Following from the stripping of the tank it was now time to address the dents in my tank. Unfortunately I found two. One on the top as I expected, the other underneath the left side tank badge.
Now the principle of filling a dent is easy – you lather on filler then sand it flat. I opted for U-Pol P38 filler. I know very little about it other than it had good reviews on Amazon and cost £6.45.
Aussies call filler bog, it’s a highly adhesive material that goes on as a goo and dries solid. I purchased a 250ml can which was more than enough for my project. You pull some of it out the tin, mix in a small amount of harder that allows it to set. Mix and apply to a clean dry surface. It then sets within a few hours as as lightweight, easily sand-able surface. Seems straight forward right? Well it’s not.
Here is a shot of the filler applied to the tank.
As you will see it’s nice and rough. From what I read though filler has to be perfectly smooth and if you can feel even the slightest mis-alignment of difference in the surfaces you will see the filled spot in the final paint. With this in mind I really wanted this to go well so took my time. I did it this once, went to primer then sanded back and re-did the process as I was not 100% certain of myself. It is better to re-do it at this point then to have to strip off paint.
Based on what I had read, others suggested the way to approach it was use a course 120grit sand block, slowly going to finer grits and use straight sweeping motions. This sorta worked, I got a nice flat finish but I could still feel the tiniest imperfection when running my fingers gently over the surface. The best way I can describe this is a high point. Imagine your sanding a piece of wood, and that piece of wood had a Knot in it. You sand it straight for 30 min, and whilst the knot is there, all be it smaller, you have also unintentionally taken some of the wood’s surrounding surface off at the same time meaning you have a high point but this high point is made more noticeable as the surrounding area is now also lower. That’s pretty much what I felt I had done on the tank by using a hand block.
So take 2. I went back to the drawing board, sanding the filler down with 600 grit and re-filling the lot over the top. Rather than using a sanding block I went back with my random orbital sander and attacked the middle (where I perceived the original dent to be) with a 320 grit paper. I very lightly used this as my central point and went out from this – there is the risk you could cut into it too deeply, but a risk I was willing to take. I continued on this till the dent was no more and used many light passes, the edges of the filler were almost transparent but you had a hard time feeling anything. I then went over with 1000 grit by band. As a precautionary measure I cracked out the original can of spray primer. With a few light passes I had a base coat and could not see or feel the area that was filled. This process was repeated for the 2nd dent (even though this would not be visible under the tank badge.