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Date: Tue, 15 Mar 2005 17:27:54 -0600
From: Jim Sower <canarder@frontiernet.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Mogas sealants/leaking mogas
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<... 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 ...>
You're probably right.  I've heard the same thing.  At the very least, 
ethanol is LESS harmful.  The conventional wisdom seems to be that it's 
too fine a distinction to draw when we're all dealing in pretty general 
terms regarding contaminants, sealants, materials, etc.

I stay away from ALL alcohol, ALL proprietary additives... Jim S.


Charlie England wrote:

> 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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>>>