Rusty keels - primocon?

[TimLamb]

I have read all the previous posts I could find on this subject but they have left me a bit confused.
The rusty sections of my keels have come up pretty well with a bit of scraping and wire brushing.
My question is, should I put Primocon straight onto the bare mettle, or something like a rust preventer first, followed by the Primocon?
Last time I did it (a few years ago) I used International Keel Primer (straight onto the the rusty parts) and it seems to have done quite well, but I mention Primocon because it seems to be well thought of judging by previous posts.
Thanks
TJL

 

[markleuty]

We just put 5 coats of primocon straight on top of the bare metal.

Seemed to work OK for us.

Mark

 

[Impaler]

5 or more straight onto the bare spelling mistake.... sorry I had to say that...

 

[MoodySabre]

I used a rustconverter (Vactan is excellent and cheap from and ebay sop) on the bare metal then two coats of underwater primer then AF. Results have been good with very little spot patches to deal with in subsequent years.

 

[johnalison]

Something to control the rust is a good idea. I used to use Hammerite because I was too lazy to look for the right stuff & it also worked well.

 

[samwise]

You need to apply a two pack epoxy undercoat BEFORE the Primocon or whatever. I have used Blakes EPU on our keel after burnishing to bare metal. You need to get the stuff on immediately after the burnishing because the rust process starts immediately. Then a couple of coats of underwater primer, followed by two coats of antifoul of your choice. Sadly the rust will always tend to come through a bit by the end of the season and haul out, but usually it is in just a few patches that are easily treatable.

 

[AIDY]

either an epoxy or just primocon on it's own seems to work well. but may need a bit more attention in a few years time.

 

[Bilgediver]

You need to apply a two pack epoxy undercoat BEFORE the Primocon or whatever. I have used Blakes EPU on our keel after burnishing to bare metal

****************************************************

Primocon works best when used as it is designed to be used....ON BARE METAL!

Check out the Primocon instructions which clearly show that it is intended to be used on bare metal immediately after sanding or shot blasting.

The reason is that for full effect Primocon offers galvanic protection it is not just a passive paint and this will not happen if it is painted over a layer of two pack epoxy. If using two pack epoxy you might as well topcoat with dulux floor paint .. and save money .

One intersting effect of this active protection is that if you paint a good coating of Primocon on top of a secure layer of antifoul then it still seems to work through the existing antifoul without having to sand back to bare metal every year. Primocon is also an excellent tie coat between layers of antifoul if say putting hard antifoul on soft antifoul or a soft antifoul on top of an unknown antifoul . However for steel protection there is no need for two pack epoxy if using Primocon as it is designed for application to bare steel.

 

[samwise]

I was using Blakes stuff and their advice was EPU two pack epoxy on to bare metal, then Underwater Primer and then antifoul. Obviously International see things differently and Primocon is a different animal. The yard here has had a few problems with Primocon, chiefly finding poor keying to the antifoul coats. I always use Blakes anyway, and not having a tin of Primocon handy, made the mistake of thinking the same rules applied. Sorry for any confusion.

 

[Bilgediver]

I always use Blakes anyway, and not having a tin of Primocon handy, made the mistake of thinking the same rules applied. Sorry for any confusion.

**************************************************

Lots of us adopt our own procedures and maybe they are different animals.

Primcon is probably a zinc rich primer and if so then needs direct contact with the steel to protect it...If you use Primocon on top of two pack epoxy then you are not using its steel protection properties but just using its tie coat properties.

It can be confusing when a paint has dual personalities like Primocon in that it is both a good tie coat as well as good steel primer.

As I have said on here before, there is no need to remove sound antifoul on keels. Just remove loose paint and sand smooth before giving a good coat of Primocon. I am not sure of the mode of protection it gives however Primocan even when sandwiched in layers of antifoul still seems to protect keels. Mine were last shot blasted about 10 years ago and still show little signs of further corrosion. Just the occasional point sanding if there are small areas of corrosion.

Primocon also has this other property of being an excellent tie coat so if faced with antifouling over unknown antifoulf or areas that were loose then clean up and remove all flaking antifoul and either paint Primocon on affected areas or if required a complete coat. This applies as well to GRP hulls as well as steel.

I am curious your boatyard has problems as I have found it very satisfactory.

