Damp-Proof Membranes

DPMs are available as either Water based, or Epoxy systems. Epoxy systems are two-pack solvent free systems consisting of a Base and a Hardener which are mixed by using a slow speed industrial hand drill and helical spinner. Water-based systems are normally supplied as a liquid and a powder, and are mixed with a drill and paddle.

Both system are applied as a two or three coat membrane designed to reduce the passage of water vapour, and are applied before laying screeds or proprietary levelling compounds.

A DPM works by suppressing residual moisture in concrete floors, the addition of a DPM permits the early installation of moisture sensitive floor finishes even when the relative humidity of the base concrete is in excess of 75%. A DPM needs to be applied where there is no functioning DPM, and can also for used prior to the application of tiles, soft flooring or wood flooring to screeds which are not yet fully dry.

The number of coats required will be determined on the basis of hygrometer readings in accordance with British Standards, and the following table is a general guide.

Relative Humidity 75-85 – 1 coat
Relative Humidity 85-92 – 2 coats
Relative Humidity 93-97 – 3 coats

When installing a DPM, apply first coat and allow to dry. When applying the second coat, apply at a right angle (90°) to the first coat to negate the possibility of any pin holes.

Tests for DPM’s will include Moisture Vapour Permeability in accordance with BS standards and have been carried out and show a reduction in vapour transmission to less than 4g/m?/day.

When installing a DPM, consideration has to be given to the possible presence of hydrostatic pressure and the consequences of creating a barrier layer resulting in the pressure/water flow being directed elsewhere.