sikaflex

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MCL

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After reading sika marine handbook
(the sika marine handbook), on the correct application of there 292i sealant for use in a keel-hull joint. I have been left with a couple of questions:

Where can I get the recommended spacers at 50 shore A hardness at a thickness of 10mm? - after 3 days searching the internet, I can't find anything suitable.
From what I can tell spacers are left in-situ indefinitely, does this compromise the integrity of the seal? There is no information on how to position the spacers.


For substrate preparation they recommend:
1st sika 208 remover
2nd sika aktivator
3rd sika 206 primer

Primer alone is £40 for a 250ml pot, I was hoping I could clean the surfaces (GRP hull and galvanized steel keel) with acetone, lightly abrade the surfaces, then apply the 292 sealant, thoughts/opinions appreciated.
 
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I would have thought that, within limits, the spacers should transfer the load across the joint making it more stable. Obviously, there must be sufficient thickness of sealant around them to maintain the integrity of the gloop. I have tried using various modern sealants such as Sikaflex variants without the whole primer sequence and found that over time they lose their adhesion to the substrate. With an application such as a keel joint, I'm afraid it really is worth following all the manufacturer's advice - you don't want to have to repeat the process after a year's sailing, do you?

Rob.
 
MCL said:
Where can I get the recommended spacers at 50 shore A hardness at a thickness of 10mm? - after 3 days searching the internet, I can't find anything suitable.
From what I can tell spacers are left in-situ indefinitely, does this compromise the integrity of the seal? There is no information on how to position the spacers.
Click to expand...
Try these people for a small sheet and cut your own... http://www.rhnuttall.co.uk/sheeting/neoprene-sheet/

I've used CT1 to replace a raked out keel joint (not the whole keel) and the adhesion has been excellent without primers.
 
I cut my spacers out of very dense nitrile rubber, and originally was going to use 292 to do my Centaurs keels until i too totted up the price of 4 tubes plus solvent, primer and activator and came up with a figure of over £200 then went to LIBS in 2010 and met the guys from Marineware.com based in Southampton who market Saba sealants and went with their structural sealant called Saba 750XL, it worked a treat as although my boat hasn't been in the water i had the boat sat in a box cradle for best part of six months with the keels dangling free and had no movement.

www.agentlemansyacht.com
 
I am considering using 3m 4200FC or 3m 5200FC instead of sika, as they don't need primers (some substrates may require scotch weld primer). They did well in the recent PBO sealant review. In relation to primers they found that it sika primers improved the bond with sika products but could weaken the bond with different manufactures products, makes sense I suppose!

in relation to sabatack 750XL PBO found it to be best on metals but gave worse performance on GRP.
 
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MCL said:
After reading sika marine handbook
(the sika marine handbook), on the correct application of there 292i sealant for use in a keel-hull joint. I have been left with a couple of questions:

Where can I get the recommended spacers at 50 shore A hardness at a thickness of 10mm? - after 3 days searching the internet, I can't find anything suitable.
From what I can tell spacers are left in-situ indefinitely, does this compromise the integrity of the seal? There is no information on how to position the spacers.


For substrate preparation they recommend:
1st sika 208 remover
2nd sika aktivator
3rd sika 206 primer

Primer alone is £40 for a 250ml pot, I was hoping I could clean the surfaces (GRP hull and galvanized steel keel) with acetone, lightly abrade the surfaces, then apply the 292 sealant, thoughts/opinions appreciated.
Click to expand...

Surprised at the thickness of the spacers .... I guess from the ? that you are too. Only 1mm suggested for other fittings

Shore A 50 hardness is marginally softer than the cured Sikaflex (55). I guess the idea is that that are hard enough to initially tighten on to but soft enough that the joint can be fully tightened onto the cured Sikaflex. It would be mistake IMO to use anything harder than the Sikaflex as they would prevent the joint from being fully tightened onto the Sikaflex

Id guess washers ( need not be circular ??) cut from suitable sheet as suggested by alahol2 and fitted over the keel bolts/studs would be the way forward.

If you opt for a less expensive sealant you will have to match the hardness of the spacers to the hardness of the cured sealant, what ever that may be. CT1 is 60. So not enormously different.
 
