Porcelain has offered many challenges to the industry since its commercial inception by Fiandre in the very early eighties. However most of the early challenges centred on installation issues due to the high density of the porcelain body. The first European standards were very tight almost guaranteeing a high quality material that once successfully installed was extremely easy to maintain. Although sealers were discussed with regard to use on porcelain our recommendations back then were not to seal due to their inherent almost total vitrification. However times have changed. More counties now manufacture porcelain and many do not manufacture to the original European standards. The result is that the name “porcelain” no longer guarantees a specific standard of performance. One of the most common issues resulting from this “relaxation” of standards is that of haze on polished porcelain. We are seeing more and more installations where a haze is visible on the polished surface and is deemed a problem. Unfortunately the haze can occur for several different reasons and therefore I want to discuss the main underlying reasons and their likely solutions.
Haze due to the polishing process: This is perhaps the most common reason given to a visible haze on polished porcelain (PP). Porcelain is made from high quality kaolin clay blended with other high quality refractories and fluxes creating a very hard body. The harder the body and more uniform the vitrification the better the polishing process will create a flat smooth surface that can reflect light which we see as a polish or shine. When a manufacturer formulates a body with a lower content or poorer quality of kaolin the resulting porcelain body will be more difficult to polish resulting in reduced reflectivity and hence a lower degree of polish. This can manifest itself as a hazy look. In this case this is not a fault it is simply a manufacturer creating a PP for a price. There is no real solution in this case because the quality of the clay will most likely not allow for improved insitu repolishing.
The haze can also be caused by poor polishing. The polishing process is exactly the same as for natural stone where the tile is exposed to a number of wet polishing stones which progressively get finer. If the stones are not replaced as they wear then they can grind unevenly resulting in fine grinding marks which can look like a haze. However in these cases circular grinding marks should also be visible. This is certainly a manufacturing fault. Although it is possible to rectify this after installation in most cases it is not in fact practical for two main reasons. Firstly most ceramic tile floors are not installed totally flat and hence will not polish evenly. Secondly the stones that are available are used mainly for natural stone and in most cases are not hard enough to polish the vitrified surface. The tile industry uses a specially designed alumina silica-carbide block to polish the “harder than granite” porcelain surface and unfortunately these are not readily available.
Grout or Sealer Residue: This is in fact the most common reason for a hazy appearance on PP. Grouts these days in most countries are polymer modified, This is good news for the fully cured grout as the polymer helps to assist in hydration resulting in a much denser stronger high performance grout. However it is in some way bad news for anyone trying to remove any grout residue not completely removed at the time of installation. Like the cured grout the residue is also much stronger and therefore more difficult to remove. Polymer modified grout residue will not always respond to traditional methods of removal and is a reason why after cleaning many clients believe the haze is not grout. Polymer modified grouts need to be removed with either a combination of a solvent and a diluted acid (Aqua Mix Sealer and Coating Remover and Aqua Mix Phosphoric Acid Cleaner 50:50 – the solvent attacking the polymer so the acid can then work on the cement); or the more user friendly and safe specialist products such as Aqua Mix NanoScrub. With the advent of the “wider” performance parameters of porcelain penetrating sealers are now recommended for many of them. When the excess sealer is not totally removed a hazy look results. Like grout residue this is easily removed. If it is an Aqua Mix penetrating type sealer Aqua Mix NanoScrub will safely and easily remove any sealer residue.
Kiln related issues: The most common kiln related issue is that of overall poor combustion and therefore lower vitrification. If the kiln temperature is lower than required or varies within the kiln then vitrification will also vary and hence so will the quality and evenness of the polish. This will most likely manifest itself as pieces of tile within a batch looking less polished or hazy compared to others. This is a manufacturing fault and the only solution is to replace the affected tiles. However a more uncommon reason for some haziness is the incorrect oxygen mix of the flame in the kiln. Almost all porcelain and contemporary tile are fired in gas kilns, due to reasons of cost and also glaze and tile aesthetics. With gas one can control the oxygen content in the kiln atmosphere moving between different degrees of oxygenated and reduced (reduced oxygen) atmospheres. Different glazes will fire different shades etc depending on the amount of oxygen in the kiln. For example most red tiles use selenium and if not oxygenated correctly it will turn black. The control of the atmosphere is done by adjusting the amount of oxygen in the gas flame burners. If this is not set correctly then tiles closest to the burners can either end up harder (more oxygen) or softer (less oxygen and a reduced atmosphere). However the whole tile will not normally be affected instead it is the side of the tile in the shape of a flash that will be affected. If this tile is a porcelain that is to be later polished then the polish will not be as high (hence hazy) in the flashed area of less vitrification. This is once again a manufacturing fault with the only solution being replacement of the affected tiles.
Factory applied waxes and or Pre-Seals: This is the most recent issue contributing to haze on PP and certainly the most problematic. Many factories are now applying factory waxes or protective surfaces over PP. The main reason for this is to protect the surface during installation. Most of the high quality European manufactures’ do not apply these types of finishes as they still manufacture to the original porcelain standards and hence do not need any further protection. It must be noted that some European manufacturers do apply a small bead of wax between tiles however this is only to protect the tiles from scratching during transit as all tiles are usually made under slight compression rather than being totally flat and hence are prone to movement and scratching during transportation.
The factory protective waxes and finishes are designed to be removed after or during the grouting process. If they are not correctly removed then they leave a hazy look to the porcelain. Unfortunately the manufacturers do not all use the same type of finish. Some use traditional paraffin based waxes while others use more sophisticated harder wearing polymer modified materials each one requiring a different type of chemical to remove.
Thankfully the care and maintenance industry has kept up with these procedures and now offer products such as Aqua Mix NanoScrub that safely and easily remove most of the varying types of protective finishes. However there are some that still require the use of a combination of chemicals to completely remove.
In very recent times some manufacturers are factory applying sealers to their PP. In most cases these are penetrating types of sealers. However due to the density of porcelain and the speed of the manufacturing process the excess sealer is not always totally removed from the surface. This leaves the PP looking hazy. In many instances products such as Aqua Mix NanoScrub will remove this excess and haze. However there are some that are purporting to use Nano based sealers. These are applied in the same way as normal penetrating sealers and hence can also leave a haze due to the excess left on the surface. Some of these are becoming very problematic to remove and currently are a work in progress for the care and maintenance industry.
Conclusion: For the most part issues regarding haze on PP can be split into two groups. The first being those manufacturers that produce products strictly to the original European standards. Their problems relating to hazy looking porcelain are restricted mainly to issues of manufacture such as kiln defects, polishing defects and of course some of the installation issues such as grout haze. The second group (those that manufacture to more relaxed standards) are prone to these same issues but also the issues relating to lower standards of polishing as well as the problems associated with the application of protective factory applied finishes and sealers. One additional issue that the second group has created by applying factory applied protective finishes and sealers is that the tile surface cannot be inspected by the client or installer until after installation. In many cases we have seen a haze problem supposedly solved by the complete removal of the protective finish only to reveal haze created by a lower standard of overall polish or polishing defect. In other words in this secondary group the actual cause of a haze can only be totally and accurately determined once any protective finish has been totally removed and in some cases this can in itself become problematic.