What are Rectified Tiles & Why is it Important?

Rectified tile are tiles that have been mechanically processed to ensure that all the tiles are uniform in size and are perfectly square.  If you've ever baked bread, you know that it's impossible to predict the exact eventual size of the product: it expands. While ceramic and porcelain clays do have more predictability than dough, they still are subject to size variability based on tiny differences in firing temperatures and composition of materials: tile shrinks upon firing. So, ordinary tiles that are molded and then fired, but not rectified, will have slight dimensional differences that may affect how neatly and precisely the tiles are laid out.
Note that rectifying affects only the tile's edge dimensions not the thickness of the tile.

If you want thin grout lines of 3mm or less
The main reason for rectified tiles is to allow for minimal grout joints. look at the picture above, a floor like this would be impossible with unrectified tiles.
The thicker the grout line, the more tolerance you have available to accommodate oddly sized tiles. You'll notice that quarry tiles, those thick, often red, and often unrectified tiles you see outdoors, may have lines as thick as a centimetre or more to cover for imperfect dimensions.

If you are laying 45cm or larger tiles
It's rare to find small rectified tile. Mostly 30x30cm tiles would be the smallest rectified tile. Mosaics are also often cut and rectified.
If you're laying polished porcelain tile, you'll almost certainly be setting thin grout widths.

Lippage
Though this is not a grout-line issue, you need to make certain that your substrate is absolutely flat when laying large tile. Lippage will be immediately apparent when laying tile with thin grout lines.

Rectified applies only to fired tile. You won't find rectified marble, granite, or travertine. Since these are natural stones, they are by definition rectified since they need to be cut from larger blocks of stone.
Since rectification is an additional process, rectified tiles are often slightly more expensive.
Below a rotary blade slivers off a few millimetres from each edge, a noisy process. To prevent dust, water is used.

We are currently planning a KREM Technical catalogue specifically aimed at architects. All tiles in these ranges will be rectified. Any suggestions for product or technical content to be included are welcome. Contact us here.

All the best,
The Link International team, KREM tiles.

What are Technical Tiles?

Although Technical or Engineering Ceramics are properly the hi-tech ceramic composite materials used in aerospace, military and medical applications, the term is used more broadly in the tile business to refer to any high-end tile with tested characteristics that can be specified with confidence by an architect or product specifier even where the application is expected to survive extreme wear or climatic conditions. Technical tiles in this context are invariably true porcelain with a water absorption of less than 0,5% whereas Engineering Ceramics may not even contain clay but alumina, silicide or carbide instead.

What we would call Technical tiles include in particular such products as large format thin tiles used for cladding or thick format tiles used for access floors. These products are specified in even greater detail than normal wall or floor tiles owing to the unique mounting mechanisms used to install them.

International ISO and European EN standards are used to define the most important features of Technical tiles. The most common technical characteristics are as follows:

Regularity
Dimensions/thickness/straightness of corners/ right angles/ flatness
Extremely important for cladding and applications where a smooth bump free surface is required.

Structural features
Water absorption
Water absorbency is dependent on the porosity of the material’s surface. The least porous ceramic material is porcelain, at levels of below 0.5%.

Massive mechanical properties
Resistance to bending
An important distinguishing element of floors is a material’s ability to resist given breakage loads.

Surface mechanical properties
Resistance to scratching
Ceramic materials must be resistant to scratching and wear from foot traffic and the movement of furniture, chairs, wheeled trolleys, etc.

Thermal and hygrometric properties
Resistance to temperature variations; resistance to frost; coefficient of linear thermal dilation
The thermo-hygrometric properties of porcelain stoneware are dependent on its extraordinary density. As porcelain has the lowest porosity among ceramic materials, it absorbs less water and therefore is at less risk of cracking or crackling under pressure caused by the increase in volume of water as it freezes.

Chemical properties
Resistance to chemical products
In order to resist the attack of chemical substances such as those contained in cleaning products or resulting from use of acids in particular working environments, the compactness of the surface of the material (which, in the case of porcelain extends throughout its entire thickness) constitutes a very important quality once again linked with the material’s low porosity. Good porcelain does not contain microscopic cracks that can permit penetration and stagnation of aggressive substances. This is aided by the high firing temperatures reached in ceramic kilns (1200°C), permitting achievement of greater chemical inertia.

Lightfastness
The chemical and physical properties of Technical tiles require lightfastness of colour. The need to test this property is demonstrated by the fact that Technical tiles are used in outdoor flooring or on the façades of buildings, where the material is exposed to sunlight for prolonged periods. 

Safety features
Coefficient of friction 
A floor’s slipperiness determines the safety of people walking over it and is therefore an essential requirement in commercial and industrial floors.
The slipperiness coefficient, represented by the value “R”, refers to a method which classifies products on the basis of their friction coefficient in response to the specific requirements of a given environment. The higher the friction coefficient, the less slippery the floor.
The standards distinguish between the slipperiness of floor surfaces in areas where people walk with their shoes on (R9-R13) and with bare feet (A,B,C).

R9 - entrances and stairways accessed from outside; restaurants and canteens; shops; clinics; hospitals; schools.
R10 - shared toilets and showers; small kitchens in restaurants and cafés; garages and basements.
R11 - food production facilities; mid-sized kitchens in restaurants and cafés; working environments where there is a lot of water and sludge; laboratories; laundries; hangars.
R12 - production facilities for foods rich in fats such as dairy products, food oils, cured meats; large kitchens in restaurants and cafés; industrial areas where slippery substances are used; carparks.
R13 - places where large quantities of fats and oils are used; food processing areas.

