Need opinions on Silicone and bulkheads

[Greg P]

No reason that the gasket will herniate if there is no rotation of the flange.

Sorry, but I disagree.
Many years of sealing industrial/automotive flanges showed many failures where silicone was improperly used.
When the silicone causes the mating surfaces to become slick, the rubber will be squished out (herniated) versus being compressed.

 

[ca1ore]

I’d certainly defer to your experience, just not clear to me that the amount of compression in an aquarium bulkhead is comparable. The other option, if one is using silicone, is to not use the supplied gasket at all.

 

[Greg P]

I've personally never applied silicone to bulkhead gaskets, just viewed pics of them when the gaskets have squished out, so I can't say how much torque was applied to cause the herniation

 

[Greg P]

I can say though that a cork or nitrile gasket with a regular torque of 7-15ft lbs, when covered with silicone/rtv, will squish out with only a few lbs
It is then useless

 

[DaddyFish]

So I’m going to be the contrarian here as I see nothing wrong with using silicone on bulkheads. While it really isn’t necessary in most cases, a few tricks and it works just fine. When I had a plywood tank in the 1990s I siliconed all the bulkheads. Had all sorts of problems with the tank, but the bulkheads were fine LOL.

You have to put silicone sealant onto both sides of the gasket and make sure that you don’t spin the flange, just the nut. No reason that the gasket will herniate if there is no rotation of the flange. After all, once the silicone cures it’s just a rubber gasket.

I'd be interested in hearing your Top-5 List of Things NOT to do when constructing a plywood tank.

 

[mehaffydr]

I think I’m going to take the safe long term plan and sand the area smooth and flat so that silicone won’t be needed

 

[mehaffydr]

I'd be interested in hearing your Top-5 List of Things NOT to do when constructing a plywood tank.

I would also but it may be too late for me

 

[ca1ore]

I'd be interested in hearing your Top-5 List of Things NOT to do when constructing a plywood tank.

Hah .... a very long time ago. First mistake was using crappy plywood. Should have either used hardwood ply or a proper fiberglass coat. Epoxy paint caused the face grain to split in places. Second was having external corners exposed to the water. Epoxy paint split along the sharp edge. No external edges inside the tank. Those were the major mistakes. Seem obvious now, but I was young and stupid LOL. Sump I built at the same time avoided both and lasted 25 years. Tank failed after only 3.

 

[Valum]

I throw the washers away completely and make a silicone gasket without issue to date, not to sure how the two fair together but I just feel more confident doing it this wayb