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Traditional lime mortar and plaster : Reconstruction with emphasis on durability
Chalmers Tekniska Högskola. (Företagsforskarskolan NMK)ORCID iD: 0000-0002-2994-1766
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lime mortar and plaster have been investigated with the aim to improve the knowledge on how to make them as durable as before the cement technology was developed. The background was the durability problems experienced for newly produced lime plaster on the medieval churches on the island of Gotland, Sweden. In some cases the new lime plaster façades showed severe frost damages after only one winter. Although the lime was burnt and produced according to old local traditions, the lime mortar was still mixed and worked onaccording to methods developed for lime-cement mortar. This often led to a very porous lime plaster with a lime shell in the surface and such a plaster has been shown to be sensitive to frost expansion. Field studies were combined with laboratory studies of thin section specimens. Optical microscopy and scanning electron microscopy have been important analytical methods showing the porosity and the structure of the binder and aggregate materials. The investigations have been carried out on both historic and on newly made reference mortar and plaster. The field studies were carried out mainly on Gotland, using local materials. The influence of the raw materials, i.e. lime, aggregate and blending ratio was investigated. The focus has been on the workability of the fresh mortars as well as the pore structure of the carbonated plaster. The craftsmanship, meaning mixing and application of mortar and working the plaster surface, was studied in order to clarify its final pore structure. The pore structure in a material determines many of its technical properties, such as moisture transportation, compressive strength, permeability and frost resistance. All these properties are closely connected to the durability of the mortar and plaster. The permeability of the plaster has an impact also on the durability of the covered construction materials. Behind low-permeable plasters made with hydraulic binder, examples of extensive damages of rotten wood and leached lime have been shown. The investigations have shown the importance of choosing a mortar adjusted to the building construction. They also showed the importance of choosing a blending ratio adjusted to the specific binder and sand used in order to get a mortar with a suitable pore structure and good durability. It has also shown the importance of knowing when and how to work on the plaster surface in order to obtain a homogenous material that is well receptive for lime wash and has a good frost resistance. The combination of all the investigations has led to a method for reconstructing historic mortar and plaster with good durability.

Place, publisher, year, edition, pages
Göteborg: Chalmers Tekniska Högskola , 2007. , 94 p.
Keyword [en]
lime plaster, lime mortar, masonry, craftsmanship, pore structure, frost resistance, historic mortar
National Category
Natural Sciences
Research subject
Conservation (HGO)
Identifiers
URN: urn:nbn:se:uu:diva-220119ISBN: 9789172919907 (print)OAI: oai:DiVA.org:uu-220119DiVA: diva2:704140
Public defence
2007-09-27, Wisby Strand, Visby, 09:00 (Swedish)
Opponent
Supervisors
Funder
Knowledge Foundation
Available from: 2014-04-16 Created: 2014-03-11 Last updated: 2014-04-16Bibliographically 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
4. Lime-based Repair Mortars: Influence by Surface Working Methods onBehaviour and Durability of Mortar
Open this publication in new window or tab >>Lime-based Repair Mortars: Influence by Surface Working Methods onBehaviour and Durability of Mortar
2006 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The main purpose of this study was to observe the influence by different surface working methodson behaviour, durability and appearance of lime-based stone-repair mortars.The findings are based on:

- Observations made during restoration work

- Observations from field stations

- Microscopic analysis of thin sections of mortar

- Parallel studies on lime plaster

The results show clear differences in durability, appearance and behaviour of lime-based mortar dependingon at which stage of the drying process the mortar is worked on. For achieving durable mortar it is importantto avoid the development of a surface lime-film. The study implies that the mortar, only when worked on at aspecific stage of drying, will be durable and have a structure, texture and porosity compatible with the surroundingstone material.

