Replacing loose stones on fireplace and foundation
Our fireplace is made of cinder blocks which are covered with real, irregularly shaped stones. Some of the stones have “popped” out of the mortar bed which held them in place. The same happened with stones on our foundation wall. The only difference is that the foundation is made of poured concrete as opposed to cinder block, and the foundation problem is on the outside. Some of the stones are more than a foot square and about two inches thick, so they can be heavy. Also, our house is located in central New York, where it can get really cold in winters. If it helps, most of the “popped” stones are close to ground level.
I want to reattach the stones, but have been unable to find a suitable method for doing so. Any suggestions would be appreciated.
Replies
Is the mortar bed behind the stones still firmly attached to whatever surface is behind it? Are there visible cracks in the mortar bed?
In some places, particularly on the foundation wall, some of the mortar has crumbled. However, there are no visible cracks on the underlying wall. In the case of the fireplace, the mortar is still intact, but the stones have fallen out.
The thing is, you can have several issues. The failures could be due to simple poor adhesion -- the wrong mortar for the type of stone, or the mortar somehow not mixed right. The exterior failures could be due to frost action. Exterior or interior you could have problems with thermal stresses. Or you could have small cracks in the foundation that are creating the stress.
Thanks for the reply.
There are no cracks in the foundation. I scraped off the bad mortar down to the foundation and saw no cracks. Also, there are no visible cracks on the inside of the foundation wall. I believe that the stones got loose because a concrete slab had been poured too close to the foundation wall. This slab heaves up to two inches during the winter, applying upward pressure on the stones. I have since corrected the slab issue so that the slab cannot come in contact with the stones. I need to know what kind of adhesive I need to use to reattach the stones.
I believe that the fireplace problem is due to a bad selection or mixture of mortar.
Well, for the inside stones, if the mortar is still mostly in place, you could probably get away with siliconing them back into place.
Thinset mortar would probably work for reattaching the stones, but I don't believe it's the most "appropriate" choice (ie, the choice least likely to cause the experts here to get their shorts in a bunch).
So far, it sounds to me like you have moisture issues to resolve. Ground water is draining to the dfoundation or roof runoff is hitting and splashing.
Then the mortar with water in it is freezing to destroy the bond.
So until you solve the moisture problem, it can be a waste of time to fix the stone work
A slab does not heave up two inches unless there are water issues in the soil under it.
A slab on expansive clay CAN heave two inches, without there being anything vaguely resembling a "water issue". And he implied (but didn't state clearly) that this was an outside slab, where frost can easily cause a 2" heave.