Outside render on horizontal surface

a&akay

I have a 1950s house with a front porch consisting of a rough concrete slab rendered afterwards to give it a smooth finish. The underneath suface is delaminating due to water penetration from above. I can sort this water problem out but need advice on the render mix to use on the underneath surface to get it to adhere and set without falling off. Any suggestions please. Epoxy mortar is too expensive for the area concerned.

ariba10

Do you mean the concrete slab over the top of the porch?. If you are I think you may find that water has got to the reinforcing steel inside the slab and is rusting.
If so it will mean changing the slab.

Sorry to be so pessimistic but there has been a lot of trouble in this area with houses of the same age.

a&akay

The porch is the slab ie it is above the front door as a simple concrete casting away from the house supported on steel columns. You are correct in that the water has reached the underside via the reinforcing but I can tackle this problem from above. I need a render formula to smooth the underside once the penetration from above is sorted.

boogiemaster

When I did some rendering I mixed three parts sand to one and a half of cement and made a firm mix by not adding too much water.
Just make sure the surface is rough so the render sticks to it, also depends on how much rendering you have to do as the size of the mix.
Someone else should come by soon that does this for a living, my dad is a builder and he knows what parts you need but he’s away or I could of asked him for you.