Sealant for bedding new skin fittings?

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CJ13

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I'm planning to replace my below waterline Seacocks & Fittings next year, using reinforced plastic fittings made by TruDesign.
I normally use Dow Corning sealant, but is there something higher spec i should be using for this critical application?

John
 
Polyeurethane can be difficult to dismantle. NASA used to warn against using it on some of their fittings, so I would check with TruDesign first.

I use whatever is in the shed, usually a part tube of silicone from the pound shop.
 
doug748 said:
Polyeurethane can be difficult to dismantle. NASA used to warn against using it on some of their fittings, so I would check with TruDesign first.
Click to expand...

NASA still recommend silicone, I suspect because of the increased brittleness that can result from solvents on certain plastics. This has been a problem with e.g. stickers on safety helmets. I guess that if a solvent based sealant was used and the fitting tightened with excessive force the plastic could suffer stress corrosion cracking. Silicone is water based and would not cause the same problem.
 
doug748 said:
Polyeurethane can be difficult to dismantle.
Click to expand...

How often do you plan to dismantle your seacocks? :confused:

I've just spent a weekend changing them all on the new boat - several of the old ones put up a fight but it was the nuts seizing onto the threads that was the problem, not the flanges being glued to the hull. The ones I could unscrew the nuts on, a moderate "bop" with a hammer knocked the fitting out of the hole.

Pete
 
Just make sure the selected sealant is compatible with the seacock material.

The reason I say this is that I was called-in as a consultant to a high containment medical research facility in London in 2004 to see if I could find out why a one year old reverse osmosis water treatment system, installed in 2003 in ABS pipework that was commissioned well with no problems, one year later developed mysterious leaks/cracks, nobody could find the reason why.

We had several sections removed for lab analysis and to cut a long story it was the sealant used to seal the pipes where they penetrated walls. I think the problem component was called 'dioctilephtalate(?)' or something, Vics may know. Would not want that to occur with seacocks so make sure you check it!
 
prv said:
How often do you plan to dismantle your seacocks? :confused:

I've just spent a weekend changing them all on the new boat - several of the old ones put up a fight but it was the nuts seizing onto the threads that was the problem, not the flanges being glued to the hull. The ones I could unscrew the nuts on, a moderate "bop" with a hammer knocked the fitting out of the hole.

Pete
Click to expand...

Were they sealed by a rubber gasket?
When I changed some on the Oyster, the sealant held the fitting in place, you could force the fitting a millimetre or two out of the hull without the sealant failing. If you let go, the sealant pulled the fitting back into place.

With plastic fittings, it is probably best to check the plastic is compatible with the sealant.
Silicone can work absolutely fine, but the surfaces must be really well degreased, I don't think it's as reliable as polyurethane on waxy plastics.
 
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