Keel bonding to hull, and sealant.

[Rappey]

Westerly centaur. The bilge keels have hollows in the casting filled with expanding foam.. This has been replaced , epoxy filled over the top of the foam giving a large flat surface to bond to the hull. The keel has then been coated with a few layers of epoxy paint
This is where it gets interesting..
Sikaflex has been used for the job and the person whos boat it is took advice from sika technical which sealant/adhesive to use and how to use it. Apparently they have a lot of information on how to bond keels to hulls.
A 5mm gap is to be left between the keel and the boat hull which is totally filled with sika. Once cured the keel bolts can be torqued up to the required amount which was achieved.. while maintaing the 5mm gap. Ive never heard of anything like that before and think the keels should be touching the grp.. What do others think or know?
Im helping a friend on a boat next to this centaur.. We have been doing some serious work filling/fairing with jotun mega filler (2 part epoxy) and then 4 coats of jotun epoxy on the hull below the waterline.
The centaurs keel was sealed/bonded about a month ago. The sealant went of like sika does..
But now the sika is going soft.. Its like its reverting back to how it came out of the tube?
A few smears of sika were on the surface of the keel, probably from wiping it off ones fingers ..These smears are now very sticky and its like its not set, but it had previously..
Has anyone come across sealant reverting back to sticky before?
The centaur owner has suggested the dust from my friends boat alongside in the yard from sanding the jotun mega filler may have affected it or possibly the fumes from the epoxy paint has had an effect? We used ct1 to go around the keel/hull joint on my friends boat and its perfect..
What is also a little strange is that only the sika on the outboard side of the keel facing my friends boat has gone sticky, the inside is still solid.

 

[PabloPicasso]

Are you sure it's Sika and not a bird poop?

 

[Wing Mark]

Westerly centaur. The bilge keels have hollows in the casting filled with expanding foam.. This has been replaced , epoxy filled over the top of the foam giving a large flat surface to bond to the hull. The keel has then been coated with a few layers of epoxy paint
This is where it gets interesting..
Sikaflex has been used for the job and the person whos boat it is took advice from sika technical which sealant/adhesive to use and how to use it. Apparently they have a lot of information on how to bond keels to hulls.
A 5mm gap is to be left between the keel and the boat hull which is totally filled with sika. Once cured the keel bolts can be torqued up to the required amount which was achieved.. while maintaing the 5mm gap. Ive never heard of anything like that before and think the keels should be touching the grp.. What do others think or know?
Im helping a friend on a boat next to this centaur.. We have been doing some serious work filling/fairing with jotun mega filler (2 part epoxy) and then 4 coats of jotun epoxy on the hull below the waterline.
The centaurs keel was sealed/bonded about a month ago. The sealant went of like sika does..
But now the sika is going soft.. Its like its reverting back to how it came out of the tube?
A few smears of sika were on the surface of the keel, probably from wiping it off ones fingers ..These smears are now very sticky and its like its not set, but it had previously..
Has anyone come across sealant reverting back to sticky before?
The centaur owner has suggested the dust from my friends boat alongside in the yard from sanding the jotun mega filler may have affected it or possibly the fumes from the epoxy paint has had an effect? We used ct1 to go around the keel/hull joint on my friends boat and its perfect..
What is also a little strange is that only the sika on the outboard side of the keel facing my friends boat has gone sticky, the inside is still solid.

Is the sticky side the side which gets sun on it?
Is this all outdoors?

Was your friend making dust before the sika work was done or only after?

Sika make dozens of varieties of snot.
I would think it unlikely that dust had any effect. Likewise vapour unless there's vast amounts of it in the air, condensing on the cold keel.
Much more likely to be something leaching out of their keel? Wrong sort of epoxy? Epoxy used at wrong temperature?

As for the 5mm gap, designing joints which seal is not trivial. Sealant does often work better in joints which are not squeezed to zero gap, but having a layer of sealant right across the joint will have consequences , the keel will move as the loads on it change. I would think it's necessary to know what the mechanical designer intended, not just the sealant supplier.
Things I've worked on with sealed joints, you might have an area of the joint which locates things mechanically, bolted up tight, but a sealing area which is a gap full of sealant.

 

[Neil_Y]

I don't know about Sika but we advise bedding shaft bearings on epoxy, and less than a mm thick it doesn't bond so it's easy to peel off when you change bearings. I've used arbothane sealant adhesives and they also detail leaving a thickness of sealant to bond with max strength. Follow the manufacturers instructions.

 

[jwilson]

I am not sure I'd want to sail far on a boat with 5mm of Sikaflex between top of metal keel and GRP hull. There's a blot of sideways bending force on the joint once a fin-keel boat heels, and very variable bending force applied to bilge keels.

