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Catalina/Capri 25/250 Sailor's Forums

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Rebedding Deck Fittings

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GaryB
Master Marine Consultant

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USA
4304 Posts

Initially Posted - 04/18/2008 : 20:23:47

Someone on another forum brought up this question so I thought I would see what you folks think.

Why don't we use a thin rubber gasket type material to seal our stanchions, mast plate, handrails, etc...?

Seems like it would seal better and last much longer than 4200 or poly-sulfides. Would also make removing these parts much quicker and easier.

Thoughts?

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GaryB
Andiamo
'89 SR/WK #5862
Kemah,TX

Edited by - on

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts

Response Posted - 04/18/2008 : 20:54:13

I've wondered this same thing, and I'm curious to see what the answer will be.

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 04/18/2008 : 21:15:07

Normal stresses tend to pull or pry bedded components apart. If the bedding compound is both adhesive and elastic, it will stretch like the bellows joining the two sides of an accordion. Cured silicone sealant exhibits amazing elasticity, but its adhesion is temporary at best. Movement between bedded components tends to break the seal. This is precisely why normal expansion and contraction soon enough lead to leaking deadlights. - Don Casey

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/18/2008 : 21:34:30

A rubber "gasket" (1) isn't really sealed to either the deck or the hardware, (2) has very limited elasticity, and (3) doesn't seal the bolts from water migrating down from their heads. Polysulfide is a very sophisticated sealant, with great elasticity and a moderate amount of adhesion (so hardware can be removed). If you do it right, there's virtually no better way. By right, I mean:

1. Bevel the bolt holes with the tip of a larger drill bit so you have more of a gasket around the bolts. (Run the drill in reverse so it doesn't grab and cut too deeply.)

2. Apply polysulfide to the bottom of the hardware with the bolts in place, and then insert the bolts into the holes.

3. Hand-tighten the nuts enough to queeze some of the sealant out around the edges of the hardware.

4. Let the sealant cure for at least two days (or according to its directions).

5. While holding the screws stationary from above, wrench-tighten the nuts from below to put pressure on the gasket you've created, without turning the bolts, since that will break the seal around them.

6. Run a blade around the hardware base, and then zip the excess polysulfide off.

Edited by - Dave Bristle on 04/18/2008 21:38:31

John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 04/18/2008 : 21:50:21

Dave, I've read your description of this process so many times, I think that even I could do it. You oughta make a video training piece and post it here.

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jaclasch
Navigator

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USA
104 Posts

Response Posted - 04/19/2008 : 00:03:28

For a long time I have wondered about using gaskets as an alternative to sealants. I do not like to use sealants anymore than absolutely necessary for these reasons.

1. It is difficult to get a uniform thickness that gives the best seal.

2. Old sealant is tiresome to remove

3. Sealant is messy as all get out because it has transference characteristics like printers ink. One little smirch gets great mileage even though you think you are being ever so careful. By the time you notice it, it has cured and very difficult to remove.

Check out this link. http://www.kelcom-tapes.com/

Look under Aquablock.

A couple of years ago I learned of this company that produces marine closed-cell gasket material. I would dearly love to try this sort of product in some specific places. First would be the sliding hatch grooved teak pieces. Second would be stanchion bases.

At present I use strips of neoprene under the grooved teak pieces as shown here.

I found the strips in a pile of neoprene scraps and they have worked well. No leaks and it is very easy to take the teak off for refinishing and replace it without all the work entailed in the marine sealant routine.

The only problems I have with the neoprene are lack of real pliability, black color, and it is difficult to cut to match the piece it is sealing.

Unfortunately Kelcom became an OEM supplier and ended the retail business. Surely gasket material similar to their product must be available elsewhere but I have not found it to date. If anyone knows of a source I would be happy to put it to the test in a place or two including a couple of stanchion bases.

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Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 04/19/2008 : 00:07:35

I modify that technique by assembling the parts and use blue masking tape to mask everything I don't want polysufide on - it gets everywhere if you're not careful. Then disassemble, seal, and re-assemble. Scrape the edges with a squared popsicle stick and wait for it to skin, then pull the tape.

