How should I prep steel gal posts for painting?

jnk40 · May 27, 2015 3:47 pm

Wanting to paint 15 gal posts (75mm square) on the verandahs.

I have 6L of Taubmans All Weather Exterior paint in the dark Monument colour I was hoping to use. Open to other suggestions though.

Question is how do I prep the posts first? Only want to do the job once and don't want it lifting in a few years.

Posts have been up for 12 mths so most of the anti-corrosion film has gone but will still give them a good wash down first.

Do I need to use something first so the final coat has a 'key' to adhere to.
Have got differing opinions from hardware and paint shops.
Everything from Penetrol, cold gal, etch primer to just plain old metal primer.

Any paint experts here that can give some definitive advice.

rebuilder86 · May 27, 2015 8:26 pm

I am a paint expert!! and i love it when someone wants to do something propperly!
firstly,Cold galv is for mild steel and should never be applied to galvanized iron. dont do it.
Any metal primer will be oil based , and oil based paints to not cope with the zinc coating.
Some say to use etch primers, but this should only be used when the galvanised substrate is going to be subject to some form of abrasion.
The galvanizing of steel is enough protection against rust for metal protection primers to not be used.
The best thing to use is this...
http://www.dulux.com.au/specifier/produ ... oduct=2132
You can get this at a dulux trade center near you!
As for top coat, the best product is simply a self priming exterior acrylic gloss, or if you must, semi gloss, Not low sheen.

jnk40 · May 27, 2015 9:05 pm

Thank you for your advice, much appreciated.
Had a couple of queries below.

rebuilder86

I am a paint expert!! and i love it when someone wants to do something propperly!
firstly,Cold galv is for mild steel and should never be applied to galvanized iron. dont do it.
Any metal primer will be oil based , and oil based paints to not cope with the zinc coating.
Some say to use etch primers, but this should only be used when the galvanised substrate is going to be subject to some form of abrasion. By abrasion do you mean regular contact such as a hand rail?
The galvanizing of steel is enough protection against rust for metal protection primers to not be used.
The best thing to use is this...
http://www.dulux.com.au/specifier/produ ... oduct=2132
You can get this at a dulux trade center near you!
If, as you say, the galvanizing is enough is this product still required. Does it simply act as an undercoat?
As for top coat, the best product is simply a self priming exterior acrylic gloss, or if you must, semi gloss, Not low sheen.Would my Taubmans All Weather Exterior be suitable as a top coat. It's a gloss.

Lastly, should I use mineral turps or soapy water to wipe down the posts first to remove any possible remaining anti-corrosion treatment - when they first went up they had a slightly greasy feel.

rebuilder86 · May 27, 2015 9:34 pm

abrasion, i guess like a handrail yes. very good explanation and a realistic use for galvanised iron also!
In commercial terms, an industrial handrail would be coated in an epoxy - urethane system in most cases, but for DIY, this is beyond expensive!!
The point of the Arylic galv primer is to adhere to the zinc lined surface, and dry with an open pigment, which will allow the opcoat to dry evenly. Imagine if you tried to paint acrylic onto glass, as it is drying the paint at the surface would skin and the paint at the glass substrate would stay wet for longer, affecting its ability to dry bottom up.
The primer (in this case galv iron primer) is designed to create a porous yet perfectly flat, thin film for which the top coat will cure from the bottom up.
You could simply avoid the primer all together however this will greatly affect the longevity of the coating. If you do decide to circumvent the primer, ensure you are applying very thin coats at a time, or better still spray it on without thinning at all and get a very thin film build for reach coat. Ideally, use the primer!
Your paint is perfect for the top coat!

jnk40 · May 27, 2015 9:43 pm

Again, thank you, excellent advice and clear definitive explanations!
Will definitely use the Dulux primer you suggested.

And sorry, I added this bit after you replied.

Lastly, should I use mineral turps or soapy water to wipe down the posts first to remove any possible remaining anti-corrosion treatment - when they first went up they had a slightly greasy feel.

rebuilder86 · May 27, 2015 9:56 pm

Bah sorry missed that bit, was too keen to respond...
yes get some good clean shop rags and soak them in turps, and go bananas. there will be heaps of grease on them!
Try not to scratch the galvanizing with any wire brushes as this will likely allow lines of thicker paint which will promote crocodiling or flat out peeling!

jnk40 · May 27, 2015 10:26 pm

Roger that. The misses will be on turps duty.

My wise old neighbour next door reckons I'll regret painting them and should just leave them but I'd like to dress them up.
Do you think I'll get 10-15yrs by doing it properly as you've suggested?

rebuilder86 · May 28, 2015 12:48 am

it should last more than 20 years. Company i work for will guarantee that coating system for as long as you live in your house!

jnk40 · May 28, 2015 8:35 am

Thanks. That's good to know. Very much appreciate all your help with this.

beness · Nov 23, 2016 5:48 am

Thanks for this info rebuilder86, really helpful!

I had one question, does this same paint and process apply to a hot dipped galvanised steel?

Thanks!