Building a Masonry Firebox with Refractory Mortar Cary NC

Many fireplace masons in Cary 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'.

Stonebridge Yards
(919) 267-5121
109 Parkcanyon Ln
Cary, NC
 
Carolina Stone Setting
(919) 467-4693
603 Page St
Cary, NC
 
Byrd & Goff Construction Co
(919) 854-0800
202 Travis Park
Cary, NC
 
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(919) 469-4522
101 Brady Ct Ste A
Cary, NC
 
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(919) 906-0741
11457 Claybank Place
Raleigh, NC
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Residential Construction Services Inc
(919) 467-4335
118 E State Ave
Cary, NC
 
Vertical Walls
(919) 468-0313
104 Woodwinds Industrial Ct Ste D
Cary, NC
 
Bill Ibison Stone Company Llc
(919) 851-3835
2509 Piney Plains Rd
Cary, NC
 
American Chimney Sweep Co A
(919) 467-5088
303 Trappers Run Dr
Cary, NC
 
Moore'S Masonry Contracting
(919) 361-3060
5505 Kemmont Dr
Durham, NC
 

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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