Damp Proofing Treatment To Basement

Basics in Building Construction 4(2+2)

Lesson 05 : Damp Proofing Treatments

Damp Proofing Treatment To Basement

Groundwater always produces hydrostatic pressure and poses problem of dampness in the basement. In sites where subsoil water table is low or where the hydrostatic pressure is not nuch , a D.P.C treatment can be provided over the entire area of basement floor and can be extended in the form of vertical D.P.C. on the external faces of the basement walls. The D.P.C. material can function like a water-proof tank on the external faces of the basement.

It is common to use bitumen felts in multilayers for damp-proofing treatment to basements. In places where moisture ingress is not considered excessive, two layers of bitumen felts are used. In case of heavy duty treatments or in places where heavy moisture ingress is encountered, three layers of bitumen felts are used.

The sequence of operations for treatment to basements in ordinary soil are

  1. Apply hot bitumen at the rate of 1.5 kg/m2 over the prepared surface to serve as primer coat.
  2. Lay bitumen felt in single layer over the primer coat.
  3. Apply hot bitumen at the rate of 1.5 kg/m2 over the bitumen felt.
  4. Lay another layer of bitumen felt in single layer over the hot bitumen layer in step (iii) above.
  5. Apply hot bitumen at the rate of 1.5 kg/m2 over the bitumen felt laid in step (iv) above. When basement is in damp soil the three methods that can be adopted are
    1. Provision of foundations drains and D.P.C.
    2. Provision of R.C.C. raft and wall slab.
    3. Asphalt tanking.
  1. Provision of foundation drains and D.P.C. : When basement rests on soils which are not properly drained, ( such as peat soil etc.) great hydrostatic pressure is exerted and the floor as well as wall receive water continuously oozing out. In such a case it becomes necessary to make a trench all round, upto foundation level and fill it with gravel, coke and other pervious materials. Open jointed drains may be provided to collect the underground water. Drainage pipes, embedded in gravel bed, may also be provided before foundation concrete. Horizontal and vertical D.P.C. are provided in wall as well as foundation concrete. The drain may have suitable longitudinal slope, ultimately draining the water into a catch drain. Drain pipes under the basement slab may be provided at some suitable interval.

  2. Provision of R.C.C. raft and wall slab: Where underground water pressure is severe, the drainage system may not solve the problem effectively. Also, constant pumping out water may be costly. In such a case , floor slab as well as walls may be constructed in rigid R.C.C. structure. Horizontal and vertical D.P.C. treatment is also provided. Atleast 3 layers of bituminous felts are used as D.P.C. Half – brick thick outer protecting wall is provided at the outer face of R.C.C. wall slab.

  3. Asphalt tanking: This is adopted when the subsoil water table is not very high. The treatment consists of horizontal D.P.C. in the form of asphaltic layer of 30 mm thick in three coats over the entire area of basement floor and then extending it in the form of vertical D.P.C. on the external faces of the basement walls. The thickeness of vertical asphaltic layer may be 20 mm, applied in three coats. The D.P.C. thus functions like a water proof tank on the external faces of the basement, thus keeping it dry. A 1 ½ brick thick outer protective wall is constructed. The vertical D.P.C. is taken atleast 15 cm above ground level. A protective flooring of flat bricks on foundation concrete (1:3:6) is provided to protect the D.P.C. from damage during the construction of floor slab.
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Last modified: Wednesday, 29 February 2012, 7:34 AM