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Category: Conservation (page 2 of 4)

The Power of Pozzolans


The use of lime dates back to pre-historic times. Lime is derived from limestone, a sedimentary rock formed mainly of skeletal fragments of marine organisms such as coral and molluscs. Its major materials are the minerals calcite and aragonite, which are different forms of calcium carbonate.

It is generally held that the Greeks began the large scale production of lime-based mortars in Europe and it was from there that the technology spread to Rome.

The Romans early recognized the need for a mortar that could be used under ground and under water – the development of hydraulic mortars is credited to them and the use of Pozzolans was crucial for this.




Pozzolans would include volcanic ash or clay brick/tile dust – these would be added to the lime mortar mix to create a faster set and reduce the mortar’s vulnerability to frost and rain.

Vitrivius describe Pozzolans as producing “astonishing results” and he explains the process behind them:


The Ten Books on Architecture, Vitrivius


Lime Pozzolan binders are obtained by the addition of a Pozzolan (natural or artificial) to the lime while mixing mortar. A natural Pozzolan is a volcanic material, which originally derives from Pozzuoli, an Italian region around Vesuvius. Pozzuoli earth was used in the Roman mortars but other natural Pozzolan are Santorini earth (Greece) and trass (Germany).

Artificial Pozzolans include metakaolin, silica fume, brick dust (preferably low fired brick) and others such as fly ash.


Caesarea is the earliest known example to have used underwater Roman concrete technology on such a large scale. Photo by James Cocks


Pozzolans became the backbone of Roman construction and were incorporated in the ‘Roman Concrete’.

Pozzolans of Pozzuoli were used to build ‘La Via Appia’, the Colosseum and the Pantheon of Rome. The fact that the mix could harden under water allowed the Romans to extend their empire along their coastines which gave them a strategic advantage.

Interestingly, lime Pozzolan concrete still has a place in today’s construction technology, not only because of its original characteristics but particularly because it can also offer significant carbon savings and potentially present huge environmental benefits. After all, lime is a remarkably efficient natural absorber of carbon dioxide and it could sequester carbon emissions in a very effective way.

Interesting readings:


River House – Kilkenny



There is something magical about being so close to the water.

From the very first visit we felt this was a unique location and we wanted to make the most of it. The brief asked for additional accommodation to meet current lifestyle demands.




The site presents a number of challenges, including a house over 150 years old, the proximity to a Special Area of Conservation (River Nore),  the existing topography, and so on…



Early in the design process a strong direction was identified as being the one that would respect the existing wood while taking full advantage of the river views.




The proposal calls for an adaptive reuse of the existing house. The new volumes create an amicable relationship with the old house, mimicking it in a contemporary way.

A new axis is created to link the different elements. This axis regulates the space by creating a clear circulation path that works like a journey of discovery around the house. The light and views are captured and framed to enhance the all experience.

The main living space offers a full open view to the river. Framed views of the surrounding landscape are provided by projecting windows that puncture the main structure.

The concept resolves the complex constraints on site by designing a house that is in harmony with the site and with the existing old house, which dates back to the early 1800’s or possibly late 1700’s.






The main living space offers a full open view to the river.



Framed views of the surrounding landscape are provided by projecting windows that puncture the main structure.



See more animations here.

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100-Year-Old Chimney Breasts


Accurate conservation of a building requires historical research. When we work with old buildings we often have to study the construction methods used many years ago so we can propose and develop an appropriate approach.

Intervention in old buildings must be based on knowledge of the works and techniques of the past. Old books and/or illustrations are one of the sources regularly used to understand historic buildings and devise appropriate intervention.

Chimney breasts in Party Walls 1916 Jaggard and Drury

Chimney breasts in party walls by Walter R. Jaggard and Francis E. Drury, Architectural Building Construction – Vol. II – Cambridge University Press


Here we share with you a beautiful illustration from Vol. 2 of the Architectural Building Construction book by Walter R. Jaggard and Francis E. Drury. with a 1st Edition dated from 1923. The authors illustrate in Detail no. 20 of their book the construction of chimney breasts in party walls. The illustration is beautifully hand drawn and is self explanatory. However, we highlight some of the text that accompanies it:

Jambs – Jambs to the sides of fireplace openings may project to any required distance but must be at least 9” wide, and, if the projection be more than 4 1/2” and the width less than 13 1/2”, the jambs must be tied by a caulked chimney bar of wrought iron (or steel) where an arch is employed to support the breast walling above.

Thickness of flue walls – The brickwork surrounding a flue, in jambs, breasts and stack, must be at least 4 1/2” thick.

Size of flues – While some local authorities require dwelling house flues to be at least 14” (13 1/2”) x 9”, this size of flue is not specifically mentioned in the Model Bye-laws. The adoption of the above size is due to a provision in the Act for the Regulation of Chimney Sweepers and Chimneys, 1840, but it is now generally adhered to, 9” x 9” flues being common.

Pargetting – All flues must be pargetted, viz. rendered inside with lime or cement mortar as the flues are built, unless lined with square or cylindrical fireclay tubes.


Isabel Barros is a RIAI Architect Accredited in Conservation at Grade 3. Please contact if you need assistance with your Conservation project.

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