Sikaflex and skin fittings

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roberth

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Just so as I know (too late now!) why should one avoid sika flex?

I have used this to bed new skin fittings and it seems to have been fine...

Do I have a disaster in store?
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This got lost on a previous thread on fitting new seacocks (posted by GreyishBeard), and I too would like to know some more.

As I understand it, those-who-know-these-things would agree that sikaflex is fine for bedding skin fittings. But there seemed to be some doubt about using it on threaded fittings elsewhere.

I used PTFE on the actual seacock threads, and also smeared a small amount of sika on the last two to three threads just to be sure (I know, entirely unnnecessary, but the cockpit drain is left open all the time, so it's for added peace of mind).

Will I now never be able to undo these again? Or will I just need to top up on the spinach?

As ever, awaiting instant wisdom from the assembled experts

Robert
 
The two main Sikaflex products are both polyurethanes: 291, a good general pupose sealant for use both above and below the waterline, and 292, best regarded as an above-the-waterline sealant glue. Why avoid them?
 
For maximum adhesion the surfaces should be cleaned with Sika cleaner-205 and primed with the appropriate Sika primer. So if you want to be able to separate them again don't get them too clean or use the primer.

Ptfe tape should be adequate on screwed joints although it will be easy to unscrew them again. Dont use more tape than necessary and take care not to overtighten. Easy to do that due to the slippiness of ptfe.

What alternative is there to Sikaflex. Silicone sealants are said to be unsuitable below the waterline.

I thought 291 and 292 were the opposite way round to the way Guernseyman says!

Take a look at www.sika.com/cmi-marine-index.htm
 
[ QUOTE ]
Silicone sealants are said to be unsuitable below the waterline.


[/ QUOTE ]
Not at all, choose a Marine grade silicone sealent thats is suitible bellow the waterline there are many on the market, as i have said on many threads. I use this not only to seal the actual skin fitting to the hull but also to seal threads,( pastic, nylon etc and brass) , aswell as sturn tube assebleys, 'P' brackets to hulls weed filters etc and never had a problem!
But remember at the end of the day its your choice
 
[ QUOTE ]
What alternative is there to Sikaflex.

[/ QUOTE ]

There are many alternatives. You dont really need to use polyeurothene adhesives except for hull to deck or hull to keel joints. You can use a less agressives polysulphide adhesive like 3M 101.

I wouldn't use silicone below the waterline though.
 
Silicone sealants are not very adhesive and absorb water and expand so need to be in dovetail shape joints.

Sikaflex, Purflex et al are polyurethanes which have much stronger adhesion , stretch and absorb almost zero water are usually more suitable for water immersion.
 
OH-MYGAWD-GETYOUR-BOAT-OUT-THE-WATER-NOW

It's simple - for insurance purposes use SIKA 291 or 292 (BLACK) below the waterline for all purposes. The numbers 291 and 292 refer to the uktraviolet retardation of the product.

DO NOT EVER USE SILICON BASED PRODUCTS BELOW THE WATERLINE - Your boat will sink.

DO NOT USE SIKAFLEX products marked as 'DC' below the waterline.

SIKAFLEX 'DC" refers to - "Deck Compound" and is an elastic compound used to seal Teak Deck Structures
 
[ QUOTE ]
I thought 291 and 292 were the opposite way round to the way Guernseyman says!

Take a look at www.sika.com/cmi-marine-index.htm

[/ QUOTE ]

Were you perchance thinking of the Irish documents?

More seriously, the Sika Technical documents do differ from one country to another. It was only when I was reading the Canadian version one day that I came across a prohibition on the use of Sikaflex 292 below the waterline.
 
Sikka product information notwithstanding (is that still a word??) I suspect this dates back to a spate of reported failures of NASA through-hull log fittings. This focussed attention on the NASA fitting instructions which were quite specific about the type of sealant to be used. I think the original thread has fallen down the back of the archives, but there is some post-mortem discussion here

It was a "popular" discussion topic for a while /forums/images/graemlins/smile.gif

I keep an open mind as to whether this was a NASA exclusive "feature", or even anything more than a co-incidence. I think someone even went as far as sourcing a bronze equivalent.

