Keel prep before Coppercoat - further info

[zeds]

Anyone who found the earlier post on preparation for Coppercoating useful might like to see the spec sheet for Hycote 152LV, the 2-pack epoxy preparation for keels before Coppercoating.
*Hycote 152LV is a high performance two component anti-corrosive epoxy coating, for protecting steel surfaces in the marine environment.
* . . is specifically designed to provide long term corrosion protection to steel and concrete surfaces.
* . . can be applied to damp surfaces, and consequently is ideal for coating hydroblasted steel.
* . . is a 100% solids, high-build resin, that shows excellent tolerance to manually prepared substrates.

It is not practical for me to clean to SA 2.5 standard (grit blasting) but I am aiming for a very thorough grinding/wire brush finish followed by Hycote applied during a mild, dry spell (optimism!!!). Will update on experience of doing job in due course.

 

[ianabc]

Hydro blasting..... in my experience doesn't work!
Acid washing same.

Cleaning by grit blasting, possibly black copper slag, (not sand as it's toxic ...the silica) or similar to white metal works.

Cleaning with a grider appears to clan the metal but the shiny metal provides a poor "tooth" for primer.

Grey to white metal, no finger ( grease marks) dry with heat gun, or sun, then 3 coats of zinc rich primer. 3 coats of epoxy.

 

[ianabc]

The thinking behind the coating substrate is that the copper and iron provide a fine potential for voltage..... probably .06 volts or more, on the other hand a thick keel will take aq whileto corrode, but then their is a potential for the coatings will peel in the meantime!

 

[flyingscampi]

I used Hycote 152 & Coppercoat on my keel following a farrow blasting. I'll be reporting on the performance of the Hycote over the next year (hopefully years) in preventing rust from flaking off the Coppercoat.

 

[Pasarell]

Hydro blasting works very well - provided the pressure is high enough. It needs to be minimum 35000psi and can be up to 55000psi. Also rotating heads with head held no more than 15cm from surface being cleaned. Done properly the water is very abrasive and removes not just the corrosion products but also any salts that would be crushed into the steel by dry blasting. Also the pressure heats up the steel so that it tends to air dry very quickly and is suitable for coating. Unfortunately many operators talk of hydroblasting when they mean high pressure washing at too low a pressure.
Grinding is not as good as blasting but much better than wire brush which just polishes the rust without removing it.
I agree with you about zinc rich primers. Much better than pure epoxy, especially if surface preparation is not perfect.

 

[oldsaltoz]

Just a few points to ponder:
Cast Iron is porous and any moisture or salts trapped will cause further limited corrosion. It is most important the keel is DRY prior to treatment.

Cast Iron will "flash Rust" meaning rust will form on the surface in less than minute, so any protective must be applied as soon as possible.

Grinding, sanding, wire brushing or other methods will produce a spreading rather than removal action causing contamination.

Grit blasting is a constant flow of clean material leaving no trace of contamination, it avoids the spreading and closing of pin holes produced by circular motion tools.

Applying a resin suitable for application will trap unwanted moisture. Almost all epoxy resins are 100% solids.

Blasting should be done to class 2.5 (no shadows) or 'some' contamination has been left behind.

Hydro blasting increases the moisture content and should be avoided.

Coating a properly dried and blasted keel with a good quality zinc is good, however too thick and it will mud crack, too thin and it will not work or last long, take care to read the manufacturers directions when applying any zinc based products, most are around 70 microns thick.

Coats of epoxy over a zinc primer is good, then an epoxy primer after washing the epoxy to remove residue left by the curing process; do not sand until washed.

Adding a good thick coat f the paint used on steel piles will also help.

I hope this helps, it's the system I have used for many years on clients keels.

Avagoodweekend......

 

[Pasarell]

Have to take issue with a few of your points I'm afriad Oldsaltoz as I think they could be misleading.

Fully agree it is important to make sure a keel is dry before coating but also important to make sure all salt is removed as well, and that means fresh water washing. Salt trapped in the pores of the iron will quickly initiate rusting which will blow subsequent coatings off. Flash rusting, if gingering from clean water is not too much of a problem to many modern coatings designed for hydroblasting. Black rust caused by impurities (usually salts) is much more of a problem.
I agree with your comments about grinding, sanding and wire brushing but if those are the only options available then grinding is far superior to the other 2.
Don't quite understand your point about resins "suitable for application" but any coating will trap moisture if present. Most epoxies are not 100% solids although increasing numbers are. In the UK you cannot use a 100% solids epoxy at this time of year unless indoors with good heating and humidity control so most products sold for this sort of use are solvent based, often no more than 60% solids. Most 100% solids epoxies need a minimum temperature of 10C or more to cure and that isn't going to happen here for a couple of months at least.
The standard you mention, Sa2.5 is for steel and is not really applicable to cast iron, the material most keels are made of. I find you just hope the blaster (probably slurry rather than dry) gets the metal as visually clean as possible.
Proper hydroblasting should not increase moisture content if the pressure is high enough. 35Kpsi minimum will heat the metal and cause the moisture to quickly evaporate. Unfortunately you are very unlikely to get a true hydroblaster to be interested in a keel here as the kit is way too expensive. I agree water jetting from someone who claims to hydroblast will increase moisture content. On the other hand it will help to remove the salt. Swings and roundabouts!
There are various zinc based coatings but unless it is epoxy it is probably unsuitable to overcoat with an epoxy. We supply moisture cured urethanes and then overcoat with an intermediate moisture cured urethane. All the performance of epoxy but much less sensitive to low temperature and humidity variations.
When you talk of steel piles I assume you mean a bituminous coating. At the top end this used to be coal tar epoxy which is no longer available. Nor are conventional bituminous products. If you have a well prepared substrate and have used a high performance coating to the correct thickness they would not add anything anyway.

I expect your climate allows a different approach to what we can do here unless lucky enough to have the boat indoors.