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Green Building Bible, Fourth Edition
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    • CommentAuthorYanntoe
    • CommentTimeJul 22nd 2020
    Over the last 5 years we've painstakingly restored our 1870 stone built house.
    We,ve stripped off the cement and repointed it all with NHL lime, we've used limecrete on the floors and replastered/repaired using lime. We've used clay paints and it looks great.

    But, the water just comes through the reveals and the weather facing walls.

    Stripped back one of the window "Pallistrades" on the outside yesterday and the water is clearly running down the inside of the walls rather than coming in round the window - you can see the water mark on the internal wooden lintel which is above the opening in the stone work. Tested the "inside" /middle of the wall and the outside with moisture meter and it's all "OL" i.e. WET.

    Of course I understand that the wall gets wet and then dries out in the sun 'cos it's breathable, but if its saturated in July there is absolutely no chance that it'll be dry over the winter.

    Having taken advice I replaced all the pointing (again) on the weather facing wall, replacing NHL 3.5 with NHL 5, as we do live in a very wet area. Delayed the incoming water until february but it's been marking the walls ever since.

    So, short of rendering the West facing wall that gets most of the rain and wind, and the Northern wall which shares some of the weather but not the sun, can anyone advise on how to proceed?
    • CommentAuthorgyrogear
    • CommentTimeJul 22nd 2020
    what is the stone used in the walls ?

    • CommentAuthorrevor
    • CommentTimeJul 22nd 2020
    When we did our build refurb I was concerned about water penetration as the house was very damp in places and had cement render inside and outside. Everything was hacked off. We built around the old part so enclosing the house but parts were exposed to the weather. We dealt with this by externally insulating and cedar cladding with a cavity between the cladding and insulation. We were "fortunate" that the stone was in no way considered decorative having been originally built to be rendered so it was an easy decision.
    • CommentAuthortychwarel
    • CommentTimeJul 22nd 2020
    Traditionally in exposed areas stone work was never left unprotected,
    It is unfortunately a legacy of a Victorian myth that rubble stone should be exposed.
    Around here, "Heads of Valleys" South Wales the exposed elevation was always slate hung or in later times clad in corrugated iron known locally as wriggly tin.
    • CommentAuthorYanntoe
    • CommentTimeJul 22nd 2020
    So, after all this we need to render the West and North elevation - I guess with something waterproof - i.e. not lime?

    We actually thought of using a paint-on water repellent - any experience of this Green Forumers?
    Yanntoe - If you are going down the render route to prevent water penetration I would suggest putting on EWI using EPS as the industry standard system with thin film acrylic or silicon render. This will give good (water proof) weather protection, allow a level of breathability to the wall and of course will give some thermal advantage depending upon the thickness chosen.
    • CommentTimeJul 22nd 2020
    Posted By: YanntoeSo, after all this we need to render the West and North elevation - I guess with something waterproof - i.e. not lime?

    I wouldn't recommend render. Tychwarel's traditional solutions are much better since they include a 'drainage plane'.

    If you rely on an external 'waterproof barrier' to keep the wall dry, then you are vulnerable to any crack, hole or other imperfection in the barrier, and the barrier is exposed to the full force of the weather.

    A better plan is to build a solution with multiple layers and specifically include a drainage plane. Just like how roofs are built. There are a variety of schemes and materials that are possible, including rendered external surfaces, but it is the internal part that is waterproof. The idea is to have an external surface that is weather-resistant but not necessarily totally waterproof, and behind that a gap and at the back another waterproof layer, which doesn't have to deal with as much wind and doesn't need to be as weatherproof.

