paint system for galvanised mast bands

[thebrushand]

Back in the UK I was taught to degrease galvanised "Crittal" window frames with mineral spirits, prime with calcium plumbate ( a lead based primer) and finish with an alkyd undercoat and gloss paint. Looking around the products suggested on US painting sites, I guess I was stuck in the dark ages, because I cant find mention of that technique for painting galvanised steel anywhere.

Sat here in California with recently hot dipped mast bands to make look shiny white, I realise I do not have the experience to judge which combination of primers, etch coats and or top coats available here would be most durable.

What do the painting specialists here recommend for that perfect bombproof brush finish? I have got as far as vinegar to degrease the surface, roughed up with a scotchbrite pad. What next please?

cheers

[djyachting]

Last time I painted some galvanised steel - a large centreboard - I started off with a coat of epoxy, wet sanded into the surface with 120 grit paper. The idea is to remove the oxidisation from the zinc by abrading the surface with the epoxy to act as an oxygen barrier. When the epoxy cures it locks the clean zinc away from oxygen.

After that messy job, I filled with an epoxy filler, sanded fair and then gave it four coats of International two pot polyurethane.

The boat is in the water from about April to the end of September on a drying mooring. After three years the surface is still good - it has lost its gloss though - and the only problems have been with scratches where stones have lodged in the CB case. They are dealt with by fairing the edges of the scratch, wet sanding more epoxy into the exposed galvanising and then filling and finishing.

The basic idea is covered in the Gougeon brothers' WEST system book.
DJ

[JimD]

Aquick google says wet sand with paper dipped in mineral spirits and prime with a primer formulated for galvanized such as:

http://www.kilz.com/dbimages/HamPrimGal.gif










HAMMERITE® Galvanized and Aluminum Primer is an acrylic latex coating formulated to bond to galvanized metal, aluminum, tin and other smooth metal surfaces.
http://www.kilz.com/pages/default.aspx?NavID=45 http://www.hereandthere.org/oldhouse/painting-galvanized-gutters.htmhttp://www.ehow.com/how_14414_paint-galvanized-metal.html (http://www.hereandthere.org/oldhouse/painting-galvanized-gutters.htmhttp://www.ehow.com/how_14414_paint-galvanized-metal.html)

But you probably already googled that much yourself :o

[thebrushand]

Thanks for the input on taking the epoxy route. I had never thought of that sort of process.

Does anyone have good experience of non epoxy systems that would match the durability of diyyachting's idea?


Aquick google says wet sand with paper dipped in mineral spirits and prime with a primer formulated for galvanized such as:

http://www.kilz.com/dbimages/HamPrimGal.gif

But you probably already googled that much yourself :o
I wouldnt google Hammerite. ;) Back in the day, hammerite never remotely worked as well as it claimed even on its specialty surface - cast iron downpipes with minor surface rust - so the thought of putting it on a marine application, I am cautious.

The fact it is a primer for aluminium and galvanised also makes me nervous, because they are two different metal surfaces - (The rule of thumb was never prime a metal with itself, hence zinc chromate on aluminium, but on galvanised? definitely not recommended. But there seems to be no differentiation now, which leads on to another rule of thumb about primers from college - an all purpose primer is not very good at anything!

But i have an open mind and chemistry has moved on. I am sure Hammerite will say it works a treat on galvanised in 2008, but does someone have real life experience of this product? Or any thing else? Thanks

[TMny]

Hello Brush-
Not a coatings expert , but some experience...
>zinc chromate on aluminium, but on galvanised? definitely not recommended
It IS recommended by some paint mfgrs -- not sure how/what specifications would be met.
For Aluminum zinc chromate is a generally less effective initial step than a conversion coating , i think. I think Pettit suggests a zinc chromate primer applied over/after a conversion coating. Gougeon provides a conversion coating for aluminum , but i dunno if it is also suggested for galvanised (suggest check there first). Since your app will see some salt spray , impermeable/submersion-resistant is good.

