Keel to hull joint: does new Sika adhere to old?

[Skylark]

I had a very small, less than 10mm, line of "rust bleeding through" the Sika from the trailing edge of the keel to hull joint. This was a new boat, seen at the time of haul-out at the end of the first season. The dealer repaired it under warranty.

A bead of Sika about 100mm long was removed from both sides of the keel. The minor rusting was cleaned and painted and a new bead of Sika applied. At next haul-out, this U shaped bead came off during jetwashing of the hull. I wasn't unduly concerned and thought that the ambient temperature may have been too low for successful application. I did a similar repair myself at the start of the following season but waited for the temperature to increase, a couple of weeks before launch. Guess what? This U shaped bead also did not adhere.

This second picture shows that the bead had not adhered after 6 months under water. It came off a few minutes after I took the picture.

I'm now preparing for season launch so I'm hoping for "third time lucky!"

Has anyone successfully repaired a bead of Sika along the hull/keel joint, butting against an old run? I've used 291i and cut the old with a sharp knife to create an angled overlap. I've read a lot about CT1 on this forum, would this be better than Sika? I'd really appreciate to learn from the wisdom and experience of the forum.

Many thanks.

 

[guardian]

I had a very small, less than 10mm, line of "rust bleeding through" the Sika from the trailing edge of the keel to hull joint. This was a new boat, seen at the time of haul-out at the end of the first season. The dealer repaired it under warranty.

A bead of Sika about 100mm long was removed from both sides of the keel. The minor rusting was cleaned and painted and a new bead of Sika applied. At next haul-out, this U shaped bead came off during jetwashing of the hull. I wasn't unduly concerned and thought that the ambient temperature may have been too low for successful application. I did a similar repair myself at the start of the following season but waited for the temperature to increase, a couple of weeks before launch. Guess what? This U shaped bead also did not adhere.

This second picture shows that the bead had not adhered after 6 months under water. It came off a few minutes after I took the picture.

I'm now preparing for season launch so I'm hoping for "third time lucky!"

Has anyone successfully repaired a bead of Sika along the hull/keel joint, butting against an old run? I've used 291i and cut the old with a sharp knife to create an angled overlap. I've read a lot about CT1 on this forum, would this be better than Sika? I'd really appreciate to learn from the wisdom and experience of the forum.

Many thanks.

Nope, you might get better results hooking the whole lot out drying, abrading priming then re-applying or (what i'd do) go and get some sabatack 750XL and tidy up the front edge, no primer required. Have used sika in the past and have found it an expensive pain in the arse unless conditions (temps and humidity levels) are absolutely perfect.

 

[Channel Sailor]

CT1 or similar such as Sabatack from what I recall cure at lower temperatures and can cope with some degree of moisture in the substrates (grp), they are softer when applying at the end low temperature range which help getting it deep into the gap.

Which ever bonding you use think about shrinkage when they cure and make sure it cures completely before painting and immersion. Of course have the surfaces clean and dry before application.

Your keel bolts are holding the keel on rock solid against mating surfaces, so the sealant/bonding does not need any shear and tensile strength. Therefore all you need is something that sticks really well, does not shrink much on cure, easy to apply and cures quickly. Oil based bonding such as 291 could well be overkill on the strength requirement. CT1 or Sabatack (similar I understand) might be better and more tolerant of your application conditions. Sabatack is resistant to some oils (diesel for example) so might be a better choice for painting over with single pack primers and antifouling.

Epoxy resin mixed with a thickening powder to make a bonding/filler paste is another option. But unbolting the keel one day way in the future, it might need a grinder. Which is no big deal on a keel off job because a grinder would probably be needed to cut through the Sikaflex anyway.

Maybe take the opportunity to check the torque of keel bolts as well.

... but if a new boat then maybe ask the designer or get it done under warranty.

 

[Sneaky Pete]

Try some Puraflex 40 it has all the properties you would need for the job and it's well under a fiver.

 

[Yngmar]

Stuck on mine with the usual preparation - sand to key, wipe with acetone to clean, squirt the goop in and smoothen with finger (gloved or ungloved). Clean the mess that somehow mysteriously got on your elbow and spread around everywhere with builder's wipes.

Never came off anywhere. Not even my clothing

 

[Neeves]

Both Sika, and I think your CT1, cure in the presence of water - read this to mean - they need moisture to cure. The most common issue is cleaning the old mastic out and then wiping down with turps and/or cleaning up with turps afterwards. The Sika (and I assume CT1) will not stick to turps and the turps weeps under the surface and reduces the bond strength.

