A few days ago, friends on a Facebook group page were discussing the best way to create a substitute gasket for an antique tractor. All manner of methods and materials were cussed and discussed.
Overbay andy
Extension Agent / Virginia Cooperative Extension
Andy Overbay holds a Ph.D. in ag education and has 40+ years of dairy and farming experience.

One material that brought back memories of my dad was gasket paper. Dad had rolls of gasket paper from which he would scribe out shapes and carefully cut out duplicate gaskets for machinery.

While gasket paper is less commonly used now, there are no shortage of choices when it comes to gasket makers and sealants. In fact, the plethora of “gasket goop” choices can be a problem if you make the wrong choice. Adding to this problem, if you make the wrong selection, cleaning the surface of the parts may be the worst part of correcting the situation.

Like anything else, doing your research and asking the opinion of trusted and experienced sources is always a good first step. To be honest, I had to do a bit of research just to be sure I covered as many different types of sealants as possible. I also will share that even my dad, with his decades of shop experience, made some bad decisions on gasket sealants. One choice, frankly, contributed to his fatal shop accident. More on that as we move along.

So let’s dive into different sealants and their appropriate use. Often referred to as “Indian Head” after a popular product, shellac is ideal for thin paper or cardboard gaskets used in low-temperature and low-pressure environments. What is low temperature? 300ºF to 350ºF. Shellac is resistant to engine fluids, so it is commonly used on thermostats, timing cover and differential cover gaskets. Shellac is not resistant to many shop solvents, which is good because it can be a bear to clean off parts.


High tack is a non-drying cousin of shellac that can sustain temperatures of up to 500ºF. It will remain tacky and is resistant to kerosene, propane and diesel fuels.

The family of “Form-A-Gasket” sealers is substantial and falls into three main groups. No. 1 is fast-drying and fast-hardening. No. 2 is slow-drying and non-hardening, and No. 3 (also known as aviation sealant) is brushable, slow-drying and non-hardening. All three types are rated to withstand temperatures of 400ºF, but there are differences. No. 1 is usually used on repairs you expect to never have to deal with again, like engine freeze plugs or metal-to-metal flanges. No. 2 works best on cork or paper gaskets, especially if there is a possibility of the need to remove parts and reseal them. Likewise, No. 3 is easier to clean and reseal but, because it is brushable, you can lay down a thin coating to seal highly machined surfaces with less mess.

RTV silicone sealers come in many colors and delivery formulas. RTV stands for “room-temperature volatile,” and they are effective as a gasket sealer or as a gasket by itself. Applications from different companies are usually exhibited by colors of the formula, but a word to the wise: Colors of these sealers are not universal. An orange or red sealer might be good for applications up to 650ºF for one manufacturer, but another brand may not have near that capability.

Like oils, RTVs are available in conventional and “ultra” products. The difference is that ultra products are sensor-safe and may be most appropriate for today’s electronically controlled machinery.

Hylomar is relatively new in the public sector but has been used by machinery manufacturers for several decades. It is a urethane-based product that withstands temperatures up to 500ºF without hardening. It can be used as a gasket sealer or as a gasket like RTVs – and because it doesn’t harden, it is easier to deal with in situations that require repeated disassembly and re-assembly, such as racing engines. Hylomar has been called the adjustable wrench of sealers, as it fits many different uses and applications.

There are more types of sealants available, but in the interest of time and column space, I need to move on to Dad’s favorite: copper sealant.

Copper gasket sealant is available in both brushable and aerosol forms. It is fast-drying, and the metal contained within the sealing compound helps dissipate heat and promote even temperature transfer between metal parts. Also, because it contains metal, it can be used to fill small imperfections on metal surfaces. Being heat-resistant to 500ºF, copper gasket sealant works great on manifold gaskets and cylinder heads. It is easy to clean even after extended hours of engine operation.

Copper gasket spray was Dad’s go-to sealant … to a fault. He used it on everything, including transmission gaskets. The same properties that make it excellent for parts like exhaust manifolds make it terrible for transmissions. Often, after a repair involving splitting a tractor, that copper sealant Dad used liberally would stop up the hydraulic filters and screens of the tractor. That scenario was exactly why he had a little tractor in the shop on Nov. 3, 2005.

He had put a new hydraulic pump in the tractor and used copper sealant to secure the gasket on the transmission housing. The sealant stopped up the pump’s screen as he was using the tractor to run his wood splitter. He pulled it into the shop, pulled and replaced the filter and cleaned the screen.

When he fired the engine to check for leaks, the tractor had been left in gear. He had deleted the clutch safety switch when it failed a few weeks prior, and the tractor ran over him. He died of his injuries a few hours later.

Yes, it was not a smart move to remove the safety switch, but the use of the incorrect sealing product was why the tractor was in the shop that day. A hard lesson was learned, but that makes it all the more important to share the lesson.

Do your research. Make smart, informed decisions and never cut corners – especially when safety is involved. end mark

Andy Overbay holds a Ph.D. in ag education and has more than 40 years of hands-on dairy and farming experience.