It's a common issue - you have a scratch or a dent in a wall and you want to fix it. There are 3 main possibilities - dent in a wall face, scratch at the ceiling where it meets the cornice (or another internal edge) or dent on the external edge of a wall. Let's look at each one.
You will need:
Filler - I used Polyfilla Multipurpose Interior Powder Filler
Filling knife
Consider sealing before filling, especially if you are doing part of a paint job.
After each use of a load of filler (I do about 65 g of mix at a time) clean everything used to place the filler. For the filler that comes as a powder, which I recommend, it sets faster if it comes into contact with old filler.
Also consider sealing after filling. For an external edge, I would highly recommend it, as an external edge is most vulnerable to damage.
Dent in a Wall Face
This is the easiest one. Simply scrape the filler in with the filling knife, leaving no excess if possible. If you leave excess, you will need to sand it off after drying.
Use a light to identify all the scratches. A phone light will work fine - you want it to be side lit to cast a shadow in the dent.
Dent in an Internal Edge
A dent in an internal edge is more tricky. In my case, this was left after I removed loose material and even flexible sealant with a box cutter knife.
First, remove any protruding sharp edges of cut or broken paint by sanding or with a knife. I cut two fingers by not doing this before the next step.
Next, wipe filler in with your finger.
Using the filler knife, put in more filler. It can be easiest to do this in multiple applications. Follow the instructions on the filler for drying time. Test for flatness by placing the knife vertically on the wall (or perpendicular to the edge). Even if it isn't flat, slightly concave (curved inwards) is easier to paint than convex (curved outwards).
Dent in an External Edge
And finally, the most difficult case - a dent in an external edge. Here, sealing first will really help the filler to adhere to the edge.
Major (over 5 mm long continuous) dents
First, use a kebab skewer to roughly fill to the correct vertical line. A plastic skewer would be easiest if you have one as it would be easy to clean. Unfortunately a straw would be too flimsy. Easiest to explain with a video.
Next, spread it out across by rolling the skewer.
Next, remove any excess. Bear in mind this excess will dry quickly if it has been in contact with older filler. Consider using for wall face filling or a similar easy job.
Allow to dry then sand. Follow the instructions for the minor dents remaining.
Minor (less than 5 mm long) dents
After drying, fill over the top using a clear sheet of plastic like a bound document cover. A pet food bag may also work but I like the document cover because it's transparent. This leaves a nice, smooth finish that's also rounded. For minor dents, you will only need to do this step.
The excess will set quickly if it has been in contact with older filler, so use it for an easy job like dents in the face of a wall instead of mixing with the rest of the filler.
Good luck! 🍀