Laundry renovation

Hi just wondering if anyone can give me some advice, Im half way through re-doing my double brick downstairs laundry, I have removed the sloping mortor floor and smashed out a lot of of the surrounding render above the floor as it was loose and crumbly, Im guessing from moisture migrating into it from historic water leaks in the laundry OR moisture coming up from the concrete pad.... I need to re-render the walls back to a consistent depth for the new tiles, and Im wonder what sort of water...

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