Sikaflex and Iron?

[joe17]

I am going to patch up part of the hull/keel joint which is causing a small weep on one of the keel bolts with sikaflex

The keel is iron. The question is any advice on how to prepare the iron for the sikaflex? I understand it is necessary to use the specified sika primer, but should I do something before that? I will remove the pain from the keel and remove rust and clean etc. but should I consider applying something else to the iron before using the sika primer??

Thanks for any help.
Joe.

 

[bluedragon]

You should definitely try to get a copy of the primer data sheet or application guide (Sika website possibly) but failing this with most adhesive sealants the answer is to get back to a fresh metal surface by removing rust, paint etc, then degrease with a solvent that will not leave a residue. If I remember correctly iron is more difficult to bond to than steel or aluminium...so do try to get some advice from Sika.

 

[eyehavit]

Three years back the advice we received this advice from the Sika rep assisting us to stick Sikaflex to bronze:
Primers assist only with adhesion but have poor moisture resistance. They did not recommend use of their primers as a nexus between metal and Sikaflex for permanent water immersion.
His advice was to put a film of epoxy on the metal first, let that cure, roughen the surface a little and apply the Sikaflex.
You might want to consider:
Remove all loose rust.
Make sure surface is free of oil or grease.
Warm the part to around 60 deg.
Apply epoxy. At this temperature it will flow and soak in like kerosene.
Allow to cure.
Apply a second coat if neccessary.
Allow to cure.
Slightly roughen the surface.
Apply Sikaflex

 

[joe17]

Would you then use sika primer after the epoxy?

Thanks for that info. It makes sense to me.

Would you then use sika primer after the epoxy? Or straight with Sikaflex onto the epoxy?

 

[joe17]

I couldnt find any straight info on iron from the Sika websites

I couldnt find any straight info on this from the Sika websites. I have sent their technical support and email similar to the questions I posted here. Lets see if I get a reply.

 

[wooslehunter]

Re: I couldnt find any straight info on iron from the Sika websites

Keep us posted on the recommendations.

I did a similar thing. A previous owner had uses some kind of sealant around the keel joints. Water had go underneath.

I just cleaned out the old sealant. Primed any bare metal with a iron keel primer & added the sika fillet. I had no leaks but just neaded some work to stop the iron keel corrosion. I'll re-seat another year.

 

[TigaWave]

We had this done by a yard that had done several with good results...
Clean and dry complete keel,angle grind a V around joint to give mor surface area for bodning, two coats epoxy, roughened in fillet area...and 3M5200/Sika291. 6000 miles later still looking good.
If you have a leak, the joint will need doing at some point by dropping the keel 10mm or so, on the hard its under compression and probably not leaking so its holding salt water in the threads (with no oxygen supply) which you cant easily clean and dry.
With the keel dropped slightly you can remove each bolt one at a time clean dry and use a corrosion block grease, which will de-activate any residual pockets of corrossion and remove moisture. Otherwise each bolt could be sat in nice salty moisture in the keel corroding away.
Have you removed any bolts to check their condition?

 

[eyehavit]

Re: Would you then use sika primer after the epoxy?

Sorry, should have made that clearer.
Apply the Sikaflex directly to the epoxy. The rep said water attacks their primer -so don't use it for jobs which you know will be permanently immersed in water. Apparently water slowly dissolves the primer away.

 

[joe17]

Sika291 or 292?

Hi,

Thanks for the info.

You said they used Sika 291. The sika web site has a pdf for redoing the whole seal (remove keel) and there it specified 292. From reading the data sheets I got the impression that 292 is more adhesive than 291. But 291 specifies good for salt water. 291 seems to be half the price.

So 291 it is then!

Joe.

 

[TigaWave]

Re: Sika291 or 292?

They used 3M5200 on mine, 5200 is stronger (trensile strength) than 291 or 292.
292 is it seems simply a stronger version of 291, so better where things are likely to be moving it will hold them together as well as seal.
291 1.8N/mm
292 4N/mm
5200 is 4.8N/mm
I havn't looked at the price of 5200, but the yard we used prefferred it.

 

[joe17]

Answer from Sika

I sent Sika UK technical department an email and they (eventually) called me back with some advice. Most of which seems to be in line with what was given here already!

For the iron the recommendation is to remove the old paint and rust. Clean with Acetone and then prime with Epoxy primer (2 or more coats). No need to use any Sika primer on the Epoxy.

For the GRP the recommendation is to remove the old paint. Degrease/clean and then use Sika 206 G-P primer.

The edges of the old sika should be cut away and then clean with acetone. No need to prime.

Then Sikaflex 292 to do the job.

I will give this a go in a couple of weeks time. The weather is still too cold here (<5C) for effectively working with Epoxy and sika.

Thanks for all the advice.

Joe