Adding a little fire clay to mortar?

[Squirt Reynolds]

Hey Gang,

about to start laying floor, and I chose a little red fire lay to mix with sand for the initial base.
but I was thinking, I like the red colour, and can I add a bit to my bagged fire lay I bought. Just for a little tint or would that compromise the formula in the bag?
im assuming yes, but not sure if anyone tried it…

thanks

[david s]

It shouldn't matter, but not to exceed 10% by volume in any mix.

Here's a great study of the effects of clay in mortar, done way back in 1909

[Squirt Reynolds]

Very useful. Thanks