Let’s talk Pros & Cons of Silicon Caulk on Boats!

Archives
1

Posted by Skip Turpin (skipperf33@…>)

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!

  1. Application:
    Is there sufficient working time so that I can take my time? If I
    screw up, can I easily correct an OPS?

  2. 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!

  3. 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!

  4. Re-bedding:
    Can the mating surface be easily cleaned to accommodate re-bedding?

  5. Wet Bonding:
    Will it bond to a wet surface? Have you noticed that the house never
    leaks on a sunny day?

  6. 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?

  7. Painting:
    Can I paint the stuff once it is set?

  8. 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!

  9. 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?

  10. 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 that :frowning:

If 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.

2

Posted by michel.capel (michel.capel@…>)

Skip,

I wholeheartedly agree with your pledge not to use silicone caulk on a
boat. I always say that silicone caulk is made to glue aquarium
windows, and it’s not even good at that.

For bedding hardware I use Bostik caulk tape. It is like putty, a
little greasy, and it stays soft. It’s sold on a roll between two gray
plastic sheets. It’s grey of color. Easily removed, somewhat flexible.
Did a lot of rebedding with it two years ago (see
www.flickr.com/photos/alabama_queen) and have no leaks. Advantage for
bedding is that it does not glue. No need for that when there are
screws or bolts, right? For gluing jobs on deck I mostly use some type
of Sikaflex. The strongest Sikaflex is like 3M 5200, so take care what
you buy.

Best, Michel
F44 #4 1981 Alabama Queen

3

Posted by George Huffman (thatboatguy2@…>)

Hi Skip,

In a former life I was a missile technician. I’ve been a boat
mechanic/electrician/refrigeration/custom electronics/rigger guy for
the last 12 years or so although I did all my own work on my boats
since I was 10 years old or so. In boating and in the military I’ve
used silicone successfully in a variety of applications.

I’ve seen silicon sealant hold up well under some pretty fantastic
circumstances including sub-sub zero (North Dakota), well over 100
Fahrenheit (Saudi Arabia, and UAE) mach speed(motor fire wires on
AIM-9) Missiles for some examples. I’ve also used just about every
other product out there. I used 100 percent silicone on our new ports
as that’s what the manufacture more or less “demanded”. heh heh

As to removing old silicone. Well… either it wont stick to anything
or you cant get it off of anything bro… you cant have it both ways.
:slight_smile: I used sandpaper to get the 30 year old silicone residue off of
Marquesa where it was used to bed the original ports. If I can get
another 30 years out of this installation I’ll be pleased. Don’t
think that I didn’t give it a long hard think before I went with
Beckson’s directions. I, like you, have enjoyed a lot of features of
modern sealants.

I think like with anything else there are levels of quality that
varies with manufacture. I would not go up to Ace Hardware and get
some bathroom caulk to use on our portlights. I stick with 3M
(literally!) and have had great luck.

We had about a foot or rain it seems right after my installation and I
had one little leak that was due to my own mistake (missed an old
screw hole). I’m waiting for a warm dry day to deal with that.

Rest assured my friend… when I go to bed the new handrails to the
cabin house… it won’t be silicone!

George