Technical Guide
Bonding New Concrete To Old
Whenever new concrete is to be placed over old concrete or hardened concrete (even if it is only 24 hours old) there is a fear of inadequacy of bond between old concrete and new concrete.
To overcome this situation provide a bonding coat of Polymer based chemicals & Cement.
Method:
a) Clean the surface of all loose particles and moisten it
b) Apply Polymer based chemicals & Cement in the proportion of 1:1 (by weight) by brush.
c) Provide a thin layer (chat coat) of 1:2 cement sand mortar.
d) Immediately place a new concrete over it and carry on with the rest of the work as usual.
Note:
Provide a thin layer of 1:2 cement sand mortar.
It is advisable for the mortar mix to nearly match the proportion of cement sand part of the concrete e.g. if mix of new concrete is 1:1
½ : 3 then the thin mortar layer should preferably be 1:1 ½.
Sometimes longish aggregates are left protruding above the lower concrete and this would be helpful to increase integrity.