The use of lime based materials and period properties.
Period Houses are Made with Different Materials

Not all buildings are built the same way. You’ve seen cottages built in a collection of various sized local stones right? And you can tell the difference between period bricks and modern bricks? These materials are all slightly different. A bit like card, paper and kitchen roll, so to speak. Same same, but different.

Some bricks are softer than others and likewise, some mortars are softer than others too. Yes, it’s all mortar and it all holds your house together, but the exact ingredients and ratios might be different.

In period buildings, traditionally when it was built, the mortar was made from lime. As was the plaster, any exterior renders and even the paint. All lime-based products! And what makes lime special? It’s porous, making it breathable.

More about Lime based products: What Is Lime Mortar?| Our Knowledge Base | Lime Green (lime-green.co.uk)

Breathability in Period Buildings

When victorian houses were built, they were designed for that era. They had chimneys to house coal fires to keep the house warm, cool cellars for storing food and even the single glazed draughty windows provided the ventilation a house needed. What seems like poor choices in a world of modern technology, was probably once upon a time, clever design ideas.

And that breathable lime I was talking about? It allowed moisture IN and OUT of the building structure. Whether that’s in liquid form, or as gas, it meant there was a balance of intake and evaporation. A natural equilibrium and the ability for buildings to “breathe”.

To put this into context for you, it would mean any internal moisture from drying clothes or cooking, for example, would penetrate the lime plaster and then simply evaporate back out. External moisture too, such as from rain would do the same. It would enter the lime mortar (or render) and then evaporate right back out.

Those draughty windows and warm coal fireplaces acted in favour of this natural drying cycle and because of these breathable materials, water was never trapped within the building. Which meant, these old buildings did not typically have damp problems.

Any moisture within the building had an escape route.

The Problem with Modern Cement, Gypsum Plaster and Damp Proofing Paints on Period Buildings

Modern houses are built very differently from period buildings. They’re built with much harder bricks, they’re designed to be waterproof, highly insulated and with zero draughts. Basically, the exact opposite!

The materials they’re built with, like cement, prevent moisture from getting in or out and are NON-breathable. In theory, this may sound great, BUT when combined with period materials or within a period home, it simply doesn’t work and instead, traps moisture within the building.

Some bricks are softer than others. If you replace lime mortar with a cement mortar, not only will you be trapping that moisture within the building itself (as it no longer has an escape route), but it will also cause those softer bricks to deteriorate. You’ll often see this where the face of brick has crumbled away (known as spalling).

Similarly, if you cover lime mortared bricks with gypsum plaster or certain modern paints, (like weatherproof masonry paint which is non-breathable), you’re disrupting that same natural balance and again, trapping moisture.

These materials simply weren’t designed for old buildings and don’t work well when used with traditional materials.

What Does Trapped Moisture cause
Damp Patches

Where moisture cannot escape, you’ll find damp patches. This might be from condensation within the home or water trapped on the outside of the home. Where it would once upon a time have simply evaporated away, it’s now stuck within the very fabric of the building.

Peeling Paints and cement rendered wall surfaces
Cement rendered walls to Victorian property
Cement rendered walls to Victorian property

 

Many modern paints and cement based render are also non-breathable. Ever seen a Victorian house covered externally in peeling paint? When moisture wants to get out, it will find any possible way to get out. In time, the paint will flake and peel away from the surface. This is a particular problem with masonry paint. Cement based rendered  wall surfaces also trap moisture preventing the walls  to breath.

Spalling Brickwork

One of the worse effects of trapped moisture is spalling bricks. As I mentioned previously, this is when a brick is deteriorating. Usually, the face of the brick will burst off and eventually, the whole brick will crumble.

This often happens specifically when moisture within the brick freezes (and expands as doing so), therefore breaks the brick. Over time, spalling bricks allow more moisture to penetrate the brick, creating more problems. Eventually, these bricks need to be replaced and many over a large span can even become a structural issue.

Many modern paints are also non-breathable. Ever seen a Victorian house covered externally in peeling paint? When moisture wants to get out, it will find any possible way to get out. In time, the paint will flake and peel away from the surface. This is a particular problem with masonry paint.

How about Damp-Proofing Treatments?

There is a vast amount of different damp proofing treatments available and each work in different ways, but essentially, they act to prevent moisture from entering a building. However, if you’ve read the above, you’ll know this has a similar effect as cement and doesn’t FIX the issue, it simply traps water, or masks over it until the moisture can find a new route to escape.

Many believe the whole damp proofing industry is a con and I’ve read some debate that there is no such industry in certain countries across the world. Rising damp, in particular, in a greatly debated topic.

I could write a book on the topic, but there is evidence to suggest that many damp proofing treatments simply don’t work in period homes and that they weren’t required in the first place!

There are many reasons for damp, including the external ground being too high, leaking gutters or porous brickwork things like cement being used in period homes and I could rant on. These issues are often overlooked when damp-proofing is advised.

Improve Ventilation and Air Circulation

Despite lots of character and plenty of charm, one of the major issues with refurbished period homes is poor ventilation. This ultimately leads to condensation and mould growth; an unsightly and unhealthy prospect for homeowners.

Opening up fire places and keeping the original sash windows will help with air flow throughout the house and installing a good mechanical ventilation system will all help with ventilation.

Condensation

Condensation is caused lack of ventilation and the cause of internal dampness.

Causes of condensation are as follows:

• Water vapour generated by normal activities such as cooking, bathing, breathing and clothes- drying will cause raised humidity if there is a failure to ventilate the property adequately on a constant and daily basis.

• Cool air holds less water vapour than warm air. Repeated cycles of warming and cooling will result in the condensation of water vapour on the colder wall and window surfaces.

• Inadequate levels of heating combined with a lack of insulation within the fabric of the building. Condensation will be avoided if the fabric of the building is maintained at a reasonable and stable temperature. Heating should be constant but low-level avoiding significant fluctuations. This will be more easily achieved through the use of a central heating programmer and room thermostat.

Below are listed reasonable and practicable solutions which are both ‘building-related’ and ‘lifestyle- related’. Addressing all together will significantly reduce the moisture, condensation and mould growth within the property.

Mould growth which appears must be removed immediately with a proprietary cleaning product. Mould is harmful to health. More about condensation:your-guide-to-condensation-in-your-home.pdf (nhbc.co.uk)

The Drawbacks of Lime Plaster

Despite lime plaster being better suited to building practices of the Victorian period it has two major draw backs; the finish & the price. Even with the more modern derivatives of traditional lime you will not achieve the finish of today’s renovating plasters. It has a rougher texture to it that is visible from distance. See the side-by-side comparison image later in this post to get a full feel for this.

The lime plaster cost may not fit your budget. You should expect to pay up to three times the amount for a lime plaster job as you would for Gypsum. The reasons for this are both the cost of materials and the length of time required to apply it. Lime plaster has to be applied in different layers allowing sufficient drying time between them. You will find that the plaster needs to return on multiple days to complete a single wall.

More on Victorian properties :  Victorian Society

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