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I was told that silicone grease shouldn't be used on a silicone seal or gasket, as it will swell or even destroy the seal.

I know that some hydrocarbon-based greases are bad for rubber seals, but what about silicone seal?

It's for an outdoor floodlight. No grease is applied on the silicone seal and water easily leaks in.

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    Is there a weep hole in the bottom of the floodlight? If not, pressure differences between the inside and outside of the floodlight will act to drive water across the seal... – ThreePhaseEel May 8 '17 at 11:44
  • Is it a super cheapie light from our friends across the ocean? Those seals are mostly made of wishes... Shockingly I get very good performance from the midgrade cheap Cheese products, i.e. The ones sold for 30% more and marketed under a domestic sounding name... – Harper May 8 '17 at 15:03
  • First verify where and why water is leaking. Is it actually at that seal rather than other openings or joints? Do the parts mate tightly without the seal? Is there stuff inside the box preventing the cover from closing tightly? Are there gaps or irregularities in the edges being mated? Is the cover screwed on tightly? Are you sure it is a silicone rubber gasket? Some other types of rubber gaskets dry out or permanently deform over time so that they are no longer really being compressed between the surfaces. – fixer1234 May 8 '17 at 21:40
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Every time I used any type of grease on a rubber type gasket the gasket would slip out as the screws/bolts were tightened. My recommendation would be to use RTV silicone instead of any grease. The RTV can be purchased at an auto parts store or at most home/ hardware stores. It will seal out any water, dust, etc, better than grease.

  • But with RTV it may be very hard to remove. – Jim Stewart May 8 '17 at 17:53
  • Mine has been up 18 years so far and I have never had to remove it. – d.george May 8 '17 at 22:20

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