Hairline cracks

It's one of the things for which I'm prepared to pay for millionaires' Polyfilla - the ready to use 'flexible gap' version in the blue squeezy tube with the nozzle. It's easy to follow the cracks with it, rub it over and along the crack, then wipe off the excess. The fact that's its flexible might mean it takes longer to open up again, but if there is any dynamic movement and cracking of wall, you're going to continue to get existing and new cracks opening over time.

Toom

polyfilla's as good as any. Wiping it with your finger's quicker than a metal scraper.

NT

Had a similar problem with year-on-year movement in some hallway plaster (1850 house). As experiment, injected a couple of gallons of diluted PVA at a number of points at cornice level. Sorted it!. It's now a sort of plaster/brick/plastic composite and I've an 'orrible feeling that the whole wall may now be 'stressing up prior to exploding ;). I'll make do with fine surface filler next time around.

I too have a 19 century house with dodgy plaster in stairs and hall. I too drilled holes at various points and injected pva and polyfilla solution. That was over a year ago and so far it has held up well. The only problem I have is when putting wall plugs in. The plaster still seems a little crumbly. I find drilling the hole and filling with decoraters caulk then pushing the plug in and leaving 24 hours to set seems to work. It really needs a complete replaster but I'm too knackered to do that sort of job now and too skint to hire it done.

there is a filler on sale a bit htinner than normal polyfiller called something like crack attack

In message , freecycle writes

I just use Polyfilla fine crack filler. it's much finer than normal filler and can be wiped into the cracks leaving hardly any sanding to be done.

Gives a good finish and is quick, but if there is any movement in the plaster the cracks will eventually come back (I use mine on some fine cracks that appears in newly skimmed walls, seemed fine for the couple of years after that we were there.