cracks*.
The smaller the joints, the less shrinkage cracks.

So, if your joints are larger, use larger aggregate and less water. For thin joints, use more water and a finer aggregate.

*provided the units you are laying are not bone dry.
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Old 02-15-2010, 04:36 PM
Join Date: Jan 2010
Location: North Carilina
Posts: 1
Default Re: Refractory Motar Cracking

An old mason's trick we use here in the Carolinas is a small amount of dish soap in the mortar to slow curing.This does not affect the strength or color.
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Old 02-16-2010, 05:07 AM
Join Date: Feb 2010
Location: Australia
Posts: 5
Default Re: Refractory Motar Cracking

Hi Guys,

Thanks for the kind reply.

I am using a motar mix which requires only the addition of water.

I will try firstly adding less water and wetting down the bricks.

Would you suggest utilising the same refactory motar to coat the bricks, 1 inch, as illustrated in the pompei oven instructions before applying the insulation. My only worry is that I will still get te same hairline fractures I have been getting in the brickwork.


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