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Grout formulations for a failure-free future 

By Gareth Lewis, Technical & Specification Manager, Kerakoll UK Ltd

The purpose of grout is to fill the joints that are left between tiles, make them watertight and protect the tiles themselves from water damage. There are two basic types of grout to choose between when specifying tiling.

The first is cementitious grout which is a powdered mix of cement binder and aggregate to which water is added. More advanced grouts have additional components, including polymers, to give them enhanced characteristics such as mould- and bacteria-resistance or faster setting times.

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The second type are resin-based grouts. These normally comprise an epoxy resin mixed with a filler: the type of filler depends on the brand of grout. However, a new sort of water-based resin has recently been developed which has advantages over the traditional resin-based grouts.

Resin-based grouts tend to be more expensive than conventional cement-based grouts. They can also be more difficult to use. However, they set harder and do not break down as easily as the latter, giving them advantages in certain situations such as areas where hygiene is very important or where the grout may be subjected to aggressive chemicals, such as swimming pools.

International Standards
The international standard for grouts for ceramic tiles and natural stone is ISO 13007-3, while its UK equivalent is BS EN 13888. Both of these standards look at the same criteria to decide whether a grout is fit for purpose. These are compressive and flexural strength, abrasion resistance, and water absorption.

Cementitious grouts are classified as CG1 or CG2, with CG2 grouts performing to a higher standard. CG2A grouts have better abrasion resistance, while CG2W absorb less water than standard grouts. Reactive resin grouts are classified as RG.

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Other values to take into consideration
While not included in the standards, there are other very important factors that should be taken into account when specifying grout.

Colour fastness and uniformity
In contrast to the situation a few years ago, when the only colours that were available were grey or white, grout is now available in a myriad of colours which can either be matched to the tile causing the grout lines to recede or used in a contrasting colour for decorative effect. In both cases, it is imperative that the colour is uniform and does not fade with time.

Most colour degradation is caused by three factors: light, temperature, and humidity. Together, these factors can cause more damage than the sum of their individual parts. The grout, therefore, needs to be tested to stand up to all of three.

Resistance to microbial attack
Many micro-organisms do not grow in environments with a pH value greater than 9 and the pH value of cementitious binders is higher than this. However, over time, their pH value drops due to salification and this allows mould, fungi, and bacteria to grow.

There are various ways to limit the growth of such micro-organisms, although some of them engender other problems. The use of chemical, anti-mycotic and bactericide substances in the formulation of products for the building industry can lead to a wide range of diseases and dysfunctions depending on the active principle used. That is to say that several of these substances, which to all intents and purposes are common pesticides, have been classified as potential carcinogens based on their inherent toxicity and tendency to migrate and enter the atmosphere. While their use in farming is very strictly regulated, there is no similar regulatory system governing their use in indoors, although it is the major area of exposure for most people.

Resistance to chemical attack
Resistance to attack by household and industrial chemicals is another area that is not covered by the standards. While most grouts are inert and will resist chemical attack when newly installed, over time the grout can break down and be affected.

When to use resin-based grouts
The surface of epoxy grouts tends to be smoother and more resistant to attack by chemicals and the growth of mould and fungi than that of cementitious ones. They are, therefore, more suitable for use in areas where this needs to be taken into consideration; for example, clinics, hospitals and other hygiene areas, food preparation areas, saunas, spas and industrial areas that could be exposed to harsh chemicals.

Another factor to be taken into account is the surface of the ceramic tile: soft glazes, often present on hand-made and hand-decorated tiles, can be scratched by cementitious grouts if they have coarse grains, whereas a resin-based grout will be less likely to scratch the surface.

Fugalite range
Kerakoll’s Fugalite Bio is a range of water-based resin grouts, certified EMICODE EC1-R Plus with very low VOC emissions. This new class of grout has various characteristics that make it superior to reaction resin grouts formulated in the traditional manner.

UV resistance
Colour durability tests to standard ASTM G 155 have shown that Fugalite Bio fades less and keeps its colour longer when exposed to direct sunlight than other tiling grouts. The tests were conducted by CATAS, a European centre of excellence for research in the wood furnishing, industrial and environmental sector and apply to external use.

Hypoallergenic
One of the problems with normal epoxy resin grouts is that they can cause contact dermatitis in the people that apply them. Fugalite Bio has been tested by the Modena and Reggio Emilia University Hospital and found to be hypoallergenic. There were no positive allergic reactions in a sample of 200 adults who suffer from contact dermatitis but had not previously been exposed to epoxy resin. Old-fashioned reaction resin grouts caused 3 to 3.5% of subjects to react.

A second experiment carried out on people that suffer from dermatitis through contact with resins and amines showed that a significantly lower percentage reacted to Fugalite Bio than the comparative products (12% compared to 20% to 36%).

Waterproof
Tests have shown that the whole of the Fugalite Bio range meets the criteria for being classified as water resistant. However, resistance to surface water absorption (water repellence) hugely reduces water absorption and Kerakoll’s research team test for this in addition to performing the standard test.

