A JOURNAL

The Strength Of Lime Mortar For Sustainable Building

ABSTRACT

Various recent Restoration Charters recommend the use of lime-based mortars for the restoration of ancient European buildings because of their compatibility with the original masonry mortars, renders, plasters and bricks. The paper presents test results and experiences obtained with industrial and traditional lime putty-based mortars. The obtained results show that with mature traditional lime putty we can obtain lime mortar with superior properties in fresh and hardened state, compared to the lime mortar from industrial lime putty. The “traditional” lime render on the outside walls behaved very good and is after one winter still in the same condition. The use of plain lime mortar from industrial lime putty for rendering does not seem to be a very good decision, since this mortar needs too much water for good workability, which is a great drawback for the later process of the hardening. The addition of 10% of cement to the “industrial” lime mortar can improve some properties of the lime render in its “green” stage due to higher early strength of the render. On the basis of obtained results the addition of metakaolin to the lime mortars for rendering can not be recommended. The reason is wet spots on the render that are very unaesthetic and could also be harmful. In cases when higher ductility of the hardened lime renders is demanded, the incorporation of fine, flexible and evenly distributed fibres in the lime mortar could be a solution.

The Strength of Lime Mortar for Sustainable Building

Introduction

Lime used to be traditional binder, used for a large variety of mortars for brickwork, stonework, renders and plasters in the ancient buildings of Europe. But for restoration purposes usually current materials and techniques are employed. These are often found to be ineffective and can cause damage. As a consequence there has been a renewed interest in ancient materials and technologies. These new developments are reflected in various recent Restoration Charters, which recommend the use of lime-based mortars for restoration works, because of their compatibility with the existing walls. In the same documents, the need for the redevelopment of ancient crafts is emphasized.

Before cement was introduced to the market, lime had been traditional binder for mortars for brickwork, stonework, renders and plasters also in Slovenia. Smaller-scale production, sufficient for local community needs, was typical for our country. Types of lime kilns used differ substantially between different regions of Slovenia. Two examples are presented in Fig. 1 and 2. Since the lime kiln named Frnaza from the Kras, Slovenian region near to the Italian border, was built only for a one-time use, the lime kiln from the Goricko, Slovenian region between the Austrian and Hungarian borders, was made from limestone blocks and clay bricks and was used frequently. It is interesting that this kiln was used also for burning clay bricks.

Lime kiln from Goricko In the last few years also in Slovenia the demands for the reintroduction of the limebased mortars for restoration works are more and more frequent, ...