Cement render and crumbling mortar

[ShelleyM]

Hi

I have an 1860 mid terrace labourers cottage built of stone/bricks and rubble infill. I have posted a photo of the exterior wall which has cement render on to brick and I believe a stone wall. The inside wall is showing damp spots especially after heavy rain and has moisture readings of upto 19%. Should I remove the exterior cement mortar and repoint and lime wash the brick I was considering just even removing the bottom 1 metre only. This eternal wall is under a shared alleyway with the adjoining house. In addition I have signs of damp in the first floor wall at the ceiling moisture readings of 18% and when I went into the roof space I discovered the same wall / chimney breast the mortar is crumbling. The fire and chimney has not been used in over 20 years and I noticed the chimney has no cap, not sure yet what condition the external chimney stack is like eg if it needs repointing or not. Should I rake out the mortar in the wall?chimney breast in the roofspace and should I use lime mortar for repointing? Or do you have any other advice re the chimney breast wall internal and external chimney stack

 

[ShelleyM]

Here are some photos of the same external wall after heavy rain you can see the water on the ground and the wall wet do you think this is the cause of my internal damp spots? Any idea why someone would have renewed this wall in the first place ? Just too highlight this is a covered alleyway the first floor of the adjoining house is above as you can see from the photos open to the elements at both ends. The drains sewers for both houses run underneath the ground, not sure if this has any relevance or may be a cause?

 

[Cubist]

Hi There,
I notice that you've had no replies offering advice as yet but hopefully this may help to stimulate sone additional input.

Regarding the alleyway - it looks like rainwater is migrating up through the render and may then be finding its way into the body of the internal wall producing the damp patches you are seeing. The render, having been applied from ground level, is bridging any damp course that may have been included in the wall when it was built; but in fact there may not be one at all. I would suggest that you remove the render and expose the brickwork to a height of 2-3 courses along the length of the wall. Hopefully, this would expose the damp course (if it was ever installed) but this should also significantly reduce if not eliminate the leaching of water further up the wall. As you expose the brickwork be sure to make good by re-pointing with a lime mortar where necessary. Don't be tempted to consider any of those damp proofing injection methods.

Regarding the internal chimney breast - from your photos it looks like mostly lime mortars were used in its construction but there seems to be evidence of repairs to the pointing using a cement based mortar. I would suggest that ideally this latter should be removed and replaced with a lime mortar while you make any other repairs.

Oh, and as you're not using the chimney a rain cowl may be a good idea to limit water ingress via that avenue.

Hope this helps and good luck.
Cubist

 

[ShelleyM]

Hi Cubist

Thank you very much for your reply and advice. Yes I can confirm there is no DPC in this part of the house and I plan to do what you suggested. I was also advised to consider a French drain along adjacent to the wall. I would be curios to hear if you or anyone else believes this would also help with alleviating the problem. Again thank you for your reply very much appreciated.

 

[Cubist]

Hello Shelley,

I think that you have precious little room in which to install a French Drain and it's unclear where any such might be able to drain to. Also, given that the alleyway is perhaps little more than a metre wide and the extant foul-water drainage pipes from your, and your neighbours, properties run beneath it, would make installation very difficult and risks damage to the extant foul-water drainage system.

Before doing anything else I think you need to confirm definitively where the water is coming from and why it seems to collect near the wall long enough for it to begin leaching into the render. From what you've already said it's likely to be surface rainwater from one side or other of the property that is draining through the alley toward lower ground. En-route it may simply be puddling in a low spot thus giving it the chance to lie beside the wall. Another alternative is that strong air-currents, common in alleyways, may be acting to prevent rapid exit of the water on the low side and thus creating the conditions for a puddle to form up-stream. In both these cases some simple contouring of the surface of the alleyway may be sufficient to prevent puddling and, combined with the action to remove the render, could stop future damp indoors.

There is, to my mind, one other possibility. In periods of heavy rain over lengthy periods surface and foul-water drains can be overcome by the shear volume of water from its many contributing sources and it can then begin escaping through the man-hole and other inspection covers elsewhere in the network.

I would strongly suggest that you need to get out into that alleyway during heavy rainfall to directly observe what is going on and while doing so take a look at the guttering and drainage pipes of properties on the uphill side to see if these are directing large volumes of water toward the alley.

