[Closed] Masonary cracks, flexible filler or cement mortar?

Think I'd go with mortar.
If there's no further movement then you're done, if there is movement then the mortar will show it and you'll need to get it fixed properly.
Flexible filler is a bodge.

(If moisture is getting in then it sounds bit structural and you need to find out what's happened)

If it's rendered then I'd cut channels and then render those - trying to force mortar into small cracks isn't a long term solution.

If it's bricks then cut as much mortar out as you can before repointing you don;t just want a skim across the existing stuff.

When out builders were doing the back of the house they chem-fixed a couple of reinforcement bars across a crack that had been there a while.

They were rendering after so might not be appropriate if you've got exposed brick.

pics?

We did a few things depending on the seriousness.

Scrape out and repoint in a few areas. Above one window the builder added some reinforcement rods. We ended up having a lintel replaced because the previous owners had done nothing and it had gone rotten.

If you just wanted to go down the crack repair then there are specific products available. Sika make some that I think are available retail. They can be cement based or epoxy based. They'll be formulated to aid crack penetration unlike normal mortar. Also they'll be flexible and have good adhesion.

The wall has a very thin 1-2mm render +paint, so I’ve not scraped it off yet to see what is going on. The lime mortar is very weak, you can gouge it out with your finger. Suspect the mortar joints have opened up a few MM. There is not a lintel as far as I can see, just a very shallow brick arch, I think cement mortar will probably be best to hold it together.

Thanks for the tips

If you use mortar you can get a Roughneck Mortar Gun which fills small gaps well.
For finishing, you can't get better than Toupret exterior Filler.