Who says railway modelling isn't art ?
Here we see a keen exponent of the hobby creating scenery using Polyfiller and a palette knife in a similar way to that employed by many artists for applying oil paints to canvas. Only the medium is different. And that we are making 3D and they were doing 2D.
For scenic work, the palette knife is a very handy tool. I used one to put the rock strata in the Flockburgh cliffs. For trowelling on plasters or other gloppy materials it really can be beaten.
You can buy these things from proper tool shops but far better to try the local art shop or even remaindered bookstore. The later often offer packs with several shapes for very little money. I think the one in the photo has been adapted by cutting it shorter than intended to give a flat point. At the price though this isn't a problem, just a few seconds with some big scissors or tin snips and it gets into the parts other palette knives cannot reach !