Cracks in the refractory mortar after drying perhaps due to high humidity?

[leslys]

Thank you James for the reply about the gas line. We will not install one.

We put the refractory mortar about 10 days back on our Casa2G 110 and now after drying we see some cracks appearing on the surface of the mortar (see pictures attached).

Is it possible that its due to the humidity and temperature?
Its been very humid here in Portland - some days >95%, rainy (whats new) and quite cool (50-60 deg F).

How should we rectify this?

Lesly

[Tscarborough]

Those are shrinkage cracks. For an application that thick you need more of a larger aggregate and less water.

[Tscarborough]

To rectify it, you can remove it, and should if you are planning an igloo style oven, or leave it, parge it with a proper mix, and continue with your house.

[leslys]

Originally Posted by Tscarborough

Those are shrinkage cracks. For an application that thick you need more of a larger aggregate and less water.

Hmmm. We used the "Sairset" refractory mortar that came with the Casa2G kit. It was already pre-mixed and we stirred it up to homogenize the mix before putting it on.

Lesly

[RTflorida]

The Casa kit comes with mortar? Not listed as one of the provided components.

Sairset (wet mortar in a bucket)? The wet mortars are generally considered a no-no for oven applications, use only if there is nothing else available.

It it were me, I would be asking where the hell is the DRY FB mortar - REFMIX, as it used to be called.

Just my opinion, I would remove it and get the right stuff. The wet mortars vary so much from manufacturer to manufacturer and have precise curing and temperature schedules, not to mention - you can't get it wet once it is curred......Oh, it also cracks when applied too thick - as you have found. I'd be pissed if I were sent that stuff. Keep in mind, I am an igloo style person; if you are building an enclosure just put a parge coat of the right material and move forward with insulation and the enclosure.......keep it dry in the mean time, rain may wash it away.


RT

[james]

Hi Leslys,

Sairset is a well respected refractory mortar -- it cures to the same hardness and refractory characteristics as cast Casa2G dome (they were designed to work together). It looks like it might be a little thick, which is the source of the air drying cracks. It will cure when you go through the curing cycle for the oven dome, and the cracks won't be problem.

One important thing to note is that the Casa2G has interlocking dome pieces, so that the dome assembles very tightly. The mortar seals the outside of the joint, and the basic assembly is much more secure than a butt joint or a joint between two bricks.

If you have any additional mortar, you might want to close in the surface cracks, but other than that, you are in good shape. It looks good.

James

[100million]

Lesly

I TOTAL AGREE WITH JAMES but if you want to go the extra mile do this.... and it is pretty much what james said.....


I think I would skim Coat what you have and make sure and pack the cracks as you skim coat it. Once you have dry refractory mortar with none ot little cracks I would let it dry for about a week under a tent and covered... then I would start the slow firing process that James talks about .....I would do this with out the Insulation on this is so u can see what kind of results u have with the mortar... after curing the oven and you like the results I would insultate it and the complete the stucco process....I really dont think you will have a problem becasue this is a modular unit and not a brick unit.

[leslys]

Hi,

Thanks for the ideas on repairing the cracks. We went with a fireplace caulk (Rutland #63 Black) which is rated up to 2K deg F. The nice thing about the caulk is that you can work it into the cracks with your fingers and it dries quickly (see picture).

So, now we will start the slow cure (before we put the blanket insulation) and repair any cracks that appear. Also, the temperature in Portland is now in the 70s and its stopped raining.

In the mean time, my husband built the decorative brick arch.

Lesly

[100million]

I really think you are golden....... But as I said I would Cure your oven and cook in it before you but the insulation on and the reason is that what ever you get with the insulation off you get with the insulation and stucco on.......

Enjoy

[Neil2]

Mortars of any kind are designed to be used in joints. If used in thicker applications (over 1/4 inch or so), you can avoid / minimize shrinkage cracks by extending the mortar with sand (silica or mortar sand). For example for a 1/2 inch thick layer I would mix it 1:1 with sand.