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Fuel Tank Sealant, Proseal I

Aircraft wing tanks come in different size and shapes. Some aircraft have a separate fuel tank build into the wing in the form of rubber bladders or even composite tanks built inside the wing. Cessna, Piper, RV and Murphy type aircraft have a wet wing. This means that the fuel is contained / carried in the wing itself in separate bays usually close to the wing root.

To successfully carry fuel by the wing one must make sure that this section of the wing is absolutely leak free. And as the wing is drilled and riveted (either with special tank Avex- or blind rivets) this means we need to seal this construction to keep the fuel inside. Proseal is used for this.

Proseal must be mixed in the proper ratio taking into consideration ambient temperatures and a clean work area if you wish to obtain good results and a leak free fuel tank.

Which is important, as fuel can be very flammable and the result not so pretty.

Using Proseal

Proseal is a two part fuel tank sealant mixed together just in time and in correct quantities to do the job at hand. It can be a real messy job but if handled properly, easy to work with.

By following a few simple rules, it will be a lot easier for you to apply and work with Proseal. Lets establish some need to know items before we start, this will save time:

  • The cure rate is thermo exponential, i.e. the temperature effects the cure rate
  • You can mix smaller quantities by volume and have the same cure rates and results
  • Like most resins and epoxies you will use a catalyst to cure the product
  • Long strands of fiberglass (angel hair)
  • Obtain syringes of different sizes (5 cc, 20 cc and 100 cc types) to apply the Proseal when it is mixed
  • A small 3" paint roller cut to 1"
  • Get latex gloves, some raiser blades, paper towels and MEK or thinner for cleanup


When mixing Proseal in smaller amounts up to 40 or 80 cc by volume we use large syringes available at most medical, agricultural and veterinary outlets. This process insures that the Proseal is accurately measured and easy to handle and apply. You will need three syringes: two for parts A and B with the end cut off by the raiser blade (open cylinder) and the third with and opening of 1/4" for applying the mixed Proseal.

Modified syringes

By cutting off the ends of two syringes so just an open cylinder is left on the end of the syringe it can then be used to accurately suck up measured amounts of the base and catalyst. Using the 10-1 base to catalyst ratio 2 cc of catalyst for 20 cc of base. Two syringes must be used to prevent cross contamination of the products A and B components.

Applying proseal

After the measured components are mixed thoroughly on a flat plate for at least one full minute they are then loaded in to the plunger end of a third so called application syringe. This is usually done with an oil artists knife or spatula. Once it is in the application syringe you can apply it exactly where you need it and just the right amount of it.

Paint brush

A small 1" diameter fine felt paint roller or heavy brush can then be used to uniformly spread it on surfaces. Buying the 3" long by 1" diameter paint rollers and cutting them in to 3 separate 1" x 1" paint rollers works very well. It helps to use a small tube to take up the slack in the paint roller reel.
You can rapidly measure, mix, and apply proseal by doing it this way and there will be hardly any waste product or expense to contend with after.

Our next article describes the cure rate and how to handle and apply the mixed Proseal.

Written by EAI.

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