What are they used for?
AXIOM® gasket-forming sealants are intended for so-called flange sealing, that is, for sealing the joints of flat surfaces. They can be used as gaskets for the valve cover, intake manifold, engine sump, water pump, thermostat, timing chain cover, gearbox sump and the differential cover of the drive axle. They can be used both as gaskets and together with gaskets to improve the quality of the seal.
What are they?
AXIOM® gasket-forming sealants are silicone-based materials that self-vulcanise at room temperature (RTV – Room Temperature Vulcanizing) by means of the moisture present in the air. They have good adhesion to most materials. They are highly elastic and strong and can be used to seal gaps of up to 6 mm. As regards the temperature range, AXIOM® sealants can be used continuously at temperatures of up to 250°C, and thanks to the introduction of special additives they withstand short-term heating to 350°C.
Acid or neutral?
To keep the sealant liquid during storage, it is modified with acetic acid or with alcohols. Depending on this, sealants are either acid (in the AXIOM® range these are the red and the black one) or neutral (in the AXIOM® range this is the grey one).
How do they differ?
Acid sealants are cheaper than neutral ones, but they have certain limitations in use. They must not be used in contact with alkalis, for example concrete and stone, which is, however, more relevant in construction. They also react with metals and some types of plastic. However, because of the small amount of acid they contain, this does not, as a rule, lead to any noticeable corrosion of vehicle components.
Neutral sealants do not react with alkalis, metals or plastics at all. They are also noticeably more elastic than acid ones: the elongation at break of the grey AXIOM® sealant is three times greater than that of the red or the black one. High elasticity can be important when fitting pressed steel covers and sumps, which are less rigid than cast aluminium or plastic ones.
How should gasket-forming sealants be applied?
First of all, the surface should be cleaned of the remains of the old sealant. This can be done with AXIOM® sealant remover A9605. Then degrease it with AXIOM® brake and clutch parts cleaner A9601. The fastener holes in pressed steel covers and sumps must be flattened with a special mandrel in order to remove the deformation around the holes caused by the previous tightening of the fasteners. Apply the sealant in an even, continuous bead along the outer edge of the mating surface and around the fastener holes. It is very important to understand that the principle “the more the better” does not apply here. If too much is applied, the excess sealant will be squeezed out after the fasteners are tightened, including into the inside of the unit, where it may interfere with its normal operation. The sealant therefore has to be dosed fairly accurately. After application, without waiting for a surface skin to form on the sealant, press the surfaces to be joined against each other and tighten the fasteners. Remove excess sealant with a plastic scraper. After assembly the unit should not be filled with fluids and put into operation straight away. The sealant must be given time to vulcanise. Under normal conditions (at a temperature of +23°C and a relative humidity of 55%) the curing rate is 2 mm per day. If the temperature or the humidity is lower, vulcanisation proceeds more slowly.
How are gasket-forming sealants removed?
Uncured gasket-forming sealant can be washed off with white spirit or acetone. If the sealant has already cured, it should be removed using AXIOM® sealant remover A9605. Treat the hardened sealant with the remover, wait 10-15 minutes for the compound to take effect, then remove the softened sealant with a wooden or plastic spatula. A metal one should not be used because of the risk of damaging the mating surface.