replacing sealant

[Paddydog`1]

My boat has a cast iron keel and where the root of the keel meets the GRP of the hull there is about 1 cm gap all round which has previously been filled with sealant. Some of the old sealant is deteriorating and falling out. How best do I remove the lot? Is there a solvent I could use or must it be scraped out and if so how best to do that?. Finally do I need to prime the cleaned out area and what best to seal it with again. The boat is 35 foot
Thanks

 

[ghostlymoron]

I did this by taking out the old stuff to depth of about 25mm. Then replaced with new Sikaflex. However it has been suggested that it would be better to do the refilling with the boat hanging in a boatlift so that the gap is stretched rather than compressed.

 

[vyv_cox]

The choice of sealant is a little problematic. Ideally the keel and hull should be primed before applying the sealant but it may be difficult to apply a sufficiently thin coat in such a narrow gap.
I am told that just about the best sealant for rebedding the keel is called flexpoxy https://www.defender.com/product.jsp?id=1971041 but it only seems to be available from USA.
CT1 seems to have been used successfully, with the advantage that it can be applied to wet surfaces.
Sikaflex might not be the best choice in this regard as dryness might be difficult to achieve. I have seen reports of good results with 291i if it was applied liberally with a fillet about an inch wide. This seems to give the sealant something to grip.
3M 5200 is their recommended product for the job but its spec looks very similar to Sikaflex 291. 5200 FC is their highly recommended one. http://solutions.3m.com/wps/portal/...pair/GeneralBoatRepairs/SealantAdhesiveGuide/

 

[Yngmar]

For actually bedding the keel (when initially attaching it to the boat), Bavaria uses Plexus MA310 after Plexus PC120 primer.

For fixing up an area of damaged sealant, I've used Sikaflex 291i and it did the job just fine, although I was out for 6 weeks and everything was plenty dry.

 

[Quandary]

If it has previously been sealed with a silicone sealant you will need to remove all traces of it if you are planning to use CT1, it gets on with silicone like Mia and Woody.

 

[Neeves]

If it has previously been sealed with a silicone sealant you will need to remove all traces of it if you are planning to use CT1, it gets on with silicone like Mia and Woody.

And you will need to abrade the surfaces that were coated with silicone. Use an abrasive disk (abrasion both sides and 'semi' flexible discs work well) on a large angle grinder or drill and abrade both sides simultaneously. If you leave ANY traces of silicone - nothing else will stick (and you are wasting your time and money). Don't be afraid to be aggressive - no-one will see it.

Jonathan