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yes, I can understand the logic. I agree that 10mm spacers seams excessive. I emailed rhnuttall but they can only provide rubber at Shore A 60 and as you say anything harder than cured sikaflex maybe problematic.
 
just a thought, could you make spacers out of cured sikaflex to the desired depth size? maybe I could just let some small patches of sikaflex cure on top of the keel before applying the proper seal and lowering the hull? At least I would know it was the right hardness, not sure how I would get a uniform thickness from them all.
 
This question raised about the 10mm spacers.
Surely this must be wrong.

If the keels are spaced 10mm off the hull by these spacers and then held in compression by the keel bolts this must result in the keel bolts being in bending to some degree. The spacers and sealant will not stop the keels being deflected by sailing forces.


I know the OP has checked this again but to me it is unsound as an engineering proposition.
The width of the keel to boat joint provides support for side loading on the keels.

As others have noted 1 or 2mm seems correct for the washers or complete sheet of neoprene etc.
 
I think the rational of sika is that the 10mm spacers compress with the final tightening of the keel bolts to ensure a watertight seal. However I agree it does seam excessive.

I am interested to know others thoughts on making spacers by just letting some small patches of sikaflex cure on top of the keel before applying the proper seal.
 
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I will Nuttall's another try they quoted me £32 for a 30cm x 30cm x 5mm sheet. Way more than I need, maybe I should ask for a 10x10 sheet.

essexboy: whats a misper? I googled it but all it came up with was a police "missing person" report.
 
MCL said:
.

essexboy: whats a misper? I googled it but all it came up with was a police "missing person" report.
Click to expand...

I think he meant misprunt.

A bit of a puzzle this thickness thing. They say 1mm in the section about other fittings, not 1.0mm. You'd expect a bit more thickness for the hull to keel joint perhaps ???????

They say to apply the sealant in 20 to 25 mm high triangular profiles ...... clearly expecting a finished joint thicker than 1 mm!... or you'd waste a lot!

I reckon it means what it says ..... 10mm

They say that the joint "absorbs the dynamic stresses generated in this area"
 
I think you are right. My boat is 14 foot and has bilge keels that weigh 30 kg each, the biggest spacers I think I would need is 5mm!
 
MCL said:
I think the rational of sika is that the 10mm spacers compress with the final tightening of the keel bolts to ensure a watertight seal. However I agree it does seam excessive.

I am interested to know others thoughts on making spacers by just letting some small patches of sikaflex cure on top of the keel before applying the proper seal.
Click to expand...

go to ebay and buy yourself some nitrile rubber, you can buy sheets, i did; of the 3mm variety, its of a density that will compress abit but i ended up with a perfect 2mm seam all the way along the hull to keel joint using 3mm rubber. i made mine by simply putting the sheet on a pillar drill, drill the outside dimension first then drill the diameter of your keel studs (centres) its an easy way of making keel spacers.

i wouldn't put patches of sika flex on the top of the keel as if its eneven it'll be a pain in arse to get the keel seated, dense rubber is the way ahead, here have a look what i did:

https://picasaweb.google.com/110182886418433827802/GoodThingsAComing?authuser=0&feat=directlink

cheers

roger

www.agentlemansyacht.com
 
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Roger, looked at your phots and the last one seems to imply you're going to glass over the keel to hull joint. That would be a bad idea as there needs to be some flexibility in the joint.
 
There is, theres a two mil elastomer washer in the form of the saba sealant and a flexible epoxy used to tape the joint. FWIW i'm not advocating MCL glasses over his keel joint i was trying to show the 3mm spacers i fitted before sealing the joint.

IMO i think flexibility in the joint was part of the problem and Westerly realised this around '74, '75 as the entire keel and stub arrangement got re-designed. We know this by the fact that on the Centaur Westerly increased the number of keel bolts from 7 to 9 as well as drawing a new keel profile and altering the angle of the keel stub relative to the keel. To copy this improved design I Increased the thickness of the inside of the keel stub some 20% so the stub angle matched the keel so less eneven loading on the inside of the keel and then took the glass up onto the hull when sheathing the rest of the hull after a gel strip.

As i've said to anyone thats asked about the validity of my approach, time will tell...............

cheers

roger
 
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