dirty water marks on new rendering

[Daniel3103]

Hello,
I am posting here to get advice about dirty water marks that are appearing on my new rendering when it rains.
Recently, I had my boundary walls and the front elevation of my bungalow rendered. I was happy with the job but, every time it rains, the water makes vertical marks on the rendering when it runs down against the walls. Those marks start about underneath the joints between the coping stones, and they can go all the way down to the ground - as you can see from the photo.
It is worth noting, however, that the problem doesn’t happen under every joint and that there is sometimes a slight offset between the joint and the vertical line underneath. Also, on the other side of the wall - not shown on the photo -, the water makes a vertical line that is close to the middle between two joints.
All the marks disappear in a few days after a rainy day, and they come back at the next rain.
I thought the problem was happening because the joints between the coping stones were not waterproof, so I coated those joints with a waterproof layer, but that didn’t change anything.
So, my questions are:
-Do these dripping marks indicate a problem that is more serious than just the cosmetic issue?
-Why is water dripping from specific points at the top of the walls, not from everywhere along the walls?
-If I need to do something about this problem, what can I do without causing any collateral damage?
As you can see on the second photo, the same dripping problem is also happening on my bungalow’s front wall, below my windowsill which is cracked and hasn’t been painted yet.

 

[ree]

OP,
Moisture is tracking back from the coping on the garden wall - feel underneath the projection that the drip channel is not blocked?
Same with the bay render stain - feel for a clear channel.

You should cut back the lower render to break the ground contact by, say, 50mm.

 

[opps]

OP,
Moisture is tracking back from the coping on the garden wall - feel underneath the projection that the drip channel is not blocked?
Same with the bay render stain - feel for a clear channel.

You should cut back the lower render to break the ground contact by, say, 50mm.

Good point about the drip channel, but why the need to cut back the lower render on the garden wall further? It already has a beading which is above the grass.

 

[ree]

Poster #3,
The beading in the bay pic or the garden wall pic is irrelevant - best practice is to break any render ground contact 50mm above ground level.

I was giving the OP a break, however:
There's also the matter of low render bridging any DPC's which would require the render to end just above the DPC. Plastic Bel Casts are typically the correct drip beads for render.
OP, the air brick needs replacing with a plastic 9" x 6" air brick. A/B centres are every 1500mm.

 

[Daniel3103]

With regards to the drip channels, are these the grooves that run along the lengths of the coping stones underneath those stones? If so, I can’t access these grooves because they are above the rendered wall. I attach four more pictures, two of them showing where the coping stone run ends at each extremity of the longer part of the wall, the other two taken underneath the coping stones at the points where the water starts to drip down.
Based on these photos, what’s the best remedy to my problem? Should I chip away some of the render where it meets the coping stones underneath, or would that make the problem worse? Is there a better remedy?
And, as the problem is now, is it just a cosmetic issue or could it cause more serious damage?

 

[ree]

OP,
Thanks for the new pics.
The coping stones are not wide enough - on either side the coping's should project about 50mm beyond the face of the finished wall.
All is not lost: use a small angle grinder (115mm - 125mm) with a stone cutter.
Angle it up and cut new channels (simple slots) in whats left of the coping stone projections - this will also work with the window sill.
After grinding new channels you can then grind and rake out all the joins on the copings and the sill - then fully fill with a sand & cement 3:1 mix. Dont skimp - fully fill.
Building & Plumbing suppliers stock small repair bags of sand & cement.

 

[Daniel3103]

OP,
All is not lost: use a small angle grinder (115mm - 125mm) with a stone cutter.
Angle it up and cut new channels (simple slots) in whats left of the coping stone projections
After grinding new channels you can then grind and rake out all the joins on the copings and the sill - then fully fill with a sand & cement 3:1 mix.

Thanks for this advice.
I’m not sure I understand you correctly though. Are you advising me to cut new channels and then fill them? I can’t see the point of cutting something and, then, filling the cut straight away. Or am I misunderstanding you? I think I understand your first bit, but I don’t understand what you mean when you mention grinding and raking the joins and filling them.
Also, do I need to do this work urgently or can I wait a bit? I’ve got a lot to do on my bungalow, so I probably won’t be able to get on straight away with the job we are discussing. How long can I afford to wait before some serious damage is caused?
And as for the channels in the coping stones, should these channels be right against the wall or should there be a gap between the wall and the channels?