Building renovation system
Over the past 50 years, research into the mechanisms of building materials damaged by moisture and various aqueous salt solutions has allowed precise definition of corrosion mechanisms and strategies to reduce or eliminate these processes. Based on this knowledge and experience, insulation and renovation systems for damp buildings have been developed.
Proper diagnosis and evaluation of the root causes of corrosion play a crucial role in selecting the best technical solution. This approach not only ensures prolonged building operation but also minimizes repair costs, enabling efficient planning of workload, labour, and material expenses.
Corrosion effects intensify over time. Performing only superficial or delayed "cosmetic" repairs results in a substantial cost increase. Elements that initially didn't require replacement may become necessary to change. Therefore, the initial stage should focus on identifying the type and extent of dampness and corrosion. Measures may include determining the level of groundwater and the direction of water runoff, conducting structural and surface moisture tests on the masonry at various levels, and assessing the salinity of masonry and plaster in the building.
The structural moisture content of masonry is high at the basement floor and decreases with increasing height of the masonry, at a certain height reaching the value corresponding to dry masonry. Such a situation indicates the occurrence of capillary rise in the masonry structure and can be used to determine the extent of the problem.
The structural moisture content of the masonry is relatively low, corresponding to dry masonry, and then increases sharply at a height below ground level around the building. This indicates the local migration of water into the masonry structure, e.g., through damaged layers of vertical insulation.
- Paint coating damage
- Plaster damage
- Brick damage
When formulating recommendations, the repair scope and method (including area reprofiling, rainwater drainage, and runoff strategies) should be chosen based on an analysis of the causes of dampness. The second step is to specify the repair scope and method for damaged building elements and identify those requiring replacement.
Then, the approach for vertical insulation and overall renovation should be determined, including the possible restoration of the horizontal membrane in the masonry structure.
The chosen solutions should specify the membrane's location and its correlation with other insulation types, whether inside or outside. All of this guides the material selection for effective renovation.
Structural dampness in masonry primarily results from rainwater, runoff, and groundwater present in the soil. Water can infiltrate the masonry structure through inadequate insulation or damaged coatings. When addressing corrosion in damp masonry, careful consideration of the chemical composition of the water is crucial.
Subsoil water, primarily sourced from rainwater, runoff, and used water, carries chemical compounds from air pollution (especially in industrial areas), leached by rain (sulphur compounds, carbon compounds, etc.), and extracted from surface soil (e.g. nitrogen compounds).
Underground parts of buildings are also subject to impact from groundwater, the level of which can fluctuate greatly depending on the seasons, precipitation, etc. Its aggressiveness is much lower compared to subsoil water. Both types of water may be additionally influenced by wastewater, altering their chemical composition and intensifying their corrosive potential on insulation coatings. In diagnostics, analysing the content of different types of salts in plaster or joints is recommended to identify sources of dampness. However, detecting dampness effects - stains, patches, salinity, fungal growth, and structural damage of masonry - is generally much easier.
Relationship between the height of dampness in the exterior and interior walls of a building due to rainwater and runoff. Direct runoff of water is directed to the exterior walls, resulting in the higher dampness level.
Relationship between the height of dampness in the exterior and interior walls of a building due to groundwater. Exterior walls have a higher capacity of moisture diffusive evaporation, which results in a lower dampness level.
Water penetrating the masonry structure is gradually transported to higher sections through the network of capillary pores in masonry elements and joints. The parameters of this capillary transport of moisture, including the height it can reach and the rate of flow, depend on various factors:
a) the type and arrangement of soil layers and topographic features;
b) the moisture uptake capacity of the wall, influenced by insulation condition, groundwater and subsoil water levels, and the filtration coefficient of adjacent soil;
c) masonry parameters such as porosity, absorbability, sorption, hygroscopicity, capillarity, and capillary diameter;
d) the chemical composition of the water transported by capillary action; and
e) the capacity for diffusive evaporation of the masonry above the dampness level, considering weather conditions and water vapor diffusivity through wall surfaces.
