Marelon seacocks - Sikaflex or PTFE between through-hull and seacock?

KompetentKrew

KompetentKrew

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I have a couple of TruDesign seacocks to fit - the through-hull screws very easily into the body of the seacock, and I thought that it would be appropriate to wrap the thread in PTFE tape before installing the seacock on it.

I searched to check what the manufacturer says - I can't find any manuals on the TruDesign site, but the FAQ seems to suggest that Sikaflex as an alternative on the thread of the through-hull when fitting the seacock. Is this really right? It seems a bit permanent.

Q: What sealant should I use between a bronze or stainless skin fitting and a TruDesign ball valve ?

A: The same options as you would use for sealing any TruDesign composite fitting to a TruDesign composite Ball Valve:
  • 3M 5200
  • 3M 5200 FT (Fastcure)
  • Sikaflex 291i
  • Loctite 55 Pipe Sealing Cord
  • Standard PTFE thread tape
https://www.trudesign.nz/marine/que...nless-skin-fitting-and-a-trudesign-ball-valve
Click to expand...

I originally started writing this in discomfort at their advice to use Sikaflex or 3M, having overlooked the last bulletpoint which states PTFE tape is OK. But having typed this all out, I might as well press post and see what you all think.

I'm not very experienced in DIY, and assumed to use a wrap or two of PTFE, just enough to make it feel more comfortable and not loose. With a dry fit the seacock rattles a fraction of a mm on the thread.
 
I used Sika 291i for the through hulls and plumbers thread sealing compound (cant remember the make) on the valve threads. If you use 291i on the threads, then it's a permanent fix. Are you not replacing hull fitting and hose tail as well? They are more prone to failure than a valve, as I found out.
 
I use Sikaflex, or more often these days Puraflex 40, the same stuff as far as I can tell for half the money, for just about every sealing job above and below the water. It may not be the absolute best for every one but is certainly good enough. A genuine jack of all trades that saves stowing half a dozen tubes that will all have gone solid by the time you want to use them next.
 
vyv_cox said:
I use Sikaflex, or more often these days Puraflex 40, the same stuff as far as I can tell for half the money, for just about every sealing job above and below the water. It may not be the absolute best for every one but is certainly good enough. A genuine jack of all trades that saves stowing half a dozen tubes that will all have gone solid by the time you want to use them next.
Click to expand...
How much do you use on threads please, Vyv? Are you able to undo them again afterwards?
 
KompetentKrew said:
How much do you use on threads please, Vyv? Are you able to undo them again afterwards?
Click to expand...

Use enough that sealant extrudes from the end of the fitting. It's a myth that it is so strong when cured that it cannot be undone. Big flanges need to be levered from one end but it will always part.

The only rider to this is that liquid PTFE, as sold now by Screwfix etc., is a brilliant sealant. But if you were to use it on a screwed fitting you would need a lock nut to prevent rotation in use. Probably not with Sikaflex
 
Marelon is a brand name owned by Forespar, which also make plastic seacocks. It has nothing to do with TruDesign.

A PU adhesive sealant is probably best (one of the first three). It's meant to be permanent! Why would you want to unthread the seacock off the thru-hull ever again? Otherwise Loctite's pipe sealing cord. Definitely not PTFE tape (has that ever sealed properly anywhere?).

I've used Sikaflex for the thru-hulls and seacock when I installed my TruDesign ones in 2015 and they haven't leaked a drop. I also used PTFE tape on the elbows and two of those did leak ever so slightly (a drop a day or so, but annoying) until I undid them and replaced the rubbish tape with more Sikaflex. So save yourself doing it twice and use the sticky goop. Below decks/waterline (away from UV), PU sealants are excellent. Above, not so much.
 
KompetentKrew said:
I have a couple of TruDesign seacocks to fit - the through-hull screws very easily into the body of the seacock, and I thought that it would be appropriate to wrap the thread in PTFE tape before installing the seacock on it.

I searched to check what the manufacturer says - I can't find any manuals on the TruDesign site, but the FAQ seems to suggest that Sikaflex as an alternative on the thread of the through-hull when fitting the seacock. Is this really right? It seems a bit permanent.



