Rendering an old house

[jmsgld]

Old farm house, approx 200 years old solid walls 1-2' thick, mixture of stone, flint, chalk and brick.

Previous farmers rendered with a cement based render many years ago, variously blown, cracked etc. causing damp.

Obviously old render needs to come off, question is what next?

Lime render sounds like a PITA, costly, maintenance etc. Internally is largely modern plaster, we did lime render one wall about 5 years ago and it has almost dried out! We have internally insulated one aspect upstairs, allowing recommended air gaps etc.

Is there another option ? was thinking a more modern render and then external insulation, particularly the end gable as it bears the brunt of the weather. We replaced the roof a couple of years ago and increased the overhang to allow potential external insulation in future... the damp is largely mid wall, not close to the ground.

Hoping to get this done in the summer, so need to get talking to trades, and would prefer to not go in completely blind.

Thanks for your input

[gangzoom]

No idea what works on a 200 year old wall, we used Silicone render on our build. It's suppose to last much longer than other renders and have loads of colour choices.

[48k]

The centre section of our house is circa 120 years old and part rendered and when we bought it the surveyor was good at explaining these old buildings were not designed to be heavily insulated and rendered so my advice would be get somebody in who knows what they are talking about to survey what you have and recommend a solution.

[Lotobear]

I would use a NHL render (probably a 3) - this will allow moisture/vapour pressure from inside to pass through through the structure avoiding a build up of moisture in the outer zone of the walls, as will almost certainly be found when the cement render is removed - a wet wall has much lower resistance to the passage of heat. A nylon mesh in the base coat will deal with any variability in the walling material and control cracking.

Putty lime would be better still but it is a PITA to manage while it takes a set, so NHL provides a pragmatic solution with similar characteristics to an 'air' lime if not in terms of ultimate vapour permeability.

[swanseaboydan]

If there is cracking - check the state of the lintels above the windows. If they are old rotten wooden timbers they will need to be changed before you render to prevent new render cracking in my experience .

[OutInTheShed]

I would consider some external insulation and a rain screen of hanging tile or slate.

[bangerhoarder]

Wood/slate/tile cladding, especially the walls facing the prevailing winds?

[Magooagain]

You don’t mention if the house is ‘listed’ or not, as this would dominate the rendering decision if it is.

[jmsgld]

Thanks for the replies.

Not listed (wouldn't buy a listed property again!)
No wooden lintels left, previous farmers rather ingeniously managed to pour reinforced concrete lintels in situ. I know as we removed a load bearing wall and had to use a world of steel, and replace the nearest lintel with an RSJ as the engineer wasn't happy with the overlap.

Yes, cladding is kind of what I was getting at, but although not listed, it is in a conservation area, so easier if it doesn't materially alter the aesthetics.

I'll certainly get an old buildings guy in, but I imagine he will suggest lime, which is perhaps the way to go.

I appreciate that cement based render is completely wrong for the building, as it is impermeable, inflexible etc.
My thoughts were to apply a cement based render (as it's cheap) to stabilise the wall and provide a stable structure to affix an outer later to protect it from the elements eg cladding or rendered external insulation. The moisture then making it's way in over time and the walls drying out, and when it cracks in the future it will be largely protected . Or that there might be a more modern flexible and vapour permeable render that is lower maintenance than lime.

My issues with lime are that it's expensive, limited people use it hence longer lead times on labour, from my experience takes an age to dry out, increased maintennance, and with internally largely being plastered with modern plaster we are still going to have issues...

[Magooagain]

I m with Lotobear on this, about using an nhl 3 lime.
Bear in mind we ve seen no photos etc.
A mortar mix I have used on some stone buildings at the owners request is one part lime, one part masonry cement with five parts 0/2 or 0/4 sharp sand.

As with all surfaces, preparation is key for a good completion of works.

Edited by Magooagain on Sunday 1st February 11:26

[jmsgld]

Thanks for the input, sounds like lime is the way to go (bugger!)

I regularly drive past a place that specialises in supply of lime and associated stuff (https://roseofjericho.co.uk/) I'll pop in and get some recommendations on local tradesmen to have a look / quote. I am guessing that the walls will be in a pretty poor state once the current render is removed.

They mostly seem to stock / make their own stuff, one thing they do stock is "Cornerstone Insulating Render", NHL 2, seems to be suitable as a basecoat for crumbly walls. Any opinions on this?

Thanks

[Magooagain]

You’ve not understood what we’ve said. The lime I’m talking about is just from a sack in powder form. It’s not ‘slaked’ lime or any other sort of ‘live’ lime.

Nhl3 is just used like you would cement powder.

[jmsgld]

Awesome, I am glad I have not understood what you have said!

That sounds exactly what I was asking for, now I understand

[Snow and Rocks]

Be careful - there's no end of BS written about old buildings that often really has very little basis in reality. It's become a whole cottage industry where so called experts spout no end of crap.

As a Geologist the most important question in my mind - what type of stone is the house made from? Highly permeable sponge like soft sandstone or almost completely impermeable and incredibly hard granite?

What’s true is not “lime is always right, cement is always wrong”, but rather:

Lime render is probably wise where the masonry is more vapour-open and weaker than cement.
Lime render isn't always beneficial where the masonry is dense and strong.

The stone’s hardness, porosity, and capillary behaviour are fundamental to how decisive the lime-vs-cement choice really is.

After all, endless old buildings here in Aberdeenshire are rendered with cement based harling but are bone dry inside - granite and gabro are unbelievably hard and impermeable on their own so what difference does the harling make?

[C Lee Farquar]

jmsgld said:

I appreciate that cement based render is completely wrong for the building, as it is impermeable, inflexible etc.

Worth bearing in mind as you consider your options that cement render isn't impermeable and becomes less so the weaker it is.

It's not a back and white decision process.

[cliffords]

In our previous 200 year old solid wall house,we had one wall that was noticeably less damp than some of the others. It was the wall where the render had fallen off.