Mortar is flaking

[JDT]

Hello everyone,

I recently finish building a brick pizza oven. Some of the mortar is flaking. When I rub it with my hands or a tool it turns to a powder. The mortar I used was heat stop 50. The oven is only two weeks old and I didn’t even start a fire in it yet. Not all of the mortar joints are like this some are solid. What gives?
Thanks for any help. I’m torn.

[JDT]

[Hattori-Hanzo]

Could it be the mortar has dried to quickly in some parts?

As long as the mortar underneath is intact it shouldn't be a huge problem.

[Kvanbael]

I wonder about the color variation. It seems related. Could it be that while the mortar was still soft, you cleaned it with dirty water (eg. containing saw-dust from the bricks?)
In that case, it's just the outer layer.

I'm just guessing.

[JDT]

Thanks guys for your replies. I contacted the manufacturer of No Heat and it turns out that the maximum joint thickness is 1/2”. I have 1”. This is causing the joint to turn to a powder when rubbed.

Joe