Weathering techniques, how to paint a rusted metal roof

Rust has to be one of the hardest substances to recreate as it is so varied in appearance. To take paint and brush, and try to attempt it was always thee most daunting of tasks for me. Well I am happy to say after ten or twenty tries at it, I am confident I can pass off the guidance and tricks to you.

The process of rusting metal is on that creates its own textures and colours. Reds, browns, Greys they all seam to grow out of the flawless surface of metal.

Scale sized corrugated metal comes with an oil applied to it, during the process of manufacturing it. We want to wash this in dish soap and hot water. This will clean up the surface so that we can start sticking paint to it. Let the metal dry completely.

We need to prime the metal to further improve our ability to stick the paint and weathering the the metal panels. I used an Earth/Tan colour for priming. This is because I am going to add darker colours on top and I want a variation to be created. The edges of the panels were painted Oxide Red to further add the pattern to the variations.

When all the preliminary layers are added and cured. We can then cut the panels in 4' widths with a pair of scissors. Sticking the metal to card or wood will only work with a few products. One I know works is panels will stick very nicely to two-sided tape (carpet tape).

The roofing doesn't at all look good right now, I know but you have to think of this in layers. The drab base coat is just getting covered anyway. This next step we want to lightly imply the pattern of weather.

We could go on painting in every direction and cover everything up. Or we can add a layer of Oxide Red that runs in the same direction as rain would. GO lite as we have more to add, we want to cover 10-20% of the Tan colour. Remember in the direction rain would run. Follow up by streaking burnt umber at a 5% coverage. If you do it quick enough it will mingle with the oxide giving you just what we need.

Again we need to allow everything to dry. Next we start using pigments to put on the finishing touches. 

The product I use is probably the best available. As it is made for the hugely popular military model market. Mig Pigments/fixer, and Washes are thee premiere product for adding dirt, especially in my tool box. The alternatives are many but two I don't mind mentioning are BragdonEnt, Sinopia and DrBen's.

I start by using a dry flat brush to apply the pigment powder to the roofing. The amount you apply is not as much as you may think. I don't scoop it out, more like I dip the brush in allowing just what sticks to the dry brush stay on. Factory Grey, Cargo Dust and Rust are the colours I used.

First I added Rust, in a few vertical streaks to about 50% of the roof. The powder will need to be dabbed with the dry brush to cover the streak locations. Next I applied the Factory Grey to 20% of the roof, more vertical streaks, try to keep these separate from the Rust so that they become distinct dark streaks down the roof.

To finish off the Mig pigments I use their product called the "Fixer", a substance that smells remarkably like paint thinner. To apply the fixer I use a separate clean brush and add the fixer at the top of the roof. Use the brush to first work the fixer into the Rust, then Grey. After all the pigment is wet then allow it to dry and cure overnight.

Last step to this is to add another separate layer of pigment to top it all off. But to add it we have to place a barrier between. Using flat matte sealer spray the roofing and allow to dry. Next apply the Cargo Dust pigment to 90% of the roofing and fix it in after. Remember to use separate brushes.