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The Alphabet of Tiling
Part Four: NVQ - pools

David Rowley

Many Tile & Stone Journal readers have years of experience, while others are relatively new to the industry. As none of us would claim to know everything there is to know about tiling, a handy reference guide to some of the industry's common terms could be useful. With thanks to BAL for creating this definitive A-Z, here is the fourth monthly part of your ‘Alphabet of Tiling' - remember to keep it safe and watch out for next month's instalment.

NVQ

National Vocational Qualifications recognise competence in a variety of work-related skills, with more than 1,300 occupations covered. An NVQ demonstrates that the holder has the ability to do a particular job. By 2010, a fixer wanting to work on a construction site will need to hold a Construction Skills Certification Scheme (CSCS) card, which will require the achievement of NVQ Level 2 in Wall and Floor Tiling.

There are no formal entry requirements to NVQs, which are earned through assessment and, where necessary, training. A qualified assessor will test a fixer's knowledge and ability across a number of areas, ranging from general workplace safety, through materials handling and surface preparation, to tile fixing. The fastest route to a Level 2 tiling NVQ is through Experienced Worker Practical Assessment (EWPA), in which fixers with at least five years of checkable experience can be assessed on-site during two to three days. Others could qualify through the On-Site Assessment and Training (OSAT) route, probably involving either refresher training or short courses in particular areas. Even the most experienced of fixers could be in need of training to meet NVQ standards if they have specialised in a particular area. A fixer who has mainly or entirely worked on floors, for example, would probably benefit from reviewing wall fixing skills.

For both the EWPA and OSAT routes to qualification, government help with the costs is available through grants from the Construction Industry Training Board. Less experienced fixers will certainly need some degree of training before reaching NVQ levels of ability. Before undertaking any tiling training, a fixer should check the credentials of the prospective trainer. The best training centres will be those which are also accredited to carry out NVQ assessments.

opacity

A tile may be fully or partially opaque or, as with glass tiles, transparent. Any tile which, when fired, would normally be transparent can be rendered opaque by the use of a coloured or colourless glaze prior to firing. When using transparent or only partially opaque tiles, consideration should be given to the colour of the dried adhesive. In most cases, an adhesive which dries to a white finish is advisable. In addition, care will be needed when fixing such tiles. The spread of adhesive needs to be uniform, with no gaps which could show through the tile as discolorations.

open time

The length of time after adhesive has been applied to the substrate during which it retains its ability to adhere to and bond a tile. An open time of 20 or 25 minutes is typical for most tile adhesives, including ready-mixed products. In other words, after the adhesive has been spread on the floor or wall, there is then a period of 20 or 25 minutes for tiles to be placed, into the adhesive successfully. Open time should never be confused with pot life.

orange peel

Some tile glazes are pitted after firing and resemble the surface of rough orange peel in texture, if not in colour.

overglaze decoration

A raised addition used to give texture to the surface of a tile, normally in the form of a ceramic decoration applied directly onto the tile front and covered with a transparent glaze.

packing house tile

An unglazed tile made from natural clay, similar to a quarry tile but typically of greater thickness.

paver

An unglazed natural clay or porcelain tile for exterior use in such areas as drives and patios. Formed by dry pressing, pavers are thicker than standard flooring tiles.

peeling

Splintering which can occur in fired glazes, caused by critical compressive stress.

PEI rating

Originating with the Porcelain Enamel Institute (PEI) in the USA, these classifications indicate a glazed tile's suitability for varying levels of foot traffic. They describe how well it will withstand friction, scratching, wear and tear etc when subjected to various levels of traffic. The internationally recognised classifications are defined by the standard BS EN ISO 10545-7: 1999 and are:

Class 1    -           domestic, bare feet or slippers
Class 2    -           soft-soled or normal shoes                                 
Class 3    -           domestic kitchen, halls, corridors etc, normal shoes
Class 4    -           light commercial use, regular traffic, normal shoes
Class 5    -           high traffic areas, commercial use

pendulum test

The pendulum coefficient of friction test was developed with the intention of providing a ‘portable' method of assessing slip resistance on flooring, where slips account for at least 35,000 accidents annually in the UK. The standardised test, as defined in BS  7976: Parts 1-3, 2002, is used to measure skid resistance of tiles and other flooring, particularly important in testing non-slip surfaces. A swinging imitation heel, with a standardised rubber sole, is swept over a set flooring area in a controlled way. The slipperiness of the flooring is shown as a pendulum test value, also known as a slip resistance value.

perimeter movement joints

Required where tiles meet restraining elements, including walls, window and door frames, baths and other fixed building elements. They provide the flexible connection necessary to accommodate any movement of the tiled surface caused by environmental and other changes. These can include temperature or humidity changes or increased loading.

