Lime mortar pointing - water penetration

[CliffordPope]

A few years ago our house was suffering from damp, clearly resulting from faulty cement rendering, which was bowing away from the walls and falling off in sheets.
So at some expense we had all that hacked off, and the stone walls repointed using lime mortar. It looked lovely, now highlighting the contrast between the pale stone/mortar and the red brickwork, previously all hidden in decaying mouldy rendering. Everyone said this was the correct thing to do. The walls could now breathe again as intended.

That was until the autumn storms, and weeks of constant driving rain. Water poured through the walls, ran down the inside forming puddles, and wrecked all the old wallpaper.
So last year I ignored all the received advice, and during a long dry spell sprayed gallons of silicone water sealant into the walls until they would absorb no more. I got them nicely saturated. Even though two feet thick I could smell the stuff on the inside.

The test came this recent autumn. Weeks of driving rain again, and guess what? The walls are bone dry on the inside.
My observation and conclusion is that lime mortar is porous. It may be breathable, it may work well when dry, but if you direct a hosepipe constantly at it for a month then the water runs through.
Would a lime mortar enthusiast care to comment?

 

[skier-hughes]

That is what it is intended to do, allow water in and out. Having it breathable (penetrable) from both sides means any water from the outside can get in, any water from the inside can get out. Now the water from the inside cannot get out through the wall, you need to ensure you have plenty of other ventilation to allow it to escape the wall, so open windows, powered vents etc.
It may have worked by putting a lime render on to the wall, may not, as I don't know how much driving rain you had, but a Lime render specialist would no doubt have been able to tell you the correct depth to apply to work with the local conditions? I'm only assuming that a deeper depth of render would hold more water, thus it would pass all the way through causing puddles on the inside.

 

[formerly known as]

perhaps your stone walls also needed to be grouted to fill voids prior to repointing. interstitial condensation springs to mind.

 

[Superhans]

It's interesting to hear reports like this. What type of brickwork is it?

I am getting turned off by a pure-lime mortar for different reasons, but this helps my decision making.

 

[MatthewC]

Where in the country are you? Places like Cornwall and Scotland generally seem to have even modern houses rendered rather than plain brick, especially if in an exposed position, presumably because of the same problem. I recall my two winters near Newquay - horizontal rain or fog at high speed!

Even though it has been a wet autumn, I would not have expected water to be pouring through the wall as much as you say; my house has been absolutely fine, but it's not that badly exposed. Is your house really exposed to the wind and rain? How thick are the walls? Are there any other local properties with the same construction walls, or are they all rendered? Perhaps rendering in NHL is the answer.

Matthew

 

[CliffordPope]

We are in west Wales. The house is isolated, exposed to prevailing south westerlies. When it blows the rain comes horizontally.
We had the decaying render removed, cement pointing and any original loose lime pointing raked out, and then all repointed in what the builder, a specialist in old stonework, said was the appropriate lime mortar.
The stonework itself was in good condition.

The problem really seems to be that the lime mortar is porous. With moderate wetting it absorbs a certain amount, and it then evaporates when the rain stops. With constant sheeting water it just goes on soaking in until it emerges on the inside.
Traditionally houses seem to be clad in corrugated iron, or replaced with modern presumably cement renders and then painted with modern coverings. One or two have been restored to stonework and lime pointing. That seems to be the correct advice in restoration circles.
Of course I don't know how many have then resorted to silicone damp treatment. The builder did himself apply some when it leaked around the porch, and that entirely cured the then localised problem.

How is moisture inside the house meant to "breathe" through a wall that is already soaked on the outside?

 

[Flyfisher]

I sympathise with your problem. One winter we had a leaking pipe and it completely saturated a lath and lime plaster ceiling to the extent that the ceiling paper fell off! Breathable or not, these materials can become completely sodden if overwhelmed with water. Fortunately, the ceiling itself did not collapse and eventually dried out perfectly, as I imagine your walls will, though not before any decorative damage.

