Building a Masonry Firebox with Refractory Mortar Warren MI

Many fireplace masons in Warren are not familiar with refractory mortar, or they confuse the product with fireclay mortar. Masonry fireboxes are often laid in ordinary portland cement mortar, sometimes with a little extra cement or some fireclay added to make the mixture 'fireclay mortar'.

Builder Mike
(586) 446-4640
11193 E 13 Mile Rd
Warren, MI
 
Debacker & Sons
(586) 775-8700
21750 Schmeman Ave
Warren, MI
 
Marcel Construction
(586) 757-8392
26242 Grobbel Ave
Warren, MI
 
K C Masonry And Concrete Impressions
(586) 795-9401
6345 Product Dr
Sterling Heights, MI
 
Stone Doctor
(248) 698-3161
White Lake Twp
Sterling Heights, MI
 
A Ct
(586) 772-1660
25530 SchoenheRR Rd
Warren, MI
 
Expert Construction Co
(586) 293-0920
31056 Shawn Dr
Warren, MI
 
Silverado Construction Inc
(586) 758-2600
2055 E 9 Mile Rd
Warren, MI
 
Unique Pools & Masonry
(586) 610-9939
33567 Ryan Rd
Sterling Heights, MI
 
Giannola Masonry Co
(586) 792-2070
35086 Cordelia St
Clinton Township, MI
 

Building a Masonry Firebox with Refractory Mortar

Provided By:

Source: MASONRY CONSTRUCTION MAGAZINE
Publication date: October 1, 2006

By Bob Rucker

Many fireplace masons are not familiar with refractory mortar, or they confuse the product with fireclay mortar. Masonry fireboxes are often laid in ordinary portland cement mortar, sometimes with a little extra cement or some fireclay added to make the mixture “fireclay mortar.”

This approach is not surprising since the major building codes have been unclear, inconsistent, or silent on the subject. The ICC codes – recently adopted in many states –require refractory mortar for the construction of fireboxes, smoke chambers, and flue linings, but a short while ago only the NFPA 211 code called for “refractory mortar (ASTM C199, medium duty).” The BOCA code required “medium-duty fireclay mortar,” the UBC just required that the “joints in firebrick shall not exceed ¼ in.,” and the CABO One and Two Family Dwelling Code did not specify the type of mortar or size of joint to be used.

The problem with using ordinary mortar is that portland cement can't take the heat. Oddly, portland cement retains its strength up to fairly high temperatures, but deteriorates as it cools down through about 600° F. Eventually all that is left of the mortar is the sand and fireclay, with no cement binder. The mortar has no strength and easily falls out of the joints, especially if they are wide.

Refractory mortar, on the other...

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