 

[Gary007]

Priacon is fine as a temporary measure. But the correct way to fix the problem is to sandbalst the keel. Treat the rust, and apply 5 coats of epoxy over a couple of coats of primacon.
I couldn't get the guys to blast my keel this year, so I'm gonna treat the keel for rust.. (Bought some stuff from frosts), fare it with epoxy filler, , and put back on the three or 4 coats of primacon that I originally put on 5 yrs ago and havebeen fine untill this yr.

 

[atelford]

I used rust eater like hammerite, then primocon, then antifoul... needed only light touch ups after 3 seasons.

 

[BOATPOWER]

Primocon problems

I have been maintaining my steel yacht for 21 years and hope the following will help fellow sailors. The hull was sandblasted above and below the waterline to class 2.5, then carefully dusted (important), and coated with a high build epoxy coating (3 coats) using airless spray. The humidity was very low (should not be done if over (60% as rusting starts as soon as bare steel is exposed to the air). There has been no breakdown in the coating in 21 years and continues to perform. However there were two many zinc blocks on the hull caused by reverse osmosis (saponification) occurred. Also over the years some welding was done with the boat in the water and this has caused some blisters (water is found under the paint blister).
Recently I used Primocon to provide a uniform base to apply new anti foul over, within six months the paint had broken down blowing off the antifoul. I believe the cause is the sacrificial nature of the paint. The aluminum that is in the paint corrodes swelling and pushing the paint off the hull. I have taken some paint samples and will get them lab tested and post the results to confirm. I would recommend that for all steel surfaces they be sandblasted as above and epoxy coating applied.
If anyone else has had similar problems with primocon failure I would like to hear about them too.

 

[KellysEye]

The only way to get rid of rust permanently is to sand blast it, otherwise it will come back whatever you coat it with. The first coat must be zinc rich epoxy applied very quickly after blasting. Then a couple of coats of underwater epoxy.

 

[geoffatstanpit]

However there were two many zinc blocks on the hull caused by reverse osmosis (saponification) occurred.

You've lost me there???

 

[savageseadog]

Whatever paint you use there is no substitute for plenty of coating thickness.
I'm not sure that electrochemically active paints with zinc and aluminium are the way to go as electolysis will blow the paint off in my experience.
The best high build primer I ever used was Leighs Resistex, it's a Vinyl bast paint.

 

[KellysEye]

>I'm not sure that electrochemically active paints with zinc and aluminium are the way to go as electolysis will blow the paint off in my experience

Certainly doesn't. We have a steel boat and it has zinc rich epoxy as it's first coat below the waterline. No problem at all either with corrosion or electrolysis - reason, the zinc epoxy is covered by three coats of underwater epoxy of different colours to get the thickness right.

 

[actionoptics]

Primocon

Tim.
Four years ago I removed all of the old paint from the twin
keels of my LM 30; wire brushed; fresh water washed and then let them dry.
That June was hot so they dried quickly.
I then applied 6 coats of Primocon.
Both keels are still rust free.
Seems if the conditions are right, Primocon does what it claims.

 

[Kim Bay]

Steels vary and are different again to cast iron, which is porous enough in some cases to retain salt in microscopic quantities once it has been exposed to seawater, almost whatever you do. Usually it is better not to mix conventional and two-pack materials except where the manufacturer specifies them. Allowing for the fact that once rusted, however well prepared a keel is the rust will always return some day, a good coat of something forgiving and relatively cheap (like Primocon) is probably a better bet than epoxy. A perfect expoxy scheme before the iron keel or steel hull is ever exposed is of course the ideal.

Excessive cathodic protection will saponify paint coatings (i.e. "turn to soap") because of the alkaline solution built up at the protected surface. It does for paint and for timber alike.

 

[gasdave]

I have just finished taking my keels back to metal with a powered steel wire brush (not allowed to blast!). Then washed with fresh water and de-greased. Then two coats of Fertan rust treatment, followed by dusting off.
They are now receiving five coats of Primacon before finishing with two coats of antifoul.

I think the important message with any of these products is to follow the instructions as closely as possible. Some of the failures appear to be the result of less than adequate preparation or insufficient coats.

Although it should all probably be supplemented with a large dose of optimism!