In the conditions you describe, corrugated iron cladding sounds like a very good idea - technically if not aesthetically. An impermeable layer mounted slightly off the stone walls protecting them from water bit with a gap allowing ventilation and not compromising the inherent permeability of the walls - unlike most 'damp-proofing' treatments. I guess that weatherboarding would do much the same job, but of course either option would completely transform the look of the building and may therefore not be acceptable.

Perhaps this is another example where 'true period living' was simply not as comfortable or convenient as we expect these days?

 

[plasticpigeon]

This does sound like an example where a cavity wall would be the best solution, or and external cladding with a cavity between external surface and present wall. I'm sorry for your woes. Lime obviously hasn't worked here.

 

[88v8]

Yes, universally the advice now in old-building circles would be to repoint in lime. Perhaps the wrong grade was used, NHL5 is of course less absorbent.

I suppose though, there was a reason for buildings being rendered, or clad in weatherboard or hang tiles. In some cases it was the only way to make the structure weatherproof.

The most exposed wall of our house was pointed in cement in the 70s, I keep thinking I ought to redo it in lime. Indeed, I know I ought to, as otherwise the stone is liable to spall. We've all seen pics of awful spalling in brick and stone where cement has been used. Otoh it hasn't spalled so far, and I'd hate to find I'd made the wall wet.
Hmmm.

Ivor

 

[formerly known as]

although the wall may already be damp due to interstitial condensation / external hairlines. I think that a lot of stone work was clad as the stone was laid in very weak mortar - often clay - without ensuring the core was suitably packed. Hence my earlier comment re grouting (filling loose/voided/settled core work with liquid mortar)

 

[88v8]

I think that a lot of stone work was clad as the stone was laid in very weak mortar - often clay - without ensuring the core was suitably packed.

Yes, our early walls are laid in clay/straw. There seem to be, in effect, two walls with no through-stones. Just some loose small rubble between the skins. I viewed this as a benefit because it means any water penetration cannot reach the inside.
Some Georgian(?) rebuilding seems to be bedded in lime with through-stone.

Ivor

 

[formerly known as]

Ivor - building up what appears to be fully intended paired leaves of a wall is more often than not a demonstration of a lack of material and wanting to erect the walling quickly. We probably interpret it as a designed form of construction as we have been subconsciously conditioned to explain the construction as something akin to modern cavity. In my experience, it is only the 'best' work that was suitably backfilled with mortared rubble and through ties; the vast majority of stone walling was built up overhand, with the loose material and waste dumped in the core. In some cases, this loose core can settle and cause bulging. Loose core work will also allow more water to enter a wall, finding its way to the interior. It may have been mentioned, but a lot of stone/rubble walling would always have been rendered over - we can blame the Victorians for several things, including the stripping of walls to reveal the stonework, and the introduction of strong opc based grouts.

Interestingly, I was working on a friends house near Limoge and the 'post-primary-build-exposed-stone-walling' was built up in what appeared to be 2 distinct leaves with a core of soil and gravel. More recently, I have found similar in pre-dissolution monastic structures. The moral here, is that you can never assume what might be lurking in the core and that could be helping the transfer of moisture to the interior.

 

[88v8]

Ivor - building up what appears to be fully intended paired leaves of a wall is more often than not a demonstration of a lack of material and wanting to erect the walling quickly.

That could be.
Our oldest wall, built on quite a steep side-slope descending towards the house, is not only two skins, but has a stepped foundation where the inner wall is deeper by about 12". So I even wonder whether it was originally a single skin and when it was thickened for whatever reason they couldn't be bothered / didn't see the need to dig to the full depth.
And when someone added another room to the original building, they didn't see the need to tie them together, one wall just leans companionably against the other. Bodging that has proven durable by sheer mass.

And as regards water penetration, luckily we have none, but while the inner (cement) pointing was out of the 18" thick dining room wall, the wind was blowing through. Lord knows how, as there were no apparent gaps in the outer skin. Prior to repointing I repaired the blow-through by stuffing it up with pages from The Times, thus leaving a clear timeline for some future owner to tut-tut over.

