Cheek Block Bedding Compound?

Little Rascal

Little Rascal

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Hi, I have removed, cleaned and am about to replace a couple of cheek blocks (used as deck organisers) on my coach roof. They have SS plates, bolted down onto my textured GRP deck.

What should I use to bed them on? I have standard silicon sealant, or should I use Polysulphide... or something else. I need to waterproof the boltholes too. No chandlery handy unfortunately...

Ta
Jon
 
Domestic silicone is rubbish generally.
I tend to always use Sikaflex. They do small tubes these days which seem to last longer before going solid. The sealant seals the holes as well as bedding the plates.
Clean up with meths afterwards.
Get it on-line.
 
I don't use silicone anywhere on my boat. Its mechanical strength is poor, it inhibits many curing reactions such as polyesters and it cannot be overcoated with anything.

Sikaflex 291 is probably the best for the job but you may not want to buy a whole tube for one small job. Caravan shops sell alternative polyurethane sealants at half the price, as far as I can see for virtually the same stuff. I haven't come across the small tubes mentioned by Lakesailor but one of these would be ideal. Polysulphide is probably perfectly OK and does come in smaller packings but is also quite expensive IIRC.
 
Little Rascal said:
Thanks.

How easy is it to remove fittings once the sikaflex 291 has gone off? At some point I may decide to change my deck layout...
Click to expand...

No problem at all. Easiest way with a robust fitting like your blocks is to insert something sharp, I use an old 1/2 inch chisel, under one edge. The fitting then peels off the Sikaflex. With lighter fittings, such as my aluminium window frames, you need to insert at several points and feed around to gradually peel them off.
 
I'm just wondering what the best method for masking and tooling 291 is?

Should I mask, tool and remove tape before it cures? Or can I let it cure and cut and peel off the excess like with silicone?


Thanks...
 
Little Rascal said:
I'm just wondering what the best method for masking and tooling 291 is?

Should I mask, tool and remove tape before it cures? Or can I let it cure and cut and peel off the excess like with silicone?


Thanks...
Click to expand...

I don't think you can as it's glue as well as sealant. I've used CT1 (which is also glue as well as sealant) to bed a couple of cheek blocks & just wiped off the excess with a damp cloth after tightening the securing bolts...
 
Ok - old thread I know but I started it.

I used Sikaflex 291 last year and had no problems - unfortunately the tube has gone off (inspite of being in the fridge all year)
and I can't get it locally.

I can get 3M 4200FC though - anyone got any experience of it? Is it as good?

Thanks.
 
Before you throw the old tube of Sikaflex away it may be worth trying one final attempt. The sealant cures from the nozzle down, often leaving some liquid at the piston end of the tube. By punching a hole in the side of the tube it is often possible to get some more out, enough for one job.

Otherwise, Toolstation sell PU40, which is indistinguishable from Sikaflex 291, at not much more than £4 per tube.
 
I have a little tip...
I got SOOOOO fed up with paying a fortune for Sikkflex, only to find it had 'gone off' after a couple of months, I found a solution.
Homebase (and many other outlets) sell an 'Evo-stik' product called 'Serious Stuff'. And it most CERTAINLY is serious stuff. It looks like sikkaflex, smells like sikkaflex, feels like sikkaflex, and even seems to work like sikkaflex. What's more, once opened, it never seems to go off when properly sealed.

It's a bit like the old 'No more nails' only it bonds much better. No idea about it's UV properties, but then Sikka is no good for that either unless you get the special one.
 
I'd probably use a piece of neoprene sheet, with sealant just on the holes.
If the sealant is not squeezed too thin, it has a much easier time.
So use rubber to take the compression forces from the fittings.
Then any sealant will work much better, low modulus silicone will work fine if the fitting is mounted intelligently, and the surfaces are clean.
PU sealant sticks better to some surfaces though, and is easier to smooth off to a nice edge if required, using a spatula and rag dipped in white spirit.
 
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