Measuring is Key - Determining How Much Heat Stop Product You Need

December 1st, 2015

Whether it's building a bake oven, repairing a chimney or working on fire pits, fireplaces, furnaces or kilns, using the right amount of Heat Stop product is critical. Heat Stop is an important component of many successful projects, but using the product properly is essential to achieving the desired result — and in obtaining the best product performance.

Successful mortar projects rely on successful product use.

In 40 years of using Heat Stop products, I've had many questions about product measuring and use - here are my top four tips and lessons for measuring and using Heat Stop products in your projects:

1. No two projects are the same. There are several factors that affect the amount of Heat Stop product needed for your project. These of course include the type of project being done, joint mortar thickness used, and waste, among other factors. But most importantly - each of these factors varies from person to person. It's important to understand the specifics of your own project and habits to determine the steps and use that will lead you to success.

2. Understanding the basics of product use is key. Before you can consider the variables affecting your project, you should understand the basics. Here is a "quick guide" to Heat Stop measurement basics:

In general, Heat Stop premix and Domestic Fireplace Mortar premix, which are refractory mortar products, should be applied with a maximum joint thickness of 1/16-1/8". Heat Stop II and Heat Stop 50, which are dry refractory mortar products, should be applied with a minimum thickness of 1/16-1/8", and may be applied in thicker joints as desired. For each of these products, installers will need approximately 50 lbs. of product to lay up 100 firebrick (assuming the joint thickness is 1/16-1/8").

Heat Cast 40 should be applied 2" thick when used to cast shapes or installed as a hearth in a heat chamber. Installers will need approximately 20 lbs. per square foot when applied 2" thick.

Insul Stick, which is used to parge over firebrick in a smoke chamber or for exterior applications, should be applied 1/4 to 1/2" thick. Installers will need approximately 2.5 lbs. per square foot when applied 1/2" thick.

Finally, Insul Cast, which is a backup insulating product that can be applied under the hearth or over the dome in a fire pit or bake oven, should be applied with a minimum thickness of 2". Installers will need approximately 6 lbs. of product per square foot when applied 2" thick.

3. Pay attention to the details. While following the guidelines above is the best way to ensure you're using the correct amount of Heat Stop product, paying attention to smaller steps and details is also important. Heat Stop pre-mix products can be used as is, but we recommend installers give the product a thorough mix or stir before using. Depending on your specific needs or preferences, you may want to add a little water to thin the product consistency, but you'll then need to mix the product thoroughly again before using.

4. Be ready for extenuating circumstances. Refractory mortar products may take longer to dry if the joints are thicker than 1/8", and/or if conditions are extremely humid (which occurs in certain climates or after rainfall in many areas). To enhance the drying in such conditions, open the damper, place a fan in front of it, or use other means to get some air or heat passing by the installation.

Consider and follow these tips, and you'll be well on your way toward a successful project!

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