Cracked Roughcast

Some of the external walls of my house are showing signs of wear and tear, most of which can be freshened up wityh a good coat of paint. But I have noticed some of the roughcast has started to crack in some places. It doesn't seem to have got behind the mortar, which is still solid on the wall, but I am keen to address the issue and prevent the problem progressing.
Can anyone advise on the best way to seal these (cosmetic) cracks in the roughcast? I've heardmention of some sort of solvent spray which seals the cracks, but elsewhere its been said that they need to be patched up with fresh mortar prior to painting.
Could anyone with experience of this letme know what my options are, and what the best products to use are?

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