Chemical Sealants Replace Traditional Gaskets

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Written By Jim J Neal

Chemical and gasket sealants have replaced many traditional gaskets and seals in our cars and homes. Here’s what you need to know.

In the 1970s, room temperature vulcanizing (RTV) gasket makers began replacing time-honored pre-cut gaskets in automobiles. At the time, the pros who made their living repairing cars had two thoughts on these chemical gaskets: This stuff is great, or this stuff won’t work. Both were right. Read on to see why.

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Traditional Gaskets

Gaskets (and seals) are asked to do a lot. Under harsh conditions, they keep vapors, gases and fluids from leaking between two imperfect surfaces, while keeping out impurities. Gaskets must:

  • Withstand extreme temperature fluctuations and pressures;
  • Be corrosion resistant to additives in oils, solvents and other fluids;
  • Move and flex with parts made from unlike materials that expand and contract at different rates;
  • Resist weathering under external environmental conditions, such as road salts.

Traditional pre-cut gaskets (AKA compression gaskets) provide a mechanical seal between two mating surfaces. Made from cork, rubber, synthetic blends and various metals, these gaskets have been around forever, filling the not-so-perfect gap between those surfaces.

Gasket sealers and dressings, available for decades, hold gaskets in place during positioning and assembly. These products do not replace traditional gaskets

Chemical Gasket Makers and Sealants

Many components in today’s vehicles are machined to incredibly close tolerances. This allows manufacturers to move from pre-made, custom-cut gaskets to chemical form-in-place gasket makers and sealants to help prevent and eliminate leaks.

Chemical gasket sealants use a base material (rubber, silicone or other compounds) that’s blended with a plasticizer (for flexibility), fillers (for specific applications) and a curing or drying agent. They’re also an adhesive that ensures a foolproof, leakproof seal.

Although they look like gel or caulk, form-in-place gasket makers are a liquid. That’s why RTV fits exactly to a part’s shape and form, completely filling surface imperfections and forming a leakproof barrier.

The key to a leakproof gasket/seal is proper surface preparation, allowing time for the gasket maker to fully cure. Without following those two steps, RTV will quickly fail.

Why Use Chemical Sealants?


  • Works in most applications;
  • Convenient and easy to store in the garage;
  • Works on imperfect surfaces;
  • Provides an effective long-lasting seal;
  • Less expensive than pre-cut gaskets.


  • Can be messy;
  • Difficult to remove;
  • Needs cure time.

The first silicone-based gasket makers worked great, as the pros hoped. As long as both parts were clean and dry, you coated one part with gasket maker and bolted them together. By the time you put your tools away, RTV would cure and you could add fluids, enabling you to quickly finish the job.

Yet these same silicone gasket makers ruined oxygen and other computer sensors. New chemical formulas have made form-in-place gasket makers trickier to apply. They can take up to 24 hours to cure before you can add fluids or solvents, which the pros don’t like.

Recently, Permatex, an industry leader in automotive chemical maintenance and repair solutions, developed form-in-place gasket makers they claim are road-ready in one minute.

Different Type Of Form-In-Place Gasket Makers for Different Applications

Still chemical based but now O2 sensor safe, RTVs have different characteristics for specific applications. To avoid leaks, choose the right RTV for the job.

  • For stamped metal parts with flanges (lips), or parts made from composite materials (oil and transmission pans, valve covers and timing covers), choose a flexible, oil-resistant form-in-place gasket maker that’s unaffected by oil additives and remains flexible under all temperature conditions.
  • For more precisely machine parts, including water pumps and thermostat housings, choose a vibration-resistant form-in-place gasket maker that stays rigid and withstands vibrations under high torque loads. This type of gasket maker is also recommended to fill and seal the gap where a cut-gasket and rubber seal butt up against each other.
  • When working in high temperature environments found in four-cylinder engines, exhaust systems, headers and manifolds, turbochargers or slip-fit exhaust systems, choose a high temperature gasket maker resistant to aging, weathering, shrinking and cracking.
  • Differential (gear) oil produces caustic acids that break down normal RTV. Look for a gasket maker produced specially for differential (front and rear) covers and transfer cases.
  • Coolants have evolved over the years. Manufacturers recommend form-in-place gasket makers that don’t contain properties that interact with their specific coolant and cause premature coolant system, radiator and heater core failure. Before making thermostat, water pump and other cooling system repairs, check your owner’s manual to identify the type of coolant your vehicle uses.
  • Anaerobic gasket makers and sealants work differently than silicone-based sealers. Anaerobic gasket makers and sealants dry in the absence of air. They seal rigid, machined surfaces with extremely close tolerances of less than .001 inch. (A human hair is about .003 inch.)

Thread Lockers vs. Thread Sealers

Chemical thread lockers are liquid adhesives that, when fully cured, “lock” mechanical fasteners together, preventing them from vibrating loose. Depending on the application, thread lock comes in different strength formulas: low, medium and permanent.

Although hand tools can remove fasteners sealed with permanent thread lock, choose wisely. Especially if you plan to ever disassembly whatever parts you assemble using thread locker.

Thread sealers lubricate, seal and protect pipe threads and compression fittings from damaging liquids and gasses. These sealers work better than Teflon tape or pipe dope to prevent liquid and vapor leaks in pipe fittings and joints.

Bob LacivitaBob Lacivita

Bob Lacivita
Bob Lacivita is an award-winning ASE and General Motors auto technician, educator and freelance writer who has written about DYI car repairs and vehicle maintenance topics. His work has been featured in The Family Handyman, a Reader’s Digest book and Classic Bike Rider magazine. He has been a career and technical educator for 25 years teaching automotive technology, as well as writing state, federal and organizational foundation grants. He also helped design a unique curriculum delivery model that integrates rigorous, relevant academic standards seamlessly into career and technical education.

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