In the presence of water, where people walk barefoot, the flooring is subject to even more restrictive requirements.

A - dressing rooms; areas accessed barefoot.
B - showers; swimming pool sides.
C - sloped swimming pool sides; steps for climbing into pools.

Beyond Technical
There are of course many further technical features that may be specified and required by an architect or specifier developing a project. These could include such diverse features as the material's ability to absorb pollutants, photovoltaic efficiency, thermal or sound insulation effectiveness, light emitting characteristics. We'll discuss some of the more esoteric qualities of ceramic tile in future posts.


We are currently planning a KREM Technical catalogue specifically aimed at architects. Any suggestions for product or technical content to be included are welcome. Contact us here.

How to easily test tile hardness yourself.

The basic principle of the Mohs scale is the scratch resistance of a softer mineral being scratched a harder mineral. A common requirement in our industry is to find out whether a tile is real porcelain or ceramic. You can do a Mohs test in seconds using commonly available materials.   Hardness of some common items on the Mohs scale. 2-2,5    Fingernail 2,5-3    Gold or silver jewelry 3-3,5    Copper coin 4-5       Iron 5-6       B2b ceramic tile 5,5       Steel knife blade 6-7       Glass 6,5       Steel nail 7          B1a porcelain tile 7+        Hardened steel file 8,5       Masonry drill bit  9          Quartz crystal   How to test tile hardness in 5 steps. 1.    Find a clean surface on the tile to be tested. This is the 'unknown'. 2.  Try to scratch this surface with the point of an object of known hardness, by pressing it firmly into and across your test specimen. For example, you could try to scratch the surface with the point on a crystal of quartz (hardness of 9), the tip of a steel file (hardness about 7), the point of a piece of glass (about 6), the edge of a copper coin (3), or a fingernail (2.5). If your 'point' is harder than the test specimen, you should feel it bite into the sample. 3.    Blow or wipe off any dust. Examine the sample. Is there an etched line? Use your fingernail to feel for a scratch, since sometimes a soft material will leave a mark that looks like a scratch. If the sample is scratched, then it is softer than or equal in hardness to your test material. If the unknown was not scratched, it is harder than your tester. 4.    Now repeat the test, using a sharp surface of the known material and a fresh surface of the unknown. 5.     Most people don't carry around examples of all ten levels of the Mohs hardness scale, but you probably have a couple of 'points' in your possession. If you can, test your specimen against other points to get a good idea of its hardness. For example, if you can't scratch it with a copper coin, you know its hardness is between 3 and 6. If you scratch your specimen with a piece of glass, you know its hardness is equal to or less than 6 or 7.   Quick answers. Tiles are 'vitrified' i.e. 'turned to glass'. Ceramic tile will be scratched by glass but not by a copper coin. Real porcelain can be scratched by quartz but not glass.  You can buy quartz online, from new age shops, gemstone centers and some garden nurseries. A piece like this is perfect.   Visit our updated website or Contact us for enquiries. All the best, The Link International team, KREM tiles.

PEI and Mohs. What's the difference?

PEI ratings and Mohs both measure hardness, so what's the difference?

PEI (Porcelain Enamel Institute) ratings have been used since the 1930s to help determine the hardness and durability of tile. This is crucial because not all tile can be used in all areas. PEI ratings act as a kind of shortcut to decide where the tile can be installed. Tile that experiences much foot traffic should be harder and denser than tile that receives no foot traffic such as wall tile. From a technical perspective PEI ratings are actually determined by a measurement of Abrasion Resistance on a machine which counts the number of revolutions under a standard abrasive load. When the tile shows damage the revolutions are counted which gives the PEI rating.

Mohs ratings (named after geologist Friedrich Mohs in 1812) specifically measure the hardness of the tile glaze on a scale from 1 to 10 with 1 being soft as talc and 10 being as hard as diamond. Mohs is tested using scratching picks with alloy tips that match the traditional minerals of the Mohs Hardness Scale. 

The table below gives common objects that can be used to provide similar results in your own shop.
The PEI method was developed on the basis that the degree of deterioration of a floor should be determined by the visible difference in appearance between the worn surface and the unworn surface, assessed at a defined distance under standard conditions of lighting. It is important to stress that, for the same degree of abrasion, wear is more noticable on dark surfaces. 

PEI 0 - Tiles technically unsuitable for floors.
PEI 1 - Residential and commercial wall and barefoot traffic. < 154 revolutions.
PEI 2 - Wall and residential bath floor, and soft soled traffic. 300, 450, 600 revs.
PEI 3 - All residential floors and light commercial floors. 750, 900, 1200, 1500  revs.
PEI 4 - Medium commercial, light industrial and institutional, moderate soiling. 1500+ revs.
PEI 5 - Extra heavy traffic, abrasive dirt, chemically more resistant. Up to 12000 revs.

The particular number or PEI rating is a measure of the durability of the tile surface only. It does not determine the slip resistance, overall strength, moisture absorption, or quality of the tile itself, only the quality and durability of the surface or glaze. For most residential flooring applications it is always best to go with a PEI rating of three or higher, although two is suitable for some applications.

So, PEI and Mohs both measure hardness but in different ways. PEI measures resistance to visible wear, Mohs measures actual mineral hardness. A PEI number can be a bit vague so look at the actual abrasion resistance in revolutions to see whether the rated tile is at the high or low end of the PEI number.

Visit our updated website or Contact us for enquiries.