Chemical delignification has been found in some metal and concrete tiled roofs around the Perth region, and primarily in properties close to the ocean. However, the deterioration seems to be more related to the ‘Terracotta Tiled Roofs’ which is similar to clay bricks, than to the actual location.
Before we explain in more depth what chemical delignification really is, we need to understand what products and conditions can lead up to this happening to the roof timber structure. So, let’s start from the beginning.
Understanding the cause
The source of chemical delignification is the efflorescence bleeding from the terracotta roof tiles onto and through the veins of the timber elements that the tile is affixed to. The timber may not be able to support the amount of salt entering the timber and the efflorescence starts to reveal itself like white veins running over the woods.
Where does the efflorescence (salt) come from?
The salt can appear naturally in timber if the property is near the ocean, or it can occur from the ground. Salt can also be produced from industries or manufactured from products such as mortar, clay bricks and terracotta tiles.
Terracotta, which literally means ‘baked earth’ in Italian, is made from a natural material that has been used in a wide range of applications throughout history, including pottery and architecture. It is made from fired clay, resulting in a red-brown tone that is warm and natural. The clay roof tiles may have a finish of a matte or glossy glaze. Because the terracotta tile is made of natural material that includes salt, over time the matte or glossy glaze slowly loses it productive coating. This allows water and possible other salts to penetrate the porous tile product.
What happens to the terracotta tile over time?
A fairly common problem with terracotta roof tiles in Perth is called ‘fretting’. Fretting to the terracotta roof tile has various causes and salt is one common culprit. However, some brand and production lines of roof tiles seem to suffer a lot more than others. Some very old terracotta roof tiles do not fret at all – yet younger tiles do.
Various terracotta roofs near the sea suffer bad fretting, while others fair quite well. Salt is also a decaying component of various masonry materials like stone, brick and mortar, by soluble salts forming crystals within the pores of the material.
There needs to be an accumulation of sufficient amount of salts to cause major decay to the terracotta tiles over time. Only once the efflorescence concentrations are high enough, the salt crystals grow and cause disruption to the tile. It then decays by fretting and loose surface skins is produced. The underside surface of the terracotta tile (noticeable in the roof void) is normally laden with additional salt that has been forced through the tile from a mixture of both water and salt.
So finally, what is chemical delignification?
Chemical delignification is a reaction within a timber element caused by efflorescence. It is a migration of a salt from top timber surfaces connected to such porous products like ‘Terracotta Tiles’. The salt wicks into the timber when wet and as it dries, it crystallises because of the chain reaction in separating the lignin from the fibre. Lignin is an organic natural ‘glue’ that binds the timber cells together. When the lignin is destroyed, the surface of the wood becomes “hairy” which causes the timber to gradually weakens and finally collapses.
The timber type, the size and the environment will determine the time before the wood becomes defibrated and spread throughout the rest of the timber structure.
Outcome of the Chemical Delignification to the roof structure
If chemical delignification is detected early, it can be treated by a Profession Roof Restoration Company. However, as nature and time progresses so will the destruction of the timber roof components causing deterioration of the wood. Eventually, the timber surface will become very hairy and fall onto the top of the ceiling/insulation like dead leaves of a tree. Chemical delignification will spread rapidly over the structural elements of the battens and onto the rafters and should be stopped in its tracks when identified.
The battens are the first to be struck by the efflorescence to a point where it will be unsafe to walk on a roof. The question to ask is: are the ‘Terracotta Tiles’ responsible for the efflorescence causing chemical delignification or is it caused by natural events? It may not be enough to just treat or replace the battens and/or rafters in some situations, but to replace the roof tiles additionally.
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