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Most marble slabs and marble tiles contain a polyester resin coating while most granite slabs and granite tiles contain epoxy
resin coatings. The polyester resin coatings and the epoxy resin coatings provide structural strength to the stone slabs and
prevent cracking, chipping and breakage during shipping and handling. These coatings also provide a glossy or satin surface
finish and help seal the stone surface.
The polyester resin used on marble slabs can discolor when exposed to temperatures gre ater than 150
o
F
and will structurally fail at temperatures above 230
o
F. The epoxy resin coating used on granite slabs are
resistant to discoloring and structural failures up to 3 50
o
F.Mendota does not assu me any liability for
discoloring, flaking or crackin g of marble or granite.
Temperatures on facings around Mendota Gas Fireplaces can reach 350
o
F
directly outside the top convection air gap and as high as 210
o
F at the
maximum allowed mantel protrusion level above the top convection air gap.
These temperatures can discolor polyester resin coated marble facings and
can cause the polyester resin coating to fail near the top convection air gap.
Mendota Fireplace cannot guarantee suitability of use of any
marble slabs or tiles that have a polyester resin coating applied
to it and cannot guarantee against discoloration or structural
failure of marble or polished stone facings that have a polyester
resin coating. Consult with your local stone supplier.
Prior to use of any marble, granite or polished stone facing material, especially white colored ones, run heat exposure tests on a
sample piece. Expose sample pieces to temperatures between 275
o
F and 350
o
F for a period of eight hours. Compare the heat
exposed sample to a control unheated piece and judge for color changes. Do not use if any color changes are evident.
Mendota recommends the use of honed bare marble and bare stone facing materials or honed ba re granite
and epoxy resin coated granite only.
Mendota cautions that due to natural structural defects that can exist within marble and stone pieces, cracking and/or flaking
of the marble or stone is possible and must be considered prior to selection and application around Mendota Fireplaces.
Mendota further cautions that proper adhesives be used to attach stone facings. Pay attention to the potential of off-gassing of
chemical vapors from mastic and other adhesives. Improper selection can lead to emission of chemicals with unwanted smells.
Suitable Backer Materials R-Ratings
R-Values of Common Backer Materials
Material
Thickness
R-Value
Mineral Fiber Board (Backer 160)
1/2"
1.270
Mineral Fiber Board (Backer 300)
1/2"
1.030
Ceramic Board (Rescor 360)
1/2"
1.110
Ceramic Board (Fiberfrax Duraboard LD)
1/2"
1.100
Common Brick
2-1/4"
0.450
Common Brick
4"
0.800
Gypsum or Plaster Board
1/2"
0.450
Cement Board (Durock Next Gen)
1/2"
0.390
Cement Board (Wonderboard)
1/2"
0.260
Cement Board (Hardibacker 500)
1/2"
0.200
Cement Board (Hardibacker)
1/4"
0.130
Figure 3-22 Top Air Gap
