Firebox question - InspectionNews

wayne soper · #1 (**permalink**) 10-02-2009, 03:59 PM

First time i have seen this, what appears to be Belgian block of the driveway variety installed in a firebox. Anyone seen this before?

wayne soper · #2 (**permalink**) 10-02-2009, 09:19 PM

Bob, did you see this? Or ever see this?

Bob Harper · #3 (**permalink**) 10-03-2009, 09:06 AM

The IRC and NFPA 211 both recognize stone as a "solid masonry unit" and are therefore acceptable firebox lining materials. If your AHJ "approves" this stone as an acceptable lining material as a subsitute for firebrick, then the total firebox wall thickness can be reduced to 8". Otherwise, the wall thickness would have to be at least 10". Regardless, the firebox should ba laid with a medium duty refractory mortar conforming to ASTM C-199.

Yes, I've seen Belgian block, ballast stone, soapstone, brick pavers---you name it.

HTH,
Bob

Matt Fellman · #4 (**permalink**) 10-03-2009, 10:15 AM

Good info... thanks Bob. Assuming the mortar conforms to the spec you give is there any maximum on the size of the joints?

Bob Harper · #5 (**permalink**) 10-03-2009, 12:00 PM

Per the 2009 IRC, 1/4" max. btw firebricks. It does not provide a specification for stone since this would be impractical due to stone's infinitely variable edge profiles.

The intent, regardless whether fireboxes or flue tiles is to use the minimum mortar necessary to bed and bond the masonry units--a novel concept to most masons. The BIA technical notes and other sources have more info. on what constitutes good masonry practice. The BIA has produced the Masonry Fireplace and Chimney Handbook, 3rd ed., which would be one decent Beginner's reference book along with the current edition of your codes and NFPA 211. However, to make sense of it all, I highly recommend you attend the FIRE course, which will also shed light on many other aspects of the home, documentation, liability, and inspection skills.

Good point Matt,
Bob

wayne soper · #6 (**permalink**) 10-03-2009, 12:07 PM

Thankyou Bob!! Good info, Had not seen this before or mabey just didn't seeeeee it before YUKYUKYUK