Waterproofing on uneven walls and screed finish

Hi everyone, wondering if someone help me with this... I have gutted a bathroom (the building is brick construction throughout) and the walls are dented/uneven from the jackhammer and chisels. Do i need to render the walls smooth first before applying the waterproof, or is ok to simply waterproof over the walls as is? Also, when finishing a screed prior to waterproofing, what is the difference between finishing with a wood float and a foam float? i have seen someone finish with a foam...

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