    Our walls are lime-rendered and have been fine, because we're not on an exposed site. But if they hadn't been, I would have put timber boarding over the outside to protect them. Making the external render completely water resistant would just cause condensation problems inside the wall.
    • CommentTimeJul 22nd 2020 edited
    • CommentAuthorYanntoe
    • CommentTimeJul 22nd 2020
    Thanks Peter,
    Sadly, the detailing on the relevant walls (Victorian barge boards, fascia boards with cast Iron rainwater gear, conservatory etc.
    ) mean that anything thicker than around 2.5 centimeters depth won't work without major work so not really an option.
    Posted By: YanntoeThanks Peter,
    Sadly, the detailing on the relevant walls (Victorian barge boards, fascia boards with cast Iron rainwater gear, conservatory etc.
    ) mean that anything thicker than around 2.5 centimeters depth won't work without major work so not really an option.

    assuming your walls are 500mm thick with 20mm internal plaster, a quick calculation gives U of 1.65
    Put 20mm of EPS EWI on gives a U of 0.87 a useful reduction in heat loss. If you put up 50mm EWI then the U is 0.51 With insulation it is the first bit that makes the greatest difference after which it is diminishing returns.

    Architectural goods (fascia boards with cast Iron rainwater gear etc.) can be removed and replaced on top of the EWI. Detailing around windows can be made up with an additional layer of EPS. Conservatorys are more of a problem but I have seen a step in (reduced thickness) of EWI starting about 200mm from the conservatory. It actually looked OK.
    • CommentAuthorYanntoe
    • CommentTimeJul 22nd 2020
    I'll dig out a photo in due course, but the house has been restored to its original Victorian glory - and having finished all the work on the outside any further structural work will need to be bequeathed to our successors.

    I did check all this out before starting the project and all sources of the green persuasion said Lime would be Fine. And it's not. I could pin back the downstairs shutters to cover the reveals but prefer to stop the water getting into the walls rather than doing this.

    The house is referred to here as "the prettiest house in the Valley" and the idea of timber cladding it or insulating the outside which would have a very negative effect on its appearance is a non stater.

    We have wrapped a Conservatory and "barn" round 40% of the downstairs which solves the insulation problems for that part of the house and built a highley insulated 2 story extension on one Gable so I guess that's another 20% of old house covered up.

    Concerning breathabiliy, my contention is that the house is built of stone which is not breathable, held apart by lime pointing which allows air and water into a cavity which is filled with rubble (no Lime) and there is air travelling around this internal "space". Therefore breathability is ensured by this non airtight rubble filled cavity. Internal to this is a structure of significantly sized Impervious stones held apart by lime. So the idea that the external leaf needs to breathe is, I feel, somewhat flawed once one leaves the spreadsheets and text books behind.

    The internal leaf is pretty airtight in so far as we have insulated limecrete floors downstairs (which are warm and eliminate draughts). However, these do not keep water out as evidenced by all the joints in the slate floor which sits on them, and which are pointed in lime, showing water marking. In between floors the walls are no lime parged and draft free.

    The stone is a mixture of slate/granite/volcanic rock I suspect most is "Felsic" - whilst there's all sorts in house, the softest is slate but most is very hard (to the extend that it is difficult to drill/cut with a stone saw. i.e. it is not porous!

    So, the question remains - has anyone any experience of using water repellent chemicals on such a structure?
    I have used them on a Derbyshire (?Gritstone, maybe limestone?) house. The product I used is not the well-known one. I'd still get one that claims breathability since we probably all have our stories of 1980s/1990s silicone-based 'sealers' sealing moisture *in*. The house in question receives most of its rain horizontally and, while it obviously did not stop all ingress, it improved matters significantly. That was about 10 years ago, but I only got feedback for the first year or so.
    • CommentAuthorowlman
    • CommentTimeJul 22nd 2020
    Some years ago, 10 or so, I used this product, ( no connection with the company,), on a couple of sides of brickwork of an exposed two-storey, old N Yorkshire farmhouse. It seemed to work and there were no complaints, but I do remember getting good advice from the company on the way to proceed.

    P.S. It's not the cheapo usual builders merchant white spirit solution.

    • CommentAuthorYanntoe
    • CommentTimeJul 22nd 2020
    Many thanks Nick, Owlman, I have my eye on a "breathable" product which if the price reflects it's "efficacy" might be OK. I'm only going to do the exposed walls at the West and the North of the property and clearly I have a small concern that if water gets in it will find it difficult to get out, but the current solution of re-pointing it with some "better" magic lime ... again, isn't an attractive proposition.

    Don't get me wrong, I like the look of lime so much better than cement and as long as the area it's going to be used in is somewhat sheltered, then great.

