Caulk the threads on a thru hull fitting or not?

[benethridge]

Hi, everyone.

I'm installing my first thru hull, a Groco. All is complete except for caulking and threading on the flange (i.e. the piece that screws on outside the hull).

I've googled and read the instructions from Maine Sail, who says to "lather it up" with a large quantity of Sikaflex 210 or 3m 4200:

https://marinehowto.com/replacing-th...-and-seacocks/

... and I've also read the instructions from Groco, but neither really specifies whether or not I'm supposed to coat the THREADS with caulk and if so, how much.

If I coat the threads, instead of say, applying teflon plumbing tape around the threads (which I typically do for interior plumbing, then I'm worried that the caulk might make the threading bind up as I screw it in, and getting it back off and cleaning up the mess for a re-try would be difficult and time-consuming.

On the other hand, if I apply NO caulk to the threads or don't apply enough teflon tape the first time then obviously water is going to get down between the threads and the hull, and if I haven't perfectly sealed the valve against the inner hull, I'm going to have a bad leak and will have to re-haul the boat and start all over...

...so I want to get it right the first time.

Some experts recommend using 3M 5200. Others (like Maine Sail) recommend something less permanent, in case you ever have to take it off and re-bed it.

What is your experience with this particular part of the procedure?

What kind of caulk should I use and why?

More importantly, should I apply caulk liberally to all the threading? or just a little bit of caulk at the top of the threading? or no caulk at all? or plumbing tape to the threads plus caulk to the flange base and hull?

Respectfully,
Ben Ethridge

[Sparx]

I would focus on getting the mating surface of the through hull that touches the outside of the hull caulked without any gaps or bubbles in the caulking. This includes caulking right up to the threaded section that passes through the hull. I would not worry about getting the threads caulked, but if some caulk gets there it is ok.

[Sparx]

And i would NOT use 5200. Silkaflex would be my preference

[peghall]

Originally Posted by Sparx

And i would NOT use 5200. Silkaflex would be my preference

+1 re 5200! It should be banned for use on boats!

Doesn't anyone still use silicone bedding compound any more???

--Peggie

[Sailmonkey]

Originally Posted by peghall

+1 re 5200! It should be banned for use on boats!

Doesn't anyone still use silicone bedding compound any more???

--Peggie

Silicone?!? Horrible, especially below the waterline.

+1 for NO to 5200. And lather the threads with caulk, it won’t bind them up.

[chasmains]

I first read 5200 is the best ever and I like it. Now I’m reading No Way 5200. What happened?

[sailormed]

It is an awfully effectif glue, but not caulk. Taking things apart after using 5200 is a work from hell
It can take the gelcoat with it when removing it.

[zengirl]

Originally Posted by chasmains

I first read 5200 is the best ever and I like it. Now I’m reading No Way 5200. What happened?

Called the "death paste" because once it's on you can NEVER get it off without more damage to whatever it is attached to. When it came on the market everyone jumped on the bus, only to find out later it was a big mistake like using it on the keel or deck hardware.

[foufou]

Careful use of a heat gun can soften 5200 without damaging the hull. But some care is needed. Not too much heat, just enough, not aimed at the hull but only the fitting to be removed. It isn't the glue from hell!

[flyingfin]

Caulk flange only, try not to get any on the threads. I like to use Life Calk.
After thru hull fitting flange has set up for a few days, clean the threads with a wire brush, attach valve for a few turns to ensure it wont cross thread. If no issues, take it off, wrap threads twice with teflon tape then carefully attach the valve body.

[Coolerking]

4200 fast cure. Use lots.

[Squanderbucks]

I’m another vote for 5200. If you have things you want put in place and want it to stay there and not just be dependent on a few screws or fittings - put it on with 5200 and if the fasteners break - you are still good.
Don’t use it on stuff you take apart on a normal basis.
But how often do you really take off a thru hull? Maybe if you change engines or something similar. Chances then you will be replacing anyway.
There are release products that work pretty well.
Heat helps if needed.
Caulk it all around the flange, coat the hole, coat the threads up the distance to where the threads come through into the boat. Hint - cover threads with masking tape above the backing block. Peel off before placing nut or ball valve on the threads.
Silicone based materials make painting a pain because of getting it all off and it causing paint to “fish-eye” any where the dust hits.

[Cheechako]

Put plenty on there, let it extrude into the threads and out. Clean it up after.
Use 5200 and only ever do it once! That's my motto. 5200 doesn't stick to metal all that well. A heat gun + knife releases it readily.

I love it when I hear: "Dont use that, it does it's job too well!"

[HopCar]

Originally Posted by peghall

+1 re 5200! It should be banned for use on boats!

Doesn't anyone still use silicone bedding compound any more???

--Peggie

Peggie, you’re such a girl. Real men use 5200.

[Cheechako]

Originally Posted by HopCar

Peggie, you’re such a girl. Real men use 5200.

....... and Bronze Toilets!