Positive/negative waterproofing, DPC in basement

Positive side and negative side waterproofing

Positive side (external) waterproofing: The membrane is applied on the outer face of the basement wall and below the raft, on the side from which water presses. Water is kept out of the structure itself. It is the most effective method and is used in new works. A protective layer (brick wall or board) is placed over the membrane before backfilling.

Negative side (internal) waterproofing: The waterproofing is applied on the inner face, opposite to the water side. The wall remains in contact with water, but seepage into the room is stopped. It is used when the outer face cannot be reached, such as in repairs.

DPC for a basement in ordinary soil

In ordinary (non-water-bearing, well-drained) soil, a basement needs a damp-proof course on the floor and walls.

1. Floor: The ground is compacted and a layer of hardcore or stone soling is laid, then 100 mm PCC (1:3:6), then the DPC layer (a bituminous membrane or 2 to 3 layers of polythene), then a protective cement-sand screed 40 to 50 mm thick, and then the floor slab.
2. Wall: The wall faces are plastered with 20 mm cement-sand 1:3 mortar with a waterproofing compound, and two coats of hot bitumen are applied on the outer face. A horizontal DPC is placed at plinth level above ground.
3. Joint: The floor DPC and the wall DPC are joined with a lap of at least 150 mm so that the barrier is continuous.
4. A protective brick wall is built outside the membrane, and the excavation is then backfilled, with a drain at the base.

        GL ----- horizontal DPC at plinth
          |memb|wall|
          |    |    |
  floor:  screed
          membrane (DPC)  <- lap with wall membrane
          PCC 1:3:6
          hardcore