silicone sealant

I am supposed to "cushion" and adhere an aluminum wing tank to a wood spar with a bead of silicone sealant before adding tank straps around the tank and spar. Of course it should be non-corrosive to the aluminum. Where do I get such stuff. I have no luck on Google because most of the manufacturers want a large order. Has anyone used the All-in-one silicone sold by Wicks? Does putting epoxy primer on the tank and epoxy varnish on the spar provide enough of a barrier for the acetic acid normally given off by typical silicone sealants? I know about felt products but I am just trying to follow the plans directions. Oh yes, the plans also call for the nose tank to rest on a bed of silicone sealant on4130 tubes. Thanks everyone.

Hi n3pup,

I would recommend protecting a wood structure that is near a gas tank with some sort of inert coating, gas on wood is a bad combo, brushed on laminating epoxy would likely be the easiest. A small kit of West System from a local boating store may be the quickest approach. Make sure to ratio it out exactly as they call for.

As for the aluminum tank I would look into self etching primers in a spray form where it will be a mating surface (assuming your going to have a polished alu outside tank?) a simple sanding with fine grid sandpaper or steel wool should work for prep, vacuum with a brush attachment the surface. I use Dupli-Color SE primer here is a link where you can get it at spruce

http://www.aircraftspruce.com/catalo...hingprimer.php

but the auto stores have it in stock, even some walmarts at a lower cost. This prep & spray combo has produced good results for me in a high humidity climate (So Florida).

As for the silicone I would look into aircraft or automotive grade 1 part RTV silicone in a tube, spruce has that to.

http://www.aircraftspruce.com/catalog/appages/rtv.php

You may want to check in with some of the auto stores and see if they carry it,

In practice both building Piston Aircraft engines (on my own time) or my full time job working on all the Fancy P&W commercial & military aviation gas turbines, aircraft / automotive grade silicone RTV’s are usually applied to metal components with out issue in a production environment. The bigger item to look out for is corrosion from moisture on the internal aluminum structure particularly with 2024, when I used to work for Piper they would paint or coat all the interior sheet metal components & skins before assembly. The only area I would watch out for is the inside of the tank, I would follow the manufactures guidelines on that, the wrong coatings can dissolve in gas & end up in your fuel filter.

Hope this helps

Spencer

EAA Technical Counselor # 5426

There are plenty of non-corrosive silicone sealants without acetic acid available. They are commonly used in electricial and PCB fabrication. Google "non-corrosive silicon". Here are a few sources . ;)
http://www.google.com/products/catal...ed=0CD0Q8wIwBA#

Thank you. When I tried Google I found manufacturers but none that would say non-corrosive and sell by the tube. I think I will use some Stits epoxy primer for the tank and the spar is already coated with an epoxy varnish, then use the non-corrosive silicone. I am not comfortable using steel wool on aluminum so I will see what the prep the epoxy primer recommends.

Quote:

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Originally Posted by n3pup

I am not comfortable using steel wool on aluminum so I will see what the prep the epoxy primer recommends.

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You are correct. Steel wool should never be used in the vicinity of aircraft aluminum. It will embed in the aluminum and setup dissimilar metal corrosion.
A good abrasive to use is fine Scotchbrite. Most auto paint supply stores carry it. You want the red or gray pads. Most hardware/building supply places only have the household green.

You may just want to go to the DOW CORNING website, the 732 looks run of the mill in the line. Look for properties that fit your needs or use the contact and get list of products that do fit your needs from a company rep. http://www.dowcorning.com/applicatio...1&DCCT=PRODUCT

Dow 732 is classed as an acetoxy sealant. "Run of the mill" or not, you would not want to use that product on any aluminum.

N3PUP, I'm building a heavy acro, 2 seat, tube fuselage, with all wood wing, with 2 8 -gal tanks, 1 each wing. I closely fitted the tanks in between the ribs and spars, and used heavy cushions of 100% silicone from home depot, as recommended by several other builders of same plane. I did infact epoxy primer the tanks prior to "glueing' them in place. Hope this helps. Mark

Google MIL-S-8802 It is also known as PRC.....It has been used on and in fuel tanks since forever....It sticks to everything except spit....Pete......

I wound up getting some Dow Corning 832 from McMaster Carr for a very reasonable price. It does not give off acetic acid, adheres to metals and says no primer is needed even tho I am using a 2 part Stits epoxy primer. This forum is a great help to get ideas and learn. Thanks everyone for your replies.

So what are the consequences of using an sealant with acetic acid?

It is my understanding that acetic acid is a weak acid but in general, acid and aluminum don't get along very well and the acid can "eat" the aluminum.

correct. if the sealant smells like vinegar it's a dead giveaway it has acetic acid in it.

Thanks.