Removal of cement render and replacement with lime – old house content

Just been to see a house – a huge one, top end of our budget but beautiful. Perfect really. Expected it to be a horror show in the flesh but whilst a little dated, it actually looks better than expected. Electrics, heating are fine, windows are old and draughty but mleh that’s the deal with old houses

So dates are a bit vague but it seems it was built late 18th – early 19th Century. Walls are clay bat with a lime render. It’s had a cement skim render applied over the top of this possibly in the 70’s or 80’s and this is now starting to fail.

I expect the risk is that once the render is removed, the block work could be mush being held up by render?

Has anyone experienced this sort of project? Straight forward or run for the hills??

What’s it actually built of? It certainly won’t be blocks if 18/19C. Would be best to render in lime if possible – much better for breathability.

Pete Ward Heritage House, plenty on YouTube

Also limemortarrestoration on YouTube and Twitter

There are a few about in the game who will give some basic advice or recommend a suitable local tradesman

It will be most likely stone or clay brick under the render, getting the cement off will save it rather than the cement render saving what is underneath

Wall construction is clay bat – apparently it’s an unfired clay/lime/fibre thing popular at a time when bricks were taxed

My experience of trying to remove Portland pointing on a section of old house were a nightmare. It was so much harder than the bricks around it, and was a messy **** nightmare.

Look up Natural Building Technologies for modern, dry bagged, faff free lime render.

Edit: https://www.natural-building.co.uk/product-type/render-plaster/

Got it. Most of our house is cob, so similar. As above, re render in lime if you can but to be honest if the house isn’t actually damp then it’s not so much of an issue.

Quite a few of the experienced people in the game aren’t convinced by hydraulic lime apparently hardens too much, hot lime is the preferred method

Yeah we are specialist lime contractors, we work exclusively with lime mortars, clay and stone. We have undertaken projects like this, in fact a couple of years ago we did what was probably exactly what you describe on a late 1700s clay built property that was cement rendered. We removed the render, rebuilt the clay where damaged using either clay block or cob we mixed on site, replaced lintols where rotten plus additional stonework and pointing. Finally we harled the building with a hot lime render and limewashed. Here’s a link to the project – https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationid=23ed113d-f89f-43c5-9467-a98f00f99437

Realistically the work is complex and lengthy, and there are very few builders able or willing to take on the work. You need a specialist contractor who really understands what they are doing and what they expect to find, and of course how to solve it.

That said your assumptions are likely to be correct – removing the cement render is typically straightforward but slow, the underlying clay structure will require repair, either due to damage during the render removal or because of water ingress (failed/cracked render) or other degradation. It’s worth pointing out that what you find underneath the render may be radically different to what you anticipated. We often find a building has been extended or altered extensively and rebuilt in different materials, eg stone brick and clay cob within one elevation. This means you will need to think about movement and cracking mitigation when you re harl the building. Owner’s faces generally go very pale when they see how the building looks under the render….so don’t panic.

Without seeing it it’s obviously impossible to say how much it’s going to cost but if you could give me an idea of the building’s size I could probably give you a ball park figure. A photo or link to the property would be good, if you have it.

Worth noting that projects like this can often attract grant funding from bodies such as Historic Environment Scotland, in some cases up to 50%. Other bodies do similar, it depends where the building is. Are you in England?

Any questions just ask me

Thanks Vader, fascinating write up

Speak with Ty-Mawr Lime in South Wales or visit their website http://www.lime.org.uk , they can give you advice, and supply the traditionally mixed lime products. We have used their products on our recent renovation of an old school dating back to 1786.

We are repointing a stone house in Lime, takes a while if doing it yourself as you can’t work at temperatures below 5oC, so realistically you are limited to April – September.

Ty-Mawr showed me a horror show of a guy who pulled cement render off an old cottage and the gable end fell off, as the cement was too strong, I think he’d gone at it with SDS Chisel. Slow and steady with hand tools is the approach you need.

Reading this thread reinforces my total love for this forum, the breadth of knowledge from various members, as shown by Vader’s reply above! 👏🏻

Just to add to Vader’s link above, you can get a load of inform guides from HES website as well which are good to read for background. If you’re up this way I can recommend speaking with the Scottish Lime Centre Trust as well.

singletrackworld.com/forum/topic/removal-of-cement-render-and-replacement-with-lime-old-house-content/#post-11535195

thanks for that Vadar (STW never fails does it) here’s a link to the house – its certainly not a DIY job

house isnt listed so i expect that means grants would be unlikely
https://www.rightmove.co.uk/properties/98808677#/

Finally we harled the building with a hot lime render and limewashed. Here’s a link to the project – https://www.historicenvironment.scot/archives-and-research/publications/publication/?publicationid=23ed113d-f89f-43c5-9467-a98f00f99437

Impressive. Most impressive.

at this time of year i dont mind being reminded that im only half way through pointing the flint work…
cement mortar is horrible to remove, im lucky its just the odd bodge here and there, the majority, original lime is fast approaching 200 yrs.

roll on spring

That is an interesting looking house you have found there. The far end of the right elevation has a classic clay build bulge, very interesting underneath no doubt.

So doing some rough reckoning on dimensions around the building I would say that it’s going to be about £38-40k for a lime harl alone. That would be straightforward removal of the existing cement render and application of a hot lime harl and 6 coats of limewash. You’d need to add VAT and scaffold costs to that too. Bear in mind these are Scottish prices – I have no idea how much a Down South tax would add!