The dampness of masonry is also influenced by the underlying soil. Soils vary in their capillary rise capacity similarly to building materials. Consequently, a building seated above the groundwater level can be affected by moisture through capillary rise from the ground. The extent of capillary rise also depends on the type of masonry.
For brick masonry, capillary rise occurs throughout the section; in stone masonry, specifically with low-absorbent stone, it is limited to the mortar.
Most parameters are independent variables. During renovation, only the values of 'r' and 'x' can be influenced, allowing adjustments in the structure of the masonry to reduce the diameter of the capillaries and alter wetting angles.
Materials with small pore diameters resist water under hydrostatic pressure.
Materials with capillary pores (about 80 nm to 20 μm) transport moisture through capillary action.
Larger pore diameters permit water permeability under pressure, excluding capillary rise. Bricks, due to their open-pore structure, and lime-clay mortar transport moisture in the capillary structure.
The intensity of water rising in the masonry’s capillaries is determined by the following relationship:
water absorption capacity = diffusive evaporation capacity
It is assumed that the masonry can continuously draw water (from subsoil water and groundwater) and that moisture subject to capillary transport evaporates in the plinth zone. This relationship shows that any parameter change, like favourable weather conditions (high temperature, wind, partition insulation), affects moisture flow. Evaporated moisture is promptly replenished from the ground, with faster evaporation in summer on the outer wall plane and in winter on the inner plane.
In this case, capillary transport-induced structural dampness arises from the impact of subsoil water, runoff, and groundwater, while surface dampness results from moisture condensation on the surface of the masonry and its hygroscopic moisture uptake.
Relationship between the water absorption capacity of the masonry in the direct moisture exposure zone and the diffusive evaporation capacity, which determines the occurrence, intensity, seasonality, and height of capillary transport.
1 - water absorption zone
2 - moisture transport zone
3 - evaporation zone
Surface and structural dampness in the masonry.
Surface dampness
1 - condensation zone in the building, poor insulation of the building,
or accompanying local effects (i.e., thermal bridges)
2 - the area of hygroscopic moisture uptake by building materials or salt compounds accumulated on the surface of the masonry
Sources of capillary rise
3 - moisture drawn from rainwater and subsoil water
4 - moisture drawn from the groundwater table
The relationship between diffusive evaporation capacity and the water uptake capacity of the foundation shows that the height of moisture rise in two masonry walls, made of the same material but with different thickness levels, varies under similar conditions. Thinner masonry reaches a certain dampness level with an equilibrium between water intake and evaporation capacities. This level is slightly lower on the outside than on the inside (due to the diffusive evaporation capacity in the summer).
In contrast, thicker masonry exhibits a significantly higher dampness level because of its greater water uptake capacity in the foundation (larger surface area), resulting in a proportionally larger evaporation area. Cladding (ceramic, stone, etc.), paint coating (e.g. dado), or plaster coatings that limit vapor diffusion, such as cement, reduce diffusive evaporation capacity, increasing the height of structural dampness.
Limited diffusion, for example, in the plinth zone, raises the evaporation zone, elevating masonry dampness levels. This effect is also noticeable in plaster repairs in the plinth area, for example, when using traditional cement plaster.
The height of dampness in the masonry, depending on the location and the required surface area of diffusive evaporation. This relationship applies to masonry with different thicknesses and diffusion properties of external coatings, providing that water can be constantly drawn through the strip foundation.
The dampness of building partitions cannot be analysed locally. Measurements should be carried out based on the following rules:
a) identify key points of the building with discoloured plaster coating and masonry affected by moisture, salt deposits, corroded plaster coating, or joints in the masonry, etc.
b) measure the moisture content of the masonry at various heights (e.g. 0.5 m, 1 m, 1.5 m, and 2 m above the floor level) at each identified point to assess the extent of moisture capillary rise.
c) for points showing significant moisture, measure the moisture content at different levels of thickness, including the surface, near-surface zone, and mid-thickness.
With the measurements of the degree of dampness in the masonry and measurements of floor moisture, a comprehensive map of the entire building floor can be created. Such documentation can guide the precise selection of design solutions, including insulation types and the placement of secondary structural membranes in the masonry.
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