    However, I've given it a really good go, with lots of negative comments from the locals and I have to admit that for chimneys, and chimney tops, together with exposed or North Facing walls I'd say use white sand and cement for a lime look or point it all up with SBR/mortar, leaving about 12 mm or so for "decorative" lime pointing to match the rest of the house.

    I guess if there are no "reveals" round the windows it might be OK but if the wall is wet in July, its wet all year which means, even if the water doesn't make it through the structure it's going to make the whole thing very cold.

    Who knows - If the walls can be made dry, then perhaps the need for additional EWI is obviated!
    • CommentAuthorrevor
    • CommentTimeJul 22nd 2020
    I remember my lime plasterer discussing with me another job he had just about finished and the client was blaming him for the water coming in around the windows. The bottom line as I recall was that the windows were not installed properly with dpc to shed any water outwards. You mention timber lintels is there anything over them to direct water out and down the sides. in a conventional modern build there will be a cavity and where that is bridged by a lintel that is covered with a dpc. My brickie put DPC over all the lintels and at the ends directed them outwards so any water would be directed towards the external wall. Your rubble infill is a cavity of sorts so guess same would apply. I can understand your reluctance to cover what is now a restored house and external cladding of any sort would spoil it.
    Hi Yanntoe, have you looked to see whether any of the manufacturers of silicate paints offer a clear exterior product? Silicate masonry paints often being claimed as a highly breathable option... Also, have you spoken to any of the conservation material suppliers/experts, our local one is Womersleys, there's Mike Wye and others no doubt.
    • CommentAuthorYanntoe
    • CommentTimeJul 23rd 2020
    Thanks Revor and Chrisin and Artiglio
    We've had a look at several waterproofing agents and the one we have shortlisted is a breathable modern clear one - I'll have to check whether it's silicon based.
    The issue with the reveals is that the stonework beneath the upstairs windows is a single stone thick and this extends down to an internal lintel which carries the floor joists etc, these are Victorian and sit behind the slate lintel which is in turn above the downstairs window. So not much can be done with these. However, the limework in the reveal connects the outside lime pointing/mortar to the inside Lime plaster-work and so water travels via this limework from the outside to the inner structure of the house. As this plaster-work is visible there's not much that can be done with it, other than using panelling which both the Victorians and I have done, except where there are functioning Shutters. And there's the problem - in the day all looks fine - at night close the shutters and the wet reveals are on display. The water doesn't come round the windows it just travels through the lime which connects the inside to the outside via the plaster/mortar/pointing "Bridge".

    Of course tanking the reveals would stop the unsightly marks, but I suspect the water would then end up on the inside wall beside the windows in the room. So, long and short of it is that's it's a very poor design and will fail if there's enough wind and rain.
    So it's either rendering or Waterproofer ......

    So pretty similar tale to Artiglio - Cement of the outside - removed/repointed with NHL3.5 lime (Hyperlime - which was/is extremely poor) and then 2 years later all stripped out and NHL 5 (St Astier) lime used.
    Internally all wallpaper removed and any paint and waterproofing agent and replastered as necessary with Lime. New Windows, reveals stripped back to stone and insulating lime used. All painted with Clay paint.
    Pellet Boiler installed and rad in reveal and efficient woodburner put in - used daily for 6 months during winter.
    Floors removed, insulated Limecrete put in with floating floor on microjoists and then old pine floor restored.
    Now, pretty airtight. VERY breathable, mostly dry (humidity in the 50% RH range) and VERY wet in the reveals.

    And NO, it's not condensation!!