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GaryB
Master Marine Consultant

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USA
4304 Posts

Response Posted - 04/19/2008 : 09:49:44

Seems like using a gasket made of the correct type and thickness of rubber (or other material) and possibly a small amount of polysulfide around the bolt holes would work well. When you pull the bolts down tight against the rubber that would create the seal under the base plate keeping the water from reaching the bolt holes and the polysulfide would seal around the bolt holes.

Does anyone know if this has ever been tried?

Another thought, ff the gasket was made similar to the higher end head gaskets for racing engines there could be a small compression ring around the edges and around the bolt holes. A gasket under the head of the bolt similar to the gaskets uses on sheet metal screws used for fastening sheet metal roofs to a metal building would seal the bolt hole. In fact if the deck fittings were made slightly differently you could use an o-ring or two as the seal.

I know it's way out there but maybe it's time we move up to the 21st century and stop doing things the same old way. Seems like if we can "send a man to the moon and back"

we could come up with a better way of sealing a deck fitting to fiberglass.

Edited by - GaryB on 04/19/2008 09:53:50

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 04/19/2008 : 10:34:21

To reinforce Dave Bristle's how to it right. Rubber products degrade and lose elasticity from UV, oxygen, airborne corrosives, solvents and cleaners. After <u>prolonged compression</u>, it will reform to the new dimensions and no longer be compressed. Closed cell foam will do the same thing - the gas diffuses out of the cells. It is not that hard to do it right.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/19/2008 : 10:47:23

Wow--that sounds like <i>real work</i>, compared to a squirt of polysulfide which, incidentally, wipes off with a wet paper towel before it sets up, and if you avoid the temptation to do so (and thus smearing it), peels off nicely after it cures. The masking tape is not a bad idea, but not really necessary in my experience.

The thing that's missing with neoprene, rubber, or whatever, is a real seal--you're relying solely on mechanical pressure, which might not always be there--especially on stanchion bases or teak that's held by screws from below.

But then again, I'm the resident curmudgeon...

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Voyager
Master Marine Consultant

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USA
5376 Posts

Response Posted - 04/20/2008 : 00:14:52

Dave -
I went with your mantra of the polysulfide bedding. It seems to be working out nicely, but only time will tell if I applied it right.

I'll let you know whether it keeps the rain out of the boat in a couple of weekends after I pull the tarps.

The exterior teak looks great with Sikkens Cetol. I had to make a new companionway threshhold because the original one turned into toothpicks when I tried removing it last winter.

Now it's time for the Poly Glow. I plan to use tung oil on the interior trim in the cabin after cleaning it down with TSP.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/20/2008 : 13:03:25

She's in good hands!

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Deric
Captain

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USA
408 Posts

Response Posted - 04/20/2008 : 19:01:39

I just rebedded my chain plates for the very first time. I read about using the polysulfide last fall, and had developed a basic concept of the tasks I needed to perform. The project went well. I was able to lay it down and wipe the extra amount off. It was easy to work with and shape near the plate and deck.

Regarding the removal of the polysulfide, I read that polysulfide is easier to remove it is heated, for example, with a heat gun.

Next time, I'll try the tape idea.

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Leon Sisson
Master Marine Consultant

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USA
1893 Posts

Response Posted - 04/28/2008 : 18:20:34

If you would like the thickness of gasket material, combined with the penetration and adhesion of sealant, try shimming the part up off the deck a bit while the polysulfide cures. I use 3 or 4 short pieces of popsicle stick inserted a very short distance (1/16") under the hardware, as far as practical from the bolt holes. Then tighten the bolts only enough to hold the sticks in place until the sealant cures a bit. Once the sealant is quite firm, wiggle the sticks out, and snug the bolts down tighter.

-- Leon S.

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Deric
Captain

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USA
408 Posts

Response Posted - 04/28/2008 : 18:49:11

James,

I checked into the tape from Kelcom. They sell wholesale: 12 rolls to a box at 30 bucks a roll from what they told me.

I am posting the information on here for others. I use polysulfide.

I just did my chainplates this past weekend.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 04/28/2008 : 21:25:22

BTW, the windshield wipers on my $+!nkp*+ are mounted with rubber gaskets on the outside, and one of them is leaking. When it stops raining here

I might decide to do it "right". Maybe I'll buy a box of popsicles.

Edited by - Dave Bristle on 04/28/2008 21:27:09

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