Gypsum plaster covered with wallpaper makes it look like the mythical rising damp. Actually its salts being forced up behind gypsum plaster into the lime. www.heritage-house.org
I have had around 10 builders come and quote for a job at my old Victorian London flat and NOT ONE had any clue of the importance of breathability in old houses.. I try to explain I don't want any cement or gypsum or plastic paint and they look at me as if I am eccentric and then proceed to tell me what they think my wall needs.... How is this possible??? Surely this should be common knowledge?!! Am I alone in this?
Nope - they are all idiots basically - haven't a clue. If you want help, we can do a survey, recommend the specification and then put you onto the right people - we do it all the time now - we've HAD to do it, to stop people from being conned. If you drop me an email - peter@heritage-consulting.org - I will see what I can sort out for you - need address, details of work, issues you have etc., and go from there...
Nicely illustrated Mr Ward, as you have shown, the slate damp course really was pretty impermeable, add to that the air bricks and perhaps a cellar and so long as they stay unblocked and open you shouldn't have any issues because there would be a nice air flow and thus no mould or damp issues. The new holes that you have shown drilled in and above the slate barrier have some kind of liquid damp course chemical pumped into it under pressure. The idea being that this chemical magically forms a damp course barrier within the line of all the holes, soaking through the solid brick or stone to form the barrier when in fact because this doesn't happen like they think perhaps it would work better if the holes were touching one another, edge on edge but obviously you can't do that all the way around. I once saw another idea from the early 1980's where you drilled the holes and inserted a flexible tube of material that attracted the damp to it so that every few months you were supposed to take them out and either replace them or squeeze out the water in some way, perhaps even put them in a drier to get rid of the moisture before putting them back in. ideally it would actually be better if all homes were built up on stilts, brick or stone columns and just to make triple sure, a slate DPC on the top of that before the floor joists are put down. For all those poor buggers whose homes were built on flood plains the council recommend that an impermeable barrier or 'bund' is dug in around the whole house but in actual fact if you could jack up the whole building onto stilts that may be more economic. But in the grand scheme of things digging ditches, keeping them cleared, laying hedges and NOT building on any flood plains would probably be the optimum thing but as we all know, vast open tracts of seemingly dry looking open land are hard to ignore by the cash strapped councils and the profit motivated house builders are only too happy to oblige them.
Hi Peter, Thanks for your videos! What are your thoughts on anaglypta pvc free lining paper over lime plaster? I have a wall that needs a lot of repair and skim coat and I guess paper would be easier. Also they claim it's breathable... is it really?
Hi Maria - I'd be very, very careful. Even the glues will cause problems. Best option is to use the Earthborn clay paints - lovely stuff, and fills any cracks and uneven bits. Repair in skim would not be hard - can buy tubs of putty finish coat from places like Ty Mawr.. Shout if you need help - peter@heritage-house.org
Thank you for all your videos and experience. Love learning about this stuff. Have any of your many videos gone through to explain what materials SHOULD be used? Will you mention this if you make another video at this house?
See comments above - not sure what happening with house - major issues with illegal works to a Grade 2* building, so at the moment waiting for Historic England input before we go any further. Materials that SHOULD be used are very simple - what was there to start - but essentially - breathable - so lime plaster, lime mortar, and either limewash paints or clay paints - all things that are easy to get these days, and cheap. Things you can use yourself - so not rocket science - and lots of courses available to learn too... More info on website - www.heritage-hoouse.org, and heritage-consulting.org ...
I have a Victorian property with a cellar room to the front of the property. about 3 years ago I cement rendered the external wall which has now all come away. there is no ventilation down there. Would you think this is the problem.
Leave cement off - if you want a render finish use lime. Also, you need THROUGH flow ventilation - so one vent at the front aint enough. We use humidity controlled vent gear in most cellars these days. Cement render and cellars are a no-no!
i have found that if a wall is rendered in a weak lime bssed mortar, say 12 sand 2 lime 1 of cement, gypsum putty will break down with moisture. its probably the guy has rendered in 3 sand 1 cement and that is stopping the wall from breathing. An interesting comparison is in my area there is two towns only 3 miles apart.. Town A is on a sandy beach and over the past 150 years has been flooded with sea water on occasions. Town B is on a cliff top and well above sea level and on a limestone base. Which do you think is worse for damp? Town B. many old stone homes have salt damage up to two metres up the walls, and are always a problem. Town A, despite the old stone homes being flooded on accasions are generally in reasonable shape. damp is usually no more than a couple of feet up the wall.
