When do we need to repaint a Metal Surface？When you see the old paint of the front door gate is peeling off, paint blisters on the stair rail or paint flakes appear on your metal coffee table on your balcony. This is the time you need to repaint your metal piece, otherwise corrosion follows and rust starts to form.
Steps to follow for refinishing a Metal Surface
- Clean the Metal Surface
First you should clean the metal with cleaner e.g. dish-washer liquid, which works pretty good in removing the organic oil, grease and grime, then rub it dry with a cloth. The cleaning process not only remove the dirt, it also offer a good chance for you to access the metal. Locate the problem area e.g. rusting
- Scrape off the loose paint and Remove the rust
It is not necessary to remove all the old paint, you only need to clean off those flaking paint and powdery surface rust. It is important to remove the powdery rust because it prevents paint from adhering. Use a scraper to scrape off the paint flakes, then clean off the rust by metal wire brush, steel wool or sand paper. If the rusty area is large, consider using a power tool. Then sand down the area with wet/dry sandpaper, start with a 220 grit and finish off with an extra fine 400 grit.
- Priming
Priming is very important in preparing the metal surface before painting. Primer can ensure the paint adhere properly as well as protect the metal from rusting. Before you prime the metal surface, remember to wipe dust and debris away. Failure to clean the surface properly will result in a lousy paint coat which will peel off easily. Another point to keep in mind, priming should be done right after you cleaned the surface to prevent the contact of oxygen and moist in the air, as well as the accumulating of dust. Metal starts to rust in a few minutes without a proper coat protection.
There are a lot of Metal Primer available in the market, you need to have a better understanding on how to choose the correct one. Basically you need to identify what kind of metal surface you are going to paint, is the metal ferrous or non-ferrous？Then you need to decide the base of the primer you are going to use, water based or oil based？Finally you need to consider how bad is the rusted area, if the surface is deeply rusted, you need to choose a special primer that chemically converts rust to a paintable surface rather than a normal rust - inhibitive primer. If you want to have a better understanding of different primer, please go to https://www.justpainthk.com/post/primer. Choosing the correct primer is important in preventing further corrosion, as well as ensuring the top coat of paint adheres and does not flake off. Two coats of primer should be apply to ensure the coat is spread evenly, leave enough time for the first coat to cure before applying the second coat. (Follow the instructions of different primer)
Points to note: Oil based vs Water based
Oil Based Primer
- Usually contains Toxic Solvents (check VOC)
- For Enamel Paints
- Thicker (takes much longer time to cure)
- More painting technique
- Personally recommend for Outdoor Use
(Thicker Coating = Thicker Base = Better Protection)
Water Based Primer
- Non Toxic
- For Latex or Acrylic Paints
- Thinner (Takes 2-4 hours to cure)
- Normal painting Technique
- Both Indoor and Outdoor use
- Finishing Paint (The Top Coat)
With the modern technology and innovations, some newly formulated water based paints are able to paint over oil based primer. But I would rather stick to the old rule, oil based primer with enamel paint and water based primer with latex/acrylic paints. The only concern for me is the VOC emit from the oil based paint from the finished piece. If the finish piece is going to stay indoor, I would use water based primer with latex paint. If it is going to stay outside my front door, I would use oil based primer with enamel paint for their rigidity against the outdoor condition.
After the Primer coats has dried and cured, use a 220 Grit water/sand paper lightly sand over the surface, wipe away any fine particles left by sanding. This sanding process ensures a smooth surface to receive paint. Paint the next coat of paint with your favourite colour, wait until it cures. Again, lightly sand to smooth out any imperfections. Wipe clean and paint the finishing coat.
© 2020 Alexander CW Hung