Difference Between Damp-Proof Course (DPC) and Damp-Proof Membrane (DPM)
Difference Between Damp-Proof Course (DPC) and Damp-Proof Membrane (DPM)
What Is a Damp-Proof Course (DPC)?
A damp-proof course is an external membrane or flooring used to prevent water from entering a building through foundations and walls.
It consists of a thin layer of polyethylene sheeting which, along with an embedded drainage layer, is usually in contact with the ground outside the building.
The protection against dampness is carried over into interior spaces by using perforated foil strips in stud cavities, baseboards, window frames and door frames.
Types of Damp-Proof Course
1. Electro-osmotic damp proof course
When using the electro-osmotic damp proof course option, the water that is rising up through your wall is counteracted and directed back down to the ground by an electric charge.
These systems are best suited for walls that are 600mm or thicker. Historic Scotland makes extensive use of them in ancient buildings.
2. Pressure grouting
Pressure grouting damp-proofing is a cost-effective solution to protect your house from water damage.
Pressure grouting damp-proofing is a technique that fills in the gaps in a material with a liquid grout, usually containing an admixture of cement, water, and an additive such as sand or polymers.
This liquid grout is then forced into the gaps to form a strong bond.
3. Bituminous damp proof course
Bituminous systems have been used for centuries to protect buildings against rising damp. Bituminous systems are however slow acting and require a long period of time for full effectiveness.
4. A cavity wall damp proof course
Cavity Wall Damp Proof Course is the material which you place into the cavity between the two walls. This is to ensure the cavity creates a complete barrier.
Cavity Wall Damp Proof Course is made from layers of special material which can absorb moisture. It is a relatively new product.
When your house is being built, Cavity Wall Damp Proof Course is used in the construction process.
It creates a barrier that prevents moisture and dampness from entering and will help prolong the life of the brickwork.
What is a Damp Proof Membrane?
A Damp Proof Membrane (DPM) is a material with an effective vapour permeability rating of less than 0.03.
Traditionally used to seal out water, these membranes can be installed inside or outside of a building/home and are designed to mitigate risk from rising damp.
Damp-proof membrane types
Damp-proof membranes come in different forms.
1. Bituminous damp-proof membrane
Bituminous membranes are made from a polymeric, tar-like material that is poured into a trench to the side of a foundation.
It expands as it is heated and fuses when it cools, creating a waterproof barrier below the surface of the foundation.
2. External Damp-proof membrane
External damp-proof membranes are less common today than they were in the mid-20th century because they have been replaced by bituminous or have had their role augmented by it.
External damp-proof membranes are essentially a waterproof sheet of polyethylene that is placed over the surface of a foundation.
3. Internal Damp-proof membrane
Internal damp-proof membranes are used in thin-walled structures, such as the walls of a crawlspace or elevator shaft, where a traditional external membrane would not be feasible or would create an unsightly bulge in the building surface above.
Internal damp-proof membranes are installed inside (and sometimes outside) the structure being protected and create a seamless barrier against moisture.
Damp-Proof Course FAQs
1. What is the difference between Damp-Proof Course (DPC) and Damp-Proof Membrane (DPM)?
A damp-proof course (DPC) is a barrier installed through a structure to prevent moisture from rising through capillary action, such as rising damp.
Rising damp is caused by water rising from the ground into a structure. The damp proof course can be horizontal or vertical in orientation.
A DPC layer is often installed beneath all masonry walls, whether they be load bearing or partition walls.
A damp-proof membrane (DPM) is a type of membrane used to prevent moisture transmission.
A common example is polyethylene sheeting put beneath a concrete slab to prevent moisture from entering the concrete by capillary action.
How does osmosis damp proofing work?
At set intervals, the anodes are installed into brick, concrete, or stone walls. The copper cathode is placed at a lower level, at least a meter or two away from the walls.
Through the wall, the power regulator sends a little but entirely safe electrical current.
Free moisture molecules are attracted to the buried cathode and repelled from the positively charged anode zone.
The flow is initiated by the migration of positively charged ions found in damp brickwork pore fluid.
The water surrounding the positive ions flows with them as the dampness is expelled from the wall and harmlessly back into the ground, the osmosis damp proof course repelling or attracting like the poles of a magnet.
