Render after damp proofing

[wayne73]

Recently while decorating the kitchen we developed some bubbling of the paint work on a newly plastered wall. There were patched of white powered coming from the bubbles. I called in a damp proof company who advised to hack off the plaster and render back to the brick work and they will inject it. This has now been done, but whats the best way to render the wall to protect against the damp/white powder coming back again before its replastered.

thx

 

[spongey]

sounds like you may have salt in the walls, did the damp proofers spray the walls with any form of anti sulphate solution to kill of the salt?

if not this will need to be done but the injection treatment should resolve your damp problems.

why did the damp proofers not re render the wall up????

 

[wayne73]

thx for your reply spongey (you are no relation to my walls are you they seem to soak up water)

No they did not spray the wall and the guy that previously plastered the wall is coming back to render and then skim as he feels bad as the damp was pointed out to him before he skimmed last time. The damp company wanted £700 to render the wall 1mtr high by 4mtrs long, i thought this was very expensive.

For the render I want to ensure the guy uses the correct mixture, was thinking 4in1 with a damp proof additive that should protect against more salt coming back and the injections should stop the damp coming up

What are your thoughts.

 

[spongey]

the damp proofers may not have identified any salts on your wall then, its quite easy to spot as its white crystals on the wall that look like rock salt!!! if you have any then you should have the walls treated for salt ingress.

the rendering up process is pretty straight forward.

mix a scratch coat at 3-1 with a waterproofer in the mix. i always use a stronger ratio on the scratch coat then float it in at 4-1 always with waterproofer but its up to you and if you use a plasterer then he should be well aware of the correct mix to use.

make sure the spread that does the job does not bridge the injection line or the damp can bypass the injected course.

good luck wayne and you dont want to know where the nickname came from mate!!!

 

[Nige F]

I think you need to try and find where the damp is coming from outside

 

[spongey]

i would have imagined the damp proof company would have ruled out anything other than rising damp hence the injection treatment.

but check the mortar beds, outside make sure they are solid and there are no knackered brick or holes where water could be penetrating.

are the walls drying out above the injected course?

 

[wayne73]

Its a 3rd party wall and the damp patch runs from the back of the property to about 2mtrs in side along this wall, it never gets higher than about 12" from the concrete floor. The guttering, roof and rear patio doors all fine, next door have a similar damp problem in the same area of the 3rd party wall. The damp specialists think its just a case of raising damp through a fail DPC in the brickwork either side of the cavity.

 

[spongey]

from what you have described it does sound like a case of rising damp, just make sure the plasterer uses a good quality waterproofer in the mix and does not at any point breach the injected course and you should be ok.