Exterior/Interior walls re-plastering for my 100 years old Village Home In Gujarat, India

Hello, We are looking for some insight on how to best re-plaster our interior and exetrior walls. The walls are built with stone machinery using lime mortar(lime, sand, water). The mortar has lost its bonding capacity and its deterioating. The loose sand keeps falling out of the joints if we scratch the joint mortar.

Our plan was to expose all the joints about 6 inch deep, fill all the joints with cement mortar and allow the mortar set fully. After that, plaster the walls for final finish and paint. Because of the stone machinery, how could we achive the bonding the stone and cement mortar.  

We would like to rennovate the old house to maintain its historical value and are not demolition for re-construction.

Hi Hardik.
What do you mean by stone machinery?

If the old plaster is lime based and the mortar too I would be careful with using anything else.

Why not get rid of the loose parts, repair and repoint with lime mortar and finish everything off with lime plaster on the outside and maybe even clay plaster on the inside?!

Hi Hardik,
I'm in agreement with Benjamin. Here in France old houses are built with stones fixed together with either lime mortar (lime, sand, water) or clay mortar (clay, sand, water). The finishing on the outside is sometimes lime plaster, sometimes you can see the stones.

To renovate the joints, you can scratch out the old mortar to 1,5 inches deep and then point with new mortar. Please don't use cement, because it will not bond well with the old joint, and it doesn't breathe, locking moisture in places where you don't want moisture to accumulate.

You need to wet the surface you'll be putting the new mortar or plaster on, otherwise it'll just fall off.

What do you mean by stone machinery?

Happy renovation!

I think it is stone masonry.

Stone Masonry ** (Spelling) **

We would like to use cement because lime mortar is outdated practice in our area. So we would like to go with Cement fill and cement plaster.

Benjamin Dinkel wrote:Hi Hardik.
What do you mean by stone machinery?

If the old plaster is lime based and the mortar too I would be careful with using anything else.

Why not get rid of the loose parts, repair and repoint with lime mortar and finish everything off with lime plaster on the outside and maybe even clay plaster on the inside?!

Thank you for the insight. Unfortunately lime and clay mortar are no longer standard practice for construction at this time.

Do you think guniting machine would work once joints are exposed and then replaster with Cement once cured?

Nina Surya wrote:Hi Hardik,
I'm in agreement with Benjamin. Here in France old houses are built with stones fixed together with either lime mortar (lime, sand, water) or clay mortar (clay, sand, water). The finishing on the outside is sometimes lime plaster, sometimes you can see the stones.

To renovate the joints, you can scratch out the old mortar to 1,5 inches deep and then point with new mortar. Please don't use cement, because it will not bond well with the old joint, and it doesn't breathe, locking moisture in places where you don't want moisture to accumulate.

You need to wet the surface you'll be putting the new mortar or plaster on, otherwise it'll just fall off.

What do you mean by stone machinery?

Happy renovation!

Since the home is 100 years old it would be a shame not to use the tradition plaster technique keep alive the tradition.

Modern techniques are for modern homes.

And as Benjamin pointed out cement might not stick to the walls of traditional plaster.

That is such a lovely home.

This:

We would like to rennovate the old house to maintain its historical value and are not demolition for re-construction.

I would strongly recommend AGAINST using cement to replaster/repoint the existing old stone walls. These walls are probably still standing, because of compatibility of materials used.

1. Traditional stone masonry always used lime or clay based mortars, so the wall could better adjust to uneven loads (and movement) of uneven stone material.
2. Lime based mortar will allow free flow of water/water vapor that is the key to wall longevity,
3. If the wall is made of very dense rock (igneous) then plastering/pointing with lime plaster will improve the air quality in the house allowing the walls to breathe by absorbing moisture - lowering interior humidity and also the temperature. For this reason an adobe/earth wall will cool the house more than the wall made of low porosity concrete.
4. Adding moisture impervious cement based material will increase the possibility of mold formation.

Just for reason 3 and 4 it makes sense to use lime only. If the building should remain for the future generations 1 and 2 have to be considered. Using incompatible material is actually an outdated practice of the past that created more damage than good and material science left it in the dust of history.

For a mason it makes no difference with what material he is reponting. If anything - it would be easier with lime, because it gives creamy consistency to the mortar.

From Google
"A guniting machine, also called a shotcrete machine, is a construction device that pneumatically sprays a cementitious mix (gunite or shotcrete)
at high velocity onto surfaces for rapid, strong concrete application in tunneling, mining, and repairs,
working by feeding a dry mix (gunite) or pre-mixed (shotcrete) material through a hose for precise, high-pressure application."
Lime plastering is a different process and more suited to your application as Cristobal has explained.