How to Waterproof your damaged Terrace/Roof - Rescreeding / Re-laying maddi

Severe leaks in your roof slab can cause premature aging of the slab concrete. This causes

. weakening of the slab
. concrete breaking off, exposing the steel reinforcement bars (spalling)
. in milder cases, paint and putty flaking

not only giving your property a bad appearance but also diminishing its value and life. 

Screed de-bonding is one of the major causes of terrace leakage. Redoing the concrete screed on the terrace can help prevent the leakage. Proper bonding can be achieved by the following system.

Materials Required

. Latex or poly-carboxyl bonding agent

. Ordinary portland cement (OPC)

. Aggregates for screeding

. Waterproofing admixture

. Mason's tool kit

Application 

. Check the screed on the terrace for hollow spots using the wooden handle of a hammer.

. Chip off the loose material to obtain a sound surface with straight edges and repair using a polymer modified repair mortar..

. If there is excessive hollowness, chip off the complete screed using a hammer and chisel and remove the debris.

. With clean water, wash off all excess/loose dirt and debris and saturate the mother slab.

. On the side walls, mark the slope that has to be created in the screed, required for water run-off.

. Create the bond slurry using the latex/poly-carboxyl polymer, water and OPC usually in the proportion of 1 polymer : 4 water : 6-8 cement by weight.

. Apply the bond slurry using a large size brush or a hard broom, covering the entire surface evenly. Also apply the bond slurry to a height of about 100mm on the parapet walls.

. Prepare the screed concrete using OPC, aggregates and water containing a waterproofing admixture in the desired proportion (Refer to manufacturer's data sheet for the quantity of waterproofing admixture required).

. In the wet on wet condition (while the bond slurry is still wet), lay the screed concrete over the surface using a trowel to level the surface to obtain a minimum thickness of 50mm. Particular care must be taken to create slopes for water run-off while laying the screed concrete.

. Cure the thus formed cement surface using water.

. Once cured, prime the wall and floor joints using a mixture of 1 latex polymer :1 cement. Form angle fillets of 40mm x 40mm along the wall and floor joints using a polymer modified repair mortar while the primer is still tacky (wet on wet).

A sound screed gives a waterproof terrace.