Keel rust solution

[jackho]

Just had my boat lifted out and find quite a lot of rust patches - one or two quite deep. Was aware of the problem last season and now want to effect a more long term solution.
I had discussed coating with GelShield after all prep. work was completed but was advised the rust would reappear. Some opinion have suggested VC tar as a more suitable "sealant".
All advice, suggestions and tips will be very much appreciated.
Thanks in anticipation
Jackho

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[oldsaltoz]

G'day Jackho,

Your Bio has no boat details but I assume it's cast iron, can you confirm this please, rather than go into the detailed fix only to find it's some other material would be waste.

Avagoodweekend.......

<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[jackho]

Yes,cast iron it is - Look forward to your suggestions/solution.

Thanks Jackho

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[tcm]

hi.

I wonder if the time taken for the rust removal is a factor? In a engineering place i once worked we used to sandblast rusty castings and then paint the raw castings within minutes. Could you perhaps do a few minutes of rust removal then a bit of painting? bit of a mess i suppose. So how about getting rid of the main bits of rust, then finally a run over the keel with power sander/tool just before painting?

Incidentally, sandblasting is dirt cheap and effective, tho it wil be a factor how close you are to other boats of course...


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[jackho]

Thanks for your suggestion. Yes,my intention is to grind of the rust spots and paint immediately but there is a rust section a couple of inches long that is a couple of mm deep that I want to fill before painting. Also choice of paint is an issue as is fill material.

Jackho

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[tcm]

i would not fill if poss, but grind back the few mm to eliminate the crevice -otherwise the rust will continue its merry process. A deep bit like this would otherwise be a weak spot, imho.




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[gtmoore]

I had some small rust areas on the keel last winter and used a rust treatments they use on cars where you paint on a jelly like substance and it turns the rust black and inert. I then covered it in keel primer and A/f on top.

I've no idea if this has helped but will find out in a month or two.



<hr width=100% size=1><font color=blue>Gavin </font color=blue>

 

[alahol2]

A couple of treatments with Fertan seems to work quite well on my engine block. I should think if it's then VC tarred over that should give a reasonably long lasting fix. PS when using these type of rust converters, it's important NOT to remove anything other than loose rust, ie don't go down to bare metal.


<hr width=100% size=1><A target="_blank" HREF=http://www.troppo.co.uk> Follow the Tightwad Sailor</A>

 

[Ships_Cat]

As TCM has inferred grit blasting is the best preparation. Grinding is possible but not so good - I would only use it if spot patching. Use of rust killers is never anything other than a temporary fix.

For the places where there is pitting, grind it clean and then blast after with the rest of the keel. Never, ever sand the bare metal or else you will likely find that the coating system will not key reliably to it and will start bubbling after a couple of years as osmotic pressure drives moisture through the paint system.

Using International Paints as an example I would suggest blast and apply one coat of 707 polyurethane metal primer. Fill the pitted bits with epoxy filler and sand fair (but taking care not to sand through the primer to the iron, and taking the "bite" from the blasting off the metal). Then apply 5 coats (assuming brushing or rolling) of Interprotect epoxy primer and then antifoul.

Take care to keep within all the maximum and minimum coating times (and there may be a recommended maximum time within which the first antifoul coat should be applied over the last coat of epoxy).

The other reputable paint manufacturers such as Joton, etc have equivalent systems, just used International as an example. Usually, if you let them know your problem they will provide a paint system specification.

John

<hr width=100% size=1>I am the cat but I am only 6.

 

[oldsaltoz]

G'day Jackho,

Cast iron will flash rust in a matter of seconds so you do need to get some cover on it fast. Grinding is not a good idea as it will carry rust particles and embed into the area you are trying to clean, so should be avoided.

The last keel we did was as follows:

Set the boat up so you have full access to all areas of the keel, no good leaving the bottom rusty, it will spread.

Cover the areas close to the fibreglass with plastic and a double layer of masking tape, don't make the plastic a tight fit, let it move when blasting and it won't wear thru.

Sand blasting is the best method, cheap, fast and effective, a bit duty though.
check the wind direction and get the blaster to start with the wind on his back so that all sand and dust blows away from the job.

The blast should look like a dull grey with no changes in colour, follow as close as you can to the blaster, shoulder to shoulder and roll on a coat of zinc, Important note, Zinc must be applied at the correct depth, too much and it will mud crack, too little and it won't work; fortunately there is a simple and very inexpensive tool called a paint gauge, it looks like a tin credit card and has small square notches cut on the edges, drag this over the wet paint and the pattern will reveal the thickness, after a few checks you will have a good feel for the right thickness, but keep checking anyway. The zinc coat will dry very fast so work in small areas at a time.

When blasting at the join betwixt keel and craft, use a thin tin plate held firmly against the hull and get the blaster to blast away from the boat and towards the keel. zinc coating as you go.

When all blasting, zinc coating and curing has completed, give the area a very light sand to remove any runs or roller ridges.

Then apply at least 3 coats of epoxy resin, do this in one go by waiting till the previous coat is very tacky and re-coat, this will save a lot of sanding and washing.

Let the resin cure for at least 24 hours, wash it with fresh water from a running hose and use a plastic kitchen scourer to rub it down, you will know when it's clean, the water stops forming beads, this is the residue left from curing and if not washed off will contaminate the coating when sanding.
Give the resin a wipe with clean rags and let it dry for half an hour then give it a light sanding with 200 grit to remove the shine.

Now fill any voids you have with closed cell micro balloons or 'Q' cells, both are ok below the waterline, use only epoxy resins, it helps if you dab a little resin in holes about 20 minutes before you fill them. I use a soft bendy plastic ruler to remove the high areas when filling, this reduces sanding time.

When the filled areas have cured, don't forget to wash them as above prior to sanding.

You are now ready to apply some real protection, an epoxy primer, I use International but that's just me. apply at least 3 coats, wet on wet is ok, see the instructions on the can.

Another light sanding and you are ready to top coat, I used International interzone, it's the stuff they put in steel piles, goes on thick and lasts for years, another light sanding and you can antifoul her and get her back in the water.

Most important, antifouling is toxic as are most of the paints, dust and debris, so make sure you have a good mask, not the doctors over nose job, a good one, also protect your eyes and ears, I find the latex disposable cloves are very good for working with just about anything.

Andavagoodweekend.



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[jleaworthy]

The main problem I have found with my cast iron keels is that the rusting each year throws off the antifouling (and primer and anything else I've put on). 18 months ago I drilled and tapped each of my twin keels and fitted large button anodes. At the end of the first season the anodes were well consumed but the antifouling stayed on. I've just beached my yacht for the winter and again the antifouling on the keels is intact - the anodes again about half consumed. I'm well pleased with the result.

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[tross]

The only thing I would add to the advise so far is, to do the work now. That way you get a chance to redo the bits that have not taken before putting it back into the water in the spring.

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