I originally started writing this in discomfort at their advice to use Sikaflex or 3M, having overlooked the last bulletpoint which states PTFE tape is OK. But having typed this all out, I might as well press post and see what you all think.

I'm not very experienced in DIY, and assumed to use a wrap or two of PTFE, just enough to make it feel more comfortable and not loose. With a dry fit the seacock rattles a fraction of a mm on the thread.
Click to expand...

You want it to be permanent. Seacocks, skin fittings etc are only ever undone when when they need to be replaced, which in the case of your plastic ones is never.
PTFE tape is a remarkably slippery material which is used to seal joints which will need to be undone frequently during their service life. This slippery quality is not desirable in a seacock/skinfitting deep in a locker, which might be disturbed by a knock from loose equopment.
 
I fitted a Trudesign 1 1/2inch seacock/skin fitting some 3 months ago. It replaced a Forespar through hull that had become too stiff to turn and was fully sikaflexed in as Forespar recommend. The Forespar had been fitted some 5 years earlier and I was not best pleased.

If your Trudesign skin fitting and valve are similar to those supplied to me, the threads are an extremely poor fit. I considered emailing the manufacturer but thread tolerances are a difficult subject to discuss (especially plastic threads) and I did not think it would get me far, so in the end I wrapped an awful lot of ptfe thread tape around the skin fitting thread and assembled it - sikaflex on the actual skin fitting of course. I wanted to be able to replace the valve alone if it ever became necessary. I have had no issues with the setup since installation.

Interestingly I did email Forespar about their stiff valve (OEM thru valve type) and pointed out that after experimenting with it on the bench (after removal), I could release the ball valve by slackening the four bolts that hold the assembly together. To my surprise I had a reply saying that it was ok to do this. Yet their website and instructions at the time I purchased stated it most definitely was not ok to do this. In fact having just checked the website it says only do this under Extreme Circumstances, I did not consider my circumsatnces "extreme"
 
In my ignorance I've used PTFE tape on all sorts of pipefitting jobs both on my boats and at home (where permanence is also required). It hasn't let me down yet and where dismantling has been needed, as in when I fitted a new bathroom suite, it was easy.
Spirit (of Glenans) said:
You want it to be permanent. Seacocks, skin fittings etc are only ever undone when when they need to be replaced, which in the case of your plastic ones is never.
PTFE tape is a remarkably slippery material which is used to seal joints which will need to be undone frequently during their service life. This slippery quality is not desirable in a seacock/skinfitting deep in a locker, which might be disturbed by a knock from loose equopment.
Click to expand...
 
I believe Yngmar is quite correct, Marelon is a brand name of Forespar, that's not to say both companies aren't using identical plastic though!
 
I second the suggestion that Puraflex 40 is the only adhesive/sealant you need on board. It is a polyurethane adhesive/sealant, manufactured by Sika and you can buy it in Toolstation for £5.

I've now used many tubes over several years and everything has stayed stuck down. But if you do want to remove something it is possible, without damaging gelcoat.
 
I have bedded and sealed the Forespar Marelon on my boat with 291, and no leaks whatsoever.

If I thought I would need to remove the valve from the skin fitting thread then Loctite 577 would form a decent but non permanent seal.

When bedding in the fitting I do not pull the fitting up hard to the hull but leave a small gap ~ 2mm to allow the sika to form a gasket between the fitting and the hull then after a few days pull the joint up, as this provides better flexibility in the overall fitting, that a thin film of sika will not provide..
 
"When bedding in the fitting I do not pull the fitting up hard to the hull but leave a small gap ~ 2mm to allow the sika to form a gasket between the fitting and the hull then after a few days pull the joint up, as this provides better flexibility in the overall fitting, that a thin film of sika will not provide.."
A recent discussion on here concluded that it's best not do this but if it works for you, why not.
 
ghostlymoron said:
"When bedding in the fitting I do not pull the fitting up hard to the hull but leave a small gap ~ 2mm to allow the sika to form a gasket between the fitting and the hull then after a few days pull the joint up, as this provides better flexibility in the overall fitting, that a thin film of sika will not provide.."
A recent discussion on here concluded that it's best not do this but if it works for you, why not.
Click to expand...
A conclusion, on here - are you sure ?
 
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