Sikamastic SNB - a slow dryer?

[Guest]

Hi there,

 

A little while back I was looking for some sealant for a couple of cleats and a jammer. The friendly assistant at Sailor's Corner recommended to me Sikamastic SNB "Non-Setting Butyl Sealant" as being suitable for potentially removable hardware like this. And that's what the tube said too. I thought would dry into a soft rubbery removeable finish after a week or so.

 

3 weeks later (after application) and it's still fairly gooey. This is a bit inconvenient as I don't want to be smudging sealant goo over the deck, through the lines etc.

Sika's info sheet here:

http://www.sika.co.nz/nz_ind_indtds_sikamastic_snb_0510.pdf ...it says "Soft, tack, and engageable for up to 6 months after initial application".

 

Anyone familiar with this product - will it eventually set OK, or should I redo with something else? If so what? And why make a product that takes 6 months to set?

 

Cheers,

Craig.

[Guest]

The tech specs in the link you posted say it all...

 

Skin Formation Time - Soft, tack, and engageable for up

to 6 months after initial application.

 

That may not be good news.

[wheels 543]

Mastic is just that. It is a gooey substance. The idea is that it continually remains gooey'ish so as it remains kind of like a "self Healing" sealant. It is NOT a bedding compound, nor an Adhesive. It is a Mastic sealant and only good for sealing. If you are frequantly removing items and refitting, then this is a good material to use as it does not adhere. But you would not normally do that with most fittings. A bedding compound is there to add strength to the fitting by spreading the load over a greater surface area of the deck or say a thin section of mast where the thread depth is not alot and not taken just by the Screws/Bolts on their own. The fact that it seals is another additional part of it's job. A third factor in it's job is as an Isolator between say Aluminium and SST for instance.

So no, i would not have used Mastic for this kind of purpose. An Adhesive Sealant would be the best choice, which still allows removal of the fitting at a later date. it just takes a sharp cutting blade underneath or sometimes a bit of sideways force will tear it free.

[Guest]

Thanks Wheels. So something like that Sikaflex 291 would be what I'm looking for then? (I read the genoa track thread below). The book I'm reading says don't use polyurethane for removable stuff but sounds like it's the go.

 

A bit annoying that the tube has pictures of deck hardware being attached with the Sikamastic. Live and learn.

 

Cheers.

[Farrari 4]

Yep, the Sikaflex 291 did the job for my Genoa tracks. Interestingly this tube also has pictures of deck hardware being attached. I did wonder if they had used that mastic stuff previously on mine because it was still a little gooey after 20 odd years.

[wheels 543]

I guess it is just how you approach it. It may well be that ones like MrWolf or FNG do it another way, but I come from the side of the tracks of wanting to enure the part doesn't dissapear off into the Sunset with out me and the rest of the boat. I use a Urathane Adhesive Sealant. You could also use just a Urathane Sealant. Mastics have been around since Noah was boat biulding. Urathanes haven't.

I like to apply a good couple of mls thick, pull up till it just starts to squeeze out, wipe off the excess and then leave overnight. Then the next day screw up tight. You should never ever get a leak.

You can stop the mastic from getting everywhere by using some Turps and a rag and wiping around the edges till the seal is flush and you can't get it picked up on your shoes etc.

[Guest]

Mastic, sikamastic and a host of other soft seal types primarily belong in the red lead and carvel school of boat building, they semi self reseal and heal as well as adding protection to the substrate without tearing chunks out on removal as you'd find with urethanes and other adhesive/ sealants