    So that's very re-assuring to hear that it's not just me and that I have a chance with some Waterproofing agent. Following that, if it doesn't work, its divorce and re-render the outside!
    • CommentAuthorArtiglio
    • CommentTimeJul 23rd 2020
    We found that solving an issue in one location just moved it to another, any water getting in the wall just moves somewhere else to get out if its original exit is blocked, so end up chasing your tail. Silly things like poorly executed phone and tv aerial entries caused problems. ( just needed a decent drip loop) , make sure any drains in windows and drips are present and clean, over windows a lead flashing dressed into the mortar can help encourage water to drip away from the wall and doesn’t look unsightly. We’ve accepted that after prolonged bad weather there will be some penetrating damp, its now more a case of dealing with it, must be said that having dried the walls out over the years it does seem that their ability to “buffer” a degree of damp has much improved. like yourself its just one exposed corner that really suffers.
    On another building i did i was advised to add double boiled linseed oil to the mortar mix ( in that instance nhl 5 like yourself) to improve the water shedding ability of the mix.I’m sure you must have done so but standing outside watching how the water acts on the building in terrible weather really helped understand how much was hitting the wall and how it acted.
    • CommentAuthorYanntoe
    • CommentTimeJul 23rd 2020
    Thanks Artiglio,
    I think it's important to make sure people understand the limitations of the techniques used and in old buildings it is important to understand that some of decorative features were actually installed to hide problems. I'm certain that a lot of panelling round windows was to hide dampness with a "sacrificial" cover which could be replaced once it perished.
    Our house is exposed to high winds and horizontal rain - last year, having finished NHL5 ing the upper part of the Wall I tried to stop water running down the lower half of the wall as I pointed it. By the time you get 4 metres down the wall you are effectively trying to work in a waterfall. So yes, I understand the issue. I've extend the cills on the upper windows and added a drip moulding, but the windows are 1.5metres by 1 metre so the amount of water arriving on the cill is significant. This means that with strong winds the extended cills don't make much difference as the wind just blows the water onto the stonework within a few centimeters. I've put in a drip drip on the phone line and avoided any plug sockets/wall lights on the inside of the weather wall. I've inspected the wall close up from scaffolding and are no holes. I've even had a hose pipe on each window to check that they don't allow water in. After all this I'm left with an equation which says;
    IF(Water Arriving at Wall - Water repelled from wall - Water Evaporated from Outside of Wall- Water Evaporated from Inside of Wall - Water lost internally at bottom of wall) >0 = Damp on inside wall .

    It's a pity that there's not a bit more scientific rigour to all this, but I would certainly urge caution to folks trying to follow a "greener" path to building improvement.

    We'd all like our houses to breathe - but I'm sure we'de like them to breathe OUT rather than IN!
    • CommentAuthorCliff Pope
    • CommentTimeJul 23rd 2020
    Hello Yanntoe, I've experienced all the problems you've mentioned, and sympathise with the frustrations of trying to reconcile the apparent inconsistencies between the pro-lime anti-waterproof enthusiasts on one side and the enthusiasm for wanting to enjoy original features and elegance on the other.
    Our house is of a similar age to yours, and we went down exactly the same process of enthusiastically hacking off sheets of decaying external cement render that was clearly responsible for the damp problems.

    Like you we followed the standard pro-lime advice here, and used a local firm experienced in repairing period properties to clean off all remaining cement, sand-blast the stone and brickwork, and repoint with lime mortar.
    The result was beautiful. The lovely colour of the revealed stonework and lime mortaring was a revelation compared with the previous dozens of coats of white sandtex, nicely set off by the sandy red brickwork framing all the windows and doors and with low brick arches.
    Then came autumn, horizontal rain for days on end, and water seeping through the walls visible on the inside. The "breathable" limework appeared to be porous, and clearly revealed the wet outlines of stones on the inside, spoiling old wallpaper that had been there for years. It was much worse than even the decayed cement render had been.

    Like you, I'm appalled at the prospect of wasting a lot of money having the walls done "properly", only to be told that really all the elegance needs covering up again with ghastly cladding or the house turned into a corrugated iron shack.

    So my solution was to wait until the next summer and the walls were dry again, and spray Screwfix "No fuss" damp proofer over the weather-facing walls. I generously sprayed the spirit-based stuff until it the wall seemed saturated. It's an eye-opener to watch the way lime mortar just eats it up - it's no wonder the walls are damp inside when they are deliberately made so porous.
    I have to report that this treatment has entirely cured the problem. Four years on, the walls are dry inside even in the wetest winter. The only problems are very localised, the result of salt encrustation and eruption attracting moisture, cooling, and inducing further condensation at those points.
    I don't know how long it will last, but it's cheap and easy to apply, and once every 10 years would not matter, and a lot easier than regular repainting.

