In summary, can frost proofer which is *not* suitable for lime mortar be used safely in a 6:1:1 mix?
The background is that I need to do a little bit of repointing to a chimney this weekend despite the current cold weather. It's a Victorian house with soft bricks and movement so I was planning on a 6:1:1 mix. And with the cold weather also adding a frost proofer. But the ones I have found locally (eg at Wickes) say they are not for use with lime mortars(see eg
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I don't know if a 6:1:1 mix counts as a lime mortar for this purpose. Nor do I know what else I might use (and be able to get hold of on a Saturday afternoon or Sunday morning).