Sikkaflex covers a wide variety of products, though (including silicones) - need to quote the number, too.

Me?.... I went for Raymarine & polysulphide. Not sunk yet, but still plenty of time /forums/images/graemlins/crazy.gif

Andy
 
[ QUOTE ]
Sikaflex®-291
is a one-component, low viscous, medium modulus, polyurethane-based sealing/adhesive compound. This all-purpose grade is used for general sealing applications.

[/ QUOTE ]
[ QUOTE ]
Sikaflex®-292
is a one-component, thixotropic, high modulus, structural, polyurethane-based adhesive system. The product is used for a wide range of bonding applications, deck-to-hull bedding of chainplates, through-hull fittings and toe rails.

[/ QUOTE ] I can't find any recommedation on the website or in the leaflet I have that either is suitable below the waterline but I read "through-hull fittings" as meaning below the waterline.
 
The Technical Data Sheet for 291 specifically says it can be used below the waterline, and of course it is very widely used so. Unknown to many is that on the TDS there is a minimum cure time before being permanently immersed (5 days, I think, from memory).

The TDS for 292 does not make any specific reference to use under water and all the use examples, assofar as I recall, are all above water ones. In any event, one would not want to use 292 for skin fittings anyways.

John
 
Sikaflex ,the Tomato ketchup of boatbuilding..Use with everything-
it's just that there are cheaper products around..
But why carry loads of different halfused tubes of gunk on board?
 
[ QUOTE ]
OH-MYGAWD-GETYOUR-BOAT-OUT-THE-WATER-NOW


DO NOT EVER USE SILICON BASED PRODUCTS BELOW THE WATERLINE - Your boat will sink.


[/ QUOTE ]

Tell that to my friend who has cruised the Med for the last four years with underwater skin fittings sealed with cheapo B&Q silicon(e?) sealants. He isn't aware it has sunk.
 
I have a problem with silicone based sealants. The adhesion of the material to anything (other than fabric you don't want it to get on!) doesn't seem all that good after curing. This can lead to weep paths for thin bits of goop or leaks where it's used more thickly.
A solution is to stick the nut up with silicone when it's slightly loose, then let the silicone cure right through. Finally, tighten the nut and use 'Rubber-draulics' to turn the sealant into a rubber gasket, keeping it sealed forever.

Regards

Richard.
 
Thanks. I had not found that. The leaflet and the info I had found is a bit misleading. Heavens knows why they could not have put the info in the leaflet.
 
Thanks all - I never thought a simple question would create so much traffic!

Glad I used Sika 291 for through the hull, and (mostly) PTFE for threads.

Robert
 
[ QUOTE ]
Silicone sealants are not very adhesive and absorb water and expand so need to be in dovetail shape joints.

[/ QUOTE ]
RUBISH

[ QUOTE ]
DO NOT EVER USE SILICON BASED PRODUCTS BELOW THE WATERLINE - Your boat will sink.


[/ QUOTE ]
ALSO RUBBISH

If this is the case every BROOM owner from 1990 should be wearing aqua lung and be recieving a rather large insurance payouts as we speak

As i said on an earlier post in this thread there are quite a few silicone sealents made particulaly for the job and recomended for the job!!!
Rhone pollenc in norwich make one!
i think before you start scare mungering you should do a little reaserch into the facts!!
 
[ QUOTE ]
Tell that to my friend who has cruised the Med for the last four years with underwater skin fittings sealed with cheapo B&Q silicon(e?) sealants. He isn't aware it has sunk.


[/ QUOTE ]

I think someone should tell him, he has been wasting the GP's valuable resources with his constant complaints of bladder weakness whenever he is on the boat.
 
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