Introduction: How to Repair Basic Rust
Video tutorial on basic rust repair. Here I am working with a component off my snowblower, but this procedure applies to any steel components found on vehicles, recreational vehicles, etc. I will not be covering how to repair any soft, rotten, or metal with holes in the video. That will be saved for another video. When you first get into the rusted area, you won’t always know it’s structural situation until all the rust and paint has been removed from the area. If the rusted area is next to a body panel seam or trim, there is a very good chance it continues within a seam or under trim. A rust spot may too to be only 2” across, but when in reality it will actually be 4” across as the corrosion can migrate behind the paint even though it doesn’t look like it’s bubbles up yet.
- 220 to 320 grit sandpaper
- 400 to 600 grit sandpaper
- etching high build primer
- rubber gloves
- tack cloth
- clean lint free cloth
- wax and grease remover
Step 1: Removing the Rust
Start by masking off the adjacent area you do not want to damage with tape and paper. This is specifically directly towards spot repairs. This will add a little protection from the dust or whatever equipment you are using which may slip and damaged any surrounding paint.
Normally I like to start out with a scraper to remove any loose debris such as flaking paint or rust. The scraper will sometimes point out any holes or soft areas. Another way to find a soft area is to push on it with your finger. If it’s soft, you should hear a crunching or cracking sound, if you push hard enough, well your finger will push through. So be careful not to cut yourself as well.
You do have a few different options as how to remove or neutral the rust. This is a must, otherwise the rust will come back, creating bubbling in your finishes surface, along with deteriorating the metal in behind. I do have a video of this over on my YouTube channel, be sure to check it out.
Make sure all the pitted areas are clean and there isn’t any darker spots left as this can grow back into rust. Which eventually will damage your finished surface. Depending on what method you used, ensure it is dry and free of any moisture. Then sand the surface down with 180 to 220 grit sandpaper. This will remove any baked on or loose debris which could have been caused from the rust removal method.
I would highly recommend wearing rubber gloves. This will prevent the oil from your skin contaminating the area and any harsh chemicals coming in contact with your skin. After that, give the area a good wipe down with a wax and grease remover. Use only a wax and grease remover as it doesn’t leave a residue where it can affect adhesion or final paint finish, and doesn’t evaporate too fast where you have to worry about it missing any contaminants.
Step 2: Adding Primer
The best option for primer is a 2 part epoxy, but unfortunately that can be hard to find and more expensive. However, it does have the best moisture resistance and adhesion. Instead I will be using another method with an etching primer.
Mix the can accordingly and then apply the etching primer to the surface. Work in a well ventilated area and I would highly recommend wearing a respirator as well. Considering we are working outdoors, there is a very good chance we will get dust in the paint, therefore I like to wet the ground with water if possible to prevent any dust from floating, along with painting on days with minimal wind.
The etching primer does contain acid which bites into the metal surface creating a stronger bond and neutralizing the rust to some extent. It won’t make the rust disappear, but it will prevent it from growing. This is also a high build primer, which means it will fill in any imperfection in the surface such as metal pitting or scratches.
Make sure the metal does have a sufficient coating with no bare spots exposed. Lighter coats are best as it does dry quicker, wait about 10min in between coats. So you’ll probably be looking at 2 to 3 coats depending on your work piece and the extent of surface imperfections.
Allow it to dry for about an hour. Considering this was a high build primer, there was no need for an additional type of high build primer. If you are only able to find an etch primer, use high build primer over the etch primer and ensure it is a compatible project. Otherwise the surface may turn soft and not dry, leaving a mess in the end. Keep in mind, primer does not seal the surface. Primer is porous, therefore it will allow moisture in, causing rusting of the metal. Whatever you are working on, take the correct measures to prevent moisture exposure.
