Biological growth on rendered façades
Author
Summary, in English
Biological organisms have an incredible ability to adapt to almost any
environment and the humans activities on earth have created many
new habitats for different kinds of organisms. For example can certain
organisms grow on rocks and vertical cliffs, and when humans
started building houses with mineral based façades, some organisms
found that these were new habitats to live on. Some of these expansions
of habitats to our houses are not desirable for the us humans and
are considered as “contaminations". Even if this contamination sometimes
only is an aesthetically problem, some contamination is highly
unwanted because it can be unhealthy for the inhabitants - for example
the growth of moulds - or it can degrade the building materials it
grows on -as for example wood-degrading fungi.
For an organism to grow in a certain environment, different requirements
on abiotic (physical and chemical) and biotic (biological) factors
have to be fulfilled. Suitable conditions for growth of organisms
on façades are certain ranges in temperature and a high moisture level
(RH), but also the surface structure, nutrient availability, pH, cardinal
direction etc. might be influencing. Different organisms have different
demands on these factors and it is a complex interaction of these
different factors that decides if an organism can grow in a certain environment.
The last decades many houses in Sweden have been built with constructions
of thin rendering on thermal insulation, a so called ETICS
construction (External Thermal Insulation Construction System). This
construction consist most often of a framework of wooden studs with
thermal insulation in between, and gypsum boards or cement based
boards on both sides. On the outside a thermal insulation layer is applied
and the render is then applied directly on the outside of this thermal
insulation layer. This is a an efficient and compact construction
which is easy to produce. However, many of these constructions have
experienced discolourations from growth of algae and moulds on the
façades already a few years after construction. It has not always been
possible to explain this discolouration. Sometimes one part of the
façade had discolorations and another part of the same façade did not.
One possible explanation for the fast growth of organisms is the
external rendering layer (on thermal insulation that has a low heat capacity
and during night the long-wave radiation from the material to
the sky can contribute to a lower temperature on the surface than the
temperature in the air -on clear nights, when the heat loses through
long-wave radiation is high. The lowered surface temperature then
causes the RH on the surface to increase, sometimes giving condensation
-which increases the risk of biological growth.
In this project we have compared temperatures and RH on surfaces
on façade elements in a test house with constructions with low heat
capacity in the outermost layer (light walls) and constructions with
a high heat capacity in the outermost layer (heavy walls). Simulations
of the growth risk showed that thin rendering on thermal insulation
has a higher growth risk that traditionally render on bricks especially
on the north side. On the south side the most important factor
was the surface colour. In our study we compared a red and a white
surface, and since dark surface colours absorbs more short-wave radiation
from the sun they have a higher temperature during daytime
and therefore a lower RH on the surface.
Another factor which might influence the growth risk is the surface
structure of the render. We fabricated specimens with different
renders with different surface structures and with a thin and thick
rendering layer (3mm and 20mm, respectively) and exposed the specimens
outdoors for four years. This study showed that algaes preferred
a very rough surface structure while moulds (Cladosporium sp.)
also grew on more smooth surfaces. In addition we found that algaes
most often grew on the north side whereas moulds rather grew on the
south side (Cladosporium has a dark pigment in the cells which protects
against radiation from the sun). Furthermore we found a connection
between the amount of growth and the season of the year. The
biological growth was more clearly seen during spring and especially
autumn and occasionally seemed to disappear during summer and
winter. It was found that thin (3-4mm) and thick (20mm) render on
thermal insulation had the same amount of discolouration.
The activity of photosynthetic organisms -algae, lichens and mosseson
façades can be measured with Imaging-PAM. This is an instrument
that measures the chlorophyll fluorescence and gives an indirect measure
of photosynthetic activity. A pilot study was performed where
we -during three days in the autumn- studied algae and mosses growing
on render. Algae dries out easily and is dependent of moisture
from the surroundings and showed the highest activity during mornings
before the sun dried them out. The mosses were active a greater
part of the day; they are able to some extent store water in their leaves
and is not as dependent on moisture from the surroundings as algae.
Another method for measuring activity of biological organisms is
isothermal calorimetry which measures the produced heat from an
organism’s metabolism. In this project we tested a new type of calorimeter
that measures activity at four different temperatures at the same
time. With measurements of a moss (Tortula ruralis) we found that it
was possible to get an activity measure at four different temperatures
at the same time, thus being able to get an understanding of how the
temperature influences the activity. This method should therefore be
very useful in future studies of activity of different types of biological
organisms.
The aim of this project was to investigate constructions of thin rendering
on thermal insulation and the biological organisms growing on
the façades of these constructions. With a multidisciplinary approach
we have increased the knowledge of the façade as a habitat, the organisms
growing, and their interactions with different biotic and abiotic
factors.
environment and the humans activities on earth have created many
new habitats for different kinds of organisms. For example can certain
organisms grow on rocks and vertical cliffs, and when humans
started building houses with mineral based façades, some organisms
found that these were new habitats to live on. Some of these expansions
of habitats to our houses are not desirable for the us humans and
are considered as “contaminations". Even if this contamination sometimes
only is an aesthetically problem, some contamination is highly
unwanted because it can be unhealthy for the inhabitants - for example
the growth of moulds - or it can degrade the building materials it
grows on -as for example wood-degrading fungi.
