Cracks in ceiling - any suggestion?

[rhino666]

Hi

My 1970 house has hairline cracks in most of the ceilings, generally central along the plasterboard join. I tried filling one - see first photo but a few months later the crack reappeared. These cracks are less than 1mm wide and in most areas not possible to insert a stanley blade.
Would like to try and disguise with something flexible that will hide the crack and move with the board flexing unlike the filler did, before repainting. Any ideas of a product that could be used for this and be preferably be finished flat.
Just to add, these are the original 50 year old flat plain ceilings and any movement is down to material expansion contraction. Scrimming and plastering would show up more than the crack in the centre of these ceilings, so just looking for a suggestion of a filler/mastic that could be over-painted and have a degree of flexibility. I haven't tried decorators caulk yet, perhaps that would work?

Thanks

 

[opps]

Toupret Fibacryl is available in tubes like caulk but has the added advantage of having fibres in it to make it stronger. Like caulk it shrinks back though. I normally wait until it shrinks back and then top it up with Toupret Redlite filler which is a lightweight filler and a dream to sand.

http://www.toupret.co.uk/business-customers/products/specialist-solutions/fibacryl-FIBACP01G.html

You might want to use a chisel either side of the crack to "snap off" the skim coat of plaster without damaging the scrim tape. It will give the Fibacryl a bigger surface area to work with.

Alternatively, you can try to sand the crack flat and then squeeze PVA glue into the gap before filling with Redlite (after the glue has dried).

On one job I had to deal with I didn't have the opportunity to use Fibracryl and then return the next day. The builder wanted a one day solution. I used a dedicated adhesive jointing tape (the tape was about as thin as a hair) and then filled over the top of that with 15 minute Easyfill. Sanded and applied two coats of emulsion. I haven't been called back so I assume it is still ok. The down side was that I have to use a 12 inch filling knife and try to feather it out. If you put a straight edge on the ceiling you would notice that there is a very slight bulge along the crack.