    I've heard other similar stories from people who have been persuaded of the merits of lime - I do thinks it's a pity these are not more honestly set against the pitfalls that can arise.
    Please note - I said Silicate i.e Keim/Sceciltek. I wouldn't give up the ghost just yet with breathable solutions, particularly after all the hard work you describe already. Have you considered lime rendering finished with a breathable silicate/mineral paint? This would be complimentary to the work you've already done.

    Talking to people like those mentioned above or Historic Scotland, (who have highlighted an increasing occurrence of these issues), may offer approaches in keeping with your initial repairs.
    • CommentTimeJul 23rd 2020
    We have Beeck paint on our lime render - they also produce a transparent preservative for stone.

    They don't carry statements like this for the Screwfix product: "H226 - Flammable liquid and vapourH304 May be fatal if swallowed and enters airways.H336 May cause drowsiness or dizziness.H319 Causes serious eye irritation.H340 May cause genetic defects.H350 May cause cancer.H411 Toxic to aquatic life with long lasting effects." though you do need to take care with the acidic conditioners.

    We also have some Stormdry inside our showers to protect nearby lime plaster. It seems to work.
    • CommentAuthorSteveZ
    • CommentTimeJul 23rd 2020
    My neighbour recently used a penetrating hydrophobic coating on his granite cottage walls as the rain was finding a way in via the mortar. He is the building maintenance game so used stuff he uses in his work. It is apparently not a surface only treatment, but actually penetrates the surfaces. Not so easy with the granite maybe but the mortar is the problem.

    I have found something which does the same job called ProPerla Masonry Creme, but I will ask him what he used when I see him next

    This one offers a 20 yr manufacturer's warranty, for what that sort of thing is worth!

    Possibly worth having a look at the site and maybe look at a few reviews if you can find any. The principle seems OK to me, especially if it also improves the insulation value of the wall by keeping it drier.

    I hope you manage to fix this problem - very frustrating finding water ingress routes.
    • CommentAuthorYanntoe
    • CommentTimeJul 23rd 2020
    Thanks all,
    Looks Like Stormdry might fit the bill so we'll give it a go - not cheap though! Just need it to stop raining for a few days - which here in West Cumbria might be next May!!
    • CommentAuthorSteveZ
    • CommentTimeJul 23rd 2020
    Hi Yanntoe,
    Found this on t'internet - if Stormdry is similar, the results of the accelerated testing are very interesting

    • CommentAuthorMike1
    • CommentTimeJul 23rd 2020 edited
    Posted By: YanntoeConcerning breathabiliy, my contention is that the house is built of stone which is not breathable, held apart by lime pointing which allows air and water into a cavity which is filled with rubble (no Lime) and there is air travelling around this internal "space".
    Posted By: YanntoeThe issue with the reveals is that the stonework beneath the upstairs windows is a single stone thick and this extends down to an internal lintel which carries the floor joists etc, these are Victorian and sit behind the slate lintel which is in turn above the downstairs window.

    I'm not sure form the above whether you have a rubble filled wall, solid dressed stone, or both. However there are known problems in the situation when you have an exposed wall + lime mortar + impermeable stone, particularly when voids in the rubble filling facilitate the passage of water. The best source of information on the subject that I know of is English Heritage's 'Damp Towers' project, particularly this transcript: https://historicengland.org.uk/content/docs/research/damp-towers-conf2013-programme-transcriptspdf/

    If you want to preserve the stone external face then a surface coating may be the only solution, if you can't find and plug a specific ingress route. If you were at an earlier stage when you could tolerate more disruption, then grouting the voids in the wall (if it is a rubble-filled wall) may have been worth considering, though it would probably have been expensive. An external lime render would have been an easier and cheaper alternative.
    • CommentAuthorYanntoe
    • CommentTimeJul 23rd 2020
    Thanks Mike 1 - I'll have a read of "Damp Towers" later. Interesting to hear about "grouting" the inner rubble wall.

    The house (on the odd occasion it's not covered with scaffold), looks great, but we have had to resort to pointing the chimneys in cement mortar which does show how much more attractive lime is than cement!