 

[2Tizwoz]

Westerly centaur. The bilge keels have hollows in the casting filled with expanding foam.. This has been replaced , epoxy filled over the top of the foam giving a large flat surface to bond to the hull. The keel has then been coated with a few layers of epoxy paint
This is where it gets interesting..
Sikaflex has been used for the job and the person whos boat it is took advice from sika technical which sealant/adhesive to use and how to use it. Apparently they have a lot of information on how to bond keels to hulls.
A 5mm gap is to be left between the keel and the boat hull which is totally filled with sika. Once cured the keel bolts can be torqued up to the required amount which was achieved.. while maintaing the 5mm gap. Ive never heard of anything like that before and think the keels should be touching the grp.. What do others think or know?
Im helping a friend on a boat next to this centaur.. We have been doing some serious work filling/fairing with jotun mega filler (2 part epoxy) and then 4 coats of jotun epoxy on the hull below the waterline.
The centaurs keel was sealed/bonded about a month ago. The sealant went of like sika does..
But now the sika is going soft.. Its like its reverting back to how it came out of the tube?
A few smears of sika were on the surface of the keel, probably from wiping it off ones fingers ..These smears are now very sticky and its like its not set, but it had previously..
Has anyone come across sealant reverting back to sticky before?
The centaur owner has suggested the dust from my friends boat alongside in the yard from sanding the jotun mega filler may have affected it or possibly the fumes from the epoxy paint has had an effect? We used ct1 to go around the keel/hull joint on my friends boat and its perfect..
What is also a little strange is that only the sika on the outboard side of the keel facing my friends boat has gone sticky, the inside is still solid.

Sika require the 5mm gap so that their sealant can cure satisfactorily and is sufficiently thick to flex without the joint leaking.

You could have achieved the 5mm gap using 5mm thick galvanised washers on the fixing studs which were surrounded by sealant. That would ensure the keel was rigidly fixed and that the sealant would be thick enough to flex during changing load and temperature conditions.

Have you painted the Sika sealant? That may have caused it to soften if the paint was unsuitable..

 

[jwilson]

If the Sikaflex flexes with or without washers the keel or keels are moving under load: not IMHO a good idea. For many applications I'm sure a 5mm sealant bed is a good idea, just really not sure that a ballast keel is one such job. I suspect every boatbuilder winds up the keel bolts to torque ONCE, till iron or lead keel or keels are hard against the hull, with sealant just filling the inevitable small gaps and stopping water getting in to the bolt/stud threads.

 

[Wing Mark]

Sika require the 5mm gap so that their sealant can cure satisfactorily and is sufficiently thick to flex without the joint leaking.

You could have achieved the 5mm gap using 5mm thick galvanised washers on the fixing studs which were surrounded by sealant. That would ensure the keel was rigidly fixed and that the sealant would be thick enough to flex during changing load and temperature conditions.

Have you painted the Sika sealant? That may have caused it to soften if the paint was unsuitable..

Ideally the boatbuilder would design the joint to work in a particular way with whatever sealant he was designing around.
Why change what the designer designed?
Sealant will stretch so much before failing. 100% is not a bad guess IIRC. So a 5mm bead will stretch 5mm and a total squeezed out join will stretch not much at all.
Sometimes a groove around the edge filled with sealant, or a countersink of the bolt holes does the job.

The Sika turning sticky in time might be solvent entrapment in layers below it?
Or some other by product from epoxy?

There are some paints and varnishes which just don't work over some epoxies.
This bit my backside with a wooden dinghy, but I am vague about the details now. Trad varnish over West maybe?
I've been trying to forget that for over a decade now so I could be wrong!

 

[2Tizwoz]

This Technical data sheet is for a BONDIT polyurethane but similar limitations will apply to what has been used.
'Limitations
Do not use for aquarium construction. Do not use with bitumen or asphalt. Not suitable for joints with movement greater than 15%.
Discolouration of white and grey shades may occur when exposed to UV.'

'Elongation At Break ISO 8339 >500%'

Elongation before tearing is high but necking will occur long before that resulting in failure of the seal. Hence the 15% limit on joint movement.

 

[Rappey]

Is the sticky side the side which gets sun on it?
Is this all outdoors?

Was your friend making dust before the sika work was done or only after?

Not really the sunny side due to the direction the boat is facing and close proximity of buildings so its hardly getting any sun this time of year.
It is all outdorrs in a yard.
The sika was at least 3 weeks set before any dust or similar got onto it.

The Sika turning sticky in time might be solvent entrapment in layers below it?
Or some other by product from epoxy?

A few smears were on the keel plate as if you just wiped it there off your fingers. It was totally set, but is now sticky and gets on your fingers if you touch it.
Its only one side of the keel thats gone sticky, the side facing the boat we are working on which is no more then 5 ft away.. The sealant on the inside of the keel is fine.

I understand expansion gaps and similar filled with a flexible sealant/adhesive as it would have been designed for that but i would have thought a 5mm gap between keel and hull would allow flexing, eventually leading to the possibility of fatigue/keel bolts ?

 

[Wing Mark]

...

