Building moisture

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When building moisture is defined as the introduced by the building process in a structure free (that moisture does not chemically bound moisture or water of crystallization ) in liquid form or vapor form. These include adsorption water attached to phase interfaces, adhesion water adhering to the surface of polar macromolecules, capillary water in capillaries, cracks and pores, and dripping water that has passed through at imperfections.

causes

Moisture in the building is mainly caused by the inevitably wet processing of building materials such as concrete, plaster , mortar , screed and paint. However, the building materials can also contain too much moisture right from the start due to insufficient storage or transport. During or after the construction phase, if the shell is poorly protected , moisture in the form of rain or snow can penetrate the structure. In a newly completed building there is around 90 liters of water per square meter of living space.

In contrast to building moisture is the later resulting from the use of the building residential humidity . This is caused by indoor plants and aquariums, but also by water vapor, which is created, for example, when cooking, washing up, washing, showering or drying.

Types of moisture ingress

  • Moist building materials: Moisture is almost always used in the production of building materials in the form of water and is normal up to a certain point. Every building material must have a minimum amount of moisture in order not to disintegrate. With too little moisture it crumbles, with too much moisture it dissolves. This moisture is referred to as the equilibrium moisture level .
  • Diffusion : Diffusion occurs due to pressure differences or concentration gradients. If there is a large difference in the gas concentration between inside and outside, the gas exchange, or here moisture exchange or water vapor transport, takes place through the components. Temperature, air pressure and relative humidity influence the speed of diffusion and thus the amount of diffusing vapor. Diffusion is the only ingress of moisture that is unavoidable. It is therefore predictable, but can behinderedwith the help of a vapor barrier .
  • Flank diffusion: With flank diffusion, moisture penetrates into the insulation of the insulated component via a non-insulated adjacent component such as garages, adjacent walls or canopies.
  • Convection : Leaks in the component can cause air currents, so-called convection. If warm indoor air enters an external component as a result of convection, the cooling of the air in the cold component can result in condensation.
  • The different types of moisture ingress

  • Moist building materials : Moisture from building materials.

  • Diffusion : Moisture diffuses into the building material.

  • Flank diffusion : Moisture diffuses through the uninsulated component.

  • Convection : Moisture enters through a faulty point.

Determination of the moisture content

Preparing a screed sample for the CM process.

The humidity of building materials can now be determined in several ways. A distinction is made between destructive (also direct) and non-destructive (also indirect) methods. With the destructive method, samples have to be taken to a certain extent from a certain depth, with the non-destructive sensors being placed or inserted with minimal damage.

Destructive (direct) methods

  • Calcium carbide method : With the calcium carbide method (also CM measurement ) a sample is taken, crushed, weighed and filled with a few steel balls and a glass container with calcium carbide in a pressure vessel and this is closed with a cap with a manometer. The glass container is destroyed by shaking the vessel. The calcium carbide reacts with the water and forms acetylene gas, the pressure of which can be read on the manometer. This pressure is directly related to the water available for the reaction.
  • Gravimetric method : For the gravimetric method (also called Darr method ), a sample is taken from the masonry at a depth of two to four centimeters and its weight is measured. This sample is then placed in a drying cabinet and, depending on the type of material, dried at an approved temperature until no weight change can be determined. The weight of the dried sample is weighed again. The moisture content is determined from the difference between the two values.

Non-destructive (indirect) methods

Commercially available devices for conductivity measurement (left) and stray field method (right)
  • Equilibrium moisture method: In contrast to the following methods, in equilibrium moisture measurement (also equilibrium moisture method ), the moisture is not measured directly on the material, but indirectly via the air humidity. This measures the moisture that is set upon contact with the component.
  • Infrared absorption / reflection: With this method, the influence on the reflection of the infrared ray is recorded by the absorption of the water it contains.
  • Conductivity method : This method determines the conductivity of a material based on its water content. To do this, measuring electrodes are pierced into the building material.
  • Stray field method: In this method, an electrode with a coil is placed on the material. An alternating low voltage is then applied, which generates an electric field. Here the dielectric conductivity of water is used and determined with the help of the field.
  • Microwave method : This method is similar to the Steufeld method. However, other frequencies are used. The difference between transmitted and received waves is also measured here and the dielectric conductivity of water is used and determined with the help of microwaves.
  • Time domain reflectometry : In this method, sensors are inserted into the material in the form of rods. The sensors generate electromagnetic waves. The propagation speed and thus the moisture content of the material can be determined by means of the reflections of the electromagnetic waves.
  • Neutron probe : The neutron probe (also Troxler probe ) sends out neutrons, which areslowed downby hydrogen atoms . The humidity can be determined by the degree of braking.

Consequences of moisture

Mold formation from moisture.

Excessive humidity can cause numerous structural damage, which can be dangerous for the building, but also for the health of the residents.

The problem with damp components is the resulting risk of mold formation and increased bacterial load. This can cause allergies , infectious diseases and poisoning. This can be counteracted or at least reduced by drying quickly. Cellulose-based building materials such as wallpaper and drywall or carpets are ideal breeding grounds if the moisture content is appropriate.

In general, structural damage and mold occur when the moisture load is higher than the drying capacity of the building structure.

Moisture can have a devastating effect on the stability and structural design of the building, as it chemically and physically decomposes mineral and organic building materials such as masonry or wooden beams over time. In addition, the metallic reinforcement can be damaged or completely destroyed. Even in winter, the moisture can lead to frost damage in the form of damaged pipes or plaster. Heavily moistened masonry usually leads to salt efflorescence which makes plaster and mortar brittle.

A building fungus like the real dry rot can also settle due to the moisture . This fungus can destroy wooden structures and masonry.