    The structure varies, as at the road-facing side the stone is good with flat faces in the main and relatively closely spaced. As you move round the house it gets progressively more "rustic" with lots of River Boulders in the walls at around 300mm in diameter.

    The house wouldn't have been pointed as such, the lime from the inner and outer leaf was just "chopped" off I think. The middle is full of smaller stones with no mortar. The walls are around 650mm thick.

    The temperature is pretty constant at around 19 - 20 degrees over the summer, without additional heat, and it's easy to keep it at around the same temperature during the winter using a wood burning Range in the kitchen and a woodburner lit in the evening, in the lounge - this keeps the upstairs at around 14-15 degrees without additional heat. It'll be interesting to see if this increase once the walls are dry.

    The weather face was rendered at some time in the past, but the last version of this was a cement render which failed and the wall was roughly pointed in sand and cement. It was damp throughout, and cold. The windows, panelling and floors were rotten at the edges, as were the downstairs joists. All these problems are now repaired/replaced with sympathetic materials and the only remaining problem is the water penetration at the reveals.

    So I think the rubble does the trick and separates the outside leaf from the inner leaf except at the reveals where the rubble "cavity" is bridged. I'm not sure how grouting the rubble would solve this as the bridge would remain. Bloody Victorian Engineering!

    Once again everyone thanks for the advice.
    My stone walls (and others in this area) are of basalt rock because that is the local stone. The stones were used undressed, as found, and at best selected for shape (it is just too hard to dress). The construction is an inner and outer leaf of undressed stone with earth/rubble infill between the leafs. This construction was (is) always rendered both sides. When I have removed the rendering for repair I have always been surprised at the howling gale blowing through the wall. The original render is sand/lime mix, replacement render is a sand/lime/cement mix.

    Given the above construction I can imagine that wind blown rain would penetrate the walls easily (as does the wind) and without rendering or other protection (e.g. EWI) problems would arise.

    Some 30 miles away another area used red sandstone as the building material. The sand stone was dressed and fitted using a thin layer of lime mortar. Usually such walls were built as solid walls i.e. without rubble infill. often such building were not rendered outside, just internally.

    Areas without or with little stone used adobe type sun dried mud (clay) bricks rendered both in and out.

    The construction methods had little to do with what made a good building and everything to do with how far you wanted to transport materials by ox cart.

    My point is that over here the stone rubble walls were always rendered both sides for weather protection and wind exclusion and the rendering was an integral part of the structure which also added to the stability of the wall.

    A failure in the roof of the stone /rubble walls meant that the inner filling was quickly washed out followed by the collapse of the wall. A roof failure of the adobe type building resulted in the structure 'melting' The sand stone structures can withstand a roof failure for some time without damage to the walls.
    • CommentAuthorYanntoe
    • CommentTimeJul 24th 2020
    I think that the rubble in the walls up here is just an infill of smaller stones of about 3 or 4 inches in the main and often just broken stone from the building process. These are loose - so if you remove a stone for the outer leaf and move a few out of the way the column of stones above just fall down. This means that a very significant proportion of the small between the outer leaves is air.
    Any water that gets in just percolates downward and drains out of the bottom of the wall.

    So, even if the outer leaf gets saturated, the inner leaf stays dry.

    The exception is where this rubble cavity is bridged at reveals and openings.

    So, similar but different form Peter's description. Here, walls stay up for centuries even with no roof!

    So I think our forebears inadvertently made a kind of cavity wall, which is why rubble houses work, but didn't work out the "bridging" idea and rather hid, with wood panelling, problem areas.

    So, limes great - looks good, probably a bit warmer (if dry) than cement, but it won't stop water coming in if there's enough of it and the outside is connected to the inside.

    Before the vanity of the Victorians, most building were rendered or "parged" and covered in Limewash - but to be honest these are often even wetter inside than the Victorian version - possible due to incompatible technologies being employed over the years (eg Concrete aprons, water proof cement on the inside to stop the damp, lots of condensation and floors below ground level).

    Next time I'm going to build a modern, watertight structure which is inherently warm and dry, and light!!
    • CommentAuthorgyrogear
    • CommentTimeJul 24th 2020
    Posted By: Yanntoea modern, watertight structure which is inherently warm and dry, and light!!


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