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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorYanntoe
    • CommentTimeJul 24th 2020
    That'll do!
    • CommentAuthorYanntoe
    • CommentTimeJul 25th 2020
    Had a read of "Damp Towers" and I have to say it's not encouraging - unless you render the building.
    The Grouting discussion, I find a little confusing as the walls up here are not consolidated - they are effectively a loosely filled void with the stones just stabilising the outer leaves. I think grouting this would just create more of the situation that we see the reveals - i.e. bridging the two leaves everywhere so effectively make the situation much worse. I have to assume they are talking about different types of wall.

    To put this into perspective we have an average of around 2350mm of rainfall each year with eg 300mm in March this year so I'm resigned to this being a tricky problem to fix.

    However, most houses in the locality are not wet so something works!
    • CommentAuthorCliff Pope
    • CommentTimeJul 25th 2020
    It has only slowly dawned on me since following threads on this subject that a "rubble" wall meant literally that - two reasonably sturdy skins, with the internal void just filled up with rubble tipped in. I suppose I'd assumed that the word rubble was a stonemason's disparaging term for random undressed stone picked because it happened to be roughly the right dimensions for the space, with a generous bedding of sloppy mortar to fill the gaps.

    I'd also assumed that large stones that were long enough to go right through the wall were prized because they would add strength and cohesion to the wall. The best face would be on the outer wall, and the inner face was only approximately level because except in the most primitive of cottages it would be generously built up with mortar and render to achieve a nice flat smooth surface, for papering or painting.
    That is how our house (c 1880) is constructed. The internal mortar is not particularly strong - the wall could be demolished by hand alone stone by stone starting at the top - but there are no gaps and it certainly doesn't just slump or run out if you pull out some stones.

    I can see that having stones running right through the wall creates both thermal bridges and easy tracks for water to run past, so I agree it would have been logical to render the outside with something impermeable. However, that was not originally intended, unless the Victorians went to great trouble to do attractive brickwork around doors and windows and then immediately cover it over with render or corrugated iron sheeting. I don't see much vanity there!
    So the design is inherently flawed, which it seems to me can only be mitigated to some extent by a compromise, hence the invisible "render" provided by some kind of damp-proofing solution.

    An alternative would be to batten, insulate and board the inside of the walls. That requires a great deal of effort, extending the wooden panelling in the angled window embrasures, removing and refitting the surrounding mouldings, lengthening the top moulding, extending the wooden cills and remaking the moulding, and moving the skirting board inwards and refitting against the new boarding.
    That would still leave the wall below floorboard level. Conventionally this would be a void between floor and ceiling below, in our house there are no ceilings, just the underside of the exposed joists, socketed into the walls with irregular rectangular gaps, some not very straight because the wood has warped or was never straight. I'm not sure that sealing a joist into a damp wall is a good thing.

    So the whole thing has to be a massive compromise between aesthetics and comfort, complicated by the recent introduction of thermal efficiency into the equation. :)
    • CommentAuthorYanntoe
    • CommentTimeJul 25th 2020
    Absolutely Cliff. It's all a bit of a balancing act isn't it.
    We're pretty lucky as the house is now warm and mostly dry and draught free. We made a really bad mistake replacing the sash windows with replicas glazed with conservation double glazing. A local chap did them and they are not noticeably better than the ones we took out. Look fantastic, but they don't fit well either in terms of the sashes and in terms of how they are fitted into the walls - you can hear the river outside as thought they are open! I've re-draught excluded them so they don't let the wind in, but they are a real disappointment.
    Other than that we now burn wood on our range and woodburner, have a £70 a month electric bill and spend about £350 per year on pellets for our pellet boiler. Relative Humidity is around 60% all year round and we've nearly finished!

    If I can ever get to the stage when I don't need scaffolding up to fix the limework we'll be happy bunnies.
    • CommentAuthorvord
    • CommentTimeJul 26th 2020
    Sounds tricky. I have only once lived in a house with stone walls and water came in there. It used to drip from the top of a window and the crack wasn't where you would expect. It took a hosepipe to find it. Stone is really tricky to seal.

    I think Wales might be quite wet. I've heard of someone else in Wales with a stone built house applying a silicone spray product to the outside over a lime pointed wall. He shouts about it at every opportunity as it seemed to work for him.

    If you were to try a spray on waterproofing product it would be good to chose a mild one that was still a bit breathable. I've spent the last few years removing waterproof stuff as while they might work initially they tend to have little failures after a few years so water can get in but can't get out again so you have the same problem with internal damp just worse.

    Photos would be useful should the internet have developed to the extent that we can post them on here.
    • CommentAuthorYanntoe
    • CommentTimeJul 27th 2020
    Thanks Vord,
    Yep - I think I have to be pragmatic and do the best I can, so I'm going to "grout" a few areas where there might be a problem round the stone lintels above the windows and use a "breathable" Water repellent on the very exposed elevations of the house.

    The obvious problem areas I have already fixed - hopefully, but the reveals are proving very difficult.

    So - lets see.

    However, I've now identified a new "opportunity" to improve the performance of the house .... so I'll start a new thread looking for advice on that in a moment.

    Once again, thanks for your patience folks and I'm grateful for any advice.
    • CommentAuthorlineweight
    • CommentTimeNov 12th 2020
    Coming a bit late to this, but an interesting thread.

    I'm a little bit of a lime sceptic myself - but it seems to me, there are some situations where it's fairly clear that it's probably a good idea, some where it's clear it's probably a bad idea, and lots where it's very hard to say.

