The primary concern in replastering and repointing old walls is the presence of salts. In old buildings, due to their age, salts become an integral part of the building fabric. Getting rid of them is really not an option, which leaves us with managing them with building-friendly solutions, preventing them to spoil the finish, while keeping the building breathable.

Here are some renovation scenarios typical to old buildings with recommendations on how to deal with the dampness and salts in an effective way.

1. Replastering Old Walls

Let's say we have an old wall, also subject to the effects of rising damp: some crumbling and some salts crystallization on the surface (efflorescence). Here are some renovation options:

  • The typical modern builder's solution is this: hacking off the plaster, installing a chemical DPC (damp proof course), maybe covering the bottom 1 meter with a vertical waterproof membrane then re-plastering with a cement-based modern renovation plaster, finishing it off with a "pink" gypsum finish and a modern emulsion paint or wallpaper.
    The modern cement plaster in this case will apparently solve the problem for a good few years, until the crystallization pressure of salts accumulating under the plaster will eventually break it down.

    The budget version of the above solution (and from technical viewpoint the poorest option) would be only skimming the wall with a gypsum finish while leaving the old, salty plaster on. The wet skimming dissolves the salts from the old plaster which will migrate into the fresh gypsum finish, ruining it in a matter of months.

  • The typical building friendly solution is obviously using a lime plaster to keep the wall breathable, skipping the cement plaster and membrane combination.
    Lime keeps walls breathable, however the accumulating crystallizing salts will gradually fill up its pores, resulting in the breakdown of the plaster within a few years. For this reason conservation professionals call lime a "sacrificial" material. The leading mechanism behind lime's sacrificial nature are crystallizing salts.

  • RECOMMENDED SOLUTION: to prevent the breakdown of plaster and to make the renovation long-lasting, the following actions are recommended:

1. Removal of old plaster

- Remove the old, salty plaster completely at least half meter above the highest level of staining or marks. Important: partial removal of the old plaster in order to just re-skim the wall is very risky as the salts left behind will ruin the decoration within months. The salty plaster must be removed completely.

- Clean the walls of any loose debris. Any repairs (e.g. replacing missing or eroded bricks, repointing etc.) must be done at this point.

2. Replastering

- The first coat (scratch coat or base coat) in contact with the wall MUST BE a special salt-resistant lime base plaster, NOT just any ordinary lime plaster. This layer is critical as it has the role of limiting / preventing the migration of salts into the subsequent coats ensuring the longevity of the plaster.

- The main coat can be any good quality lime plaster.

- The paint should be a breathable paint such as lime wash or a mineral paint.

2. Replastering Extremely Salty Walls

Very old buildings made of very porous materials or houses situated close to the sea can have extremely high salts content.

Large pockets of salts are often visible on the surface, along the pointing or under the plaster.

Here are some examples of such walls:

RECOMMENDED SOLUTION: in order to keep the extremely heavy salts under control and preserve the finish as long as possible, the renewal of both plastering and underlying pointing is recommended:

1. Removal of old plaster & pointing

- Remove the old, salty plaster completely at least half meter above the highest level of staining or marks. Important: partial removal of the old plaster in order to just re-skim the wall is very risky as the salts left behind will ruin the decoration within months. The salty plaster must be removed completely.

Rake out the decayed salty pointing about an inch deep or as much as needed without destabilizing the structure of the walls.

- Clean the wall surface of any loose debris. Any repairs (e.g. replacing missing or eroded bricks etc.) can be done at this point.

2. Repointing

- In order to protect and increase the longevity of the pointing, repoint the building in 2 stages using the following two lime mixes: 1. in-depth use a special salt-resistant lime mix for pointing to keep the salts away. 2. Then finish the pointing with a traditional lime pointing to give the pointing its final look and color.

3. Redecoration

OPTION 1: Replastering

- The first coat (scratch coat or base coat) in contact with the wall MUST BE a special salt-resistant lime base coat, NOT just any ordinary lime plaster. This layer is critical as it has the role of limiting / preventing the migration of salts into the subsequent coats ensuring the longevity of the plaster.

- The main coat can be any good quality lime plaster.

- The paint should be a breathable paint such as lime wash or a mineral paint.

OPTION 2: Plasterboarding

- Due to its very high salts content, the walls are advised to be skimmed with a salt-resistant lime base coat. This prevents: 1. crumbling of the wall behind the plasterboard due to changes in temperature and relative humidity; 2. the transfer of salts into the plasterboard over the air through evaporation.

- Battening: the plasterboard must be mounted onto galvanized steel battens, these won't rust or rot, and it has very long service life (approx 50 years). Gypsum plasterboards have limited breathability, but the cavity behind the plasterboard as well as the room can be ventilated.

- Skim and paint the plasterboard to finish it off.

3. Repointing Old Walls

Mortar performs several functions, offering the wall:

  • Structural stability: holds the wall together
  • Flexibility: prevents the wall from cracking
  • Regulates moisture: by evaporating humidity protects the bricks from damage
  • Appearance: good pointing is easthetic

The breakdown of pointing can occur for several reasons, the most important being mechanical stresses as a result of frost and crystallizing salts.

RECOMMENDED SOLUTION: to restore the appearance and original functions of the pointing, the following actions are recommended: 

1. Removal of old pointing

Rake out the old, decayed pointing about an inch deep or as much as needed without destabilizing the structure of the walls.

- Clean the wall surface of any loose debris. Any repairs (e.g. replacing missing or eroded bricks etc.) can be done at this point.

2. Repointing

Repoint the wall with a traditional lime pointing.

4. Driving Rain

Driving rain against old solid walls (without cavity) are one of the most challenging situations to resolve. In addition to driving rain, solid walls are also often affected by interstitial (in-depth) condensation due to the cooling effect of the environment, resulting in mould growth.

  • The typical modern builder's solution to this problem is cement rendering (harling). Although cement render is waterproof, due to subsidence or ground movements, it cracks over time, letting rainwater in. Being also non-breathable, the moisture accumulates under the render resulting in dampness problems and the gradual erosion of the underlying building fabric.

    Waterproof membranes are often also applied, after which the walls are re-plastered with a modern cement-based renovation plaster. Although this apparently solves the sideways water penetration problem, walls being unable to breathe, will result in future dampness problems.
  • OUR RECOMMENDED SOLUTION: to prevent / minimize the penetration of driving rain, the following actions are recommended:

1. Pointing: the first layer of defense against driving rain is pointing. Pointing must be sound with no voids, cracks or loose bits of plaster. Please refer to the pointing section above to renew / correct any pointing defects.

2. Rendering (if applicable): using the right materials rendering can be a very efficient defense mechanism against driving rain.

- Base coat: use a special waterproof but breathable lime base coat, to prevent the rainwater penetrating into the wall fabric.

- Main coat. render the building with a good quality lime render such as Sanacolor 2000.

These two layers work together seamlessly: the Rinzaffo MGN base coat being waterproof and breathable protects the walls from the driving rain. Due to its unique micro-structure it also protects the main coat from the aggression of salts. The Sanacolor 2000 acting as an evaporative layer allows the rainwater to get dispersed and released into the atmosphere quickly.

The above information is only given in good faith as a guideline as individual situations may vary due to the combined effect of several factors. Please contact us for a professional assessment of your situation for a more accurate diagnosis and advice.