pitting

Small indentations in the finished surface of an individual tile, typically the result of corrosion, cavitation or manufacturing defects. Such indentations at the corners or edges of a tile are more likely to have been caused by the sharp edge of a trowel.

plaster

A powdered mixture of either cement, lime or gypsum and water, which may or may not be combined with aggregate, which forms a paste when mixed with the right amount of water. When this is applied to a surface, it adheres and subsequently hardens to a rigid representation of the form or texture imposed upon it while still plastic. Used to refer to both the paste and the hardened mixture.

plasterboard

<>A globally used building material, also known as gypsum board or drywall, used for the finish construction of interior walls and ceilings. Paper is used to cover an inner core of plaster mixed with fibre, typically fibreglass or paper, plasticiser and water. Various other components are added, including additives designed to retard the growth of mildew and to increase fire resistance.

plasticiser

A material that increases fluidity or plasticity of a mortar, cement paste, or concrete mixture. When added to plaster, less water is required and drying times are reduced.

plasticity

The property of a material which describes its ability to undergo a non-reversible change of shape in response to an applied force. The ease of moulding, or resistance deformation, of freshly mixed mortar or cement paste is determined by its plasticity.

pointing trowel

One of the fixer's most important tools, used in every aspect of tiling. Uses include filling depressions on float coats, marking floated surfaces, buttering tiles, straightening tiles, placing mortar in areas that are too small for a flat trowel and, using the butt of the handle, tapping in tiles that are not truly level with the other tiles. Pointing trowels are available in sizes from 10 cm to 18 cm (4" to 7") long, with the 15 cm (6") trowel being most popular. The trowel's flat working surface should be protected. It should not be used for such tasks as prying or chipping at concrete, plaster or other hardened materials.

polished surface

The face of a natural stone or porcelain stoneware tile which has been ground with fine abrasives to produce a shiny finish.

polymer modified

Polymers were first used as additives to cement mortars and concrete during the 1920s, when natural rubber latex was added to road paving materials. There has been considerable subsequent development of commercial products, called admixtures, with a significant area of polymer-modified Portland cement being the production of tiling adhesives and grouts. Polymer-modified adhesives are often referred to as thin-set mortars. The polymers interact with the cement's components when in contact with water and several different types have been used to improve application and the physical and mechanical performance characteristics.

Polymer modification of adhesives and grouts offers improvements including easier handling, increased tensile and flexural strength, enhanced adhesive characteristics, improved water resistance and greater durability. It also tends to prolong the hydration period, giving increased density and shear strength, extending the working time and, of particular importance with grouts, promoting colour uniformity in the end product. A key benefit is increased water resistance. Adding latex to a typical grout will reduce water absorption to around 3% to 5%, compared with a range of 10% to 20% for the standard product. The advantages are easier maintenance, increased durability and greater resistance to the potential damage from freezing and thawing cycles.

Both adhesives and grouts are available ready-modified, although polymer admixtures can be used for on-site application, traditionally in the form of liquid. Dry powder admixtures can also be used, being added to the adhesive prior to the addition of water, and has the advantage of being lighter and easier to transport.

pools

Tiling of swimming pools requires the same skills, techniques and, generally, types of product as tiling any other type of floor or wall. The obvious exception to this is the importance of waterproofing and correct preparation is essential. Before tiling begins, the shell has to be watertight, which means that it needs to be designed and installed in accordance with BS 8007: 1987. Timing will be important, to avoid being affected by the shrinkage that occurs as concrete or screed dries. If tiling directly onto new concrete, this will need to be at six weeks old before work begins. If tiling is not to be direct, the surface must be readied for a new screed, to be applied when the shell is a minimum of six weeks old. The screed will then need an additional minimum of three further weeks before tiling can begin.

There will not usually be a need for priming, unless the surface is very porous. The concrete surface will need to be mechanically keyed and thoroughly clear of contaminants. These could include laitance or concrete curing compounds and removal may require pressure washing or even shot blasting. In general, a polymer-modified adhesive is recommended for pools. When choosing the adhesive and grout, consideration needs to be given to the pool water and any cleaners that may be used during the pool's lifetime. If it seem likely that there will be consistent use of chemicals which are aggressive to cement-based compounds, seek professional advice from the adhesive manufacturer. If the pool water is likely to be hard, a polymer-modified cementitious-based grout may be used. Movement joints, in accordance with BS 5385: Part 4 should be fitted, with their location having been finalised before tiling begins. Once the pool has been tiled and grouted, it should be left for at least three weeks before being filled slowly with water and heated.

Further information on anything concerning tiling is freely available from BAL on 0845 600 1222.

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