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High Water Table Solutions

Conservation-Friendly Approach
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What Is a High Water Table?

High water table occurs when the level of groundwater rises to or near the surface, saturating the upper soil layers. The water table represents the upper surface of the soil, where the pores and fractures of the ground are filled with groundwater. This occurs due to excessive water accumulation beneath the ground, often from heavy rainfall or water seeping down from higher elevations into the surrounding soil. 

High Water Table Impact on Old Buildings

Old buildings, especially those constructed before the 1870s, often lack a damp proof course (DPC). A DPC prevents dampness from rising up the walls. When there’s no DPC, the bottom of the wall is directly connected to the water table, which acts as an unlimited water supply.

Here’s how high water table affects old buildings:

  1. Rising damp: the height of the water table plays a crucial role in the development and intensity of rising damp. Without a DPC, moisture from the water table can rise through the walls. Evaporation creates a pressure difference, drawing up more moisture and salts from the ground. This ongoing water intake leads to rising damp within the walls.

  2. Masonry damage: high water tables mobilize soluble salts within the masonry which are carried up by rising damp into the wall fabric. These salts harm the building fabric, leading to deterioration. Additionally, a damp masonry can be subject to more frost damage, affecting the long-term integrity of walls, plastering and other structures.

  3. Timber decay and corrosion: excessive moisture promotes timber decay and corrodes metal components within the building. Wooden beams, joists, and other structural elements become vulnerable to rot when constantly exposed to damp conditions.
  4. Structural problems: the constant presence of moisture weakens building materials, affecting their integrity over time. Foundations, walls, and floors may suffer structural damage due to the saturated soil. Settlement issues, uneven settling, and compromised stability can occur on buildings situated on a high water table. 

  5. Reduced thermal efficiency: dampness in the wall fabric reduces the thermal efficiency of the building. Cold, damp walls are less effective at retaining heat, leading to radiating cold, discomfort for the occupants, unhealthy environment and potentially higher energy costs.

  6. Health risks: mould growth due to damp conditions can pose health risks to occupants, especially those with respiratory issues.

In summary, a high water table can create significant challenges for old and listed buildings, impacting their condition, stability, longevity and habitability.

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High water table in an area

Solving High Water Table Problems in a Sympatetic Way

All the above problems can be addressed in a conservation-friendly sympathetic way, using building-friendly technologies and breathable, traditional materials. For starters, good drainage is essential to channel away as much liquid moisture away from the property as possible. However, most of the times a combination of various solutions are needed in order to tackle several problems caused by high water table.

  1. Rising damp: a non-invasive damp proof course alternative to invasive chemical DPCs is the magnetic DPC. Instead of blocking the ascent of water by physical or chemical means, a magnetic DPC takes a completely different approach: it increases the breathability of the wall fabric by decreasing the adhesion forces between the water molecules and capillaries, allowing moisture to evaporate much easier. 

  2. Masonry damages: hydrated lime (air-lime) plasters do not perform very well in the presence of high humidity and salts. Although very breathable, sustained humidity and salts decrease the longevity of lime plastering significantly, leading to frequent replastering and increased maintenance costs. A conservation-friendly much longer-lasting alternative is replastering the walls with the Roman lime plastering system.

  3. Structural problems: the sympathetic structural consolidation of old buildings can be challenging, as a result most structural reinforcement works are done with cement or other modern materials. Breathable lime alternatives exist. The Romans have created several highly breathable lime mixes which are excellent lime structural consolidation materials. More information on lime structural consolidation here. 
  4. Reduced thermal efficiency: to improve the thermal efficiency of old buildings in a building-friendly way, we have high-performance lime thermal insulation plasters, with or without aerogel. Low U-values of 0.5 or lower can be achieved with only a few centimetres of breathable lime thermal insulation. More information on the lime thermal insulation page.

  5. Health risks: lime is a very healthy material that is naturally anti-bacterial. Some lime plasters such as Cocciopesto (a traditional Roman mix of lime and brick dust) or lime-hemp or lime-clay plasters are excellent humidity regulator creating a healthy, low-humidity environment.    

Recommended Products

Here are the typical recommended materials / products for this solution. Other plaster variations are possible as we have different types of main coats (normal or thermal) and finishes (smoother, grainier, coloured etc.) depending on your needs or application. Please get in touch to discuss additional options.

Completed Projects

Here are some of our projects using this solution:

More Information

Here are some related pages with additional technical information, giving you a more in-depth understanding of this topic.

Photo Galleries

Here are some photos demonstrating this solution. Click on any image to open the photo gallery.

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Flood Proofing a Flooded Extension

This old cottage has been extended a few years ago, receiving a new extension. During flooding the waterproofing of the newbuilt extension did not hold, resulting in the flooding of the building. Using the Roman lime materials the waterproofing has been reinforced, preventing future flooding. 

Videos

Here are some videos related to this solution. Please unmute the videos when playing them.

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Any Questions? Need Technical Advice?

If you have any questions about a project, a problem, a solution, or any of our plasters - please get in touch.

We understand that each project is unique. Using the contact form below feel free to ask us any questions. Give us as much detail as you can about your project so we can get back to you with more relevant answers. 

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Plaster Application

Here are some key application points about the application of each plaster, as well as links to the full application guides. Additional documents can be found on the individual plaster pages. 