They do this by carrying out a ‘waterdrop effect’ test using the sessile drop method, and use the norms developed by the paint and textile industries to measure the grout against.

These tests show that the grout is waterproof with water forming droplets on its surface rather than soaking into the grout. It will stand up to heavy wear and tear in damp environments.

Stainproof
When tested to UNI EN ISO 10545-14 (Ceramic Tiles: determination of stain resistance), Fugalite Bio was shown to resist staining from both chemicals and common household products such as coffee, oil, and red wine.

Bacteriostatic
Fugalite Bio has been tested by the CSTB (Scientific and Technical Centre for Building) in France, and found to restrict the growth of micro-organisms without resorting to the use of harmful chemicals and so is ideal for use in damp environments.

Grouting wood-effect ceramic tiles
Using normal grout with wood-effect ceramic tiles can make it obvious that the floor is not real wood and spoil the desired effect. Fugalite Bio Parquet has been specifically developed for use with wood-effect tiles and becomes virtually invisible making the grout joints less obvious.

Grouting glass tiles and mosaics
Resin-based grout can look better than a standard grout with glass and glass mosaic tiles, and will also avoid scratching the surface. Fugalite Eco Invisible which is part of the Fugalite range is formulated for use with glass tiles. It is made from a mixture of tiny, pure glass beads and a transparent resin giving an opalescent semi-transparent appearance which renders the joint practically invisible. It works by taking the light diffused from the tiles which is reflected by the glass balls making the grout appear the same colour as the tiles.

The cementitious alternative: Fugabella Eco grouts
This range of grouts was developed by Kerakoll to perform as highly as possible in four key areas: mechanical resistance, water-repellence, colour fastness, and microbial resistance: while minimising risk to human health by developing a natural way to prevent fungus and mould development rather than relying on pesticides.

The range is made up of seven different products with different characteristics depending on size of joint, material being fixed, need for fast setting and exposure to pressure washing.

Mechanical resistance
Increased mechanical resistance means that the grout is less likely to break down and become vulnerable to chemical attack, mould growth, etc. The compressive strength of the whole range at 28 days far exceeds the 15N/mm2 required by ISO 13007-3; with Fugabella Eco 2-20 reaching 52N/mm2.

Likewise the abrasion resistance and flexural strength out performs the norms by a large margin (Fugabella Eco 0-2, the lowest performing formulation in the Fugabella Eco range, still achieves 561mm3 (vs 1000mm3) for abrasion resistance and 6.0N/mm2 (vs 2.5N/mm2) for flexural strength.

Water resistance
In addition to passing the standard test and being certified CG2W, the Fugabella Eco grouts have passed the same rigorous testing process for colour fastness and resistance to microbial attack as the Fugalite Bio range discussed above.

Colour fastness
Again as there are no specific standards for grouts, the Kerakoll research department has established an internal method to assess the colour fastness of its ranges of grouts. UNI EN ISO 11341 describes a laboratory method to assess alteration of colours subjected to constant exposure to different light spectrums over 500 hours. This is used to test samples for exposure to both daylight and light through window glass. The ISO EN 105-A05 standard is then used to convert measurements produced by the testing apparatus, a Q-Sun Xenon testing chamber, into intervals on the grey scale. All colours meet or exceed the requirements of the standard.

Resistance to microbial attack
Rather than using harmful chemical substances to prevent the growth of micro-organisms, Kerakoll tackled the problem by pursuing alternative, natural methods. The company worked with researchers in the Microbiology Department of the CSTB (Technical Scientific Centre for Construction) in France to identify a way of using NHL (natural hydraulic lime) to provide a bacteriostatic and fungistatic environment that would not deteriorate over time. Grout samples were tested by the CSTB and found to be B+ and F+.

Grouting natural stone
Water from standard grout can seep into the edges of natural stone and cause ‘picture framing’ which is visible on the surface. In order to avoid this an extra fast setting grout should be used. Fugabella Eco Flex has been developed for use with delicate natural stone. It reaches a high degree of hardness very quickly and so prevents any seepage.

Use of flexible grouts
If there is any degree of flexibility in the substrate, it is best to specify a flexible grout in addition to a flexible adhesive to avoid cracking. All of the Fugabella Eco range can withstand stresses and movements in the substrate, and Fugabella Eco Porcelana 0-5 is particularly suitable for use with underfloor heating.

Technical advice
If in doubt seek technical advice on what is the best product to specify for your project. Kerakoll’s team is always on hand to give advice and is frequently involved in the specification process to ensure that the right products are chosen to enable the project to run smoothly and be fit for purpose when complete, please do contact them if you have any questions.

Kerakoll UK is a subsidiary of Kerakoll, one of the leading Italian suppliers of environmentally friendly chemical products for tiles and construction work. For further information please contact Kerakoll UK on info@kerakoll.co.uk or 01527 578000. W: www.kerakoll.com 

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