Ivor

 

[chuckey]

I have repointed my Yorkstone cottage with NHL 5 hydraulic lime and the water penetrates. So I then have gone over it with one of those clear silicone fluids, reputed to be able the waterproof. The rain still comes through. I have tried the mortar with 10% unboiled linseed oil in it and still the rain comes through. Anyone want to buy a beautiful traditional cottage in picturesque Wensleydale?
Frank

 

[88v8]

Ivy.
It's overlapping leaves will waterproof the wall, and provide habitat and food source albeit not for you.
And contrary to received mythology, it does no harm to a sound wall.
This is however not a quick fix.

Does make me wonder about removing the cement pointing from my wall. Perhaps I'll leave that experiment to someone else.

Ivor

 

[MatthewC]

Ivy....contrary to received mythology, it does no harm to a sound wall.
This is however not a quick fix.

I'd have to agree with that (reluctantly) - the ivy I removed from my house was almost a foot thick and the limestone wall and pointing behind were in perfect condition. I lost count of the number of old nests I found. There was a single 30mm root through the mortar under the lounge floor, but the main damage is when you let it get up to a slate roof and cast iron gutters - not good!

As you say, Ivor, not a quick fix for water ingress, but in an extreme situation one that would certainly work (eventually).

Matthew

 

[momo292]

Hello first post here. Great forum and a wonderful resource

I read this article recently that tends to cover similar ground; you may enjoy reading it too: http://www.buildingconservation.com/articles/damp-churchtower/damp-churchtower.htm.

Best regards,
Momo (London, UK)

 

[88v8]

Hello and welcome.

That reports makes sad reading.
One does tend to assume that in the good old days buildings were properly constructed, and problems of damps etc were due to unsuitable subsequent interventions which could be rectified by a return to traditional materials applied in a traditional manner.
Alas.

It is not for nothing that some buildings were subsequently rendered, hang-tiled, timber clad. An obsessive insistence on maintaining the historic architectural integrity of an unsuitable design is rather daft, really. I wonder if those in the Listing Authority making the decision would be so obsessed with history integrity if it were their own house.

Ivor.

 

[Flyfisher]

Interesting points. If a building is not fit for purpose due to faulty or inadequate construction then it's difficult to see why the listing authorities would insist on it being preserved 'as is' - except, perhaps, as a specific example of poor design and/or construction.

Where such a property is institutionally owned, as in that church example, it may be possible to force the owners to maintain its inadequacies forever (well, almost) but this will not work with privately owned buildings because even if the present owners are disallowed the opportunity to 'improve' the property, those owners will eventually die and an inadequate property without permission to be 'improved' will be unsaleable. It will therefore simply decay through neglect and abandonment, and without an owner the listing authorities are effectively powerless.

 

[momo292]

One would expect a conservation officer to take an informed position in light of such instances and having read around the subject, I understand that the owner or their agent e.g. architect seeking expert analysis from an expert in the field or referencing a good book on the topic would go a long way towards sway with CO's. I have been a bit geeky of late and read several of the articles at the site I posted from above; for example this other article below eloquently reveals a very tactful yet politely persuasive method of engaging with authorities, even SPAB as was the case there.

http://www.buildingconservation.com/articles/policy-grey-areas/policy-grey-areas.htm

In reference to the original topic post in this thread, my understanding thus far into my 'education' on these matters is that buildings react to changes exacted on them slowly, thus for example the owner of a single brick exterior walled C.16 cottage experiencing damp may well find that slopping on gloopy exterior plastic based paint 'solves' the damp immediately. But the effect that has on the equilibrium of the house (or more accurately, upsetting said equilibrium) may take some years to manifest itself. Thus in keeping with this fictitious example of mine, the bricks may not spall right away, or even in a year, but perhaps a year or two later, I imagine they would.

With the property used as an example in the opening post, before I mixed technologies, something I personally would be averse to doing, I would probably feel inclined to consult with an expert or would want to exercise my own mind on options, with care. I would probably consider rendering over the lime pointed bricks in a lime based render; perhaps NHL rather than putty so as to produce a less breathable wall, given the driving rain. However if the property were listed, I imagine the CO could suggest rendering may conceal significant historic material so such proposition could lead to a bit of back and forth discourse. I suppose these matters are never entirely straight forward.