Step 3: Guide Coat
Apply a guide coat. Here I am using a very light mist of a compatible darker coloured primer. There is actually a specific product for applying a guide coat but it can be hard to find depending on where you live. A guide coat is intended to show you the high and low spots in the surface, along with where you have and haven’t sanded. If these low spots aren’t addresses now, they will show up in the final finish. Don’t expect the paint to fill in any imperfections.
Step 4: Sanding the Imperfections
Depending on the severity of the surface, you may need to start with 220 to 320 grit sandpaper. This may seem coarse, but at the moment I an trying to rough out the surface, levelling it quickly to remove imperfection. Use the assistance of a backing pad or block to keep the sandpaper even so this does not create any distortion in the surface. This will level out a majority of the surface, bring the high spots down to meet the low areas. The backing pad I am using is rubber, so it’s able to follow the contour of the object easier. Using only your fingers can create waves in the surface, giving it a distorted look in the end. As you can see the low spots are indicated by the guide coat.
Step 5: Final Coat of Primer
Finally apply another coat of etching primer to the bare metal and over the areas that were sanded. Considering the 220-320 was coarse sandpaper, it wouldn’t give a quality final finish, therefore the scratches need to be filled. Take your time, always inspecting the area. Prep work is extremely import as this greatly affects the final finish. No metal must be exposed before applying paint. If pitting still needs filling, continues the previous step with sanding until the area is free of imperfections.
Step 6: Finish Sanding Before Paint
Finish up with either 400 or 600 grit sandpaper. 400 grit is directed towards non metallic paints and 600 is better for metallic paints. Do not use anything coarser than 400 as this will leave deep imperfections and will be very noticeable in the final finish. Sanding is needs to remove any dust that may have landed on the surface and the remove any orange peal which will be magnified in the final coat.
For the inside I did not level the surface, just to demonstrate the difference between filling surface pitting and not. Being as this will be black, it will be extremely noticeable. Inside I am using a scuffing pads which is rated at 400 grit. The scuffing pad is used to gain access to those low spots, sandpaper would be unable to do this. Therefore the scuffing pad promote an uneven surface which will not remove surface imperfections unlike sandpaper.
Wipe the area down with a wax and grease remover a couple times to ensure there are no contaminants. If the contaminants are not removed, this can create fish eye, adhesion problems, paint separation and other flaws. I normally like using white clothes as I am able to see if there is any contaminants on the surface and when it’s clean. Once the degreaser has evaporated, a tack cloth can be used to remove any dust or lint stuck to the surface, normally from static.
Step 7: Applying Paint
I’m just using an off the shelf standard gloss black paint here for this piece. For paint choices, you will have a couple choices in a spray can form. Single stage or two stage. Normally I purchase a single stage paint from the local auto parts store which can be custom mixed to my vehicle. The single stage comes in an acrylic enamel, there is no need for clear coat, can be a little harder to blend, and isn’t as durable. There is a two stage paint as well, which will have a base coat and a clear coat is then required. Just like paint, there is a couple options for clear coat too. You will have 1k or 2k clear. 2k clear is the best as it’s very durable and user friendly, but two stage paint in general is usually about double the price compared to single stage from my personal experience.
Two to four coats are required, depending on the thickness of paint applied and if you plan on wet sanding to a polish after. I won’t be wet sanding this, so first will be a light coat, then a medium, and as a finish a full wet coat.
Once satisfied, allow the paint to dry. Dry times will vary depending on the climate, product and thickness of coats. When the paint is curing or hardening, do not allow any moisture to come in contact with it. If the morning dew hits the piece, the paint will go from a gloss to a cloudy finish which cannot be buffed out in most cases. Therefore it will need to be redone.
Step 8: All Done!
After that, you should be left with a final product such as this. As for wet sanding, depending on the paint, I normally like to wait a week. I do have a video on how to wet sand which is available on my YouTube channel.
The outside surface was smoothen as you saw previous, the inside was not, so you can see the difference. When painting outside, dust in the paint can be expected as it’s not a controlled environment. Sometimes the dust can be removed by wet sanding, depending how deep it sits on the surface.