ANY portland cement is not a good idea. If totally breathable - no problem. If gypsum, and / or any portland cement - damp problems. Interesting about the towns - I think more likely elevation = wind = cold thus more condensation interstitially.. Damp shouldnt be up the wall at all if they are breathable - all lime - inside and out.. Might be salts - depending on whether wind blown salt, or salts in the mortar off beach sand for eg... Hard to say.
Peter Ward i also noted that underneath the homes in town A, even though the vents where blocked the sand was dry. i think its drainage. on the semi impervious limestone, the moisture concentrates under and around the houses. Town A i lived in as a boy, and the entire yard around the house would be flooded, within an half an hour the water would be totally gone. Town A however does have a borer problem in wooden floors. A study i read done by a guy on rising damp, revealed that in his experiments he found rising damp only present in true mud mortar,(no cementitious material at all) with my years in salt damp i believe him, moisture seems more consistent right through the thickness of the wall built in mud mortar and stone. Salts however i have noted, have little effect on the mud mortar, even when exposed to the air. its the render in lime and or cement / lime mortar that breaks down. i have found long salt crystals on stone in the centre of the wall built in lime mortar, but rarely in mud mortar, strange but true. The field we play in Pete is an interesting and somewhat complex one, something that Franchise Industries, specialising in sales and profits, havee no place in
sorry pete i bave to correct myself, salt crystals were present on both the stone and lime mortar, but only on the stone in mud and stone walls. i also ote mate that in my area of Australia we have severe concentration of ground salts. i have a vid up of my little project, that is metrs from a salt lake, that was filled, and was probably scraped for salt in the early days. On Yorke Penisula, lower down there are hundreds of salt lakes. They were all fresh when the first settlers arrived, but land clearing and cultivation saw them turn to salt and also many homes suffer from the salts and the rise in the water table. water table height also has a bearing on moisture problems in a home.
Now you're talking complex stuff - I worked with AMDEL in Adelaide for a while - a lot of research was going on with salts - but they still had this fixation on rising damp and tried to relate it all to that. The mechanisms are simpler - diffusion mainly, coupled with evaporation. I still think internal moisture contributes more than we realise - moisture from people condenses within walls, and allows salts to mobilise through hygroscopicity and evaporation. Cold nights = interstitial condensation within the stonework which then allows salts to move in the pore spaces. Ground water isn't so much of an issue - its not exactly a swamp there is it! Oz is a very complex place - I'm a geologist / geochemist by background and worked in mineral exploration - looking at how orebodies oxidise, and how we find deeply buried orebodies using geochemical signatures - you get into a whole new world of metallic ion movement. Those mechanisms are partly driven by electrochemical systems - fuelled by chlorides (batteries - chloride solution - anode - cathode) of which there is plenty in the Ozzie soils as you point out. You have some very insightful points there about mud mortars and lime - very few people I've ever spoken to have that level of observation and understanding. Do you have a group over there of like minded folks? Be very interesting to compare notes.. Funny - my house is in Shropshire - found some pottery here when digging - on the bowl is a picture of a troop review at the penal colony in Adelaide - the makers mark is Bercy McCall - Rundle Street, Adelaide. Turns out the farmer here was sent to oz as an advisor to the early settlement Govt on farming practise and must have sent things back from ozzie to his family as gifts! Think you need to look at interstitial condensation as a possible mechanism - need to look at thermal imaging - we work as standard now with thermo hygrometers - work out the dew point, and then look for areas susceptible to condensation. With wild swings in temps, and high humidity, cold desert nights, you are very prone to that - and I'm certain it plays a big part.
Nicely explained Peter. I try to slake my own lime putty mortars and plasters all the time as it's fantastic to use and being a putty will never go off if you put it back n the tub with a bit of water on the top. For the record I use sisal instead of hair and whenever I come across any of the bull-nosed corner timbers in a clients house I always try to re-do the 'quirks' (the plaster line) running down the edge which so many builders filled in during the 60's, 70's & 80's because they add a touch of quality to any room.
Thanks Peter - great to hear from you - and please, please feel free to send us videos and information on your work - I'll happily put them on the website and help spread the word..
