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What is High Temperature Caulk?

By Lori Kilchermann
Updated May 16, 2024
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A high temperature caulk is a sealant often used in household and industrial heating systems as well as high temperature liquid pipelines. Created with heat-resistant silicone, the caulk is applied in the same manner as other typical caulk products. Once cured, it commonly dries to a pliable consistency while remaining flexible for long periods of time. Most types of high temperature caulk adhere firmly to metal, glass, ceramic and other commonly-found surfaces in the home and the workplace. The caulk also will commonly withstand temperatures from -80°F to 550°F (-62°C to 288°C) and will also survive intermittent exposure to temperature as high as 650°F (343°C).

When installing a new gas fireplace or furnace in a home, it is wise for people to use high temperature caulk in the joints of the flue pipe to reduce the chance of toxic fumes leaking into the living area of the structure. Besides sealing the exhaust fumes in the chimney, the caulk will also prevent flames from escaping through any joints or gaps in the pipe, which could lead to a fire within the structure's walls. Access doors on furnaces, expansion joints and damper seals are also key areas to apply the caulk. Within the home, oven doors and fireplace glass doors are also easily sealed against leaks with a thin bead of the caulk.

Industrial uses are gaskets in high temperature liquid pipelines and valves, as well as boiler lines and heat exchanging units. In some air compressor applications, the temperature of the compressed air line from the compressor to the holding tank warrants a thin coating of the high temperature sealant to prevent leaks. Using a typical caulk or sealant in this application could result in a premature failure and loss of air pressure, which could cause unproductive downtime for the workers. Most caulking will not adhere to galvanized metal, so it is important to understand the surface of the intended application.

High temperature caulk does not imply that the material is fireproof. Most types of this sealant will not withstand direct contact with fire or flame. The caulk is also not completely waterproof and will not cure underwater in most cases. The caulking does, however, require some atmospheric moisture to cure properly so it should not be used in areas that will be totally sealed off during the curing process. It is also important that the caulk not be subjected to continued oil, petroleum products or solvent in any application, or its effectiveness will be cut short.

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Discussion Comments
By indigomoth — On Jan 12, 2013

@clintflint - I'm not sure if it would, really, because most of the time if you're making something that requires hot materials, it's going to be using something like molten glass or metal and I wouldn't risk using those in high temperature caulking molds. Even if the temperature wasn't an issue, it just wouldn't be safe, it would be too easy to spill or make a mistake.

If you're at the point where you're eager to try those kinds of construction methods, you're better off using the tried and true techniques, like the lost wax method or glass kiln techniques.

By clintflint — On Jan 11, 2013

I've never actually used this stuff as caulk but it makes a really good mold if you are interested in making crafts that require that kind of thing. I usually use it for materials that don't require heating, but I wonder if specifically using the high temperature silicone would help with materials that do need to be heated up. It would probably be a good way to help prevent fumes and things.

There are a lot of really good recipes online for this kind of thing, but basically all you need to do is make a model from Plasticine and then cover it in the caulk, wait until it dries and then use the resulting shape (after removing the Plasticine) for your model.

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