Damp retaining wall

[joemac]

I have a concrete retaining wall outside my house that i want to render to match the house. My problem is that it is damp and has signs of salts coming out of the concrete. I guess it hasnt been tanked on the rear.

Can i tank this wall on the outside with bituminous paint prior to rendering? If so how do i get best adhesion of render to tanking?

Joe.

[thedoctor]

Sealing the damp in will eventually lead to trouble. The build up behind the sealer will split it or force it out of even the smallest opening causing cracks etc. If the water stays in the wall it will freeze with bad weather and crack the bricks as it expands into ice (see our project on freeze thaw action) this allows more water into teh cracks, which freezes etx etc until the wall breaks up. Better to render and then drill weep holes in the wall to allow the water to get out or render with lime and sand to allow the water to soak through slowly and evapourate to external air. You may have the job of cleaning the salts from time to time but you wont do any structural damage. See the project on efflorescence.