Need opinions on Silicone and bulkheads

[mehaffydr]

I am getting ready to start the plumbing on my Monster tank 1000 gallon plywood tank. See build thread. I am trying to decide to Silicone or Not to Silicone. What I am referring to is the drain and return bulkheads. I have never used silicone on a bulkhead before and I have never had one leak. But I have only used bulkheads on Glass ans Acrylic tanks up until now. My concern is that this new tank is built from Plywood and then laminated with Fiberglass cloth with polyester resin and then painted with epoxy paint. The surfaces are fairly smooth but not like glass or acrylic.

So I am concerned it the washer supplied with the bulkhead will seal properly on this surface or should I use some silicone to make sure there are no gaps?

Is there any concern using silicone around a bulkhead? Please give some opinions and some reasoning for your opinion. The wood against the glass is to hold the glass while silicone cures I installed the glass today.

Thank You in advance

 

[Greg P]

My 2 cents
Using silicone on bulkheads is not needed. If the surface is not smooth enough to start with, clean it up with some fine sandpaper.
If thicker gaskets are required look for Buna-N rubber material and cut your own to fit.

Silicone will allow the gasket to squeeze out of position and if it doesn't leak now it probably will later.

 

[fishguy242]

hi,i agree no silicone on bulks..leak waiting to happen ,then not just an adjustment/tightening ,if sm leak does appear

 

[Greg P]

Just to add to my reason why;
A compressed gasket will seal and stay that way
A gasket pushed out of position by silicone may seal to start with but will have much less surface area to remain sealed under pressure

Imagine that 1/2" wide gasket being pushed out of position by the silicone and only making 1/16" contact. It will eventually leak

 

[mehaffydr]

Thank You, I may have to do a little sanding in the area where the bulkheads are located because the fiberglass may not be completely smooth but sounds like that the best thing to do. I haven't been cutting corners so far no need to start now.

 

[Greg P]

Can we get a picture of the bulkhead areas you are dealing with?

 

[mehaffydr]

I think you can see the texture in this one if you enlarge it if not I will need to get a closer picture.

 

[DaddyFish]

Here's a thought...

You could glue some wet/dry 400-grit onto a large flat washer. Then use one of those big magnets chucked in a hand drill and wet sand the surface by spinning the magnet with the drill? Maybe??? Depends on how thick your bulkhead area is and how strong the magnet is.

 

[fishguy242]

i cannot see close enough,looks kinda rough,if case ,sand, fill,sand, paint. get em flat ,never want to mess with again

 

[mehaffydr]

Here's a thought...

You could glue some wet/dry 400-grit onto a large flat washer. Then use one of those big magnets chucked in a hand drill and wet sand the surface by spinning the magnet with the drill? Maybe??? Depends on how thick your bulkhead area is and how strong the magnet is.

That is an ingenious idea but the walls are 1 1/2" thick so it would take quite the magnet.

 

[DaddyFish]

Yeah, I'm thinking that surface is nowhere near smooth enough for a quality seal. Silicone will squeeze out into thin layers and lose all it's strength, so silicone is a definite no-no.

I think I'd start with super thin CA glue and saturate the crap outta the wood cutouts. Let that fully cure overnight.
Then perhaps mask off the bulkhead area, rough it up with 80-grit, build it up with resin coats, and then work my way down to a nice smooth surface.

 

[mehaffydr]

i cannot see close enough,looks kinda rough,if case ,sand, fill,sand, paint. get em flat ,never want to mess with again

I'm just going to use the orbital sander and sand that area real good and paint. I just silicone in the glass today so I have plenty of time to sand and paint. I am not adding any water for at least 4-5 weeks.

 

[mehaffydr]

Yeah, I'm thinking that surface is nowhere near smooth enough for a quality seal. Silicone will squeeze out into thin layers and lose all it's strength, so silicone is a definite no-no.

I think I'd start with super thin CA glue and saturate the crap outta the wood cutouts. Let that fully cure overnight.
Then perhaps mask off the bulkhead area, rough it up with 80-grit, build it up with resin coats, and then work my way down to a nice smooth surface.

I like the CA glue idea. I have coated the holes with the epoxy paint but the CA would really soak into the wood and seal it up.

 

[DaddyFish]

That is an ingenious idea but the walls are 1 1/2" thick so it would take quite the magnet.

You could use a quality sanding disc and get a lot accomplished. Whatever you use as the last stage, needs to be rigid, flat and 400-grit wet/dry.

 

[fishguy242]

perfect!! see ya' at your build

 

[mehaffydr]

You could use a quality sanding disc and get a lot accomplished. Whatever you use as the last stage, needs to be rigid, flat and 400-grit wet/dry.

Got it. I will start with orbital sander and finish with sanding block starting with something like 100 grit and work my way down to 400.

 

[DaddyFish]

Years ago I built model aircraft for international competition. We used CA-soaked plywood all the time for bulkheads that required high compression strength and withstanding harsh solvents. I know it works! Especially around epoxy resins and such.

 

[Greg P]

So through the side wall. Ya, there'll be a lot of pressure on the gaskets.
Definitely best to dry fit the gaskets.
Unfortunately, you'll need to fill the whole tank to test. If you get a leak, try just little tweaks on the nut at first. If you overtighten them the nuts will split and you'll have lots of water pouring out !!

Start with dry surfaces and dry gaskets. Hand tighten the nuts as much as possible - only hand tight!!
Use channel lock pliers, a strap wrench, or something otherwise appropriate to turn the nuts another 1/4 turn to start with before your test fill.
Then during your test if you get leaks you can do micro tightening.

With a plywood/fiberglass build you can be more aggressive as you're not worried about cracking glass, but you're still limited by the strength of the bulkhead nuts.

 

[mehaffydr]

Years ago I built model aircraft for international competition. We used CA-soaked plywood all the time for bulkheads that required high compression strength and withstanding harsh solvents. I know it works! Especially around epoxy resins and such.

I also build RC aircraft have been flying RC aircraft for over 30 years that's how I knew when you suggested CA that it would be a great plan.

 

[ca1ore]

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.