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Kalkputs: porstrukturens betydelse för beständighet
Chalmers. (Företagsforskarskolan NMK)ORCID iD: 0000-0002-2994-1766
2005 (Swedish)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

When restoring historic lime plaster it can be difficult to reach the required durability. Today newly made lime plaster can fall off due to frost damages after only a couple of winters. To understand and solve these problems, the subject has been studied from different perspectives. Several factors in the production step are making an influence on the durability of lime plaster: 1. A binder, suitable for the building, must be chosen along with sandthat gives good material properties in both fresh mortar and in plasters. 2. The lime/sand ratio and the mixing technique should be chosen from the properties in the lime and the sand, in order to get a mortar with good workability. 3. The craftsmanship should be adjusted to the mortar, the weather and the underlying materials. A plaster with good frost resistance has a certain pore structure. The plaster should have some round air pores that contain air even when the material is filled capillary with water. Such air pores give the water a free space to expand when it is freezing. If the air pores are missing, the ice crystals may damage the plaster when expanding. To increase the chance of making a frost resistant lime plaster, the lime/sand ration must be adjusted so the lime can fill up well in the sand. Otherwise a collapsed pore system can easily occur, which means an open pore system without distinct air pores. A collapsed pore system contains many pores well connected with each other. Such a system is easily damaged by frost. To increase the chance of success, it is of great importance to work the surface of the lime plaster at the right time and in the correct way. Before working on a surface the mortar must be aloud to stiffen. Only then a homogeneous material can be created; cracks due to shrinkage can be pressed together and the result is a more compact material with an open surface. The time necessary for mortars to stiffen is related to the water content of the mortar, the suction of the underlying surface and the weather conditions. If the surface is worked on while the mortar is still fresh, the binder can form a hard lime shell on the surface. Inside thematerial a lack of binder can appear. Such plasters have a very low frost resistance. Other durability problems related to plaster are damages in the underlying materials, i.e. rotten wood in covered constructions or leached lime in old joints. Such damages can occur if the covering mortar is made of strong hydraulic lime or cement, since they form plasters with a low permeability in comparison to lime. Due to mentioned findings, it is important to study how a pore structureis influenced by materials, mixture and craftsmanship. Only then it is possible to understand how damages can be decreased.

Place, publisher, year, edition, pages
Göteborg: Chalmers Tekniska Högskola , 2005.
Keyword [sv]
kalkputs, kalkbruk, murning, putsning, hantverk, frostresistens, porstruktur
National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
URN: urn:nbn:se:uu:diva-220085OAI: oai:DiVA.org:uu-220085DiVA: diva2:704013
Presentation
2005-04-01, Chalmers, Göteborg, 10:00 (Swedish)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2014-03-11 Created: 2014-03-10 Last updated: 2014-03-11Bibliographically approved
List of papers
1. Permeability in lime plaster in relation to durability of covered materials
Open this publication in new window or tab >>Permeability in lime plaster in relation to durability of covered materials
2004 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In restoration of old buildings, lime plasters are used for reasons of authenticity and for technicalreasons as well. In many traditional constructions, there is wood behind the plasters or there is old limemortar in the masonry. For the durability of both these underlying materials, it is important that therelative humidity, RH is not too high under a long time of exposure. This can lead to an accelerateddegradation process of wood and leaching of lime in mortars. To prevent this, the plaster must have aproper permeability.The permeability of a material determines its ability to transport gas and moisture. In lime plasters,permeability affects hardening, carbonation as well as durability of the underlying materials. In thepresent paper, eleven mixtures of lime mortar were studied. The binders used were lime slaked in fourdifferent ways, hydraulic lime and cement.The following measurements were made to analyse the permeability and the pore structure of thesamples. Gas permeability and draining curves give an indication of rate of carbonation. Vapourpermeability shows the ability of plaster to transmit moisture at different RH. Thin sections were madefor microscopically investigations of the samples.The investigations show that both the vapour permeability and gas permeability decreases with anincreased amount of hydraulic binder in the lime plasters. Even small amounts of hydraulic binderhave a significant effect.By connecting these results with examples from reality, the picture becomes clearer. In the medievaltown Visby in Sweden, there are several examples of both rotten wood and disintegrated lime mortars.It is constructions from 13th to 19th centuries and low permeable cementitious plasters have coveredthem all, during the middle of the 20th century.

Keyword
lime, cement, plaster, pore structure, permeability
National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220075 (URN)
Conference
Proceedings of the 32nd IAHS World Congress on Housing – Sustainability of the Housing Projects. Trento, Italy 2004.
Funder
Knowledge Foundation
Available from: 2014-03-10 Created: 2014-03-10 Last updated: 2016-01-28
2. The influence of craftsmanship on the inner structures of lime plasters
Open this publication in new window or tab >>The influence of craftsmanship on the inner structures of lime plasters
2005 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The use of traditional lime plaster in restoration of old buildings is motivated by bothtechnical and historic reasons. The plasterer deals daily with a multivariable problem wherethe variables are related in such a complex way that we are not even close to findingconverging solutions by traditional scientific methods. The decisions and actions of thecraftsman will have an influence on both the surface structure and the inner structure of thelime plaster. The present paper will focus on the time between application of mortar andworking on the surface to make a floated finish. In total, 32 lime plaster surfaces have beenanalysed. Half of them have been worked on after they have stiffened up and half of themhave been worked on while they are still fresh. The results clearly show that the time betweenapplication of mortar and working the surface is a critical parameter. If you wait until theright time, you receive a more homogeneous and compact material with an open surface anda higher frost resistance.

Place, publisher, year, edition, pages
Rilem publications, 2005
Keyword
lime, plaster, pore structure, frost damages, craftsman
National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220077 (URN)
Conference
Proceedings of the International RILEM Workshop Repair Mortars for Historic Masonry. Delft, Holland 2005
Funder
Knowledge Foundation
Available from: 2014-03-10 Created: 2014-03-10 Last updated: 2014-04-16
3. The pore structure in lime plaster as a key to understanding moisture transportation properties and frost damages
Open this publication in new window or tab >>The pore structure in lime plaster as a key to understanding moisture transportation properties and frost damages
2004 (English)In: 10th International Congress on the Deterioration and Conservation of Stone, 2004Conference paper, Published paper (Refereed)
Abstract [en]

The pore structure is of great importance for a materials ability to hold and transport gasand moisture. In lime plaster, it affects hardening, carbonation as well as durability againstfrost damage. In the present paper, eleven mixtures of lime mortar were studied withrespect to frost damages. The binders used were lime slaked in four different ways,hydraulic lime and cement.Several analyses were made to characterize the transport properties and the porestructure of the materials; density, porosity, sorption curves, capillary water suction andthin sections. This study shows that there is a correlation between pore structure andimportant material properties. By studying these parameters, it is possible to get a goodpicture of the materials ability to resist frost damages. The study also gives an indication ofwhat materials in the mortar such as binders, aggregates and water, give a good porestructure.

Keyword
lime, cement, plaster, mortar, pore structure, building materials, moisture, frost resistance
National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220061 (URN)
Conference
Proceedings of the 10th International Congress on the Deterioration and Conservation of Stone. Stockholm, Sweden 2004
Funder
Knowledge Foundation
Available from: 2014-03-10 Created: 2014-03-10 Last updated: 2014-04-16

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