I have had some disappopinting results with body filler. I lost my rented workshop last year and did the filling round the roof fill and then had to paint in a hurry - cellulose. The filler had a couple of coats of etch primer as there was bare steel either side and then grey primer and finally I went in with the cellulose top coat. After a while I could see a line where the filler butted the steel roof filler and its getting worse. it looks like the filler is shrinking back. I havent noticed this happening elsewhere. Its just ordinary filler not metallic that I have seen advertised. Any ideas. I'm not wroried about removing the filler and doing it again as it was a hurry up just to get something on it berfore the damp and cold got to it.