Changing through hull fittings

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Alcyone

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Our pre purchase survey suggested that we change our plastic through hull fittings for bronze. I've removed the old ones and cleaned inside and out as well as the hole through the hull. The new ones come with a rubber (?) sealing washer which goes outside.

My question is, do I need to apply additional sealant, such as sikaflex, and if so, where? Inside, outside, in the hole?

Thanks in advance.
 
I always bed mine on stickyflex, but then I have an old timber boat and I wouldn't trust a rubber gasket to seal properly. The stickyflex also helps stop the valve from turning in the hull when you screw on or change the hose tails.
 
Can't go wrong with putting sealant goop everywhere. Just make sure the inside of the hole is properly sealed, but it SHOULD be epoxied if you've got core-material. Another thing that'll be very important when you fit the new fittings: make sure there's a key for the fitting. A wedge of steel plate big enough to engage the slot or lugs inside the fitting means you can hold the fitting and turn the nut home hard enough to compress the seal.
 
When we replaced ours we put a ring of Sikaflex on the fitting (the lip where the bronze goes flat against the hull) and then some more Sikaflex on the inside around the tube where it comes through the hull.

The inside of the through-hull has two lugs on it so you can wedge a metal bar in it to stop the throughull turning whilst you screw the seacock onto the tail (there is a special tool around for this job, but we used a big metal file with the same results).

I have heard that some through-hulls come with the rubber washer and you don't need to use anything else - but I have the type without and am happy with the good dollop of Sikaflex I used! When you tighten the through-hull the sikaflex should ooze out from between the throughhull and the hull on the outside - make sure it forms a complete ring around the throughhull and wipe off any excess with acetone (if you leave it messy the sea creatures love it!!)

I'm sure you know this already, but make sure you fair the hull around the hole to give good adhesion and also to make sure the surface is as flat as possible for the through-hull to lie against.

Jonny
 
OK, cheers. I was tempted to squirt sikaflex inside the hole and on the inside anyway. It's pricey stuff, but not as pricey as lifting me boat from the sea bed.
 
G'day Martin,

You say you have cleaned out the hole thru the hull; have you checked to ensure no raw glass is exposed?

This can be an entry point for moisture in the hull.

You only need half an egg cup of epoxy resin, paint wet on tacky to get 4 coats and sleep well.

Avagoodweekend......
 
If you use the sealing ring that is supplied it goes on the outside. If it's there it keeps the water out of everything, glass layup around the hole included. It should be all that is necessary.

Think about it if there is a water tight seal between the flange and the hull that's it!

However, whether or not you choose to use it is another matter. If you use a sealant, and silicone is not really good enough, it is that outer joint that is the important one even if you put a little on the inside as well.

If you use a sealant the nut on the fitting should initially only be tightened until there is a definite thickness of sealant left to form a "gasket". It is fully tightened once the sealant has cured. Little wedges can be made with match sticks to facilitate this. They are removed before the final tightening.

Remember you want proper bronze for best possible corrosion resistance, failing that dezincification resistant (DZR) brass. Under no circumstances use ordinary brass and run a mile from a material known as "Tonval"

Remember also that plastic fittings such as a reinforced Nylon like Marelon never corrode!
 
Ordinary silicone is fine, cheap, readily available and can be taken apart when needed. As the gentleman said, always seal the raw GRP edge, I use Gelshield, but that is just because I have a can knocking about.
 
I wouldn't use ordinary silicon for bedding underwater thru-hull fittings.

All mine are bedded with an adhesive bedding compound (Sikaflex 291 etc.). Similar to VicS, I tighten them up finger tight so the sealant ouzes out of the side, then leave 24 hours to cure, and then fully tighten with a wrench. If they are fully tightened before the sealant has cured, then most of it is probably squeezed out of the side or up the hole, and little remains between the hull and flange of the fitting. That's my reasoning anyway.

Or use matchsticks of course.
 
doug748 said:
Ordinary silicone is fine, cheap, readily available and can be taken apart when needed. As the gentleman said, always seal the raw GRP edge, I use Gelshield, but that is just because I have a can knocking about.
Click to expand...

DO NOT USE SILICONE SEALANT!!!!

Silicone sealant breaks down in salt water. You'd save yourself £5 and lose your boat to Davy Jones!
 
prv said:
It was five years ago, so if he was going to use silicone he probably has by now.

Pete
Click to expand...

Ha Ha - yes I realised that but someone may read the advice and take it...even in these better informed and more enlightened days of 2013!! :)

I realise that there are sea water resistant silicones but PU is vastly superior...except when you need to remove it from skin.
 
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