Frequently Asked Questions

Can you tile over anhydrite screeds?

Anhydrite (calcium sulphate) / gypsum based screeds are here in the UK. Following years of exponential growth throughout the rest of Europe, this alternative to standard sand/cement screeds is now growing in popularity across the UK – much to the dismay, it would seem, of numerous tile fixers and contractors. Some see anhydrite as an instant problem when beginning any floor tiling project, acting with uncertainty over surface preparation techniques.
 
Working over an anhydrite or gypsum based screed does NOT have to be a problem. The ULTRA TILE team, always a pro-active force in education within the UK tiling industry, decided to meet with UK screed ‘giants’ LAFARGE to grill them on this hot topic, and ask them to provide the answers.
 
ULTRA TILE produce high performance tile adhesives, grouts and ancillaries based around the 30+ years manufacturing expertise of its parent, INSTARMAC Group plc. Frequently award-nominated and ever the industry innovators, they are very keen to put people’s minds at ease over the anhydrite issue. They could think of no-one better to get on board with this than LAFARGE, the UK market leader in the production of anhydrite screeds.
 
Paul Luff, ULTRA TILE Brand Manager, met with Technical and Specification Managers: Alan Jackson, John Fry, Jonathan Plews and Commercial Manager, Paul Pepper to ask:
 
With the variety of screeds available what’s the first thing you would recommend to do before commencing a tiling project?
Today’s market is somewhat different to that of a few years ago because there are now several types of screeds available for contractors to choose from. Therefore, we advise that you should always ask what type of screed has been used before beginning any tiling project. This may seem very simple but it’s vitally important to receive complete confirmation as it is essential that you know what substrate you are going to be working on so the appropriate surface preparation steps can be taken.
 
What is anhydrite and how do you recognise it?
LAFARGE’s increasingly popular product, Gyvlon, is a flowing calcium sulphate based screed, designed to provide a smooth level surface in both commercial and domestic applications, prior to the application of floor finishes.
 
As it is not always possible to visually recognise calcium sulphate screeds from their colour or appearance, the most precise way to identify which type of screed has been used on a contract, is to simply ask the main contractor, supplier or the floor layer.
 
 
What if it’s an old screed or refurbishment?
Due to the low shrinkage of calcium sulphate screeds during curing, compared to that of cement based screeds, they can be laid in much larger areas without expansion joints. It may therefore be possible to identify the type of screed by assessing the size of the bays (expansion joints).
 
In fact anhydrite is commonly used in constructions that are smaller than 40m² without the use of bays. However, the lack of bays alone is not enough clarification that an anhydrite screed has been used, so as previously mentioned, ask the question to gain complete confirmation.
 
What is the correct way to prepare and tile onto an anhydrite surface?
Whether the screed material can or cannot be identified, it’s standard procedure to follow the essential steps to perfect surface preparation, therefore avoiding repercussions. The essential steps are:
 
1) Ensure the screed has been confirmed dry via consistent moisture readings observed across the whole surface and not just in one location. Anhydrite screeds must have a moisture reading of less than 75% RH before any work should commence.
 
It is fair to say that anhydrite and sand/cement based screeds have a similar drying rate. Equally it can be stated that anhydrite screeds will dry quicker than sand/cement based screeds but only if applied correctly - using a reduced thickness. Anhydrite screeds can be applied a lot thinner than sand/cement based screeds and so consequently will dry quicker. For example, a 75mm deep sand/cement based screed will take 75 days to dry but a thickness of only 40mm is required when using an anhydrite screed, therefore only 40 days drying time is required (these drying times are intended as a guide only and assume good drying conditions. No screed will dry until it stops being wetted so beware, for example, of other trades using water).
 
It is vitally important to remember that an anhydrite screed has to be completely dry before any tiling commences.
 
2) Ensure that the surface of the screed is free from laitance or surface skins and then prior to continuing, the surface should be sound and dust free.
 
The removal of loose material such as laitance or dust is normally a straight forward procedure. This leaves the question of abrasion or sanding the surface. Some producers of calcium sulphate screeds have mix designs such that no laitance is evident, however the manufacturers of some adhesives (tiles or vinyl) insist that abrasion or sanding takes place in order to provide a ‘key’ to bond to.
 
ULTRA TILE recommendsthat abrasion is an essential procedure prior to tiling onto a calcium sulphate or sand/cement screed. Please also be aware that if under floor heating is present, LAFARGE would always recommend that it is commissioned prior to the fixing of any floor coverings.
 
Can you tile onto anhydrite screeds?
Once the screed has been prepared as indicated, in order to fix tiles, the surface must firstly be primed with a calcium sulphate screed compatible primer. LAFARGE recommends that you seek the advice of a tile adhesive manufacturer. INSTARMAC state thatan acrylic based primer such as, ULTRA FLOOR Prime IT AR is most appropriate. Such primers also act as a separating barrier between the calcium sulphate and ordinary portland cement based tile adhesive.
 
Calcium sulphate screeds have been used extensively in Europe for a longer period than in the UK. Typically, of the floor screeds installed in the French market, approximately 50% are Gyvlon screeds, of which around 80% received tiles as the floor finish. This equates to around 2.7million m² of tiles fitted to calcium sulphate screeds in 2008.
 