Thanks for the offer, I actually have a little place on Facebook called 'Limespred' which has a few clips and things, I have also posted a couple of articles, more rant than essay, on LinkedIn under my own name but tend not to go there that often, it's not as good as your patch but like you I give out any free advice should anybody have any questions. The most amazing place I worked in was a church in Monmouthshire which is owned by the 'Friends of Friendless Churches' and was a decommissioned building due to a few structural cracks in one of the gable ends. This church up in the Valley's has the most amazing Sgraffito murals I've ever seen, the work was executed in sand & cement in about 1880 by Heywood Sumner. I guess he did it in cement because it was the new wonder material and he wasn't to know that it was wrong for a building built in lime mortar and the pictures were done in green, brown, yellow, red, white and black plasters which he cut back into to reveal the different colours and the topography of the area with stylised sheep, hills, clouds and trees etc, quite a stunning bit of work. However, over the years, the incoming water has pushed out the mortar into rounded bulges in places at different heights and the boss decided that the best way to conserve the work was to inject lime grout into the bulges and leave them in place. The church at Llanfair Kilgeddin is built in a water meadow without a dampproof membrane but in places there was a slate one of sorts which you'd expect to find and I had to cut away the first metre of render from the ground up, all around the inside of the building. I was sleeping in a caravan in the graveyard during the week and working all day and when it rained you could almost see the damp wicking it's way up the rubblestone wall and back down again, I would not have believed it if I hadn't seen it with my own eyes, and is a nice example of why lime instead of cement should be used.
Wow! I learn something new every day - be fantastic to see a video of that church.. you should definitely have a greater presence on the internet Peter - what a pleasure to meet you in the ether... ! I'll have a look at the FB page and join - I'm thinking of starting my own conservation 'institute' - the IHBC are next to useless, and RICS conservation stuff is not much better. There needs to be a practical group that gives credibility to the stuff we do..
I have a presence as such but they aren't as in depth and comprehensive like yours, and meeting fellow builders such as your good self we can all add to a better understanding of the old materials. I get most of my materials from 'Limebase' whose propriator 'Joe' is very knowledgable though a little grumpy at times. But so long as we use like for like when we can then you can't go wrong but unfortunately because of the lack of work many new-build builders are jumping on the lime bandwagon and don't use the putty mixes. Limelite and Hansons are 2 names I see in most builders merchants and as I said, anything with the word lime in the title is used little realising that it may not be fit for the more delicate jobs like cob, old brick and the mud stones and more feeble sandstones. I started uses sisal instead of hair because Joe at limebase wouldn't use it for some haired mixes I ordered saying it would jam up his machinery which speaks volumes and says to me that it's stronger than hair. See you in the ether Peter.
Limelite is dreadful stuff - I have attacked them in the past over this - it has a healthy portland cement content and is totally unbreathable. I'll do a page on it on the website and push it a bit harder - people need to know it is unsuitable.
Thanks for this, I unfortunately have this same issue in my house, previous owners didn't know what they were doing and they damp proofed the entire bottom half of a victorian chimney breast. In order to solve this, do you have to remove the concrete and plaster and restore using the correct materials? Would the salt problem get worse if it was just left as it is?
Complex question - but yes - remove concrete and plaster - then also remove as much of the salted mortar as you can, and leave for a while then re-point in soft lime mortar. Let dry out - and brush off any salts as they appear. Also sweep chimney regularly to remove accumulated salts. Salts dont increase if you are not making more - by burning fossil fuels - coal burns and produces ammonia and sulphur dioxide = sulphuric acid = sulphates and nitrates in chimney. If leave as is - salts start to attack bricks etc - best to remove.
Thanks for the reply! The chimney breast is in a kitchen, it is no longer in use so the damage is from a long time ago and was caused by a combination of fossil fuels and more recently condensation due to lack of ventilation. Rather than fixing the ventilation the previous owners damp proofed the chimney breast and surrounding wall area, and now the plaster is showing signs of damage, the paint on it is coming off in places and there are some patches which look like damp in a few spots. It's a bit of a mess..
I always thought plaster was Calcium Carbonate (chalk?), or is that lime plaster? I now realise that plaster, plaster board is just gypsum or calcium sulphate dihydrate! Is this where the sulphates are coming from? I was alwasy under the impression you leave plaster to dry for around 6 weeks before painting or wall papering.
Correct - LIME plaster is calcium carbonate when it has cured from calcium hydroxide. Pink plaster - or plasterboard - or bonding - etc is gypsum - calcium sulphate - and yes, its where sulphates come from as it breaks down with damp - and makes the prong meters go mad. Lime takes about 6 weeks to carbonate - the lime cycle basically goes calcium oxide from the kiln, plus water to calcium hydroxide - then further slaking and mixing to make lime putty. This then reacts over time with carbon dioxide and water from the air to form calcium carbonate.. The crystals grow slowly in cold and a bit faster in warm - about 15 to 20 degrees is best - and they form long slender needles - which make lime very flexible and strong.
