[A/S] Final word on Vulkem choices

[Steve Hingtgen <steve@xxxxxxxxxxxxx>]

There has been some confusion lately regarding which type of Vulkem 
to use on the repair of Airstream trailers.  Several list members 
contacted me off-list to ask my opinion or offer their own 
experiences.  My initial response to this question was that I would 
speak with Airstream while I attended the International Rally in 
Sioux Falls and get back to the group before weighing in.  I have now 
had the opportunity to speak with Airstream and directly with Tremco 
Sealants, the manufacturer of Vulkem.

Vulkem 116 is the old standard.  Airstream restorers have been using 
it for years.  Vulkem 116 is IDENTICAL to Vulkem 616.  The numbering 
system is used by Tremco as a way to track sales only.  116 is sold 
through building trade suppliers.  616 is sold through industrial 
suppliers, like those who sell to trailer manufacturers.  They are 
both "textured."  Anyone who has used 116/616 will know what this 
means.  It isn't a big deal, but you may notice the difference in the 
finished look if you look closely.

Vulkem 631 is IDENTICAL to 116/616 except it comes in different 
colors.  The Tremco representative said the name change is done for 
marketing reasons only.

Airstream no longer uses 116/616/631 in the production of new 
trailers in places where it will show because of the texture.  They 
still use it between panels before riveting them together.  They are 
now using Sikaflex 221 in areas around vents, hatches and windows 
where it will show because it is non-textured.  It is also more 
expensive and even more difficult to find than Vulkem.  Airstream was 
selling tubes of Vulkem labeled 116/616 at the International Rally 
for $7.29 each.  They were selling Sikaflex-221 for $8.15 each.

Tremco does not recommend Vulkem 116/616/631 for the restoration of 
old Airstreams.  Instead, they recommend Vulkem 636.  Vulkem 636, 
like 116/616/631 is a premium slow-cure polyurethane sealant.  
Slow-curing is important because the slower the cure, the higher the 
ratio of solvent to solids.  The solvents are useful to cut through 
any oil/grease that may be on the skin of the trailer.  This gives 
better adhesion.  Fast-cure sealants like TremPro 650 (another 
similar product) are used in assembly-line production where material 
conditions are controlled and speed is important.  Also, slower 
curing sealants are generally stronger.  

Besides a slightly slower cure than 116/616/631, 636 has the singular 
advantage of being non-textured.  If you see a product called Vulkem 
626, you should know it is identical to 636 except that it is 
textured.  Vulkem 636 is ideal for Airstream restoration. 

I now quote from Tremco descriptions of 636:  "Vulkem 636 is 
specially designed for use in the joints of vehicles such as trucks, 
containers, mobile homes, recreational vehicles, rail cars and 
similar items where the joints are subjected to stress and vibration 
as well as expansion and contraction...Once cured, Vulkem 626/636 
exhibits tenacious adhesion and has the ability to be subjected to 
stress and vibration as well as expansion and contraction within a 
joint... Vulkem 626/636 is especially effective in holding roof 
sheets in place against normal load vibration and air forces...Rivets 
may be set through the uncured Vulkem 626/636, which will act as a 
sealer."

I hope this information has been helpful in clearing up the 
confusion.  We expect to carry Vulkem 636 at our store in the future, 
but will not do so until we can get it at a price comparable to 
116/616/631.  Until that time, I will continue to use 116 on my 1967 
Caravel, knowing Vulkem 116 has logged millions of miles on thousands 
of Airstreams over many years.

Steve Hingtgen
http://www.AirstreamDreams.com