Is Silicone mastic the same thing as silicone grease?
I've got a slight leak from where the stainless steel plug
hole insert fits into the recess in the plastic sink. The
big plastic nut is tight and the rubber washer is in place
but when the sink is full of water a small leak occurs
dripping below the sink.
Should I use silicone mastic / grease to seat the metal
plug hole into the sink recess?
I'm at the bottom end of the plumbing learning curve - so
still be bit wet behind the ears :-)
I presume what you'd describe as silicone mastic is what's perhaps more
normally known as silicone sealant - that sets solidly (well, rubbery)
whereas silicone grease is, well, grease - ie it doesn't go off, it just
stays at that consistency. It doesn't attack rubber seals like o-rings
which makes it good for plumbing use. Another type of gunk is plumber's
mait, which is a gunky sealant typically used for toilets or sinks; and
doesn't set either, but is not grease-based. I don't go fot it at all
Personally in your scenario I'd dismantle the plug/drain, clean and dry
everything then reassemble with a smear of silicone sealant over the
1) Silicone Sealant/Mastic is not the same as Sil. grease the former sets
into Sil. Rubber.
2) The leak you have is probably around the threads on the big nut?
If so: then put a little PTFE tape on the threads where the nuts will end
up before tightening the big nut.
3) Silicone sealant is mark of a bodge, when I see it I know to expect
4) There might have been a need put something like plumbers' mait between
the waste and the top of the sink.
5) If you really need to use an adhesive the a multi-resin compound like
CT1 (aka FT101 from s/fix) is more friendly as it works on wet fittings.
No. Mastic (or sealant) sets to form a rubber like seal, the grease
Both may work, but sealant will do the more permanent job. A small tube
of Fernox LS-X would do nicely as well - this is a sealant type material
that is designed for fixing leaks.
Must have you head under the sink then!
Although others have recommended the use of silicone sealant in this
application, IMO it's not ideal. Silicone sealant doesn't perform well
when permanently immersed in water.
A better alternative is Evo Stick Nail and Seal which is a
high-performance polymer sealant designed to set under water and which
performs well in applications where it is immersed for long periods.
Ensure that you clean all the parts well before using the sealant.
I find the best results are obtained by aseembling the parts and
tightening the nut partially then allowing the sealant to begin to cure.
Then tighten fully and trim away the excess sealant.
It's my opinion, and I wrote what I meant.
Did I say such a thing? No.
Let's put back the text you snipped:
Now don't you look stupid for your silly edit?
Perhaps you could comment on why Nail and Seal is, in your justifiably
humble opinion inferior to silicone in this application?
After a goodly few failures at getting this type of drain outlet to
stay leak free, I took stock & advice from this group.
What now works (for me) is to bed the steel body of the outlet into
the sink using a silicone mastic (a transparent one described as
'sanitary sealant' should be OK) then on the underside fill/seal any
gap with the sealant put on a plastic nylon plumbing washer then screw
the nut on. Take car with plastic nuts as overtightening can cause
them to break.
Wipe the away excess mastic with paper tissue. Then wrap PTFE tape on
the steel thread and screw the waste pipe coupling on.
Allow the mastic to set to a rubbery flexible state (depends on mastic
brand/type, but 20 mins or preferably overnight) before using. Do not
disturb during the setting process.
BTW thoroughly clean off any remains from any previous plughole
fixing. You need to bed the new one on an as-new surface.
Silicone is not permitted for use below the waterline on ships because
of its poor performance. They are not recommended or the construction of
aquariums of greater than five gallons capacity, nor for use as
adhesives in such applications and the silicone must be allowed to cure
for at least five days before contact with water. MS polymer sealants
such as Nail and Seal are perfectly acceptable in such applications and
cure while immersed in either fresh or salt water.
Hence although silicone sealants may be used for the construction of
(small) aquariums they are barely suitable for such use, and are IMO
unsuitable for use in sealing sanitary fittings to be used underwater
unless the user can manage to leave the fittings dry over a five day
Maybe you should stick to something you know about, if you're attempting
to score cheap points off me?
 Here's a typical quote from a manufacturer of silicone sealant:
Can I use silicone sealants underwater?
GE Silicones does not manufacture silicone sealants for use in
underwater applications. Examples of underwater applications are:
swimming pools, saunas, hot tubs, spas, Jacuzzis, boats or any other
marine vehicles. The only exceptions are the following sealants, which
may be used for sealing small (i.e., 5 gallons or less) aquariums:
GE012 -- 10.3 fl. oz. cartridge -- Clear Silicone Rubber Sealant.
GE361 -- 2.8 fl. oz. squeeze tube -- Clear Household Glue & Seal
Application must be as follows:
Glass to glass use only
Sealant must cure for a minimum of five days before exposure to water
The products listed above should be used as sealants only, not as
NOTE: Use of other grades of silicone in an aquarium or failure to let
the sealant cure for the proper amount of time could cause harm to fish
or other life forms in the aquarium.
The quote came from:
but the site
has since been reorganised by GE. A reference to the page can be found
- Can I use silicone sealants under water?
Silicone is a good waterproof material, but when used under water care
must be taken to protect for 5 days after installation from direct
contact with water.
In message , Steve Firth
>> > > >Silicone sealant doesn't perform well
>> > > > when permanently immersed in water.
>> > > That's why it can't possibly work for aquaria then!?
>> > Did I say such a thing? No.
>> The ability to happily restrain and seal glass under a load of a ton
>> of water for many years is a strange interpretation of "not performing >> well". > >
>Maybe you should stick to something you know about, if you're attempting
>to score cheap points off me?
> Here's a typical quote from a manufacturer of silicone sealant: >
>Can I use silicone sealants underwater?
>GE Silicones does not manufacture silicone sealants for use in
>The quote came from:
but the site
>has since been reorganised by GE. A reference to the page can be found >here: >