Rinzaffo

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Base, Waterproofing

  • Clean the masonry: the plaster must be applied on a cleaned and uniformly wet substrate. All crumbling and loose parts must be removed by brushing so the masonry is free of dust, salts and oils. If possible, also wash the walls with a pressure washer; this will clean and wet the walls in one go. Close larger holes with lime mortar and pieces of bricks.
  • Must be the first coat: the Rinzaffo MGN plaster must be the first coat on any wall. It should not be applied on top of other parge coats or plasters because when those fail the performance of the Roman base coat will also likely to be affected.
  • No salt-inhibitors nor PVA bonding agents should be used before the application of the plaster. The plaster bonds well on its own.
  • Masonry paints should be removed (which occasionally can be challenging) so the plaster can firmly adhere to the underlying stones or bricks. Remove at least 50% of the existing paint – the more is removed, the better.
  • Mixing: mix the material with clean tap water only without adding anything else (no other material or additive), until a homogenous, creamy-consistency mix is obtained. 
  • Wet the wall fabric abundantly before applying the plaster, as well as in-between each subsequent coat. Lime plasters need moisture as they set slowly in a damp environment. If the walls are already damp, there is no need to wait to become drier, you can proceed with the application of this plaster. 
  • Level uneven surface first: very uneven walls (e.g. stone walls or crumbling old brick walls) are recommended to be patched up and levelled first before the application of a continuous coat, to ensure the consistency and required thickness of the base coat.
  • Application: apply the plaster in 10 mm coats.
  • IMPORTANT: Respect the thickness: do not under-spec the material. Apply min 10 mm (1 coat) for above ground level walls. Apply min 20 mm thickness (in 2 coats) for underground or extremely damp or salty walls. If more than one coat is applied, embedding a 10 x 10 mm fibreglass mesh is recommended between the coats – a standard practice in the industry.
  • IMPORTANT: Close all pores, no matter how small. Treat and apply the plaster as a tanking-grade material. Attention should be paid to compact it on the wall closing off all pores, no matter how small, leaving no gaps or holes where salts or liquid water could come through. Once an area has been completed, recheck that here are no missed holes, not even small ones.

    The plaster application video below explains the concept in detail.

  • Light key: give the plaster a light key using a wet brush. Do not cut into the material with the edge of a trowel.
  • IMPORTANT: Dark patches. Allow the plaster to dry for 48 hours. Ideally, the whole surface should dry out uniformly to light brown, however you might notice some dark or damp-looking areas exhibiting surface condensation. Dark areas indicate insufficient thickness of the plaster in raport to the amount of moisture behind it. This occurs in areas where the underlying wall fabric is very damp, the intense evaporation causing surface condensation.
    The fix is easy: apply extra material over such dark areas increasing the thickness of the plaster, closing off all pores. The increased plaster volume dilutes the vapour flow allowing the surface to dry.
  • Additional coats can be applied in further 10 mm increments. Use an embedded fibreglass mesh for extra reinforcement over the recommended thickness.
  • Application conditions: ambient and wall temperatures must be between +5 to +30°C during application. Surfaces should be protected from rain and humidity until they have completely dried (approx. 3 – 10 days depending on weather conditions).
  • IMPORTANT: Please watch the plaster application video below before applying the material. Unmute the video if it plays without sound.

Cocciopesto Deumidificante

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Main

  • Clean the masonry: the plaster must be applied on a cleaned and uniformly wet substrate. All crumbling and loose parts must be removed by brushing so the masonry is free of dust, salts and oils. If possible, also wash the walls with a pressure washer; this will clean and wet the walls in one go. Close larger holes with lime mortar and pieces of bricks.
  • Mixing: mix the material with clean tap water only without adding anything else (no other material or additive), until a homogenous, creamy-consistency mix is obtained. 
  • Application: apply the plaster in 10 mm coats.
  • Additional coats can be applied in further 10 mm increments. Use an embedded fibreglass mesh for extra reinforcement over the recommended thickness.
  • Finish options: main lime coats can be optionally left without finishing. To have a finished surface any MGN finish can be applied: Calcina Fine MGN (white lime finish), Intonachino Arenino MGN (coloured lime finish) or Marmorino MGN (Venetian Marmorino finish).
  • Application conditions: ambient and wall temperatures must be between +5 to +30°C during application. Surfaces should be protected from rain and humidity until they have completely dried (approx. 3 – 10 days depending on weather conditions).

Calcina Fine

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Finishing

  • Mixing: mix the material with clean tap water only without adding anything else (no other material or additive), until a homogenous, creamy-consistency mix is obtained. 
  • Recommended thickness of the finish: 3-4 mm. For best results, the finish should be applied in two “half-coats” of 2 mm each, with a fine 3-4 mm fibreglass mesh embedded in-between. The mesh makes the finish more flexible, minimizing the appearance of fine cracks.
  • Various textured finishes can be achieved, depending on the finishing technique used:
    • Coarse finish: by finishing the surface with a sponge or wooden trowel.
    • Smooth finish: by using a stainless steel trowel, compressing and smoothing the semi-dry surface, the sand granules are pushed into the material, resulting in a smooth finish.
    • Washed finish: by finishing the surface with a sponge trowel. After the surface has hardened, the surface is washed with water and blotted with a sponge to bring out the aggregate, its specific texture and colour.
  • Painting: as this is a breathable lime plaster, wall surfaces should be painted with a breathable mineral paint. Wallpapers and modern emulsion petrol-based paints, with no or limited breathability, should be avoided.
  • Application conditions: ambient and wall temperatures must be between +5 to +30°C during application. Surfaces should be protected from rain and humidity until they have completely dried (approx. 3 – 10 days depending on weather conditions).