In the UK, the market penetration of calcium sulphate screeds currently stands at 15-20% and is growing, with some big names in construction realising the benefits of such flooring systems. These big home names include Urban Splash, Bellway Homes, Laing Homes, Barratt Homes and ECO Homes who are all already seeing scores of new build projects through with LAFARGE’s Gyvlon. Would it be wrong to assume that anhydrite is going to become preferred over sand/cement screeds?
 
The best advice both ULTRA TILE and LAFARGE can give is to not see anhydrite as a problem. Following the simple steps to perfect surface preparation will ensure a smooth running project and, let’s be honest, on most screeds you would use a suitable primer wouldn’t you?
 
The cost effectiveness of these screeds means that every tiler or contractor is going to come across anhydrite very soon, if not already. The larger names are using them with ease, so why not consider them as an open gate for more potential work?
 
For further information on tiling over anhydrite screeds, or indeed any tiling installation, please contact the ULTRA TILE team on +44(0)1827 871871

How should I correctly lift Ultra Tile paper bags?

All Ultra Tile products that are sold in paper bags should be handled correctly to avoid breakages occurring. We recommend, when preparing to lift an Ultra Tile bagged product that you should use both hands, gripping one hand on each of the two smallest sides, pushing both hands towards each other slightly during the lift. When lifting always remember to follow the principles of correct Manual Handling.

Whe installing tiles Is dot and dab fixing OK?

A simple answer is no.

The British Standard for tiling, BS5385, the code of practice for fixing wall and floor tiles offers guidance on how tiles should be fixed. The guidance below is taken from The Tile Association guide to DIY fixing, Tile it Right, and encompasses the guidance in the British Standard.

Walls
Spread the wall tile adhesive using a tile adhesive trowel onto the wall. Work in small areas a metre at a time, so that tiles are fixed before the surface of the adhesive forms a skin. Press and twist the wall tiles into the adhesive starting at the bottom and working upwards, one row of whole tiles at a time, using spacers (if required) to ensure a uniform joint. Check the horizontal and vertical lines with the spirit level every few rows.

Floors
Mix floor adhesive as per manufacturers' instructions and spread with the recommended notched trowel to give a ribbed adhesive bed on the surface to be tiled. Butter the back of each tile with a thin layer of adhesive immediately before bedding it firmly into the fresh ribbed adhesive bed with a slight twisting motion to ensure a solid bed and prevent voids under the tile.

Some "solid bedding" trowels and pourable adhesives are available that allow the floor tile to be solidly bedded without the need to butter the back of the tiles. If you want to be sure of a good quality tiling job, use the services of a Tile Association fixer member.

I'm about to tile my bathroom, is there anything I should be thinking about?

British Standard BS5385 is the Code of Practice for fixing wall and floor tiles. Part 4 of the Standard offers advice on fixing tiles in particular situations including wet areas such as in showers. When planning the tiling in your shower it is essential to tile onto an already water resistant background. Sand:cement render, dense concrete or water resistant tilebacker board are ideal backgrounds. Plaster, plasterboard, timber and timber-based products such as mdf or plywood are absorbent and should be made waterproof by the use of a waterproofing system (or tanking system).

Waterproofing systems can be painted on to the background. Most tile adhesive producers will have a range of waterproofing systems that coordinate with the tile adhesives and grouts in their product ranges. Check with your specialist TTA showroom that the tile is suitable for use in a shower and/or bathroom

The tile adhesive should be a water resistant polymer enhanced adhesive meeting the requirements of BS EN 12004 for a D2 dispersion adhesive or C1 or C2 for a cementitious adhesives and the tile grout should be water resistant, meeting the requirements of BS EN 13888. The tiles in showers should be fixed using the solid bed method, i.e. ensuring that there are no voids beneath the tiles. The joints between the tiles should be filled using a water resistant grout.

Special attention should be paid to sealing the gaps between the base of the tiling and where the tiling joins the base of shower units or bath and penetrations in the tiling (e.g. shower fittings), using a good quality antifungicidal silicon sealant. or a proprietary manufactured sealing strip specially designed for the purpose.

The shower should not be put into use until it has cured and is adequately dry.

Tiling to Gypsum Plaster

When fixing ceramic wall tiles to gypsum plaster surfaces on masonry backgrounds you should keep the following points in mind:

