How To Use Furnace Cement (Quickly & Easily!)

Upgraded Home Team
by Upgraded Home Team

Over time, your household appliances such as furnaces and boilers will develop standard wear and tear. Cement can be used to fix cracks or hold together the appliance’s pre-existing cement. Furnace cement is a ready-to-mix material intended for use in high-temperature environments.

It is made up of minerals that can withstand stress from high temperatures. Using furnace quality cement over regular cement will improve the lifespan of your furnace. So, how do you use furnace cement?

To use furnace cement on any high-temperature appliance, the entire surface must be cleaned thoroughly. Be sure the appliance surface is cool, and the unit is off. You may apply the cement with a caulking gun in the same manner as welding beads to the cracked area. To ensure stability, add another coat and spread with a putty knife or a similar tool.

What is Furnace Cement?

Another term for furnace cement is refractory cement. This is the cement that holds together refractory materials.

Refractory materials are materials that are resistant to damage from heat and chemicals. These substances are frequently used in furnaces due to their strength at high temperatures. Furnace cement is not just for furnaces; it is versatile. It is used to fill in cracks and crevices on anything that uses high heat.

It could be a furnace or another home appliance that operates at high temperatures. Some brands advertise their cement as working for boilers, fireboxes, kilns, chimneys, and other high heat appliances. Find out how to quiet a noisy furnace blower.

Why Should You Use Furnace Cement?

The temperature variations in a furnace cause its components to expand when hot and contract when cool. This stress can wear on the cement that binds the structure of your furnace together.

Regular cement does not have the ability to withstand volatile temperature changes. Though it will expand in the heat, it often fails to properly contract, breaking and cracking in the process.

Furnace or refractory cement is strong enough to maintain the structure of your furnace. It is stable enough to withstand thermodynamic stress. Furnace cement is superior to regular cement in this regard because of its ingredients. These high-temperature cement use minerals such as aluminum oxide and silicates. They have properties that work well in high temperatures.

Furnace and refractory cement have temperature limits ranging from 1,000 to 2,900 degrees Fahrenheit. It depends on the brand and product.

Choosing to use furnace cement can save you money as well. By using the proper material, you reduce the risk of damage caused by temperature stress. Maintenance costs also decrease, and the lifespan of your appliance increases.

Tools Needed to Apply Furnace Cement

Applying furnace cement is a straightforward process that requires few extra tools. Aside from the cement, you will need an application tool. There are several options, such as a caulking gun, a putty knife, or a trowel. Caulking guns are intended for filling openings up to 1/8 inch. If the gap or joint being filled is larger, the latter tools will be necessary. If you do not already own one of these tools, they can be purchased at a local hardware store or at the time you pick up the cement.

How to Apply Furnace Cement

Listed are the steps to properly place furnace cement in the cracks and how to spread it.

Step 1: Clean the Area Thoroughly

Clean the area where you plan to apply cement using water. It includes removing old, chipping cement.

Step 2: Put a Thin Layer of Cement in the Cracks

Apply the cement in a thin layer, pressing it into the cracks and openings. If using a caulking gun, squeeze the trigger at a consistent pressure and hold the gun at a 45-degree angle when filling the cracks.

Step 3: Put the Second Layer of Cement

Apply a second layer, this time liberally, and smooth the cement with your tool.

Step 4: Spread the Cement Evenly

Using your tool, smooth the edges as well.

Step 5: Remove Excess Cement

Use a cloth, soap, and water to remove any extra cement from the surface.

Step 6: Let the Cement Dry

Be sure not to apply cement while the furnace is hot. Let your cement air dry according to the directions on the label for about one hour.

Step 7: Test Your Work

After cement application, start your furnace or appliance on the lowest heat and gradually raise it. It will solidify the cement, curing it. This process should take 3 to 4 hours but check the label of your cement as some take up to 6 hours to completely cure.

Addition Notes to Steps

When gradually re-heating the furnace after cement application, do not exceed the heat cure temperature. This temperature should be listed on the cement product label. It should be the maximum heat that your furnace reaches the first time using it after application.

Usually, this value is around 500 degrees Fahrenheit. Gradually during the cement removes pores from the material and allows for consistent curing throughout.

This process only needs to occur once. After you have completed your initial curing process, you can begin to use your furnace or appliance as you normally would.

Choosing a Furnace Cement

Most furnace cement comes premixed or ready to mix. Premixed is the most convenient option available for purchase as it saves you time from having to mix the cement yourself. Before you go to the store, make sure you know the parameters of your appliances.

Think about the following questions:

  • What is the maximum temperature your furnace or appliance reaches?
  • How often is your appliance at this temperature, or what temperature is it most consistently?

Different types of cement have different heat resistance. Therefore, it is imperative to select the right one.

If you choose one with a lower heat resistance than the heat of your appliance, you will get cracks in the cement. It can damage your work and require you to repeat the process. Be sure to carefully read the label before purchasing.

Look at the fine print as well. OSHA, the Occupational Safety & Health Administration, has requirements for the level of silica in cement. Breathing in tiny silica particles can damage your lungs and cause cancer or kidney disease. Make sure the product you choose meets or exceeds OSHA standards for hazardous material. Furnace cement should also be free of oils and asbestos as these pose health concerns as well.

If your home is older than 1980, check with an asbestos expert to ensure that your furnace is not contaminated. The application process of cement can irritate asbestos fibers, which are toxic to the human body.

Additional Information on Furnace Cement

Cement is an alkaline material. It is important to clean surfaces and avoid contact with any acidic material during application.

Additionally, materials such as oil, paint, and grease can interact with the cement and release toxic fumes. For tough buildup, you may need to use a stiff brush to remove residue.

Clean-up is essential to the application of furnace cement. Once the cement is cured, it cannot be removed. As mentioned before, make sure not to use any acid-based cleaners, or they will interact with the cement.

As you can see, applying furnace cement does not require an expert. The process is easy, and there are many cement options to choose from.

If you catch the cracks early, they will be easy to repair. Sealing cracks and broken concrete on your furnace early on will prevent further damage from occurring. It will increase the lifespan of your appliance, allowing for many more years of service.

Related Questions

Can I apply furnace cement outdoors?

Yes, but if you need to use the cement outside to seal a grill or outside boiler, choose a non-water-soluble mortar. Also, note that the freezing point for a lot of furnace cement is 10 degrees Fahrenheit when uncured.Check to make sure your cement is graded for what you need. If you are using it outside on a high heat surface, you may need a special type. Most brands suggest not exposing the cement to weather as it may damage it.It is imperative during the application process as temperature regulation and time to dry are essential factors.

Does furnace cement work on all heating systems?

Furnace cement works to seal any furnace or high-temperature appliances like boilers, furnaces, or stoves. It is safe to use on a variety of systems, including oil, gas, woodburning, and coal systems.

How do you store leftover concrete?

Leftover concrete should be stored in an airtight container. Most furnace cement comes in resealable plastic tubs or buckets because the material is often premixed. These containers should be stored in a dry place, ideally with low humidity. If the cement is exposed to air, it will age faster, decreasing its shelf life for later use.If you wish to dispose of your leftover cement, first let it dry. You cannot throw out wet cement. Once it is dry, take it to a local recycling or waste center.

Related Articles

Upgraded Home Team
Upgraded Home Team

We are a team of passionate homeowners, home improvement pros, and DIY enthusiasts who enjoy sharing home improvement, housekeeping, decorating, and more with other homeowners! Whether you're looking for a step-by-step guide on fixing an appliance or the cost of installing a fence, we've here to help.

More by Upgraded Home Team