Mounting deck fittings

[rossd 16]

Wanting some advise or what others are doing. I am remounting all my deck fittings and have used sika 291 between fitting and deck. Have done stem fitting , backstay fittings , and tracks as these fittings are not likely to have to come off for another 20 years. The pushpit I did with Sika mastic which I wont use again as to soft and guey. I still have pulpit, Stanchions , winches to fit still. Now the jobs half done I decided to read the instructions! These things are not likely to be so permanent and they recommend a 1 to 3 mm gap between deck and fitting so as a knife or wire can be used to cut it off in future. I was thinking of making some spacer washers out of plastic bottle tops that the bolts can go through. Is this the way to go?

[wheels 543]

I usually just fit as normal, but I don't tighten the fitting down hard. I then wait for a few days for the sealant to cure and then tighten the bolts/screws home.

[John B 106]

If you countersink each hole you in effect create an extra O ring of rubber around them.

Generally what ' they 'say is to bed the things down relatively lightly ,then go back a day or three later and torque em up a bit more . That compresses the rubber and gives you a better seal. Works for me anyway.

oops , what Wheels said.

[Chewing Gum 17]

I use sikaflex MS which is a modified silicone (don't use ordinary silicone) and dont bother with the retorquing and have no leaks. I prefer it to the polyurethane Sika sealants because it is easier to remove fittings and does not wreck the substrate when you pull fittings up. Our boat is timber with ply and teak decks but I would do the same with a GRP boat. Use lots of masking tape to avoid mess and for cleanup meths works well.

[rossd 16]

What I am thinking about is ease of removal in future. Has anyone removed a fitting that has been attached with Sika 291? I know removing bonded glass would be a nightmare without a gap.

[John B 106]

It doesn't seem overly aggressive to me, not as if was 5200 or anything. I use it for all that sort of stuff now .

[wheels 543]

I like using Adhesive Sealants so as the load is spread over an area, rather than just on the screws/bolts. Especially if it is just screws. You can still get the fittings off when the time comes.

[Terry B 71]

I ain't no expert (and I HATE drilling holes in the boat) - so I search the net for "experts". http://www.boatus.com/boattech/casey/be ... rdware.asp

Here's what Don Casey says about tightening the bolts/screws right down after the sealant has set - he makes sense - if you tighten the screws (or bolts if you can't just tighten the nuts) then withdraw the bolt/screw carefully, add more sealant to the bolt/screw and tighten her all up.

Makes sense as if you turn the screw/bolt after the sealant has hardened then you break the seal.

 

And yep, always countersink around the bolt/screw head.

 

Or am I wrong???

[Chewing Gum 17]

Sounds like a lot of hassle to me. I don't like retightening for the reason mentioned that it disturbs the seal around the bolts. I have had no problems with leaks with just tightening once using sikaflex ms and I don't bother with the countersink idea either.

[Guest]

I always countersink

 

you can use sika snb if you want to remove the fitting easily, we call it chewing gum. lots of rags and kero handy.

 

Sika or bostick Ms compounds are very good, or use the old faithful 291

 

always try and turn the nut instead of the bolt/screw

[rossd 16]

The Sika handbook is pretty detailed.

 

http://www.bluemoment.com/downloads/sik ... ndbook.pdf

 

Pretty much people following advice from handbook apart from spacers to prevent dry joint which sounds like no one is using!

 

Quote from book:

 

It is vital to ensure that the

adhesive is not simply squeezed out

again when the fixing screws are

pulled up tight. To prevent this

happening, shims approx. 1 mm

thick should be threaded over the

screws on the underside of the

fitting to act as spacers. The screw

holes themselves should also be

filled with sealant prior to fixing.

Spacing the fitting off the deck by

2–3 mm also facilitates its removal

at a later date, when a cutting wire

or knife blade can be inserted

between the base of the fitting and

the deck. Sikaflex®-291or 292 should be applied to the deck and the fixing screw holes in a bead of

the required thickness. The fitting is then pressed into position.

The fixing screws should be tightened sufficiently to pull the fitting down on the spacers,

but no more. Use a plastic spatula to remove excess sealant squeezed out around the

edges. After 24 hours tighten the screws.

[John B 106]

Here's an odd one... I have a minor mod/ experiment I'd like to make over christmas below the waterline. What would be nice is to have a sealant with some underwater sticky properties , even a tape. Does such a thing exist ? If it doesn't I'll just go without ,but as I say ... it would be nice .

 

don't worry , it'll be removed or refixed properly when the boat is hauled in feb/ march.

[rigger 47]

have not used them:

 

http://www.chisholms.co.nz/productinfo.php?prodID=86

 

or

 

http://www.maxilam.co.nz/shop/Sealants/ ... wer-2.html

[wheels 543]

Epoxy puttys like Selleys Aqua will work underwater and harden underwater. But it will be a solid bond.

There is also that clear (I think it's a selleys product) in a tube sealant that is supposed to stick and seal to wet surfaces.

[rigger 47]

There is also that clear (I think it's a selleys product) in a tube sealant that is supposed to stick and seal to wet surfaces.

 

Thanks wheels the mention of selleys reminded me of Seal Once http://boat.net.nz/index.php?route=prod ... ct_id=3295

Have used this one - sticky S%!^