Most of these products describe cleaning up afterwards as with soapy water - but turps is so much easier (but is a complete waste of time - and money). I don't know where acetone and meths fit into the cleaning regime - but if the instructions say soapy water - they say for a reason (and I don't think they own shares in soap companies).

I would grind back, or wire brush on angle grinder, wash with soapy water, wash with fresh water, apply and then clean up with soapy water. If you had rust weeping from the joint you had water in the joint - I'd have demanded the keel was removed, under warranty, and re-bedded.

Yachts are not cheap, there should be no moisture in the joint. Keels I have seen attached usually with a shim of Sika, or equivalent. The whole lot bolted together and torqued. There are 2 schools of thought let the keel hang or sit the yacht on the keel - until the Sika is cured. But rust weeping out implies a break in the seal - and given the cost of the yacht I would demand a re-seating.

The first 'repair' was not - it was a bodge.

Jonathan

Edit We don't have your CT1 in Australia, but we have other products competitive to Sika - which are water cure. We don't have issues of low temperature - but do have issues of high temperature - check with the instructions.

 

[Javelin]

Er why are you using a bonding sealant for the keel?
Worried that your bolts are going to break?

Saba, Sika and the bloody expensive 3m one I cant remember all fail with age as they harden and stop being flexible and eventually will leak.
We see this a lot. I mean a lot, maybe 25 to 30% of the boats we take out show signs of seal failure.
Even on a southerly that has a huge ballast plate with over a foot of undisturbed sika, we have seen water ingress over time.
90% or even 95% will be ok (and make it dammed hard to drop the keel if you have too) but you only need a little fault for water to work its way through.
A little bit of water is all you need along with a lack of oxygen to then have serious keel bolt issues.

Use Arbokol 1000 which is not a bonder, its a sealant and stays flexible and hence retains the seal much better.
You really do need this flexibility especially on modern builds as the hull flexes a lot compared to the old long keel boats.
Sure if your keel bolts fail the keel will fall off but I reckon that would happen with the others anyway.

 

[thinwater]

When you speak of "Sika," is it understood that you mean Sika 291, or are we talking about something else? To me, it's like saying "use 3M," knowing that they make many marine sealants based on many chemistries. So does Sika, most of which are polyurethane, but some of which are silicone or polyether.

So I assume we mean Sika 291?

 

[Skylark]

So I assume we mean Sika 291?

Yes, if you re-read my post to the final paragraph you’ll see that I mention 291i.

I really appreciate everyones responses. The several alternatives being proposed, will they successfully butt alongside the existing beads? If so, what’s the best preparation? I’m assuming cut at an angle, sanded to key and cleaned with soapy water?

 

[Spirit (of Glenans)]

Perhaps someone bodged up the original repair with silicone, which leaves a residue to which nothing will stick.

 

[AndyL]

I agree with Javelin, Arbokol 1000 is the correct stuff.

 

[Skylark]

Perhaps someone bodged up the original repair with silicone, which leaves a residue to which nothing will stick.

The original repair was done by a Technical Service Engineer employed by the largest UK Dealer representing a well known French boat builder. I’d be disappointed if his work was a bodge rather than in accordance with established guidelines. He did use Sika 291.

I agree with Javelin, Arbokol 1000 is the correct stuff.

Thank you both for the recommendations. I’ve ordered a tube. I’ll ensure that all surfaces are keyed, clean and dry. Noting that the cure time is shown as 14 to 28 days I need to get on with it as my launch date is mid April.

 

[Javelin]

Don't worry about the cure time, arbokol skins in hours and is good to launch in 24hrs in normal conditions.

 

[Tranona]

Agree. I have used polysulphides, either Boatlife or Arbokol for sealing under water for years. Skins over quickly and continues curing even under water. For the OP's application it is more a filler than a sealer and should adhere well.

 

[Skylark]

I’ve contacted Arbo Technical Services regarding substrate adhesions. Very helpful. The guy responded “gut feel, Arbokol 1000 may not bond with Primocon. A better alternative may be Arbomeric MP20, Modified Polymer which shows consistently good results on all painted surfaces”

Any comments from those with experience of this?

 

[Channel Sailor]

I’ve contacted Arbo Technical Services regarding substrate adhesions. Very helpful. The guy responded “gut feel, Arbokol 1000 may not bond with Primocon. A better alternative may be Arbomeric MP20, Modified Polymer which shows consistently good results on all painted surfaces”

Any comments from those with experience of this?

“modified polymer” to me means Sabatack and probably CT1 (not used it myself). See my comments above if of interest.