Rendering over the DPC

[amatureleccy]

On my extension one wall's exterior side is the boundary to the neighbours property. I got the builder to render a skirting along that wall in order to make it match the rest of the neighbours exterior walls. However, he didn't do any rendering on the walls within my property.

I think that all the builder did was mix up some sharp sand and cement and trowel it onto the wall smoothing it with a float. He also rendered across the DPC.

Is it right to render over a DPC. Is it right to render using sand cement mix (if so what is the ideal mix). Is it a simple job or should I get a builder to do it.

Cheers

 

[masona]

Is it right to render over a DPC.

Yes, it's okay

Is it right to render using sand cement mix (if so what is the ideal mix).

Sharp sand 3:1 ratio

Is it a simple job or should I get a builder to do it.

Can be tricky if you're not experience

 

[amatureleccy]

Thanks Masona,

Should the 3:1 sharp sand cement mix have any waterproofing additives added. If so, what type?

Cheers

 

[masona]

You don't have but you can add Unibond to it.

I think the best method is to seal the wall first below the dpc with bitumen paint then render over that

 

[DAZB]

It is not good practice to render over a DPC because you have then effectively bridged it and the damp will travel over the render onto the wall above your DPC and render (pun intended) the DPC useless.

 

[masona]

That's very true but it would need a awful lots of rain to do that & providing you use the correct paint method on the cement plinth.

The best one I've seen is a 3" wide gap all round the property with pea shingles for drainage to stop the rising damp.

 

[DAZB]

That would be ok if damp was caused only by the rain but the damp will be starting below ground level where the bricks are in contact with the soil and where there is no air circulating to dry it and then it starts to travel up the courses of bricks and where it would then be halted by the DPC it will now creep over it via the rendering and continue upwards and inwards and if it then gets into the ends of your floor joists that becomes another story.