One possibility from Pettit (actually reads like the Goug conversion coating) :
http://www.pettitpaint.com/catalog_browse.asp?ictNbr=86
Browse Catalog >Products > Primers >Primers for Below the Water >Metal Primer 6455/044
Metal Primer 6455/044 is a two component product which is a self-etching type wash primer for use only on bare matels such as steel, stainless steel, cast iron, copper, bronze, galvanized steel, lead and aluminum. It forms an excellent adhesive bond to metal hulls, keels, centerboards, and other underwater running gear. Can be used either above or below the water. Can be overcoated with either epoxy primer, topside enamels, or antifouling paint.
Part Number Description Size
16455/104406 Metal Primer Pack 6455 GL PDS MSDS
16455/104408 Metal Primer Pack 6455 QT PDS MSDS

A useful site/archive:
http://www.paintcenter.org/
http://www.paintcenter.org/pexpert.cfm
http://www.paintcenter.org/pexpertqa1.cfm

An apt posting:
http://www.paintcenter.org/rj/mar08b.cfm
by Ron Joseph March, 2008 Zinc Chromate Primer and Topcoat Compatibility

{good luck! coatings are roughly as effective as the preparation/application complies with mfgrs instructions , if the conditions are within spec}

[TMny]

Hello Brush-
Not a coatings expert , but some experience...
>zinc chromate on aluminium, but on galvanised? definitely not recommended
It IS recommended by some paint mfgrs -- not sure how/what specifications would be met.
For Aluminum zinc chromate is a generally less effective initial step than a conversion coating , i think. I think Pettit suggests a zinc chromate primer applied over/after a conversion coating. Gougeon provides a conversion coating for aluminum , but i dunno if it is also suggested for galvanised (suggest check there first). Since your app will see some salt spray , impermeable/submersion-resistant is good.

One possibility from Pettit (actually reads like the Goug conversion coating) :
http://www.pettitpaint.com/catalog_browse.asp?ictNbr=86
Browse Catalog >Products > Primers >Primers for Below the Water >Metal Primer 6455/044
Metal Primer 6455/044 is a two component product which is a self-etching type wash primer for use only on bare matels such as steel, stainless steel, cast iron, copper, bronze, galvanized steel, lead and aluminum. It forms an excellent adhesive bond to metal hulls, keels, centerboards, and other underwater running gear. Can be used either above or below the water. Can be overcoated with either epoxy primer, topside enamels, or antifouling paint.
Part Number Description Size
16455/104406 Metal Primer Pack 6455 GL PDS MSDS
16455/104408 Metal Primer Pack 6455 QT PDS MSDS

A useful site/archive:
http://www.paintcenter.org/
http://www.paintcenter.org/pexpert.cfm
http://www.paintcenter.org/pexpertqa1.cfm

An apt posting:
http://www.paintcenter.org/rj/mar08b.cfm
by Ron Joseph March, 2008 Zinc Chromate Primer and Topcoat Compatibility

{good luck! coatings are roughly as effective as the preparation/application complies with mfgrs instructions , if the conditions are within spec}

[thebrushand]

Metal Primer 6455/044 is a two component product which is a self-etching type wash primer for use only on bare matels such as steel, stainless steel, cast iron, copper, bronze, galvanized steel, lead and aluminum. It forms an excellent adhesive bond to metal hulls, keels, centerboards, and other underwater running gear. Can be used either above or below the water. Can be overcoated with either epoxy primer, topside enamels, or antifouling paint.
Part Number Description Size
16455/104406 Metal Primer Pack 6455 GL PDS MSDS
16455/104408 Metal Primer Pack 6455 QT PDS MSDS



Hey thanks for that info, the links answer a lot of questions and the actual primer makes sense to me too. Self etching wash primer, sounds great. I feel happy to start work now!

cheers

[thebrushand]

The full spec I ended up using was

1st coat - Petit Metal Primer Pack 6455. This is etch primer.

2nd coat - Petit tie coat primer. This is chlorinated rubber paint that binds well to the etch primer and will take most top coat finishes. Very easy to apply, and I have used that sort of coating before on swimming pools and a steel ferry, so I am quite confident it is man enough product for the marine environment at the top of our masts.

3 coats Z spar gloss enamel finish.

The finish looks really solid and the whole process was simple. I will report back in a few years time. Thanks for the pointers.

[Lew Barrett]

I've used Hammerite paint on a number of galvanized items. It's quite tough and tenacious. If you want to keep the job simple, think about it as a solution. They have a "hammered finish" product that goes right over clean galvy and looks very business-like. Zinc chromate primer is perfectly compatible with Hammerite.

Oops. I see I'm late!