Bulk caulking

Tim B from MA · Jul 21, 2008

I am mounting socket-type seat pedestal mounts (for removable pedestals) in the floor of my aluminum boat. Turns out, where I need to put the seats, there is a sealed, or semi-sealed aluminum compartment filled with foam for flotation, and potantially to stiffen the boat hull.

Now I have a 3.5 inch diameter hole through the floor(and at least one more to come), which is also the top of the foam filled compartment. The seat mount sockets have holes so water can drain through.

I can't have that here - the foam will eventually saturate with water.

I need something to put into the hole, around the seat mount socket, to seal it and not let water in.

I am thinking some silicon-based, bulk caulking material.

Anyone have any ideas?

Thanks,
Tim

Anonymous-0 · Jul 21, 2008

If I understand what you wrote correctly. What I'd be looking for is bedding compound. My experience is with wooden boats.

http://www.go2marine.com/category.do?no=12842

Tim B from MA · Jul 21, 2008

That stuff sounds like just the ticket Ray, Thank you.

Anonymous-0 · Jul 21, 2008

Not at all familiar with that marine application, but for a high quality, high strength sealant (caulk), one that has structural properties, and bonds well to most substrates ( adjoining materials) Dow 790 series, 795, 790, 791, or their latest product in that line whatever it may be. This is a silicon sealant, been awhile since I've bought or used it, I used to purchase large quantities for high end construction applications, they had the best warranty and warranty service in the industry, meaning they back what they sell, premium material, costs more than others if using large quantities, have to consider that in a budget. You have to check and make sure, I believe 795 is ok metal to metal, metal to masonry, though some of them vary as to what substrate they are compatible with, this material is very strong and durable, larger joints you may have to install a backer rod or similar to take up the annular space and support the sealant, once cured it performs great, I've worked with their reps on adhesion tests in the field, can attest to the quality when installed correctly.
DOW

MarkB_MI · Jul 21, 2008

Do not use a silicone sealant. They are not intended for that purpose and will fail. I haven't found a silicone sealant that does not have a disclaimer that it is not to be used below the waterline.

In an earlier life I was a Yachtsman like yourself. There is one product that boatbuilders, commercial fishermen and yachtsmen alike swear by: 3M 5200 Marine Sealant. It is a polyurethane adhesive and sticks to just about anything. Of course if you seal off your hole with 5200 and decide you need to open it back up, you might just have to drill a new hole.

You can get 3M 5200 at any marine hardware store, or order it from Jamestown Distributors.
Jamestown Distributors.

Anonymous-0 · Jul 21, 2008

That's interesting, polyurethane is what they like for marine applications, 3M has always made a good product, Dow, is kind of exclusive, have to go to a distributor/supply house etc. Only others I could suggests would be Sonneborn or Sika, I used a few cases of one of those, for a sealant job I did last fall, polyurethane, I liked it, even though my preference was for Dow.

These are obviously building materials, but that Dow material is like what you describe, if you have to take it apart again, good luck.

One other consideration, might want to make sure whatever foam this material may contact, is compatible, meaning it won't react with it, I can remember construction sealants M-D (Macklanburg-Duncan) M-D 200 or M-D 400 that would eat right through, blue or pink rigid foam insulation, kind like melting a styrofoam coffee cup.

Tim B from MA · Jul 21, 2008

Searching the web for sources of bedding compound, I found a site with a nice concise primer on marine sealants.

http://www.pgwebconsulting.com/boating/pages/caulk.html

Silicon is not good for below the water line, but is UV resistent and good for use above the water line.

Polyurethane is good for use below the water line but most formulations are not UV resistent.

Polysulfide sealants are good below the water and are UV resistent so can be used in exposed areas above the water line.

Handyman · Jul 21, 2008

how about trying plumbers putty, it is used to seal sink and tub drains and will stay flexible

MarkB_MI · Jul 21, 2008

I've never had a problem with 5200 in direct sunlight, but I suppose over many years it might be affected. Certainly polyurethane varnish is no good in direct sunlight; it will start to peel within a year. I suppose the pigments in 5200 give it some degree of sunlight protection.

The main advantage polysulfides have over urethane is resistance to solvents. Polysulfides are resistant to most fuels (except ethanol) and are generally used to seal teak decks because of the cleaners and finishes used on teak.

Bulk caulking

Tim B from MA

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Tim B from MA

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MarkB_MI

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Tim B from MA

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