Bricks have a long tradition in the human building practice, as they constitute a constructive element, simultaneously weather-proof, resistent to fire and insulating from the cold and the heat. Furthermore, it was easy to produce quickly and economically and its frequent use across centuries has proven its resistance and durability. See our portrait on Fabrica de tijolo rustico to look inside a functioning artisan brick factory today.
The brick traditionally used in walls can be massive or porous. The massive brick was typically pressed (tijolo burro), the volume of clay comprising up to 85% of its total volume. It hereby guarantees mechanical resistance. The porous brick is composed of parallel channels running throughout its length, thus ensuring an insulating quality through air pockets. Being the lighter of the two options often makes it the favourable one to use in practice.
Depending on its usage, brick can function as a load-bearing structure or simply as a cladding or filling, if the structural elements are made of another material.
Bricks, as a porous material, have a high capacity to absorb water. They largely react to changing water levels throughout their production process and on the construction site, due to various factors such as natural humidity, resulting from the production of the building shell, from residual water released by joining mortar, rain water, water released by capillary action, condensation, etc. On the other hand, the brick needs a certain water absorption capacity in order to adhere well to the mortar.
It is thus vital to guarantee the capability of the bricks to easily release the water they absorb.
The entrance of water into the bricks can bring with it various difficulties, such as interior humidity of the construction, decomposition of the building shell, or affecting durability. This leads to efflorescence: the powder that appears on bricks when water evaporates.
Effectively, bricks contain soluble salts, among them being calcium, magnesium, sodium and potassium. These salts can be found in the clay, can result from oxidation throughout the production process or can be triggered by soluble salts existent in the mortar.
The movement of water throughout the brick dissolves the salts and brings them to surface, resulting in visible white traces and a deterioration of the cladding.
In addition, freezing can be problematic for bricks, as it leads to the rapid deterioration thereof, damaging the construction permanently. Although Portugal typically doesn’t reach such low temperatures, some regions such as Trás-os-Montes or Beiras can. These regional factors largely influence the local use of bricks.
bricks used for arches and vaults
A historic form of spanning voids is building arches or vaults, among them the timbrel vault, a traditional construction technique used in the Portuguese region of Alentejo.
The origin of the timbrel vault is not quite clear, although it was most probably brought to Portugal by the Arabs. Their roof building techniques have been adapted over time, paired with the local brick building methods to develop the timbrel construction technique.
This particular construction method distinguishes itself from typical vault constructions, as it uses a supporting frame construction throughout the building process, even spanning voids of up to six meters.
Still today, this construction method is only known by very few brick mason families, who transfer their knowledge to the next generation. Recently, the CENFIC has launched the publication of a video manual, which explains the construction process of the timbrel vault, or abobadilha alentejana.
This text was translated by us from the Portuguese book Dialogos de edificaçao, published 1998.
The images are taken from Arquitectura Popular em Portugal, published 1988.