Cement or Lime

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I have a gable wall that needs to be re rendered. It is an external rubble stone/granite and lime wall. It is currently rendered with cement thats cracked and letting in water, rotting a number of internal floor joists.
Im intending to hack off the old render and go back to the stone outside. Ive already done this inside(the old plaster came off easily with a shovel), so i will effectively have two bare stone walls on either side, a clean slate.
So what are your opinions on how i should progress. If i render the external wall in cement and sand and waterproof paint it will be waterproof. But not breathable. If I then coat the internal wall with lime plaster, this will enable the wall to breathe and all the water that is in the wall to escape(it is already drying out which i can see). Since the wall is now sealed from the outside, then this wall will dry out over time as heat from inside keeps the wall dry.
The other option is to render with lime outside, which im not familiar with and i suspect will be more much expensive. Ive been quoted 2k (minus scaffold) to rerender in sand and cement, its a 12m two storey, is a lime render going to be more expensive?
Do my suggestion sound reasonable and would the wall completely dry out as the wall breathes through the internal plaster. Can i assume that an interal lime finish would help? Opinions welcome.
Cheers,
 
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Lime is the proper way to do it. Something I'm in the process of doing at the minute. Where I live the old local stone is sand based, I now keep looking at all the houses where they've been cement pointed, trapped moisture has then caused the stone to crumble leaving a web of cement.

Getting back to your render question, if you've got nice stone have you thought about getting the pointing sorted then covering with lime wash/slurry? you'll then see the stone(to a degree) and it'll be cheaper than a full render.
 

ree

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Do not use plastic paint or any "waterproofer" on the stone.

When the render is removed, rake out and re-point with a sand and lime mortar. Perhaps, S&L re-point the interior as well.


Depending on the condition and appearance of the re-pointed wall you can carry out your experiment of drying out the wall - or render over with a S&L render. Others, more knowledgeable than me, might explain any advantages with the new synthetic renders for a situation such as yours?

I see no advantages in using a "lime wash/slurry".
 
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Spoken to a few trades who have made the following comments.
1) Sand and lime will take an age to dry.
2) Waterproof the inside, let the outside breathe.
3) If i let the inside wall breathe i will effectively let damp from the wall into the property.
4) Sand and cement does breathe if it is a weaker mix, ie greater than 4-1. I could also line any cracks with mesh which would help with movement and reduce risk of cracking.
5) Rendering in krend monocouche (breathable), is going to double the price and is likely to crack if there is anymovement, this is 110 year old property.
6) I could seal the outside using standard sand an cement, i can the demudify/leave the inside wall for a period, then render/plaster with gypsum which would seal the wall.
Getting to the point where the Cornish weather is going to change to rain and storms soon and i need to make a decision at least on the outside.. Any comments on points above welcome.
Thanks.
 
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Do not use plastic paint or any "waterproofer" on the stone.

When the render is removed, rake out and re-point with a sand and lime mortar. Perhaps, S&L re-point the interior as well.
Are you talking S and L on the outside?
Or you suggesting a sand and cement render on top of the S and L rake out repoint outside?
 
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Getting back to your render question, if you've got nice stone have you thought about getting the pointing sorted then covering with lime wash/slurry? you'll then see the stone(to a degree) and it'll be cheaper than a full render.
Unfortunately it is a rubble stone wall, not nicely placed granite. So a cover up with some sort of render to create a smooth finish is essential.
Here is a pic of the internal wall, the external wall will be of similar construction.

 
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When I say a lime slurry, I effectively mean a thick lime wash, which will show the contours of the stone/rubble, however cover it thickly in something that can breathe.

Nothing with cement in will breathe at all. Same as adding cement to a lime mix, it doesn't allow it to breathe.

By cementing the outside, then covering the inside in gypsum plaster the wall has no way to breathe so any moisture will find its own way out creating other problems and weakening the wall.

Its a good way of masking a problem so you don't have to see it or think about it for a number of years.
 
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OP
If you can remember Who told to that you could 'seal' the inside with a gypsum plaster, disregard this .

Points you list are generally sensible, but only you will have to decide what you can pay.

Gypsum is perfect for drawing out moisture, which is why it should never be used in damp areas! it is a cosmetic application, and will not seal anything up.The wall will 'breathe' alright, then furr up with salts and degrade over time

Can I ask people why it is so so vital to have this wall 'breathable' on both sides? All this means is that you will get damp walls and damp air inside.

The main reason old buildings didn't use today's materials is not that they made a choice and thought it was better , but that had no real choice at the time.

For me seal up the inside and then trad lime render or something like k rend on the outside . It's going to cost money regardless, I am afraid.
You can stop damp getting inthe sides, but not coming up for the ground .
 
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Is a lime render a diy job?
As you said the inside of the stairs and the wall was furred up with salts. There were 3 air vents, completely blocked up. Never quite seen anything like it.
As i said i cant afford the lime render. Its a 12m wall. It looks like its going to have to be a patch job :(
Ive also heard that krend is not that tolerant of movement and will crack the same as cement.
It quite amazing to see what was there suddenly drying out. On further digging both of the door architaves in the hallway below 1m were completly rotten.
 
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