Reduction of humidity

Even during the construction phase, the shell should be adequately protected against moisture such as rain, snow and groundwater in good time. Above all, the raw concrete ceiling, unplastered walls and wall crowns should be covered with foil.

Drywall as a low-moisture alternative.

After the building materials have been processed wet, they should also dry sufficiently before further processing. Otherwise it can happen that the existing moisture is trapped. It must be ensured that when the damp building materials are dried, the moisture is released into the room air. Refurbished and new buildings must therefore be heated dry. Usually the moisture has largely dried out of the building fabric after about two heating periods. The so-called “dry living” means that much more heating energy is used in the first two winters than in the following comparable years. During and after the construction period, construction dryers can also be used to reduce moisture, which work by means of condensation drying .

In winter, however, premature heating of uninsulated, cold components in warm and humid room air can also ensure that they absorb moisture. This happens when the temperature of the warm, humid room air falls below its dew point .

The choice of construction, for example with prefabricated components or drywall, can reduce or avoid moisture. Low-moisture building materials such as dry screed, wood or bitumen can also be used.

See also

Individual evidence

  1. ↑ a b Klaus W. Liersch, Norms Langner: Building Physics Compact: Heat - Moisture - Sound . Ed .: Bauwerk. 4th edition. 2010, ISBN 978-3-89932-285-9 , Moisture Protection - Overview, p. 185 .
  2. ↑ a b Architecture Lexicon: Building moisture. Retrieved October 10, 2013 .
  3. ↑ Consumer Association Federal Association (Ed.): Moisture and mold . 5th edition. New building moisture, S. 5 ( verbrauchzentrale-energieberatung.de [PDF; accessed on October 10, 2013]). PDF ( Memento of the original from February 23, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / verbüberszentrale-energieberatung.de
  4. ↑ Patrick Denzel: Moisture in building materials. DNS-Denzel Feuchte-Messtechnik, accessed on October 17, 2013 .
  5. ↑ Peter Rauch: Moisture in masonry. Ingenieurbüro Peter Rauch, October 2005, accessed on October 6, 2013 .
  6. ↑ Gerd Hauser: Building Physics Basics Moisture Teaching - Lecture Notes Building Physics I and II. (PDF) University of Kassel, accessed on February 11, 2014 .
  7. ↑ Ralf Plag: Flank diffusion - moisture despite vapor barrier. u-wert.net, March 13, 2011, accessed October 17, 2013 .
  8. ^ Institute for Building Physics, Stuttgart: Convection - Sustainable Building. baunetzwissen.de, accessed on November 7, 2013 .
  9. ↑ Patrick zur Hörst: Darr method (moisture measurement). (No longer available online.) Drytest GmbH, December 8, 2011, archived from the original on February 22, 2014 ; accessed on February 11, 2014 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot / www.drytest.de
  10. ↑ a b c Karl Oelkers: Practical Guide to Building Moisture. (PDF) Testo AG, October 1, 2004, accessed on February 11, 2014 .
  11. ↑ K. Hoffmann: Chemical Engineer Technology . Ed .: WILEY-VCH Verlag. Volume 35, Issue 1 (02/2004) 1st edition. 2004, ISSN  1522-2640 , moisture measurement by infrared reflection, p. 55-62 , doi : 10.1002 / cite.330350111 .
  12. ↑ Christof Hübner, Stefan Schlaeger, Klaus Kupfer: tm - technical measuring . Ed .: Elmar von Wagner. Volume 74, Issue 5 (09/2009) 1st edition. ISSN  0171-8096 , Spatial Water Content Measurement with Time-Domain Reflectometry (Spatial Water Content Measurement with Time-Domain Reflectometry), p. 316–326 ( excerpt ).
  13. ↑ Hans-Peter Blume, Karl Stahr, Peter Leinweber: Soil science internship . Ed .: Spectrum Academic Publishing House. 3. Edition. 2011, ISBN 978-3-8274-1553-0 , measurement of ground dynamics in the field, p. 164 .
  14. ↑ Michael Köneke: Mold in the house: recognize - avoid - fight . Ed .: Fraunhofer IRB Verlag. 3. Edition. 2008, ISBN 978-3-8167-7295-8 , Risks and damage to health from mold, p. 10-15 .
  15. ↑ Peter Rauch: Condensation and moisture in masonry . Ed .: Ingenieurbüro Peter Rauch. 1st edition. 2011, ISBN 978-3-00-036810-3 , The moisture behavior of porous building structures, p. 14-21 .
  16. ↑ Michael Balak, Anton Pech: Masonry drying - From the basics to practical application . Ed .: Springer Verlag Vienna. 1st edition. 2003, ISBN 3-211-83805-8 , moisture in masonry, p. 20-29 .
  17. ↑ Horst Fischer-Uhlig: Ways to damage-free living: Recognize, eliminate, prevent damage . Ed .: Eberhard Blottner Verlag. 1st edition. 2003, ISBN 3-89367-094-7 , cellar masonry, p. 24-25 .
  18. ↑ Klaus Albrecht: How to avoid moisture damage to new buildings. Albrecht Services GbR, accessed on February 11, 2014 .
  19. ↑ a b Antje Lotz, Peter Hammacher: Avoid mold damage . Ed .: Fraunhofer IRB Verlag. 4th edition. 2008, ISBN 978-3-8167-7654-3 , Physical Basics, p. 15-16 .
  20. ↑ Katrina Bounin, Walter Graf, Peter Schulz: Handbook Building Physics - Noise Protection, Thermal Protection, Moisture Protection, Fire Protection . Ed .: Deutsche Verlags-Anstalt. 1st edition. 2010, ISBN 978-3-421-03770-1 , moisture protection in interior construction, p. 329-335 .