Hi, I live in a house which was build around 1950. We have just taken up some laminate flooring from the entire ground floor which had been put down prior to us moving in and we have discovered that the concrete floor underneath is damp and parts have crumbled away leaving quite large holes. We have been advised that this is down to a failing or non-existant DPM under the floor and that the best way to treat this (without taking up the entire floor) is to re-fill the holes, paint the floor with a bitumen paint and then finish it off with a self-levelling compound. I could really use some advise on whether:- A) this will hold back any damp (we are planning to carpet the floor), and, B) do we need to apply a primer before applying the bitumous paint? C) If a primer is required can this be in the form of a PVA mix?
Obviously the best course of action would be to take up the existing floor slab and replace it incorporating a DPM such as 1200 gauge polythene with sufficient lap-ups into the wall detail. If lack of funds is the issue, then you can still use a membrane over the top of the floor to reduce the amount of moisture affecting your floor finishes. This membrane can be either physical or chemical. Which one you use is dependant on the amount of moisture present within the floor slab. If only light background dampness is present, then an epoxy coating/bitumen paint could work well providing the substrate (Slab) is sound and free from holes. You do not need to prime the surface before application but do ensure the surface is dust free. If a higher moisture level is apparent, then a physical membrane such as a polythene membrane would work to a certain extent. again, make sure the substrate is sound and free of any sharp protrusions which could pierce the membrane.
These works are obviously a temporary fix and cannot be seen as a long term solution but should suit the purpose in question.
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