Hope this helps and cheers,
Cubist

 

[ShelleyM]

Hi Cubist

Thanks again I intend to follow your advice, I did go down to the house the other day when we had some heavy rain and the wall in question and ground was dry as a bone. I went down a second day and this time the wall was wet again albeit the ground was dry as a bone I can only assume the wind direction and strength has a bearing and is throwing the rain on to the wall. I think I'll need to be there during inclement weather and observe from the onset of the weather and try and work out if this is the case or not. Either way we are going to begin removing the cement render this week and I have a roofer coming too to repoint and replace some broken/missing slates. Hopefully all of this will remedy the problem. Thanks again for your helpful replies very much appreciated.

Shelley

 

[ShelleyM]

Hi Cubist

As a way of an update we have began removing the cement render on the wall to expose the following I believe its a mixture of cement mortar around some of the bricks/stones and lime mortar around the others. The lime mortar is easily removed crumbling with a chisel. Just wanted to check we are still doing the right thing eg after we remove all the render remove the old lime and or cement mortar then repoint with lime mortar and would it be suffice to just lime wash the surface of the bricks stones or will I need to render with lime instead? I also noticed a gap on the ground behind the downspout which was full of wet soil which Ive removed is it suffice to just fill this with ordinary mortar? Ive added a photo of it in its current state.

Thanks

Shelley

 

[Cubist]

Hi Shelley,
You need to make sure that all the pointing is repaired where it has been damaged or been lost over time. Any crevices between the bricks, and that cavity by the downspout need to be properly and thoroughly filled - that one may be allowing rainwater to get down to the footings/foundations.

Sadly, I think some of that brickwork is in a pretty bad condition and it's plain to see why the whole wall was rendered as it was. To prevent further deterioration at the lower levels in particular I think that simply re-pointing and painting with lime wash will not e good enough. You may not have read the Art of War by Sun Tzu, and I'm paraphrasing here, 'There comes a moment in some battles where the best option is to run away'. In this case I think your best option would be to re-render those sections after repairing the pointing and then painting that low section, two or three bricks height, with a bituminous water proof coating to prevent future leaching of rainwater into the higher sections.

That goes against the grain of the usual mantra for Period Homes somewhat, and others here may disagree and suggest alternatives, but I feel that this approach may prove to be more effective in terms of both economy and efficiency.

Keep us posted please.
Cheers, Cubist

 

[ShelleyM]

Thanks Cubist

I assume you mean I should render with lime rendering is that correct, I've removed the cement render to about 2/3 ft at present are you suggesting I should remove the rest repoint and repair and then lime render and in addition do I also render the low section 2 / 3 bricks before I paint with bituminous waterproof coating?

Thanks

Shelley

 

[malcolm]

Well done for removing the cement. Those stones look lovely!

It's a covered walkway so there won't be a lot of water getting on to the bricks apart from maybe a bit coming up from the ground. I would be tempted to just re-point with lime, perhaps replacing the worst of the really spalled bricks. You can never get rid of all the cement on the brick faces but a consistent mortar colour will make the wall much tidier. The rustic look might well look better than a rendered finish. Bitumen finish is waterproof and will stop water evaporating away from the bricks so might not be what you want.

For the drain it's a bad idea to have a drain pipe discharging into your foundations. It'll make the walls wet. Ideally it would discharge into a drain that goes to a soakaway (or in older houses often the existing foul drain). At the very least it ought to be channelled away from the house. For the ground behind the drain cement is better than lime as it's more robust and you don't want it to be breathable when there is a load of water trying to get through it from the drain pipe.

 

[ShelleyM]

Thanks Malcolm and Cubist for all your comments and advice to date , yes the exposed bricks look so much better so I will have to deliberate and decide what to do asap. I suppose I could always try first repointing and replacing the damaged bricks and see if that reduces the moisture in the walls and if not render with lime after this. I will address the drain gaps straight away then with cement.

 

[Lacan07]

Thanks Malcolm and Cubist for all your comments and advice to date , yes the exposed bricks look so much better so I will have to deliberate and decide what to do asap. I suppose I could always try first repointing and replacing the damaged bricks and see if that reduces the moisture in the walls and if not render with lime after this. I will address the drain gaps straight away then with cement.

The walk way looks covered so no need to go mad on it, repair and repoint if you want but lime rendering won't make it dry any quicker

 

[ShelleyM]

Thanks Lacan I would like to remove all the render even for aesthetic reasons but do you think I should go ahead and repair and repoint what I have exposed to date as I am under time pressure atm and first priority is to mitigate any further water entering the wall or do you think I need to remove and repoint it all now to ensure no further water ingress?

