Hi, I'm NOT a plasterer, but want some advice. A builder who I want to employ is planning to use Sika waterproof render on an internal party wall and a window wall. He is reputable. He wants to use a multi finish topcaot. Is this ok? Or should he use a limebased topcoat? The walls have a damp issue and my surveyor says not to use any chemical damp proofing as it's an older building.