Rainwater bouncing back from the ground or the plinth is another source of moisture that affects all buildings, especially older buildings built of more porous, water-absorbent materials.
This can be recognized by a green discoloration occurring towards at the base of the building. The green discoloration is green moss, thriving in wet areas, fed by the abundance of rainwater splashing back onto the wall.
Rainwater splashback is prevalent around walls with concrete paths and driveways, which provide a flat surface for water to bounce back from.
Here are some actions you can do to solve / minimize the water splashback problem:
- Re-leveling the surface: see whether this is an option, to prevent the bounce-back of water, e,g, planting grass or a flower beds to catch the water. Often, this isn't a viable option.
- Check for gutter leaks: localized splashback can be a sign of leaky gutters, here the water hits the ground with force, splashing back onto the surrounding walls.
- Pointing quality: if the pointing is in good order with no cracks, this can minimize the amount of water soaked up by the building fabric.
- Waterproofing the base of the walls: you can waterproof old walls by rendering the base of the walls to prevent the seeping of water into the building fabric.
Waterproofing the Base of the Walls
The base of many old buildings have already been waterproofed by re-rendering it up to about half a meter high, to either stop the splashback of water, or - more commonly - to cover up the crumbling of the wall fabric caused by rising damp and the crystallizing salts.
Because normal lime plasters can't withstand the effect of water and salts for very long, the vast majority of such renovations have been done with a cement render - a hard, non-breathable material, that itself creates dampness problems through several mechanism, because cement based renders are:
- Non-breathable: cement renders don’t let moisture freely evaporate from the underlying (damp) wall fabric, resulting in an excessive build-up of moisture, leading to long-term dampness problems.
- Too hard: they stress the underlying fabric, resulting in detachment of the render which can damage the softer building fabric.
- Too brittle: being inflexible, ongoing vibrations and building movement crack cement renders. Once their waterproofing ability gets compromised they let rainwater in, becoming part of the dampness problem.
- Poor heat insulator: being a non-porous, dense material, cement is a poor thermal insulator, resulting in condensation and mould problems.
The building-friendly solution to make the base of old walls withstand the effect of water splashback is by using a rendering system that is both waterproof and breathable.
The technology of such a render that fulfills both of these criteria originates from ancient Rome. Being outstanding architects and builders, the Romans have discovered that by adding volcanic soils and other minerals to lime, they can significantly alter its properties, especially its mechanical strength and water resistance, while retaining its breathability.
These lime mortars have stood the test of time, being extensively used by the Romans in very demanding environments including sewers, ports, spas and aqueducts. They have also been widely used in Venice, well suited to the humid and aggressive environment of the Venetian lagoon.
They are different from today’s NHL mortars, whose much higher firing temperatures (around 1200 °C) impair their breathability.
For a long-lasting, building-friendly breathable rendering solution, the following rendering schedule is recommended:
1. RINZAFFO MGN lime base coat [10 mm thickness]
Rinzaffo MGN is a microporous breathable lime waterproof and salt-resistant base coat. Its main role is to stop rainwater penetrating into the underlying wall fabric, keeping the underlying wall fabric dry.
Rinzaffo’s internal pore structural is formulated in a way to stop (larger) liquid water molecules, while letting (smaller) water vapours molecules through, facilitating evaporation.
The color of the base coat is dark, based on its constituent materials. This is not a problem as the main plaster coat, described below, will completely cover it, giving the walls a normal, traditional appearance.
2. SANACOLOR 2000 MGN main coat [20 mm thickness]
Sanacolor 2000 MGN is a traditional macroporous lime plaster that promotes the continuous evaporation of humidity present in the masonry, keeping surfaces dry and aesthetically pleasing.
It comes in a range of 24 colors. In addition to white, there are light pastel and vivid Mediterranean color options, mass colored with natural earth pigments that are UV resistant and do not fade.
The above solution can be applied in any building, old or now, including any listed building as it is building-friendly, based on traditional materials.