What do I need to add to the mortar mix for repointing below the damp course? I've got some Wickes Waterproofer & Retarder for rendering, but am not sure if this is suitable. Any advice greatly appreciated.
How old is your house and is the original mortar a lime based mortar?
If your house is reasonably modern (post war say) tradeaway is correct.
If it is an older property you should be wary about using waterproof additives and even cement sometimes as this could increase dampness inside the house (particularly if it is an old solid wall). Dampness in old buildings needs to be managed and sometimes carrying out works with the best of intentions can aggrevate the situation.
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