Rainwater ingress

[FRODO]

I have lived in an old (1830) South/sea facing granite built for 18 years .
Paint ect on the front elevation ( 85 sq metres ) had flaked/ discoloured / blistered and cracked
allowing moisture to penetrate.
I had builders remove the paint and strip back to the original granite .
They dug out the pointing and repointed with a sand and cement mixture with waterproofing mixed in .
I cried tears of joy to see it looking so lovely .
Fast forward 12 months and I have rainwater pouring in through the walls above the lintels ,
In all the downstair rooms including the porch . Any suggestions would be gratefully received ..

 

[88v8]

Hello and welcome.

How annoying for you. Alas this seems a not unknown problem with stone buildings facing wind-blown rain**

The paint flaking off showed that the wall was trying to breathe. The paint formed an impermeable coating which prevented it from breathing. Eventually the damp beneath the paint caused it to lose adhesion and flake off. There is also the possibility that the paint was badly applied in the first place. The base coat should have been an alkali-resist primer, but it is expensive and there are many botchers in the building trade.

Did water leak in before you had it pointed?

Had you called in at this forum before the work was done we would have said that repointing a stone Period building with cement is nowadays considered quite wrong. Cement does not 'breathe' and therefore causes damp to be trapped in the stone and leads to spalling, and the face blowing off. Even worse if waterproofer is added, as it completely shuts down breathability.
Luckily, your granite is very hard, so despite the cement pointing, the stone itself is unlikely to suffer any damage from spalling.

We would say that pointing should be done in lime - natural hydraulic lime, known as NHL, and sharp sand. Lime pointing used to be universal, but is now a specialist job. You may find local conservation contractors who can do the work. The wall will then be able to breathe through the pointing, and will be able to dry out between wettings.

In general, pointing must be softer than the stone, so that it accommodates movement without the stone itself cracking. Cement is hard and brittle and does not flex with the movement of the building. You have stone work which is almost certainly bedded in lime and will therefore move a little with seasonal temperature change, but pointing which is hard and inflexible. Thus, micro cracks develop and allow water into the wall. Once there is a moisture passage, water can wick into the wall very quickly, and because of the cement pointing it cannot dry out, so next time it rains the stone is already wet and the water makes its way further into the wall.

However, now you are where you are. The first problem in repointing now, quite apart from the cost, would be removing the cement without damaging the stone.

Does the offending wall face south?
If so, the problem is showing up first in the lintels because their expansion in the summer sun is leading to a loss of bond between the lintel and the adjacent stone, and creating a leak path through which water is penetrating and thanks to the cement pointing cannot escape. In time, other leaks may appear.

One other area in which you may experience problems is near the base of the wall - almost certainly there is no dpc, and although granite is largely impermeable and does not allow much 'rising damp', there will be a degree of it, and the cement does not now permit the damp to escape. So you may begin over time to notice some damp around the lower couple of feet of the wall.

As to the water ingress, before undertaking any general work, I would have a specialist contractor hack out the cement and repoint above the lintels with lime. No cement. If you edit your profile to show your general location, someone may be able to give you a recommendation.

If this limited repointing does not work, one will have to consider other measures.

Are there other local houses similar to yours? Are they pointed, or are they part rendered or clad in hang tiles or slate?

A picture might help. You can post via Photobucket, copy/paste the img code.

Ivor

** there have been one or two cases of forum members who have done all the 'right things' with regard to pointing, but still found water coming through the wall. This is why I ask about local examples of rendering - in lime not cement!! - or hang tiles. That could be the next step. Or a Keim paint system. Anyway, one step at a a time.

 

[plasticpigeon]

Are the lintels stone or wood?

 

[CliffordPope]

** there have been one or two cases of forum members who have done all the 'right things' with regard to pointing, but still found water coming through the wall.

There is a credibilty gap I feel regarding two apparently contradictory concepts:

1) Dampness inside the wall supposedly seeking a means of breathing to the outside
2) Sheets of driven rain washing down the wall tending to soak straight through anything that isn't impenetrably waterproof.

I just cannot picture the mechanism that causes one lot of water molecules to make any headway battling against a vastly greater number being pushed in from the opposite direction.
My experience is that they don't, unless you treat the wall with something impermeable.

 

[Roger H]

I just cannot picture the mechanism that causes one lot of water molecules to make any headway battling against a vastly greater number being pushed in from the opposite direction.

There's some good technical stuff on this in the article 'Water in Permeable Building Materials' Robyn Pender - Building Conservation Directory 2016.

"Exactly what happens inside a permeable material as the environmental conditions change will depend on the existing distribution of water within the building materials: in other words, the ‘moisture history’ is critical to behaviour. This is the key to understanding puzzling observations such as the fact that although, in theory, driving rain cannot “get through” a wall, in some cases it can be seen to cause moisture problems on the interior; or that in the laboratory permeable materials buffer humidity much less well than they do in real buildings.

To take the example of driving rain, the supply of liquid to the pores is by no means continuous (as it is, say, with a Karsten tube); even in the most violent storm it is highly unlikely that two consecutive raindrops will hit the same pore. This means that the rain will not generally penetrate beyond the first millimetre or so. If, however, a good number of capillaries are already filled with water from some other cause (such as a leaking gutter), and the raindrop stands a good chance of hitting the mouth of a wet capillary, it can be drawn in; and if that capillary is filled with liquid and connects to the interior surface of the wall, then evaporation can quickly wick the rain right through".

 

[88v8]

[... and if that capillary is filled with liquid and connects to the interior surface of the wall, then evaporation can quickly wick the rain right through".

Yes, I think this is how water gets in. There is a leak path filled with moisture, cracks or voids, need only be at the micro level. Perhaps this is why it's so important to consolidate lime pointing beyond the normal level of shoving it vaguely into the joint and hitting it with a churn brush.
But that takes a lot of time, especially on a rubble wall with variable joints; different thicknesses of tamping piece; ideally, even grades of sharp sand for thicker and thinner joints. How many people really bother, the cost might be considered prohibitive.
And on most properties most of the time one can get away with a half-baked job.

In the OP's case I suspect micro cracks between lintel and wall.

I think it no more than luck that we don't have a problem in our cottage. We don't get the sustained rain intensity, and the 2ft rubble wall has no through-stones so any damp that permeates the 'outer leaf' just falls into the cavity, if one may so call it.

Not for nothing are some houses rendered or hang-tiled or woodclad.

Ivor

 

[Roger H]

I agree with Ivor but would add that because of cement mortar's inherent inflexibility it is going to separate at points from the stone work e.g. through seasonal movement when the wall mass wants to move but inflexible mortar won't accommodate this without cracking. These fissures are going to let the water in.

With lime, you have a relatively flexible matrix in which the stone sits, accommodating movement. Historically, microcracks might have been tackled with layers of limewash, sealing up fissures but still permitting movement of the wall and also passage of water vapour.

Not sure where this leaves the OP, other than in any new work, avoid cement. Some photos would be helpful - are there any ledges on lintels or lack of drop moulds under cills that might be contributing to the problem?