For an organism to grow in a certain environment, different requirements
on abiotic (physical and chemical) and biotic (biological) factors
have to be fulfilled. Suitable conditions for growth of organisms
on façades are certain ranges in temperature and a high moisture level
(RH), but also the surface structure, nutrient availability, pH, cardinal
direction etc. might be influencing. Different organisms have different
demands on these factors and it is a complex interaction of these
different factors that decides if an organism can grow in a certain environment.
The last decades many houses in Sweden have been built with constructions
of thin rendering on thermal insulation, a so called ETICS
construction (External Thermal Insulation Construction System). This
construction consist most often of a framework of wooden studs with
thermal insulation in between, and gypsum boards or cement based
boards on both sides. On the outside a thermal insulation layer is applied
and the render is then applied directly on the outside of this thermal
insulation layer. This is a an efficient and compact construction
which is easy to produce. However, many of these constructions have
experienced discolourations from growth of algae and moulds on the
façades already a few years after construction. It has not always been
possible to explain this discolouration. Sometimes one part of the
façade had discolorations and another part of the same façade did not.
One possible explanation for the fast growth of organisms is the
external rendering layer (on thermal insulation that has a low heat capacity
and during night the long-wave radiation from the material to
the sky can contribute to a lower temperature on the surface than the
temperature in the air -on clear nights, when the heat loses through
long-wave radiation is high. The lowered surface temperature then
causes the RH on the surface to increase, sometimes giving condensation
-which increases the risk of biological growth.
In this project we have compared temperatures and RH on surfaces
on façade elements in a test house with constructions with low heat
capacity in the outermost layer (light walls) and constructions with
a high heat capacity in the outermost layer (heavy walls). Simulations
of the growth risk showed that thin rendering on thermal insulation
has a higher growth risk that traditionally render on bricks especially
on the north side. On the south side the most important factor
was the surface colour. In our study we compared a red and a white
surface, and since dark surface colours absorbs more short-wave radiation
from the sun they have a higher temperature during daytime
and therefore a lower RH on the surface.
Another factor which might influence the growth risk is the surface
structure of the render. We fabricated specimens with different
renders with different surface structures and with a thin and thick
rendering layer (3mm and 20mm, respectively) and exposed the specimens
outdoors for four years. This study showed that algaes preferred
a very rough surface structure while moulds (Cladosporium sp.)
also grew on more smooth surfaces. In addition we found that algaes
most often grew on the north side whereas moulds rather grew on the
south side (Cladosporium has a dark pigment in the cells which protects
against radiation from the sun). Furthermore we found a connection
between the amount of growth and the season of the year. The
biological growth was more clearly seen during spring and especially
autumn and occasionally seemed to disappear during summer and
winter. It was found that thin (3-4mm) and thick (20mm) render on
thermal insulation had the same amount of discolouration.
The activity of photosynthetic organisms -algae, lichens and mosseson
façades can be measured with Imaging-PAM. This is an instrument
that measures the chlorophyll fluorescence and gives an indirect measure
of photosynthetic activity. A pilot study was performed where
we -during three days in the autumn- studied algae and mosses growing
on render. Algae dries out easily and is dependent of moisture
from the surroundings and showed the highest activity during mornings
before the sun dried them out. The mosses were active a greater
part of the day; they are able to some extent store water in their leaves
and is not as dependent on moisture from the surroundings as algae.
Another method for measuring activity of biological organisms is
isothermal calorimetry which measures the produced heat from an
organism’s metabolism. In this project we tested a new type of calorimeter
that measures activity at four different temperatures at the same
time. With measurements of a moss (Tortula ruralis) we found that it
was possible to get an activity measure at four different temperatures
at the same time, thus being able to get an understanding of how the
temperature influences the activity. This method should therefore be
very useful in future studies of activity of different types of biological
organisms.
The aim of this project was to investigate constructions of thin rendering
on thermal insulation and the biological organisms growing on
the façades of these constructions. With a multidisciplinary approach
we have increased the knowledge of the façade as a habitat, the organisms
growing, and their interactions with different biotic and abiotic
factors.
Department/s
Publishing year
2011
Language
English
Publication/Series
Report TVBM
Volume
1029
Full text
- Available as PDF - 12 MB
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Document type
Dissertation
Publisher
Lund University, Division of Building Materials
Topic
- Materials Engineering
Keywords
- temperature
- render
- radiation
- photosynthesis
- moulds
- mosses
- mortar
- moisture
- lichens
- Imaging-PAM
- humidity
- heat capacity
- heat
- ETICS
- algae
- biological growth
- calorimetry
- desiccation tolerance
Status
Published
Supervisor
- Lars Wadsö
- Kenneth Sandin
ISBN/ISSN/Other
- ISSN: 0348-7911
- ISBN: 978-91-7473-127-9
- TVBM-1029
Defence date
16 June 2011
Defence time
13:15
Defence place
Lecture hall V:B, V-building, John Ericssons väg 1, Lund University Faculty of Engineering
Opponent
- Ulf Karsten (Prof.Dr.)