Is it a good time of the year to do repointing?

You can do cement work all year round, this time of year you just have to use frost proofer in the mortar mix. Also be careful it doesn’t rain whiles doing the work or for a good 4 hours after the work has been done this gives the cement enough time to set a bit and won’t get washed away. I would advice having the ridge tiles rebedded in mortar not painted if the mortar is falling away as given time it will happen again. If you rebed them it’s stronger and will last longer, I’d even explore options like dry ridge system as these are a lot less hassle, also maintenance free and get the ridge tiles up to current british standard and specification. Dry ridge doesn’t have any mortar, but instead a plastic band weathering the joins between ridges and mechanical clips and screws fixing system holding the ridges down. Hope this helps, Regards Frankie BT Roofing Services

No we are just starting to get frost. If you get a wet day then a cold night it will all fall away.