Damp external wall

[needsomehelp]

I'm hoping for some advice about a damp section on an external wall. The wall in question is rain-facing, and when it gets wet, a two-metre-high section remains wet much longer than the rest of the wall.

The problem area was actually badly pointed when the house was built (the mortar was very soft and crumbly there). I have since had the wall repointed, but it seems the damage was done, because the brickwork now seems to absorb much more rain than the rest of the wall.

I've seen water-repellent coatings to apply to external walls to cure this problem, but I've read lots of technical reports from building advice websites advising against using these products - basically, that they only last a few years and don't truly allow the wall to breathe properly.

So now I'm confused - do I apply such a product, or is there some better solution?

Thanks for any help - this is doing my head in!

 

[KonradFischer]

I suppose there are some salt deposits in your wall which will adsorb more damp than the other parts and store it. By cristallisation in dry periods they will damage your walls surface as you have mentioned.

What you have heard about waterproof seals is quite ok. That the wall will not breath is not the correct idea, more clearly - 1000 : 1 is the relation between capillar transport and vapour transport in walls when it is drying out. And all plastified synthetic seals, coatings and renders will stop the capillar transports out of the wall about 100%. So it is a big mistake to trust in industrial advertising belonging also this topic.

What I can recommend is to bring an fine pored and therefore super capillar active absorbing layer on the problematic surfaces as a offer-plaster and take it away again when it has sucked in the salty solution. Maybe this procedure must be done twice if the salt deposits are enormous.

As material you can take fine grained pure hydratic (not hydraulic!) lime mortar (0-1mm) if the wall will be rendered afterwards, if not, take only cheapest pure clay perhaps from your own ground.

Hold damp the absorbing layer by spraying it with pure water about two weeks, then let dry and take away. The clay you can first rip down very easy, the rest on the surface wash away. Let dry out the wall and watch if it will be better after this. If not, continue as mentioned. You could check the absorbed salt by analysing the ripped off layer, but this will only cost money and enriches some chemical analysts. Take your normal thinking and looking and you will bring it to a good end.

You will find some further advice about such problems here:

What to do with damp walls

Good luck!

Konrad