I haven't researched the composite issue but I'm sure Flamemaster or any other sealant mfgr will give you the straight scoop. I went to the mfgr of the sealant I used in my tanks because I figured they knew their chemistry best. Van was selling the Flamemaster brand about a year ago when I ordered my sealant so I contacted them directly about a compatible, pourable, substance. BTW, tank sealant is like medicine: if it works, it's nasty to swallow/apply/etc.

I've seen several folks on various lists say that alcohol is corrosive when found in various concoctions. I've seen evidence that methanol ('wood alcohol') is corrosive, but if ethanol ('grain alcohol' that is typically found in US gasohol) is corrosive, it's news to me. Did I miss the memo?  Now if you are talking about it acting as a solvent on various synthetics used in composite structures (or tank sealants), all bets are off.

My original 2part stuff was CS 3204. Flamemaster recommended CS3600 as a pourable topcoat 'slosh' & affirmed the recommendation when I pointed out that their current datasheet omits the info on pouring as a seam 'filler'. PDF of datasheet is attached. The other sealants were recommended to me by others when I inquired on the RV-list for other builders' experiences. My only direct experience is that the older (unknown brand) white stuff that Van used to sell has peeled off lots of tanks. It might have been poor sealant or more likely, surfaces that weren't completely clean before 'sloshing' the tank. It was a significant enough problem that Van quit listing 'sloshing compound' in their catalog.
Randolph #912 was one recommendation. Others follow, with sender's name deleted as some were sent privately to me:

I hope I answered all the questions that were asked in various emails; if I missed something let me know.

Finn: I can't recommend a fogging sealer, but I might know a guy that can turn you on to some fog that will make you not care any more...

Charlie
(sending a perfect example of why I'm a bottom feeder when it comes to emails....)

>>>

Peeling problems are due to poor surface preparation.  Check with Kreem Products
(805-386-4470).  The surface preparation is a series of chemicals that degrease
and prepare the surface for the compound.  If the tank has proseal that might be
a problem to ask Kreem about.

I had to use this on a fuel tank that was constructed using galvanized sheet
which was soldered and pop riveted.  It solved the leakage problem with that
tank and also on a motorcycle tank that had rust pinholes.

>>>
>>>

I can offer info on the tank sealant, but not on how you use it for your
problem.

The are 3 types of tank sealant as determined by their viscosity.  The
common "B" type is the paste we are used to.  There is an "A" type that is
brushable, and a "C" type the is designed to be rolled on.  I don't think
Flamemaster makes a "C" version, however PRC-DeSoto (Proseal) does.

You can thin the tank sealant.  The proper thinner is Toluene, not MEK.  The
"A" version is basically the "B" version thinned with about 7% Toluene by
weight.  You can safely thin the "B" type with up to 15% Toluene by weight
without changing the characteristics of the material.  I would be careful
using any other thinner, because while it may thin it, it may also change
the properties in some way.

You can buy most of the Flamemaster products from Sealpak (316) 942-6211.
They carry most of their products in all different sizes and they have no
minimum order.

>>>
>>>

It is interesting that Flamemaster recommended this product.  It seems to be
designed primarily as an adhesive for bonding.  By the way, the TDS you
reference is old and has been superceded by a newer version that is somewhat
different and seems to limit the product to bonding applications.  The new
version, which can be found at
http://www.flamemaster.com/Products&Services/prod02.htm eliminates any
reference to top-coating or sloshing in the application section.  They may
have run into the peeling problem that you mentioned.

Personally, I would drill out the rivets and start over with sealant, but if
I were to try an repair it in place, I would use the "A" version of the
CS3204 or thin the CS3204B with Toluene rather than use a 1 part material.

I am also surprised they recommended this for access plate sealing as it is
primarily an adhesive and would probably be difficult to remove.  They make
a low adhesive product just for this purpose, CS3330, which is probably more
appropriate.  Of course it is always nice to be able to limit yourself to a
single product for multiple purposes.  I ordered a 1 oz. kit of CS3330 to do
my access plates.  I think it cost about $8.

Barry Gardner wrote:

Charlie,

Do you know if that Flamemaster stuff is okay for composite tanks? Is Van recommending that instead of Jeffco (which I've always heard was nasty stuff to apply)?

I've heard that the pure structural epoxy coating used by the composite builders is pretty safe when you do a good job of it. However, I'm a little nervous about mogas because of its corrosive reputation and have been listening for recommendations of good sealants. In Chicago, I think all the local mogas has alcohol for emissions reasons--at least all the pumps list it.

Because Nat Puffer monitors the Cozy list and hates mogas (and auto conversions), asking about sealants is not a great question over there unless you want the lecture and cold shoulder that go with it.

Also, the latter part of your note mentioned you could recommend some other pourable sealants. What would those be?

Barry Gardner
Cozy/Aerocanard
Wheaton, IL

Charlie England wrote:

1st step would be to check the datasheet on whatever sealant you used in the tanks. The Flamemaster brand stuff Van's sells now is supposed to be immune to avgas and mogas. It seems unlikely that a few minutes of exposure would cause such a major leak, even with the old mogas-vulnerable sealant. Did you use access covers on the aux tank like the mains? If so, did you use the cork gaskets? A LOT of people have leaks around the cork gaskets after months or years of flying.

I'm just about finished with my RV-7 tanks (remember my aux tank questions about a year ago?) & I had to seal a few leaks. I called Flamemaster to ask about a compatible, pourable sealant & they recommended cs 3600, a 1 part pourable compound. I swapped a few emails with their help person because some of the datasheets indicate use as a pourable 'slosh' type sealant, other (later) datasheets omit that use in the product description. In emails, they maintained its suitability for use on top of  the 2 part paste that Van's sells. This stuff is not the same as the milky white stuff that caused so much grief in the past. It's a translucent red color & acts about like pourable contact cement. In fact, the datasheet describes it's primary use similar to contact cement application.

I was able to 'inject' it to the problem areas by sucking it into some nylon tubing & routing the tube toward the problem seam before releasing the fluid & then pushing it out of the tube with very low pressure air. I was trying to minimize the unneeded sheeting over large areas of the tank where no holes existed. The tanks now hold air, but it will obviously be a while before I can vouch for long term reliability.

Several folks on the RV-list mentioned that most peeling problems with 'slosh' were probably caused by the tank's interior not being completely clean before sloshing. That makes sense to me, since I very carefully cleaned the areas where I knew I'd be putting sealant but didn't work too hard on the rest of the skin inside the tanks.

I also got a couple of other recommendations on pourable sealants I can send you if you want.

Charlie

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