Q: Our neighbor made a nice fire ring out of those interlocking landscaping blocks to match his landscaping. It’s pretty, but I was wondering (since a rock burst in our old fire ring) can those blocks be used for that? Or might they explode? It looks beautiful — I just want to know how far back to sit.
— Pamela Flemming, Asheville, N.C.
A: Most landscaping blocks are made of pre-cast concrete. Whether or not they will explode depends on how porous they are, how wet they are and how hot they get.
Trapped moisture will turn into steam and if the concrete is unable to expel the trapped vapors, it will explode. The same thing very likely happened to your fire ring rock. Sedimentary rocks, especially, contain pockets of moisture.
Most of the time, concrete has excellent fire resistance, so don’t worry too much about your neighbor's fire ring.
If it hasn't exploded yet, it probably won't. If you're designing your own fire ring, however, use firebricks. Furnaces and kilns are lined with these and they’re designed to withstand intense heat.