1.Although ceramic tiles can be fixed to a wide variety of backgrounds with appropriate adhesives, most tiling is fixed onto cement-sand rendering, gypsum plaster systems or onto plasterboard.
2.Cement-sand rendering is the preferred background for tiling and detailed guidance is provided in British Standard Code of Practice BS5385 Wall Tiling (BS5385-1, BS5385-2 and BS5385-4). Less information is provided about gypsum plaster backgrounds and this joint statement has been prepared in order to emphasise the conditions under which gypsum plaster can be safely used as a suitable background for ceramic tiles.
3.It is very important that the masonry background is thoroughly dry. A minimum of six weeks should have been allowed between the construction of the masonry background and plastering. The presence of moisture in the background will not always be visually evident.
4.This is particularly important where gypsum plastering is to be applied onto concrete walls especially if of lightweight or aircrete (aerated concrete) blocks or onto insitu concrete walls or onto cement-sand rendering.
5.Caution: Cement-sand rendering dries gradually with shrinkage taking place. If a cement-sand undercoat is not cured and dried prior to plastering and tiling, the subsequent drying shrinkage of the rendering can break the adhesion between the undercoat and finish coat of gypsum or between the finish and tile adhesive causing failure. New concrete walls require a longer drying time to allow shrinkage to take place, otherwise similar problems will occur. The same is true of existing concrete walls which have become saturated in use.
6.If plastered or rendered walls are to be tiled, this should be decided in advance of plastering, and should be given as a separate item in the Bill of Quantities and contract specification. See item 19.
7.Plastering should be done in accordance with the recommendations given in BS5492 and modified in BS 5385-1 section 3.4. The plasterwork should be firmly adhered to its background and be sufficiently strong to support the specified tiling.
8.The maximum weight of tiling which can be supported by a dry, well-adhered plaster background is 20kg/m2, generally equivalent to ceramic tiles with a thickness of 8mm or natural stone tiles with a thickness of 7mm. When fixing directly to unskimmed paper-faced plasterboard surfaces the maximum permissible weight is increased to 32 kg/m2. These weights include adhesive and grout.
9.Proprietary gypsum based systems are recommended because both the undercoat and finish are designed to work together. Advice on which finish coats work with which undercoats is available from the manufacturers
.
10.Gypsum plaster must be thoroughly dry before tiling. New plasterwork consisting of undercoat and finish coat should have been completed at least 4 weeks before tiling is commenced. Tiles should never be fixed to plaster which is not dry throughout. Where drying is assisted by space heating or dehumidifying, care should be taken to ensure that the plaster is not just dry at the surface. The heater or dehumidifier must not be directed at the plasterwork.
11.It is important to understand that some gypsum plasters may appear dry on the surface whilst still containing moisture within.
12.Use of non-invasive radio frequency moisture meters will be of help in determining moisture levels still within rendering/plastering and/or the background.
13.When it is known in advance that tiles are to be fixed to a plastered wall, it is essential that there should be good adhesion between the undercoat and the plaster finish coat. Tiles should only be fixed to the finish coat and must not be fixed directly to a gypsum undercoat.
14.The finish plaster should be specified and applied to provide a matt finish. Excessive trowelling of the plaster to ‘improve’ its appearance must be discouraged, since this practice may result in a dusty or shiny surface which is not suitable for tiling. If the finish plaster is hard and sound but has dusty or friable residues on its surface, the surface should be thoroughly brushed down. If trowelling of the surface has produced a shiny and smooth surface, this must be removed by vigorous brushing. Where the use of a primer is recommended before the tiles are fixed the recommended primer should be applied strictly in accordance with the manufacturer’s instructions.
15.Every plaster surface should be examined carefully by the tile fixer before any tiling work is undertaken, paying particular attention to surface finish. In addition, it is important to sound the whole area carefully for any evidence of hollowness or lack of complete adhesion in the backing. Any such defects must be remedied by cutting out and replastering before tiling. The repair must also be allowed to fully dry out.
16.On old plastered surfaces any decaying or loose areas must be cut out and made good.
17.Sometime painted plaster surfaces are encountered. Hard gloss paint if well bonded is usually a satisfactory base for tiling, but any paint showing signs of flaking should be removed. Emulsion paint or distempers can break down after tiling and must be removed mechanically prior to tiling. The surface to receive the tiles must be clean, sound and dry.
18.Since thin-bed adhesives not exceeding 3mm bed thickness are generally specified for fixing tiles to plaster, the plaster surface should be plumb, true and level. Trueness of surface should be such that when checked with a 2m straightedge, any gap between points of contact should not exceed 3mm.
Note: However such close tolerances of the trueness of a plastered surface will not have been attained unless the surface was specified to be tiled prior to plastering and the appropriate specification for plasterwork defined. Explanation a plastered surface, which is not to be tiled, is not required to meet such tolerances.

19.Generally, ready mixed adhesives conforming to Types D1 or D2 of BS EN 12004 are appropriate for fixing ceramic tiles to properly prepared plaster backgrounds.
20.Where fully vitrified large format tiles (under 20kg/m2) are to be fixed the recommendations from the adhesive manufacturer regarding adhesive and surface preparation should be sought.
21.Plaster is not a satisfactory base for tiling in wet areas e.g. shower compartments. Reference should be made to BS5385-4 for tiling in wet areas. If the backing consists of existing gypsum plaster seek the adhesive manufacturers advice on suitable waterproofing systems.
The Tile Association wishes to acknowledge the assistance provided by British Gypsum and the Federation of Plastering and Drywall Contractors in the drafting of this advice note.

Footnote. This paper deals with tiling onto internal plastered surfaces. Those made with ‘gypsum plaster’ are often simply referred to as ‘plaster’ whereas those made with a ‘cement based plaster’ are referred to as a ‘cement-sand render’.