A reader's Painting question: Roof paint?

Justin W.   from   Bristol USA   had this Roof paint question.

Bill's reply

Hi Justin,
It's good that you say an old metal roof.
When we use the natural finish, galv. or Zincalume, most people say to leave it at least a year to weather. This gets rid of the oils and other by-products of the manufacturing process, and it gives the surface a bit of "bite" or something for the new paint to key on to.

• If the surface is new, then it is normal to buy the pre painted stuff in the first place.
• If the roof has already been painted you have to take off any flaky paint first.
• I always clean the roof down with a water blaster (pressure cleaner).
• This shifts the old paint that is going to move, and gets rid of all the old accumulated bird dropping tree waste etc. Ordinary hosing wont get rid of built up grime.
• Also with preparation, when the roof has got mildew etc. to kill this I use a fairly weak solution of chlorine (swimming pool stuff). Be very careful to hose it down after, chlorine lying in gutters etc. can cause rust eventually.

There are two schools of thought here. If you now have a clean bare metal roof that has never been painted before then the best way is to prime it with an etch primer. This is a solvent based primer that provides a key between the metal and the top coats.

I have never seen it used on a roof, I have used it many times for structural steel, but it is too expensive for roofs.

I have used standard acrylic house paint many times with good results. The top quality stuff that is used everywhere externally.
There are a couple of ranges here in Australia and I am sure you will get similar in the US. " Wattyl Solarguard" is one, and they advertise the fact NO PRIMER needed. These paints stick to bare metal if it's clean.

• Don't water the paint down too much, stick to the manufacturer's recommendation. No more than 10% anyway.
• If the roof surface is hot, wait until it is cooler, rather than thinning the paint down.
• If it wet with dew, wait till it dries.
• I hired an airless spray once on a large job, and it worked well. But… when I paint my own place I do it by hand. This makes sure that every litre of paint that I buy, gets on the roof at an even thickness with no wasted over spray or too thick sections.
• I have a corrugated iron profile, and I bought the foam roller that was shaped to the roof. IT WAS USELESS. It does a patchy job even away from the roof screws, you have to push too hard to get into the hollows. Around the screws I had to do it by hand anyway.
• I use a 4" brush for all the tricky bits and touch ups, and believe it or not I use a kitchen floor broom and a paint roller tray the get the bulk of the paint on. (It saves my aching back). I get a brand new one with long soft bristles.
• If you have no back worries just get a good quality 6" brush.
• If I was doing a profile with flat pans I'd use a standard long nap roller that just fits the pans and the 4" brush for touch ups.

There are a few companies here in Australia that specialise in spraying roofs.
"RoofSeal" etc. They maintain that their coating is flexible and also seals leaky roofs.
They have a bit of a reputation for "hard sell" high pressure sales tactics, and quite frankly they may work, but they are overpriced.