Posted by Roger L. (rogerlov@…>)
Skip, I’ll take the pro side. I have some expertise on the
subject of glues and sealants. In my day job I am responsible
for choosing among glues and goos for a fairly large
manufacturing company. But I do see your point about
application. Some elastomers are difficult and messy to apply
and I agree that silicones are bad about that. Not the worst of
the lot by far - but they can get messy. And it is much more
work to make a siliconed job look good because if/when the job
gets sloppy it ends up double ugly since it is difficult - often
impossible - to paint over silicone.
But I disagree on some points:
As far as retaining it’s elastic strength and toughness over
time and in difficult environments there is simply nothing else
that is half so good as silicone. Most elastomers fail in
strength, cohesion, and adhesion when they lose their
elasticity…when they get old and brittle. Silicone wins that
battle every.
As far as your argument on initial adhesion - I agree that
silicone is difficult to repair. It does stick well to properly
prepared surfaces - but not all cured silicones stick well to
themselves. However there are some that do and if universal
adhesion is your criteria then most industrial types will do
that. They are not cheap, though. In fact, Take a look at
McMaster Carr online for some of the options. And my experience
is that silicones do stick well to wet surfaces. In fact, most
silicone curing chemistries require water or damp air and many
will cure underwater.
At McMaster Carr you may find a plethora of unfamiliar sealant
types. I can sort through some of the silicones…but few of the
others. Although some of the industrial sealants are similar or
the same as the types that come in tubes at the hardware and
marine store there are also some that are far superior. These
super good ones tend to be less toxic and far more expensive.
Like everything, it depends on the application. A common mistake
with silicone is to join two surfaces when the silicone is still
wet. You must keep the thickness under 1/8 inch and wait until
it is at least partially cured before putting the surfaces
together. (BTW, few elastomers ever cure completely). Silicones
are the best at providing a long lasting elastic cushion, in
difficult hot environments, and anywhere that long duration
flexible sealing is required.
As you point out, for pure adhesion and for structural bonding
there are better goos…
Roger L. F28
----- Original Message -----
From: “Skip Turpin” <skipperf33@…>
To: <FreedomOwnersGroup@yahoogroups.com>
Sent: Tuesday, November 18, 2008 8:53 PM
Subject: [FreedomOwnersGroup] Let’s talk Pros & Cons of Silicon
Caulk on Boats!
\
Am I the only person on this board that cringes every time I
hear
about someone using Silicon Caulk on a boat?I have been wanting to say something about this subject for
quite
some time now, but when I read that one of our regularly
contributing
members was advised by the manufacturer to bed his nice new
Portlights in Silicon Caulk I just came UNGLUED, “pun most
certainly
intended!”. As EXPERIENCE IS THE GREATEST TEACHER, I would
love to
hear what some of our more experienced members feel about
this!I know we each have our opinions and of course our
preferences, but
this seems to me to be a “NO BRAINER”! Why do I say that, I
hope you
asked? Well as luck would have it, I was going to answer that
question right now!There are a number of factors I consider before choosing what
kind of
caulk to use where. The following is an off the cuff listing
of
those factors, if you can remember more, please add them.You will please NOTE that COST is not one of the factors.
This is an
area where cutting cost will likely come back to bit you in
ways that
you can’t even imagine! Trust me, an Excedrin Headache is
child’s
play compared to the pain you will endure if a bedding job
unknowingly fails!
Application:
Is there sufficient working time so that I can take my time?
If I
screw up, can I easily correct an OPS?Clean up:
Will I need special solvents to clean up as I go and after I
am
done? When ever possible I like water to be the cleaning
agent! Has
anyone noticed that we never run out of the stuff? It has
been known
to get too thin a time or two, but that’s another story!Future Repair:
Can the part being bedded be removed as needed for a repair
without
destroying the boat? Those of you that have had the fun of
trying to
remove a part bedded in 3M 5200 know exactly what I am talking
about!Re-bedding:
Can the mating surface be easily cleaned to accommodate
re-bedding?Wet Bonding:
Will it bond to a wet surface? Have you noticed that the
house never
leaks on a sunny day?Strength and Pliability:
Will it take the punishment of a storm at sea? Will it
expand and
contract with changes in temperature without leaking? Does it
have a
good Resistence to fracture from people inadvertently standing
or
kicking at the parts that will be bedded in it? In other
words, if
someone uses my portlight as a step to get up on the house,
will I
have an Coronary Event there on the spot?Painting:
Can I paint the stuff once it is set?Adherence:
How well will it adhere (stick) to the sub-straight? Also, in
the
case of a repair, will it stick to ITSELF? That is a big
plus!Fungus or Algie:
Does it have a good resistence to fungal growth? I am sure
you have
all had the pleasure of removing old nasty brown or even black
caulking that has been destroyed by a nation of fungi! Will
it turn
green at the fist drop of fresh water?Resistence to UV:
Will it dry out, crack, peal or flake off due to sun damage?So why do I have so little faith in Silicon Caulking? Because
it
FAILS almost ALL of the above criteria! You can’t paint it,
fungus
loves it, and it does not stick worth a hoot, not even to
itself!
The worst thing about silicon is that once you put it on and
then
want to remove it, the residue left behind is almost
impossible to
get off! That means that nothing will stick there ever again,
not
even silicon. I have heard that there is a solvent that
supposedly
will take that residue off, but I have not heard much good
about it:(Bottom line, there are several good caulks out there that WILL
do the
job. I am partial to BoatLife “Life Caulk” this has a
Polysulfide
base that stays soft yet can be sanded or painted. 3M 4200 is
often
another good choice. There are more products out there that I
will
let others comment on!A word of caution… Unless you are absolutely sure you will
NEVER
have to remove something, stay away from the 3M 5200, it is
meant to
be structural and IT IS! Pray you never have to pull your
aluminum
toe rail off a freedom sailboat:( Been there, done thatIf you are new to caulking, be advised that once you bring out
the
caulking, you can get that stuff on you OVER THE PHONE!Lastly, being an engineer type, I should take the advice I am
about
to give you. READ THE DIRECTIONS!!!Well, hopefully I opened the flood gates! What’s your take on
which
caulking is best to use and where? I still don’t have all the
answers, but I am hoping that once we are done with this
thread, we
will all know more about this very important subject:)Skip
1982 F33CK, Fixed Shoal Keel
Southern CA.
Yahoo! Groups Links