I understand expansion gaps and similar filled with a flexible sealant/adhesive as it would have been designed for that but i would have thought a 5mm gap between keel and hull would allow flexing, eventually leading to the possibility of fatigue/keel bolts ?

I would imagine it might change the whole structure of the join, instead of tension in the bolts reacting against compression at the edge of the keel flange, the compression is spread over an area closer to the keel bolts, so the forces are increased for the same moment?
At large angles of heel, the bolts may be in more shear than tension, or even bending?
But I am not familiar with the boat so I may be quite wrong.
I just wouldn't trust general advice as a basis for changing the way the joint is done.

 

[BigAlbatrossBird]

A 5mm gap is to be left between the keel and the boat hull which is totally filled with sika. Once cured the keel bolts can be torqued up to the required amount which was achieved.. while maintaing the 5mm gap. Ive never heard of anything like that before and think the keels should be touching the grp.. What do others think or know?

As a former centaur owner, I was under the impression that that is the standard way for the keels to be attached. If they're touching the GRP there won't be an effective way to keep water away from the keel bolts, and it's possible that if the joint doesn't have any give in it, then it might cause additional flexing in the keel stubs.

 

[Restoration man]

Maybe try and do mock up test get scrap pice fiberglass put your jotum stuff etc on and if you still have some spare sika do test and see if it sets if it doesn’t there must be some reaction, I had similar problem with a synthetic window putty and I changed my primer and I set properly

 

[Rappey]

As a former centaur owner, I was under the impression that that is the standard way for the keels to be attached.

Interesting

 

[Spirit (of Glenans)]

When attaching components to hulls and decks, it is standard practice, as I have read on this forum and in PBO, to apply a generous amount of sealant, allow it to go off, then tighten up the joint, so that the cured sealant acts as a gasket. Separating the component from the substrate with spacers of varying thicknesses, which can be removed after curing, is sometimes advised.

 

[Neeves]

When attaching components to hulls and decks, it is standard practice, as I have read on this forum and in PBO, to apply a generous amount of sealant, allow it to go off, then tighten up the joint, so that the cured sealant acts as a gasket. Separating the component from the substrate with spacers of varying thicknesses, which can be removed after curing, is sometimes advised.

I'm just an idle spectator - but how do you apply sealant, like Sika, and allow to set off and then torque up the bolts - such that the sealant is a gasket - to be a gasket the sealant needs to be devoid of spaces, or the same thickness all round with a flat surface (or more difficult, matches the surface of the hull.

Jonathan

 

[greeny]

I'm just an idle spectator - but how do you apply sealant, like Sika, and allow to set off and then torque up the bolts - such that the sealant is a gasket - to be a gasket the sealant needs to be devoid of spaces, or the same thickness all round with a flat surface (or more difficult, matches the surface of the hull.

Jonathan

Ignoring the measurements as an example. It depends on gap recommendations.
12mm of sealant all over the top of the keel joint. Tighten down to 8 mm gap. Allow to cure. Then torque up to recommended setting. Gap will now be circa 5mm.
First tightening action squeezes excess sealant out and ensures consistent coverage. Second tightening squeezes the now cured gasket up to torque required.
That's the way most modern gaskets sealants are applied now. Never fully tightened whilst still liquid.

 

[Wing Mark]

Instant Gasket type 'gorilla snot' always has instructions to let it set before torquing the bolts, it usually leaked like Whitehall.
Problem is, tightening the fasteners often shears the sealant around them.
A few motorbike types have joked about being better off making a gasket out of the cardboard box the gorilla snot comes in.
They may not be wrong.
With a bit of old motorbike, it's no big deal to have another go next weekend.
With a keel it needs to be right first time with total confidence.
If you want 5mm of rubber in the joint, you could buy some 5mm synthetic rubber sheet and do it right.

 

[Neeves]

Ignoring the measurements as an example. It depends on gap recommendations.
12mm of sealant all over the top of the keel joint. Tighten down to 8 mm gap. Allow to cure. Then torque up to recommended setting. Gap will now be circa 5mm.
First tightening action squeezes excess sealant out and ensures consistent coverage. Second tightening squeezes the now cured gasket up to torque required.
That's the way most modern gaskets sealants are applied now. Never fully tightened whilst still liquid.

This is the way I would do it and how yachts are commissioned here. Post 15 implies that one applies the sealant - let it go off and then tighten (and I was querying how you developed a flat mating surface to the sealant.

Here the sealant would be allowed to go off without the keel enjoying any support - it would be free hanging.

Jonathan

 

[Spirit (of Glenans)]

Ignoring the measurements as an example. It depends on gap recommendations.
12mm of sealant all over the top of the keel joint. Tighten down to 8 mm gap. Allow to cure. Then torque up to recommended setting. Gap will now be circa 5mm.
First tightening action squeezes excess sealant out and ensures consistent coverage. Second tightening squeezes the now cured gasket up to torque required.
That's the way most modern gaskets sealants are applied now. Never fully tightened whilst still liquid.

What he said!