Re-pointing crumbling mortar

[pissedoffpainter]

Hello all, I would like to repoint the brickwork in my loft, including the chimney stack. The present mortar is so crumbly that you can wipe it away with your finger. My questions are, will the new mortar adhere to the old? How much of the old mortar do I need to scrape out?

Many thanks
Mark

 

[Burnerman]

I'd rake out what you can for about 20mm or so, brush out the dust then dampen the joint before you repoint.
At least it doesn't have to be neat - which is just as well if I was doing it
John