Time saving ways to prepare a cast iron keel and keel plate

[Bathdave]

After taking soundings from a few people, I planned to grind back my cast iron keel and keel plate to bare metal, apply a couple of coats of epoxy primer and then a coat of primocon and then antifoul

I am running behind schedule because of the crap weather last week, and a window of opportunity to get this finished by Friday, as we have more storms coming and the yard don’t want the boat up high with the keel dropped

Having power rotary wire brushed the keel and plate today and started grinding back i am finding

1..I am not sure I am going to be able to get right back to shiny metal with my circular sander on my drill where the surface is pitted without spending many many grinding hours.

2, I’m not sure I am going to have time to properly epoxy under coat 2 coats as I understand it’s 24 hours drying time in this weather

I am pondering whether an acceptable alternative would be to use a hammerite type inhibitor instead and put a couple of coats of primocon on that to help with the antifoul bonding

I have searched through and found a couple of old threads

Some espouse the perfect preparation, frankly I don’t have the time or the tools for that

Some have apparently used Hammerite successfully, others say Dulux metalshield is better. I’ve also read of Kurust (? Is that name right ?)

One friend says several coats of Primocon on the prepared ground back surface, possibly with some spot treatment on the rust craters, will be fine

So I’m not looking for perfection, I just want do a job that will last me 4-5 years (I can live some some blistering before I know it goes with the territory and I’m not a racer)

But I want to do it in two days from where I am now if at all possible, as it gets complicated as to whether boat can stay where it is over weekend.

If there is an overwhelming consensus I’m wasting my time and will need to redo it next year if I don’t do it the ‘proper’ (perfectionist?) way then I may decide to bite the bullet on repositioning it over the weekend an buy some new tools.

Advice welcomed !!

 

[lw395]

1) An angle grinder is far better than sanding with a drill.
I would suggest either the normal fibre sanding discs
https://www.toolstation.com/fibre-sanding-disc-115mm/p38318
or a flap wheel.

2)
If time is limited, you won't get a perfect job.
Maybe take off the worst of the rust and then use a phosphoric acid rust treatment before priming.

I don't think it's worth using up lots of £££ worth of epoxy if there's not time to do a proper job. You may end up sealing in moisture and the epoxy will quickly fail.

 

[MoodySabre]

Using a wire will leave bits of metal that will probably rust under the epoxy. I take mine back using a flapwheel on an angle grinder. Whilst shiny I paint it with Vactan (the same as Kurust but way cheaper) and then an underwater primer followed be AF of choice. Very little making good required each year - this year didn't need to blitz any of the keel before AF applied.

MIne is a fin keel that the yard said was a waste of time with coppercoat as you can't stop them rusting a bit. Isn't just the wrong time of year for epoxy (or anything!)? Even the CI can't be warm enough. I'd do a quick job as above and if you want to do a proper job then do it in proper weather.

 

[Aquaboy]

If you have used a rotary wire brush why are you grinding or sanding?
Surely you have dug the brush in to the pits etc to remove the rust/loose stuff as best as possible. Then it would make sense to fair or fill the surface maybe after a rust treatment (yes Kurust) (Halfords) Shouldn't take long to dry. A polyester car type body filler can be mixed up quite strong to go off in the cold. Then sand that smooth before priming. This is all fairly simple and doesn't require heavy weight tools. I would prime with Red Oxide which again will dry quickly and is less temp sensitive.

 

[Seajet]

I have been all through this process over 41 years with a lifting keel.

I can only speak as I found, but engineer observers agree -

Forget Hammerite and Kurust

Forget epoxy - I tried this one season, the problem is the slightest chip or crack traps salt water against the metal - this resulted in fitting a new keel.

The keel was originally galvanised but this scrapes off in time.

Get back to as bare metal as possible, then apply a coat of Metalshield primer - it's one part

Then a topcoat of Metalshield, also one part.

Then antifoul on the lower third of the keel, assuming you raise it on the mooring or berth.

My Anderson has quite a tight fitting keel slot so I have to be careful I don't apply too thick a paint coating - one coat of Metalshield primer and one of topcoat easily lasts a season.

Do a trial hoist of the keel well before the crane turns up, to ensure it is not too tight.

 

[ashtead]

Could use of Fertan help maybe? Might be worth a look for a trial ?

 

[Seajet]

Tried that as well as VC Tar, you name it - singularly unimpressed, Metalshield is the only stuff which looks the same at end of season lift-out; the first time I tried it my Dad ( a lifelong engineer from steam engines & Battersea power station to Spitfires and Harriers ) and I both said ' Wow ! '

 

[ashtead]

Thanks Seajet - I have some metal garden furniture to treat which hasn't responded well to Chi climate so will remember metalshield as an alternate.

 

[vyv_cox]

The treatment required for a cast iron keel and a lifting steel plate are not the same. The most glaring example of this is needle-gunning, which is excellent for steel, second only to grit blasting, but disastrous for cast iron, where it can dig deep pits. For the same reason, although not so disastrously, wire brushing is not ideal for cast iron. It tends to drive particles into the graphite, where they create voids and may rust under subsequent paint films. Angle grinding has a different action and does not cause so much damage.

 

[Seajet]

I understood the OP's keel is a lifting one too, not that it makes much difference, I've also tried bolted on lead fins and grp encapsulated long keels, twin and triple keels in steel and encapsulated.

Show me a better treatment than Metalshield, based on actual results; my keel has a galvanised mild steel plate and cast iron ballast bulb.

 

[James_Calvert]

On preparation a cheap angle grinder will do that job most quickly and effectively. I use the sanding disc attachment. Change paper when it gets clogged.

I've always used primocon, but you do need several coats.

Getting and keeping the keel dry can be a problem. Grinding warms it up so delays dew formation, so good to follow quickly on with the paint if you can.