Why tank an outside before rendering?

C

Christonabike

New Member
I've got an external rendering job to chop off and re-render. The existing render has only been on 3 years but is cracking up and boxing all over. The customer has given me the invoice showing the date but in the job description it says;

"Render elevations using a Hey'di K11 tanking compound and finish with a 15mm ready render".

Has anyone ever come across this before? My understanding is that the tanking will be the cause of the render failing.
 
It could well be. Tanking a wall on the outside shouldn't be needed if the render is done correctly.
Depends how they applied the tanking and then the render if it's the cause of failure or not.


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Perhaps a attempt to stop penatrating damp?

I've never seen it before tbf

Just chop it all off and start again


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I think probably the k11 tanking slurry was not properly applied and so the damp wall has caused the render to fail. I have used this before to isolate a damp wall from the render such as garden walls or when i have been asked to render below DPC for whatever reason. Had no comebacks.
 
I see a strange thing the other week it was a Victorian property and on the render plinth about 800 high in the scratch coat there was slate tiles then another scratch then more slate apparently that was the way they did as a form of waterproofing I had never seen that before myself and I did wonder how long winded that must of been
 
Pagey said:
I see a strange thing the other week it was a Victorian property and on the render plinth about 800 high in the scratch coat there was slate tiles then another scratch then more slate apparently that was the way they did as a form of waterproofing I had never seen that before myself and I did wonder how long winded that must of been
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I seen similar things on dpc level on old houses it's quite common I think but not up to 800 high

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Wouldn't have thought a tanking slurry would cause render t craze, tanking = waterproof= suction control (nil) = slow to go off. Unless the tanking element was missed? Perhaps then there was too much suction, but the crazing would have been noticeable immediately. Could this be a case of abnormal shrinkage? If so might this be the result of wrong sand? Strange one.
 
What I've wrote doesn't read right, what I meant was the fact that the tanking is there is the reason for the render failing. That the tanking is covering up something, it's turned out to be the case. Water has been getting in through copings/balustrades at the top of the wall and the tanking has trapped it in causing the brickwork to break down. I've attached a photo of the building, I'm just in the process of taking it back to brick.

Why tank an outside before rendering?
 
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Christonabike said:
What I've wrote doesn't read right, what I meant was the fact that the tanking is there is the reason for the render failing. That the tanking is covering up something, it's turned out to be the case. Water has been getting in through copings/balustrades at the top of the wall and the tanking has trapped it in causing the brickwork to break down. I've attached a photo of the building, I'm just in the process of taking it back to brick.

View attachment 13842
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You seem to be convinced that the tanking is the problem !but maybe as you have stated it's the copings and balustrades?but regardless looks a great job to have ! Crack on lol
 
The problem was with the copings letting water in and running down the wall, instead of sorting that out the last guy has tanked it which has trapped all the water in for the past 3 years. The whole wall is soaked, I've just got the render off and am now taking the tanking off which is going to take a while. The builder is going to sort out the copings, we'll let it dry and render it up. Not sure what with yet though.
 
Christonabike said:
What I've wrote doesn't read right, what I meant was the fact that the tanking is there is the reason for the render failing. That the tanking is covering up something, it's turned out to be the case. Water has been getting in through copings/balustrades at the top of the wall and the tanking has trapped it in causing the brickwork to break down. I've attached a photo of the building, I'm just in the process of taking it back to brick.

View attachment 13842
Click to expand...
Nice gaff

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