Sealing Compounds

Certain areas of all aircraft are sealed to withstand pressurisation, to prevent fuel or fume leakage and to delay the onset of corrosion, by sealing against the weather.

Most sealant compounds consist of two or more ingredients that are compounded to produce a desired combination of strength, flexibility and adherence. Some materials are ready-for-use, straight from their packaging, whilst others require mixing before application.

One-Part Sealants

One-part sealants are prepared by the manufacturer and are ready for application straight from their packaging. The consistency of some of these compounds can be altered to satisfy a particular application method. For example, if thinning is required, then a thinner (recommended by the sealant manufacturer) is mixed with the sealant.

Two-Part Sealants

Two-part sealants are compounds requiring separate packaging, to prevent curing prior to application. The two parts are identified as the base sealing compound and the accelerator. Two-part sealants are generally mixed by combining equal portions (by weight) of the base and accelerator compounds. Any deviation from the prescribed ratios will result in inferior sealing or adhesion.

Many common sealants/adhesives are produced in pre-measured kits that simply require the mixing together of the whole quantities of the materials supplied. These eliminate the need for balances and other weighing equipment.

The instructions must be followed. But in general, they require the addition of the accelerator to the base compound, followed by thorough mixing before application. A working life is usually quoted, which applies after mixing, so the work must be thoroughly prepared prior to mixing. After mixing, some materials may be kept for a limited time, by the use of refrigeration. The instructions will give details if this is possible.