Terracotta – what is it?

Terracotta has been around for centuries. It was very fashionable in the 70’s & 80’s but in recent times it’s popularity has decreased. There are several reasons for this however one reason for terracotta’s decline was the number of problems associated with it’s installation and sealing. It is this area I wish to discuss because there have been numerous innovations in sealing and care products that dramatically improve the installation and maintenance of terracotta.

Problems with terracotta very often started with the installation. Tiles would often stain from the grout, watermark and suffer from the formation of efflorescence. The traditional way to install terracotta was to use cement based mortars and or adhesives. In many cases the tiles were soaked in water prior to installation so the porous terracotta would not rob the cement mortar of the water it needed to hydrate and cure. The tiles were then smear grouted. This technique obviously left a cement haze on the tiles porous surface that was very difficult to remove which in turn necessitated the use of acid to remove the offending haze. It is this traditional method of installation that is the first major cause of many of the problems.

The second area of concern is sealing. Sealer technology supplied products that either created or contributed to water marking – often turned opaque due to poor vapour transmission – could only be applied to totally dry tiles and hence could not offer any assistance in grout removal – and in many cases offered poor resistance to household contaminants. So all in all the installation process and sealer technology certainly had a major effect on how terracotta was perceived. I am happy to say that technology has vastly improved in both areas. So let’s have a look at how terracotta can be installed and protected today.

Setting Materials:

Water is a catalyst for many of the problems associated with terracotta; for example triggering any soluble salt in the tile or substrate. Therefore it is a good idea to install terracotta with as dry a process as possible. Modern polymer modified adhesives, mortars and grouts allow cement to cure with a lower ratio of water to solid content. This results in cements that are denser (less water means lower shrinkage) and therefore stronger. By encapsulating the cement particles the polymer helps the cement to hydrate with a smaller quantity of water. This eradicates the need to soak tiles and in doing so reduces the risk of water related problems.

 Pre- Sealing:

This is an area where huge gains have been made through better technology. With terracotta being porous it makes the grout residue more difficult to clean. Moreover the improved strength of polymer-modified grouts has added to the problem. It is well known that a reduction in porosity eases the grout clean up. However traditional sealers were very often made from materials that had poor vapour transmission. They could only be applied to tiles that were totally dry with their instructions calling for sealing 6-12 weeks after installation. This resulted in no pre-sealing of tiles.

Today this has all totally changed. There are now many sealers that have good breath ability and can be applied to the tile prior to grouting. In some instances terracotta manufacturers supply factory pre-sealed tiles. These pre-sealers are primarily designed to ease the grouting process rather than being the final seal. There is some debate on the prudence of using a factory sealed tile. One the plus side the sealing is done under controlled factory conditions thus guaranteeing good sealer performance as well as having a protected tile throughout the entire installation process. The main disadvantage is that the choice of pre-seal can dictate the type of final seal used and in doing so stop a client from using the final seal of their choice due to incompatibility. An example of this is the use of the new enhancing sealers. These are a type of sealer that penetrates and leaves the tile looking wet. Many clients like this effect, however they must go on to an unsealed tile and hence a factory pre-seal conflicts with their use.

 However in short whichever you use – factory pre-sealed or on site pre-sealing – the use of a pre-sealer is now the accepted way to install terracotta to minimize the problems of grout haze.

Acid: Friend or Foe?

The next stage in a traditional terracotta installation was to acid wash the tile. This was done because the grout haze was not properly removed from the surface. It was usually done using hydrochloric acid and it is the use of an acid wash that created some of the more critical problems. I could write a complete article on the potential problems acid can create – these include the aggravation of minerals in the tile and substrate such as salts and vanadium – the surface etching and colour bleaching on lower fired tiles – the damaging effect on the grout joints to name just a few. In other words an acid wash can cause potential havoc. It is not the friend many installers think it is!

Today’s technology allows the tiler to install terracotta without the use of any acid. Products are now available that stop the grout haze from forming at all. They are typically used in the final grout clean up where when diluted with water stop the haze from forming. They are alkaline materials and are therefore safe to use on any terracotta. When used in conjunction with a pre-sealer there is simply no grout haze left to acid wash!   


Sealers have come along way and now offer a much greater variety of performance to accommodate the different types of terracotta and environments they are used in. Traditionally sealers used a rather narrow range of technology. However they had to work on a huge range of different types of terracotta with varying characteristics. For example the Saltillo (or Mexican terracotta) with it’s highly porous body and well documented salt and mineral content – to the more typical Australian terracotta which is typified by a much higher firing temperature, lower porosity body and hence a vastly more inert and stable nature. With such a wide range of terracotta’s and such a narrow range of technology the traditional sealers invariably did not meet clients expectations.

Today’s sealer technology has completely transformed this. There are sealers available to meet just about every need. Penetrating Sealers/Coating Sealers/Enhancing Sealers – sealers for general areas, sealers for food preparation areas, sealers for high traffic areas, the list goes on.

Bearing in mind that no sealer is impenetrable – they will all eventually fail at some point- the reaction time modern sealers afford their user has increased incredibly. For example the traditional silicone, potassium and sodium siliconates had reaction times to oils of only a few minutes. Today’s polymers such as the sophisticated water reactive polysiloxanes and fluropolymers offer reaction times measured in the hours and in some instances several days. They now allow terracotta to be used and installed in many environments that traditionally would have been a problem.


In summary the problems created by the installation and sealing of terracotta need no longer to exist. I have no doubt that these problems did negatively impact on the acceptance and use of terracotta. Modern solutions and procedures are available:

  1. Install using polymer modified grouts, mortars and adhesives
  2. Use a pre-seal
  3. DO NOT USE ACID – use alkaline grout clean up additives
  4. Use a high performance sealer 

If they are used terracotta can be installed without the associated traditional problems making it a very versatile and low maintenance finish. With the advent of better installation and sealing technology as well as greatly improved terracotta manufacturing techniques I would not be at all surprised to see terracotta once again become the next BIG THING.

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