I've had a plasterer in to put some insulated plasterboard (dot & dab) in the garage and skim it. He's done a good job but a floor - ceiling crack has appeared, I'm guessing at the join between two boards. They seem solid and aren't moving or anything and it is only hairline. I mentioned to the guy and he seemed genuinely surprised and came and had a look. He suggested using caulk to fill it but I think that would be a bit of a mess on a flat surface, no? He also said he had some other filler that worked well for him and even popped round with a tube but it is just standard polyfilla and I don't think it will be all that successful either...I've never had much luck filling surface cracks with standard fillers, they always just crack again almost straight away. I really don't want to start scraping out a big channel all down the wall...I was thinking of trying this liquid filler stuff: https://www.jtatkinson.co.uk/polycell-hairline-crack-polyfilla-500ml.html Or maybe even the spray: https://www.jtatkinson.co.uk/polycell-quick-drying-polyfilla-spray-300ml.html Waste of time? Anyone tried these kinds of products?