National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220079 (URN)
Conference
Proceedings of the International Conference of Heritage, Weathering and Conservation HWC-2006, Madrid, Spain 2006.
Funder
Knowledge Foundation
Available from: 2014-03-10 Created: 2014-03-10 Last updated: 2014-04-16
5. The influence of particle size and structure in hydrated lime on the properties of the lime putty and lime mortar
Open this publication in new window or tab >>The influence of particle size and structure in hydrated lime on the properties of the lime putty and lime mortar
2010 (English)In: International journal of architectural heritage, ISSN 1558-3058, Vol. 4, no 2, 86-101 p.Article in journal (Other academic) Published
Abstract [en]

In this work, scanning electron microscopy (SEM) analysis of lime slaked in different ways and analysis of thin section of lime putty and mortar specimens by light microscopy was combined with practical tests and field studies to evaluate the impact of the slaking technique on the properties of the lime putty as well as the structure of the fresh and carbonated mortar. The lime slaking methods studied were wet slaking and earth slaking, giving lime putties with very different consistency and workability. The aim of this work was to use microscopy techniques to explain these differences in properties and to investigate if it is possible to use these analytical methods to recognize the lime-slaking technique used in a historical lime mortar. The results obtained by SEM show significant differences in structure between the lime putties. The earth-slaked lime consists of relatively large particles that are packed in a porous system compared with the wet-slaked lime with very small particles closely packed in a dense structure. After storing, the wet-slaked lime gives a putty that has a dense and clearly defined stratified structure, whereas the earth-slaked lime is porous and has no stratification.

Place, publisher, year, edition, pages
Philadelphia: Taylor & Francis, 2010
Keyword
earth-slaked lime, lime putty, scanning electron microscopy (SEM), slaking technique, thin section
National Category
Building Technologies History of Technology Environmental Engineering
Research subject
Conservation
Identifiers
urn:nbn:se:hgo:diva-1193 (URN)10.1080/15583050902822681 (DOI)
Note
Select Papers from HMC 2008 – The First Historical Mortars ConferenceAvailable from: 2011-12-05 Created: 2011-12-05 Last updated: 2017-01-25Bibliographically approved
6. A method to recreate historic mortars applied at Norr­landa church on the island of Gotland, Sweden
Open this publication in new window or tab >>A method to recreate historic mortars applied at Norr­landa church on the island of Gotland, Sweden
2008 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In this work, scanning electron microscopy analysis of lime slaked in different ways and analysis of thin section limeputty and mortar specimens by light microscopy was combined with practical tests and field studies in order to evaluatethe impact of the slaking technique on the properties of the lime putty, and also the structure of the fresh and carbonatedmortar. The lime slaking methods studied were wet slaking and earth slaking. These techniques give lime putties withvery different consistency and workability. The aim of this work was to use microscopy techniques to explain thesedifferences in properties and to investigate if it is possible to use these analytical methods to recognize the lime slakingtechnique used in a historical lime mortar.The results obtained by electron microscopy show significant differences in structure between the lime puttiesstudied. The earth slaked lime consists of relatively large particles that are packed in a porous system as compared to thewet slaked lime with very small particles closely packed in a dense structure. After storing, the wet slaked lime gives aputty, that has a dense and clearly defined stratified structure, whereas the earth slaked lime is porous and has nostratification. The earth slaked lime is tixotropic and has a light, smooth consistency reminding of well whipped creamcompared to the wet slaked lime that has a strong orientation and a rather stiff consistency reminding more of pudding.Microscopy investigations of thin section mortar specimens showed how the lime affects the mortar concerninghomogeneity, density, pore structure and crack patterns.

Keyword
lime putty/lime mortar/slaking technique/Ca(OH)2/SEM/thin section/craftsmanship/earth slaked lime
National Category
Other Natural Sciences
Research subject
Conservation (HGO)
Identifiers
urn:nbn:se:uu:diva-220081 (URN)
Conference
Proceedings of Historical Mortars Conference HMC-2008, Lisbon, Portugal 2008
Funder
Knowledge Foundation
Available from: 2014-03-10 Created: 2014-03-10 Last updated: 2014-04-16Bibliographically approved

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