You can put stone over a brick fireplace, but you need to make sure that the mortar between the bricks is in good condition and that the bricks are properly sealed so that moisture doesn't seep into them. If the mortar is in good condition and the bricks are sealed, then you should be able to put stone over them without any problems. However, if there is any damage to the mortar or if the bricks aren't sealed properly, then there is a risk that water will get into the bricks and cause them to deteriorate. In that case, it would be better to either repair or replace the fireplace before putting stone over it.

It is possible to put stone over a brick fireplace, but it is not recommended. The weight of the stone could cause the bricks to crumble, and it is also not as aesthetically pleasing. A better option would be to have the stone masonry contractor come in and remove the bricks and replace them with a stone veneer.