See above - remove plaster etc, ventilate and reduce the humidity - need total moisture content of around 6 or 7 g/m3 - humidity controlled ventilation is almost essential in old buildings these days - ie RH of no more than 50% at temp of 18 degrees. Sweep chimney, line with 905 grade liner if using it going forwards. Dry air doesnt promote salts - any moisture in the brickwork will gradually evaporate, bringing salts to the surface, which can then be brushed off. Removing contaminated mortar is good. Salted fireplaces are not a simple fix - combination of things really.
Hi Peter. Thank you for the videos. We are having 'new' paint and concrete render removed externally. This will be re-pointed and re-rendered with lime mortar/plaster where necessary. Then painted with lime wash. Would it be worth delaying the internal removal of gypsum plaster and 'new' paint for a while to see if the external works make enough improvement ? or should we just proceed?
Watch no angle grinders on brick - damages it beyond repair - only by hand, or using arbortech mortar saw..Depends on how damp walls were - certainly will help - if no apparent problems internally then can leave - BUT make sure internal moisture levels are low - humidity controlled ventilation is key - 6 or 7 g/m3 max - 50% RH max, at 18 degrees - this drops dew point to point where you unlikely to ever get interstitial condensation - which is what the so called rising damp really is - and if you dont get condensation = fog forming in wall and being trapped by gypsum and paint - then wall will stay dry.
Thank you Peter. I will stipulate no angle grinders when removing pointing and render. That Arbortech machine is great! (Had to Google 'interstitial condensation'!!!)
It is indeed - blimming expensive though -nearly £1000 - wish I bought some in Oz before I left. I know the man that invented them - lives in Perth. Much cheaper over there. We have one here and I'm just raking out the walls of my limestone Grade 2 listed cottage up north - so easy, and no damage to the stone. Blades aren't cheap - but worth having - I guess if you look at the cost of the machine, and increased speed of job, you'd probably end up with a cheaper job bearing in mind labour costs account for 75% of any build.
I'll think about doing a page on the www.heritage-house.org site on 'interstitial condensation' and try to explain it. Really is just like fog forming in the wall.
Hmm... Modern gypsum is usually pink.. Easier to tell if its lime - which is mostly white or grey, quite soft, gritty, and probably has hair in it. Most lime will probably have residual old paint on it - dusty, green coloured, beige, brown etc Some gypsum products are greyish so confuse things a bit.
Hi Peter. Do you cover the East London area by any chance? I have a property that has "damp" issues and I'd like to get you over for a survey if possible.
If as a diyer, i battened and plasterboarded the wall and left some sort of ventilation in behind would that work? I don't have the budget to pay a plasterer 250£ A day labour? many thanks Peter I have subscribed and am enjoying your content as a new owner of a 1930s semi.
It's not recommended - we see this sort of approach failing a lot. Why don't you have a go at lime plastering? Its not hard, you can do a course at Ty Mawr for not much, and you'd enjoy it. All the materials are cheap as chips. Many of our clients go this way now, and all of them have a lot of fun, and get great results.. much easier to get good finish with lime than gypsum - you can come back to it next day and wet it up again, and re-work it till you are happy. Then paint with Earthborn clay paints... I'm assuming you sorted cause of problems - ventilation, sub floors, drainage, ground levels etc...
Peter Ward I don't actually have damp problems other than a stud wall in a bathroom which has been tiled ie: clearly condensation!. I am ripping the tiles off back to brick on the remaining solid walls and the bathroom will then be moved upstairs, the room will then be a utility room. The Muppet who owned the house before painted the outside so that needs to be removed, and I am in the camp of prevention rather than cure. As a matter of due course I will replace the underfloor ventilation bricks and ensure they have adequate air flow. what type of finishes can be achieved with lime, as it will be difficult to appease the wife who wants ultra modern walls? many thanks for your reply. also any link as to the lime plaster you would recommend?
I've had this exact problem in my house, layers of gypsum over old plaster. The plaster was two inches thick in places where it'd had so many layers applied. Is lime render the only solution to the problem? My house is a cheap (but old) mid-terrace, not really worth investing thousands into. I've stripped the plaster off, and thought of maybe battening and plasterboarding the walls, but I'm not sure if salts would come through the battens.
Be careful about batening - it can trap moisture. The cost of doing that is similar to lime plastering - lime is really the only sensible solution. Research the cost of lime - it is mainstream these days - and coupled with gentle and constant low temp heating, will result in a warm dry home for years to come.
Hi Peter would it be possible for me to send some pictures over to you. I have wave lines and crusting around the skirting boards. One guy reckons its rising damp.
Oh, believe me, I dare! The chemical industry is enjoying a feeding frenzy on the unfortunates here who have been saddled with cavity wall insulation - they diagnose failed cwi as 'rising damp' and inject the hell out of it - the corruption and scandal is mind boggling.