 

[Lacan07]

Thanks Lacan I would like to remove all the render even for aesthetic reasons but do you think I should go ahead and repair and repoint what I have exposed to date as I am under time pressure atm and first priority is to mitigate any further water entering the wall or do you think I need to remove and repoint it all now to ensure no further water ingress?

So what do we think is the cause of the damp? I'm guessing that concrete pathway?

 

[Lacan07]

I don't like this much..is that rainwater guttering? It'll be going straight under the house.

 

[Cubist]

I assume you mean I should render with lime rendering is that correct, I've removed the cement render to about 2/3 ft at present are you suggesting I should remove the rest repoint and repair and then lime render and in addition do I also render the low section 2 / 3 bricks before I paint with bituminous waterproof coating?

As Malcolm has said, you've done an excellent job removing the old cement render thus far and I feel that ultimately you should get rid of the rest too. However, your work has revealed some bricks that ideally should be replaced, again as Malcolm has suggested, as their in-situ remnants will be almost impossible to stabilise. This is an easy enough task but can be a little unnerving for the novice - if you decide to do this now please get additional 'How To' advice.

Regarding your specific questions. Given that the aim is to prevent standing water in the alley leaching up the wall through the render, I would recommend a hard cement mortar, rather than lime, to apply a render coat to the top edge of the 2nd or 3rd course of brickwork. This could also include a wedge shaped fillet at the foot of the wall to further discourage puddling or divert the flow of water from the higher ground. Once dried, this render and the fillet can be painted with the suggested bituminous paint to further resist water penetration.

In my opinion you should continue to remove the rest of that cement render, repairing any brickwork and pointing as you go using a lime based mortar. The red-brick finish you have there is quite attractive in its own right but a lime-wash finish would help to bring some light into the alley.

One point of caution if I may; looking back on one or two of your photos I see that you seem to be using some kind of power tool to remove the render. You do need to be careful with such as, given the likely hardness of that cement render and the fact that old bricks tend to be quite soft, it very easy to end up removing much more than just the face of a brick and can end up destroying their physical integrity. Sorry if that sounds a little patronising but I'd rather you're safe and I'm not sorry

 

[ShelleyM]

View attachment 14025
I don't like this much..is that rainwater guttering? It'll be going straight under the house.

Hi Lacan Ive now cleaned out this hole and made it good so hopefully one further potential cause removed

 

[ShelleyM]

As Malcolm has said, you've done an excellent job removing the old cement render thus far and I feel that ultimately you should get rid of the rest too. However, your work has revealed some bricks that ideally should be replaced, again as Malcolm has suggested, as their in-situ remnants will be almost impossible to stabilise. This is an easy enough task but can be a little unnerving for the novice - if you decide to do this now please get additional 'How To' advice.

Regarding your specific questions. Given that the aim is to prevent standing water in the alley leaching up the wall through the render, I would recommend a hard cement mortar, rather than lime, to apply a render coat to the top edge of the 2nd or 3rd course of brickwork. This could also include a wedge shaped fillet at the foot of the wall to further discourage puddling or divert the flow of water from the higher ground. Once dried, this render and the fillet can be painted with the suggested bituminous paint to further resist water penetration.

In my opinion you should continue to remove the rest of that cement render, repairing any brickwork and pointing as you go using a lime based mortar. The red-brick finish you have there is quite attractive in its own right but a lime-wash finish would help to bring some light into the alley.

One point of caution if I may; looking back on one or two of your photos I see that you seem to be using some kind of power tool to remove the render. You do need to be careful with such as, given the likely hardness of that cement render and the fact that old bricks tend to be quite soft, it very easy to end up removing much more than just the face of a brick and can end up destroying their physical integrity. Sorry if that sounds a little patronising but I'd rather you're safe and I'm not sorry

Thanks Cubist yes I was using a bolster and chisel but had to unfortunately use a power tool for the stubborn areas I'm afraid but trying to be as careful as possible. I haven't had a chance to do any further work since the last photos but hoping to get at it again in a week or two's time.

 

[Lacan07]

Hi Lacan Ive now cleaned out this hole and made it good so hopefully one further potential cause removed

The water will need to run somewhere if you can do it, like a concrete rainwater channel embedded in the floor, or at least extend the PVC pipe a little. I assume the floor is sloping away from the house?

 

[ShelleyM]

Yes Lacan there is a channel already embedded in the floor away from the house out to the road, so that's all sorted now thanks.