Do You Put Gasket Sealer on Both Sides of a Gasket
The decision to use sealant depends almost entirely on the gasket material and the condition of the mating surfaces. Decades ago, paper or cork gaskets often required a light coating of dressing to fill surface imperfections. Today, high-precision machined parts and advanced composite materials make supplemental sealants redundant. Using them blindly creates a slippery surface that allows the gasket to slide out of position when you torque the fasteners.
What are the primary differences between anaerobic and RTV silicone sealants?
Anaerobic sealants cure in the absence of oxygen between tight-fitting metal parts, whereas RTV silicone cures by reacting with moisture in the air to form a flexible rubber.
- Anaerobic sealants provide a rigid, structural bond that resists vibration and prevents corrosion in metal-to-metal joints.
- RTV silicone maintains flexibility over a wide temperature range, making it ideal for filling gaps in stamped steel covers.
- Curing times for anaerobic products often reach handling strength within 30 minutes, while RTV may require 24 hours to fully vulcanize.
- Temperature ratings for specialized RTV can exceed 600 degrees Fahrenheit, whereas many standard anaerobic formulas are limited to 300 degrees.
Quick facts
| Gasket Type | Sealant Requirement |
|---|---|
| Multi-Layer Steel | Dry |
| Rubber/Silicone | Dry |
| Paper/Cork | Optional dressing |
| High-Pressure Flange | Dry |
Under what circumstances is it necessary to use a gasket dressing versus a dry installation?
Dressings are reserved for sealing imperfections on rough surfaces or holding gaskets in place, while dry installations are required for precision-machined components.
| Surface Condition | Recommended Method |
|---|---|
| Machined Finish | Dry |
| Cast Iron | Optional Dressing |
| Stamped Steel | RTV Bead |
| Corroded Aluminum | Resurface |
Use these categories as a guide to assess the surface roughness (Ra value) before deciding if a chemical barrier is necessary to prevent seepage.
How does the application of sealant affect the compression and torque specifications of a gasket?
Sealant acts as a lubricant that reduces friction during bolt tightening, which causes the fastener to stretch further than intended for a given torque value. This leads to over-stretching the bolt and potentially crushing the gasket material beyond its elastic limit. A lot of people assume that adding sealant creates a tighter seal, but it actually creates a hydraulic wedge that prevents the gasket from seating correctly, often resulting in a premature blowout of the material under high internal combustion pressures.
Which types of gasket materials are most susceptible to damage from improper sealant application?
Thin, flexible materials like cellulose fiber and cork are highly susceptible to tearing or shifting when thick, tacky sealants are applied incorrectly.
- Cellulose fiber gaskets absorb liquid sealants, which can cause the material to swell and lose its structural integrity over time.
- Cork composites easily crush or extrude if a thick bead of RTV creates uneven pressure points during the tightening sequence.
- Graphite facings often feature a specialized coating that is designed to bond to the metal surface, which a secondary sealant will ruin.
- Rubber-coated metal gaskets rely on precise bead geometry that is easily distorted by the presence of excess chemical paste.
What are the risks associated with using excessive amounts of sealant during assembly?
Excessive sealant creates a thick barrier that prevents metal-to-metal contact, which is necessary for proper heat transfer and structural rigidity. When you apply a bead that is too large, the material squeezes out into the internal fluid passages. This can clog oil pickup screens or lodge in cooling jackets, leading to catastrophic engine failure. For example, a glob of silicone breaking off inside an oil pan can block the oil pump intake, starving the bearings of lubrication within seconds.
The only nuance involves specific oil pan designs that lack a dedicated gasket and rely entirely on a precisely applied RTV bead. In these cases, the manufacturer specifies a narrow, continuous bead width, typically 1/8 inch. If you exceed this width, the excess material inevitably enters the crankcase. Always use a calibrated nozzle to maintain the exact diameter specified by the service manual to avoid these internal obstructions.
How should surfaces be prepared to ensure optimal adhesion of a gasket sealant?
Yes, surfaces must be cleaned with a solvent like acetone or brake cleaner to remove all traces of oil and debris. A surface finish between 30 and 60 micro-inches is typically required for a dry seal to hold under pressure without additional chemical aids.
Are there specific engine or industrial applications where sealant should strictly be avoided?
Sealant must be strictly avoided on intake manifold gaskets and cylinder head gaskets that feature integrated rubber beads or embossed steel layers. These components rely on the specific compression of the embossed geometry to seal combustion gases or high-velocity air. Introducing a foreign substance interferes with the calculated crush of the gasket, leading to localized hot spots or gas leaks that quickly erode the surrounding metal.
One notable exception occurs when a manufacturer explicitly calls for a light coating of a specific spray tack on a composite intake gasket to prevent vacuum leaks. However, this is a rare requirement for modern engines. In most high-performance or industrial applications, the gasket manufacturer has already applied a specialized coating to the material. Adding extra sealant to these pre-coated gaskets is counterproductive and usually leads to the gasket sliding out of position during the final torque sequence.
Mistakes to avoid
- Applying sealant to head gaskets. These are almost always designed for dry installation; adding goop interferes with the fire ring's ability to maintain a tight seal against the cylinder head.
- Using too much product. A bead thicker than a thin film prevents the gasket from compressing properly, which creates gaps that eventually lead to fluid bypass.
- Ignoring surface finish. If you feel compelled to use sealant because the metal is pitted, you should resurface the metal instead of trying to fill deep gouges with chemical paste.
How can a technician determine if a gasket is designed to be self-sealing or if it requires additional adhesive?
No, you should check the manufacturer’s service manual or the packaging instructions provided by the gasket supplier. If the gasket arrives with a visible rubberized coating or a printed bead, it is designed for a dry installation and requires no additional adhesive to function correctly.
Choosing the right installation method
Check the manufacturer's installation manual before reaching for the sealant tube. If the surfaces are clean and flat, a dry, clean installation remains the industry standard for long-term reliability.