If there is substantial rebuild or repair of the underlying clay structure then i’d be penciling in another £30k or so, worst case. If you were to push me, i’d say from looking at the design of the building you may get away with the bat being largely sound, which would be good news. If there is any failure/cracking in the render (very likely), the lime harl underneath will be shot but it will to a certain extent have protected the clay. The large overhang of the roof is a good thing in this respect as it will protect the walls quite significantly from rain, and therefore reduce any ingress behind the render which is bad news for the clay.

From a practical point of view it isn’t a difficult building to work on – there is straightforward access to all the elevations, plenty of space for materials and mixing. All good things for prospective contractors. It’s clearly a lot of money to spend on a building though, and the spend won’t necessarily be reflected in its resale value. You could consider doing the work in phases ie an 2 elevations each year, to spread the cost.

Lime harled and limewashed, I would expect the house to look utterly fantastic. You will need to re-coat the limewash perhaps once every five years, however the harl and structure will last many lifetimes.

Could you externally insulate?
Wood fibre with a lime render over the top, you may or may not have to remove the existing render then but specialist advice is certainly required. For the sums of money to lime render alone I would be investigating insulation.

Vader’s key point for me is ensuring you actually have someone in the area that knows what they are doing and is up to the job. I live in a simple by comparison cob walled thatched cottage with lime render but finding people who know what they are doing and can get good results is not easy.
When buying 20 years ago had all the render stripped and replaced and it was a great job.

Where I don’t agree with Vader is re-costing lime wash every five years as I have had to do it A LOT more often than that that but luckily I quite enjoy it.

That sounds like an expensive harl for easy looking walls but maybe more square metres than I’m thinking. Can’t be too exclusive a trade flat walls with a hawk and trowel not a hard skill to learn

It would be worth reading this book https://www.amazon.co.uk/Hot-Mixed-Lime-Traditional-Mortars/dp/1785005553. Some interesting stuff in there which is different from what I’ve been doing (no additive in top coat of limewash, for example).

Vader, I’m interested in your use of NHL 5. I wouldn’t use NHL on cob but I’m guessing you find it works. How hard is the harl?

Vader, I’m interested in your use of NHL 5. I wouldn’t use NHL on cob but I’m guessing you find it works. How hard is the harl?

Ah yes the million dollar question. In a nutshell, we can make the harl as hard or soft as we want as we are making a gauged hot lime mix. This means a mix contains both non hydraulic quicklime and a hydraulic lime in carefully measured amounts. Adding quicklime into an NHL 5 will reduce the strength of the mix while not reducing the overall lime content, so effectively you could go down to anything from 1.5 to 4.5, depending on quantities. The mix we used on the project above was a 1.5, however there is very little overhang on the building and there is a problem with splashback when rain hits the pavement at the foot of the wall and bounces up onto the harl.

The strength of the mix you want is going to depend on loads of factors but primarily where the building is, whether it’s exposed to weather, how hard the underlying stone/cob build is etc etc. Put very very simply, a harl (or mortar generally) in the Highlands will need to be harder than a harl in the south of England, because weather. But of course there is a trade off – Softer harl = more breathability. Harder harl = weathering resistance.

Where things get interesting is when you start looking at the make up of traditional mortars in old buildings. In Scotland for example, when you analyse the old mortar you will likely find that it is hydraulic. This is because the Scottish limestone it was originally made from is naturally hydraulic. Last summer we built a small brick kiln in the garden and fired some highland limestone, some broken marble from an old fireplace and some oyster shells we collected on the shores of the Forth in Fife. Once fired we then slaked each type and made mortar from the highland limestone and very fine limewash from the marble and shells. Some of the mortar was put in an airtight plastic bag and knotted tight – the mortar still cured which means there is a hydraulic element to it. A non-hydraulic lime would not cure in that scenario.

Interesting, thanks very much for the comprehensive reply. I’ve used non hydraulic lime almost exclusively for the last 20+ years but have recently had issues in an exposed location (still down south) so have started to experiment with NHLs.

I see the property is marked as sold STC, OP did you take the punt?

@Redmex – I was kinda hoping the flat and accessible nature of it would keep the costs sensible – and from what Vader has said, to an extent it will – but it’s still 350 m2 of wall so I guess the number is always going to be big

@oikeith – it’s STC but I know it’s coming back to market as the sale has fallen through. Still considering it – head says no, but the want is very strong!

@vadar – thanks again for your comprehensive replies – incredibly helpful. Always great to have an opinion from an expert who has no skin in the game!

it’s STC but I know it’s coming back to market as the sale has fallen through

It’s a lovely looking place, but I wonder why the sale has fallen through? The first thing that comes to mind is that a buyers survey has highlighted the potential cost involved in bringing it back up to scratch.
Playing devils advocate there but its easy to fall into the trap of thinking that remedial work isn’t going to cost too much – but when you get into it there’s a lot more that needs attention and hence the costs skyrocket.
Other than the rendering costs other things that would be a red flag are:
Windows – can be amazingly expensive to replace windows like that
I see that there’s been a new ground floor fitted – why, and what does that say about the first floor construction?
At least one bedroom ceiling has been papered – the only reason ceilings are papered is to cover something up. So I’d be looking at those ceilings as well.

As I said though……. lovely looking place.

Excellent basement man cave and next to a decent curry house – why are you worrying about the some trivial details on the external walls? 😉

Petrieboy you’re welcome, glad it has been useful. If you need any more advice give me a shout

Nice looking property but a bit too close to Flood Zone 3 for comfort for me. Looks like your access could flood, although not the house itself.

@petrieboy

I guess you didn’t go for it in the end? Just being nosey, but I noticed the sign had switched to sold as I cycled past today.