Sealants again

[Clyde_Wanderer]

I asked at my local chandlers the other day for the most suitable sealant to use for the paddle through hull unit, (plastic) and was handed a tube of Life-Calk, and told that it was the best stuff.
Got to reading the tube today, to discover it says not suitable for plastic.
So if not that, or sikaflex, What can I use, as the chandlers reckon that silicone is not suitable for under water use, and I dont know of anything else.
Help. /forums/images/graemlins/confused.gif

 

[PuffTheMagicDragon]

The transducer for my echo sounder is made of plastic and the flange on the outside is bedded onto LifeCalk. (it's made by Boat Life, no?)
There are two types: use the black one - continuous immersion. Don't tighten up hard right away. I fitted that transducer in 1998 and it seems to have been ok.

 

[Clyde_Wanderer]

Thanks Wally.
But the point I am making is that the instructions on the Life Calk tube says "Not suitable for plastic". Thats why I posted here to find out what to use.
Cheers, Eamonn.

 

[jerryat]

Well I checked with Raymarine a couple of years ago when I fitted a new set of ST60 intruments and they confirmed that Boatlife's Lifecalk was perfectly ok for their (Airmar) transducer.

Have used the same stuff on other plastic transducer too over the years with no ill effects whatsoever.

 

[Salty John]

Dont use Life Calk (a polysulphide), use a polyurethane such as Sikaflex 291. Life Calk is, as you say, not suitable for plastics to fibreglass. Polyurethane is suitable for fibreglass and plastics but not acrylic plastic such as ABS and Lexan. 3M 4200 would be another choice.

 

[Clyde_Wanderer]

Thanks all for your advice, although very conflicting.
I have just spent the last hour on the phone to Sika UK, and Nasa instruments UK and DowCorning UK.
Firstly spoke to Sika who assured me that 291 (which is a polyeurothane sealant) IS suitable for ABS, and PVC plastics only.
Then spoke to Nasa technical, who assured me that the log hull unit is made from ABS plastic, but did say to use any marine silicone which has a vinigary smell.
So I contacted DOW CORNING who recomended their 748 white silicone sealant, and I am waiting for him to email me with its application data.
Now I am as far on as I was this time last night /forums/images/graemlins/confused.gif

 

[Salty John]

Very complex subject it seems! A few years ago I copied the information from a BoatUS catalogue and have just consulted my notes. It seems that polysulfides attack some plastics; polyether attacks some plastics but is ok on ABS. Silicone is compatible with plastics but has low adhesion and not recommended for underwater. So, specifically for through hull fittings on GRP boats, they recommend a polyether such as 3M4000. They recommend polyurethane such as Sikaflex 291 for through hulls, except for ABS. A Boatlife product called Lifeseal, not Lifecalk, is also recommended for through hulls, it is a silcone/polyurethane mix.

 

[richardandtracy]

When all this conflicting information becomes too confusing, use the old adage of 'Go back to Basics'. Under this rule you obviously you need 'Plumbers Mate'. I think it's a sloppy linseed oil putty. Won't harm anything and can be used on drinking water stuff too.

Regards

Richard.

 

[pvb]

Ordinary silicone sealant...

Ordinary silicone sealant will work fine, and you'll be glad you used it if you ever need to remove the fitting. Doesn't the Nasa instruction leaflet mention silicone sealant?

 

[Clyde_Wanderer]

Re: Ordinary silicone sealant...

Yes I went with JS48'S advice and bought Lifeseal which is suitable for ABS plastic, which is what my through hull is supposed to be made of.
While applying Sikaflex 291 to my hull/keel joint today I came to a conclusion that if sikaflex 291 was suitable for plastic, it would not be in an aluminium tube, but plastic tube for cost effectiveness, where as Lifeseal and silicones are in plastic tubes and suitable for use on plastics.