    I think the argument for using lime mortar is strong where the masonry is soft/porous - old brickwork or sandstone for example. As far as I can see, it's absolutely true that cement mortars can do damage to soft masonry - the evidence is everywhere, in old brick walls and old sandstone walls where preferential erosion is clearly visible around cement mortar.

    If there's no danger of the masonry eroding in preference of the mortar - granite say - then the argument for lime seems weaker.

    A question which remains unresolved for me is how cement/lime mix mortars perform, long term, compared with "pure" lime mortars. I did a thread on this some time ago... I'm not sure if any better level of evidence has appeared since then:


    Yanntoe - moving to your case specifically - it's a bit difficult to fully understand the situation without drawings or photos, but am I correct in understanding that you've identified that the problem is at the window opening reveals because these are the locations where there's a direct connection from inside to out via a mortar joint, because at these locations stones run the full thickness of the wall, unlike the general situation where there's a rubble filled partial cavity separating inside from out?

    I'd agree that's essentially a design weakness, and one that was probably "dealt with" in the original construction by disguising it with internal panelling and/or simply accepting more damp than we consider reasonable nowadays.

    Approaches I might consider are:

    1) If the stones that for the reveals are sufficiently hard, that there's not a worry that cement render will lead to erosion, then just point these locations with a non porous cement mortar. The rest of the general wall can still use a lime mortar.

    2) Is there some way of introducing a kind of vertical DPC in line with the windows? In other words, outside of this line, it's lime mortar that you accept will absorb some water - however, from this line inwards, you use something else. I don't know if that would just be a change to cement, or digging out a significant depth of mortar over a 5-10cm length and replacing it with some kind of impervious sealant.

    If the through-stones are also of a soft material, and might be transmitting damp themselves, there's also the option of cutting a vertical slot, all the way up, in line with the window, and inserting a strip of DPC and/or sealant. This is an approach I've used for joining into existing, old brickwork walls, to minimise the risk of damp travelling from inside to out, whether through the mortar joints or the bricks themselves. Of course, you'd have to satisfy yourself that doing something like this didn't cause any structural concerns.
    • CommentAuthorYanntoe
    • CommentTimeNov 18th 2020
    Thanks for the suggestion lineweight.
    Basically, I've pretty much done what you say which is to insert an SBR/ mortar mix into the joints around the reveal, and then re-lime point the external part with NHL 5.
    I've then used a breathable water repellent, Stormdry, on the wall.

    So far, this has worked, but we're only 2 months into the wet season so far so we'll reserve judgement until the Sprng. There are still areas which need to be done, so once the weather allows , I'll finish the job.
    • CommentAuthorlineweight
    • CommentTimeNov 19th 2020
    Posted By: YanntoeThanks for the suggestion lineweight.
    Basically, I've pretty much done what you say which is to insert an SBR/ mortar mix into the joints around the reveal, and then re-lime point the external part with NHL 5.
    I've then used a breathable water repellent, Stormdry, on the wall.

    So far, this has worked, but we're only 2 months into the wet season so far so we'll reserve judgement until the Sprng. There are still areas which need to be done, so once the weather allows , I'll finish the job.

    It would be interesting to know whether the water repellent is necessary, or whether the focused approach to the reveals would have solved the problem by itself.
    • CommentTimeNov 19th 2020
    Posted By: lineweightIt would be interesting to know whether the water repellent is necessary, or whether the focused approach to the reveals would have solved the problem by itself.

    I'm sure it's a question of degree, rather than go-no go. How much penetration from how much rain, in what sort of weather circumstances.
    • CommentAuthorYanntoe
    • CommentTimeNov 20th 2020
    I'm almost certain that the water repellent is the key.
    This is the third attempt at getting the wall dry and whilst I have "grouted" the area around the windows, it is clear from the water marks in the wall that water is arriving at the location from above. Basically the lime pointing in the wall becomes saturated and eventually where it arrives at the reveals the water wicks through the wall.
    If one could grout the whole wall then I'm sure that it would work without the Stormdry, however this is essentially the same as pointing the whole wall in waterproof cement mortar. The lime would be purely decorative.

    DJH is right though, water penetration is only an issue on the wall which faces the weather and the corners at either end. The rest of the house seems to cope.

    However, I did read the research document suggested above - all of it, and the clear conclusion was that exposed lime walls get wet right through and rendering is the only thing that deals with this.

    A modern breathable repellent plus judicious use of cement mortar grouting seems like the last possible action before rendering.

    So, fingers crossed.

    NB we do get an average rainfall of 200mm per month and most of this arrives from the west. There's no way that this can evaporate from a west facing wall during the winter, so if it is absorbed by the lime pointing it will accumulate in the wall. If there is a bridge at any point in the wall, water will penetrate and become visible on internal plasterwork. So reveals are a real issue.
    • CommentAuthorlineweight
    • CommentTimeNov 20th 2020
    When you say it arrives from above do you mean it transfers via a lintel or other element that bridges between outside and in, at the top of the window?
    • CommentAuthorYanntoe
    • CommentTimeNov 21st 2020
    Not really lineweight,
    As in many stonebuilt houses, the reveals are angled which means that where the window sits, the wall is only one stone thick. At this point the lime mortar on the outside is continuous with the inside plasterwork. Moreover, there are effectively "through stones " at the reveal rather than an outer stone , rubble and then an internal stone Leaf of stonework. So here joints run all the way through the wall. Therefore if enough water arrives at any of the window margins, either from direct rainfall or seeping down from above, it will eventually get into the inside if evaporation doesn't exceed wetting.
    And in the West of Cumbria evaporation has no chance for at least 7 months of the year, or maybe more!
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