Forgot waterproofer in render

[JohnAnderson]

Hi all,

I have just finished rendering a fairly large wall and forgot to add waterproofer to my render (5+1+1, plastering sand, cement, lime). The wall will be painted with exterior paint and should be pretty water tight. However, I am worried about water seeping up from the ground that could freeze and cause the render to come away. Is there any kind of material that can be applied to the render near the ground that would penetrate and provide some kind of waterproofing function. Or am I better off waiting for the render to fail and then replacing with appropriately waterproofed version? Any help much appreciated.

Best wishes,

John

 

[tony1851]

If your render is so low that water gets up behind it, applying waterproofer to the mix would bave made no difference.
This is a construction problem you need to fix. It is usual to stop the render about 2 courses of brick above ground level, and certainly no lower than any dpc.

 

[JohnAnderson]

If your render is so low that water gets up behind it, applying waterproofer to the mix would bave made no difference.
This is a construction problem you need to fix. It is usual to stop the render about 2 courses of brick above ground level, and certainly no lower than any dpc.

Hi Tony,

Thanks for your reply. The render is on a concrete block wall, however, the bottom 1 meter of wall is solid concrete (a poured concrete footing that is adjacent to a patio). I have rendered the block wall and concrete wall down to the patio level. There is no dpc, this is effectively a garden wall. I guess I should have perhaps not rendered all the way down but I don't think water is likely to rise much up the concrete footing but probably will move upwards through the render. I guess I may be better off trying the grind off the bottom few cm of render just to prevent bridging to the ground level but thought it might be possible to paint the render with something to reduce the passage of water up from the ground.

Best wishes,

John

 

[r896neo]

The soild concrete will wick very little water relative to masonary block or brick so i wouldn;t overly worry. How did you prime the footing for render? SBR i hope?

Grinding off the bottom would be worthwhile i think.

 

[jeds]

Waterproofing admixtures are not recommended anyway. Water penetration should be avoided by good detailing. The British Standard does recommend surface treatments in some highly exposed positions - e.g. chimney stacks - but the BRE guide doesn't even do that.

 

[JohnAnderson]

Hi Jeds & r896neo,

Thanks for your comments. The shuttering used when pouring the concrete section of the wall resulted in a fairly rough, well keyed surface so I simply wet this down prior to applying the scratch coat.

I think I am beginning to learn that detailing is the key to achieving a long lasting finish in most situations. I will try and get some clearence between the ground and the render and hope this minimises the extent of wicking in this case and pay more attention during the planning phase next time.

Thanks again for your advice. John

 

[r896neo]

The concrete will save you this time i think as poured concrete is probably only about as water retentive as an engineered brick which would normally be how you deal with a wall like this. A course of engineered brick then a stop bead for the render about 4 inches off the ground

 

[theoldun]

Waterproof admix is only required in prick coat on high suction backgrounds to give you maximum time to apply floating coat. Not required on low suction backgrounds i.e concrete blocks.
Regards oldun