FAQ - Updated July 2015

Q: After Heat Stop brand products are installed, how long should I wait before applying heat?
A: With regard to firebrick, clay flue lining or any of the Heat Stop refractory mortar or castable products, simply wait one day after all the masonry in the fireplace or chimney has been installed.

Q: What types of Heat Stop refractory products are available?
A: Heat Stop products are available in premix, dry mix and castable formulations. Each has its own specific application.

Q: Which Heat Stop product is most economical?
A: Heat Stop-50, the dry mix in the 50 lb. bag is the best value. A 50 lb. bag when mixed with water yields approximately 60 lbs. of mortar.

Q: Which of your products is the best choice as joint material for the installation of clay flue lining and firebrick?
A: Heat Stop II and Heat Stop 50 are the best refractory mortar products for installing clay flue lining and firebrick because they are completely non-water soluble in service after the initial set. They have an indefinite shelf life, and excellent drying characteristics no matter the humidity. These products are specified by NFPA-211 (National Fire Protection Association), in addition to meeting all local, regional and national building codes.

Q: What ASTM (American Society for Testing Materials) specifications are called for by local and national building codes for fireplace and chimney construction?
A: Building codes require refractory products that meet ASTM C-199 (medium duty) for fireplace and chimney construction. All Heat Stop products (including the castable products Insul Stick, Insul Cast and Heat Cast 40) meet or exceed this ASTM C-199 (medium duty) requirement. Firebrick must meet the ASTM C-27 requirement, and clay flue lining must meet the ASTM C-315 and ASTM C-1283 requirements. ASTM C-105 is a discontinued specification for fireclay and should NOT be used in fireplace and chimney construction. Fireclay mixes with regular mortar do not meet current building codes.

Q: Where are Heat Stop refractory products available?
A: The family of Heat Stop products can be found at many masonry supply yards or concrete block dealers across the USA. Heat Stop products are also available through our convenient authorized online dealer, www.MyBuildingSupplyStore.com.

Q: Which of your Heat Stop products may be colored?
A: Heat Stop II and Heat Stop 50 can be colored just like any mortar – just follow the color manufacturer’s instructions. Heat Cast 40, Insul Stick and Insul Cast can also be colored.

Q: How thick should the joints be when applying Heat Stop refractory mortar products?
A: A joint thickness of 1/16” to 1/8” is recommended for all Heat Stop refractory mortar products. If a thicker joint is required, we recommend the use of a dry mix - Heat Stop II or Heat Stop 50. For all of the refractory mortar products (Heat Stop Premix, Heat Stop II, Domestic Fireplace Mortar or Heat Stop 50), you will need approximately 50 lbs. of product to lay up 100 firebrick.

Q: How thick should Heat Stop castable products (Insul Stick, Insul Cast, and Heat Cast 40) be applied?
A: Insul Stick is usually applied as a parged product ¼” to ½” thick. It may be cast thicker. Insul Cast is typically cast 2” thick under the hearth, behind the firebox or over the oven dome. It may be cast thicker. Heat Cast 40 is typically cast 2” thick for replacement of firebrick in a firebox smoke chamber or oven. It may also be cast thicker.

Q: When should I use Heat Cast 40 and how should it be applied?
A: Heat Cast 40 is designed for casting shapes or is used anywhere instead of firebrick. It can also be used as a hearth in a heat chamber (e.g., bake ovens, fire pits, fire boxes). You will need 20 lbs. per square foot when applied 2” thick. There is 40 lb.in each bag.

Q: When should I use Insul Stick?
A: Insul Stick is also a castable restoration product but is more specifically used for parging over the firebrick in the smoke chamber or for exterior installations. It provides insulating value and strength, and can also be used to seal masonry wall penetrations. It can be cast, parged, or troweled and should be applied ¼” to ½” thick. You will need 2.5 lbs. per square foot when applied ½” thick. Insul Stick is packaged in 5 and 20 lb. pails.

Q: When should I select Insul Cast instead?
A: Insul Cast is a backup insulating product that can be applied under the hearth, behind the firebox, or over the dome in a fire pit or bake oven. It is ideal as an insulator for bread and pizza ovens, and should be applied with a minimum thickness of 2”. You will need 6 lbs. per square foot when applied 2” thick.

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