Tiles and tiling FAQ

Compiled by John Schmitt (john49@mdx.ac.uk)

Disclaimer: This information is given in good faith, based upon the typical properties of these products. Different manufacturers have different specifications for their products, so, if you are in any doubt ask the manufacturer's technical department. The packaging normally also carries detailed information about how to use the product inside.
 
 

There seem to be an awful lot of tiles on the market,
what should I look for?

In general you get what you pay for. Pale coloured tiles with a dark biscuit (the bit behind the glaze) may let the biscuit grin through. For floors a lot of tiles aren't really tough enough for e.g. a kitchen. In that sort of environment I would use Quarry tiles or the fully vitrified type. For a bathroom most tiles are suitable but avoid shiny smooth finishes on the floor to avoid a bad fall. Mosaic tiles on a sheet of paper are another option, but for wet areas avoid the type of mosaic with the paper or cloth scrim stuck to the backs of the tesserae, as the adhesive used to do this is frequently not waterproof.

Where do tiling jobs go wrong?

The number one cause is failure to follow the adhesive manufacturers' instructions. Read them. The manufacturer has probably spent years finding out the best way to use his product. "Professional" tilers are the worst for this because they "know it all". Surface preparation is essential. Failing to clean the surface properly leaves a weak link in the system. Kitchen grease and bathroom scum have virtually no tensile strength and guarantee a failure. The next most common reason for failure is tiling tight into corners. All buildings suffer some degree of movement, and if the tiling is tight the tiles will develop stress cracks and "blow" off the wall. It is quite possible that the tiles will stay there held by the grout but completely free of the wall. Go into a few pub loos and knock on the tiles. IMO about a quarter of all the premises I visited (for research purposes, honest) had this problem to some degree or another. The tiles will sound "hollow" and may have lots of near- parallel cracks. The secret is to leave a gap of about 6mm around the edges of the wall and grout it. The grout is compressible enough to accommodate the movement. You could use silicone sealant, particularly if the area is going to experience a lot of water. My Black Museum of Building Defects contains a beautiful example of the result of tight tiling with a more extensive commentary. A rare mode of failure is the use of cement-based adhesive onto plaster. If there is any damp, a mineral called ettringite forms at the interface between adhesive and plaster, and the job fails.

Where do I start?

Decide on a pattern. Printed patterns will eventually wear out, fired- in won't. The difference in sheen gives away the printed tiles. Gold doesn't last forever either. Plain white never goes out of fashion. Mural sets can be effective but be very careful not to break one of the set.

Now What?

Decide the layout of your tiles. Take all your tiles and shuffle them together, if they are not a mural. The individual boxes (even from the same batch) may vary slightly in colour, and if they are randomly distributed, this will be less noticeable.

Walls;

Centre on a window or other feature. Work outwards to meet the walls to find if the cut of a tile you are going to have to make is near the centre of a tile. If it is going to be a fiddly cut centre the tile not the grout line, or vice versa.

Floors;

Start in the centre (approximately) of the room about parallel to one of the walls. (I say this because very few rooms are truly right-angled, and few walls are truly straight.) From this tile work to each wall to form a cross on the floor. then fill each quadrant. You can, if you prefer leave the edges ragged until the end of the job, and do all the tile cutting in one go. (this also means that if you have hired or borrowed a tile cutter you only need it for one day)

IMPORTANT NOTE

If you try to start at a wall the slight difference between the angles of your room and a true right angle will mean that there will be some difficult cuts to make, either a whisker off a lot of tiles, or worse, lots of minute slivers to fill a small gap. In either case the departure from square will be accentuated by square or rectangular tiles.

How many tiles should I buy?

As a general rule area +10% but if you buy from one of the multiples buy an extra pack as you can return it for a refund if it is left over.

What else do I need?

Adhesive, Grout, Bonding Agent, Tile cutter, Spirit level,  Adhesive spreader, Beating Block (maybe), Grouter, Spacers. See below.

Adhesive; Two main types, Powder which is cement based and is suitable for outdoor use, including swimming pools, and paste which is suitable for indoor walls. Cement based adhesives are *not* suitable for use on plaster. (see below) Epoxy adhesives cost the earth and unless you are converting the spare bedroom into a car battery factory can be ignored. If the tile manufacturer's instructions are to soak the tile, While the adhesive manufacturer's are not, do not soak. Modern adhesives control suction much better than the old sand and cement used up to about 1950. Their adhesion is something like 50 times greater. Sand/cement fixed tiles can be "pinged off" intact, tiles correctly fixed with modern adhesive will not come off in pieces bigger than 1"sq.

Grout; again two main types Powder, again cement based so do not mix it the day before. (I know, but it has happened) Easier to use and good enough for most jobs. Normally applied with a sponge, or a soft-faced float. after a few minutes when the grout has stiffened up, a rounded end stick is useful for finishing the groutlines to a neat concave finish. a wipe with a damp cloth will remove most of the excess, and when the job has dried out, it can be polished with a dry cloth. Ready mixed, Not my choice, because it often develops shrinkage cracks and can be difficult to clean off. And again epoxy which is for operating theatres and possibly (if you must) tiled worktops. Epoxy grout is hard work to use, particularly the cleaning off bit. You have been warned!

Bonding Agent; PVA is the most common usually used at 4:1 dilution and allowed to dry over night. For really demanding applications more water resistant bonding agents are available. Not strictly necessary but recommended. Bonding agents do not make up for poor surface preparation, but enhance the effect of good surface prep.

Tile Cutter; Ideally one of the diamond saw variety like a miniature table saw about UKP100 from DIY shops. For about UKP40 there is a score and snap variety and the cheap ones are all right for thin tiles. Also available is a tile sawblade which fits a standard hacksaw frame and allows curves and holes to be cut in tiles. They are really only suitable for wall tiles. To cut a circular (or any other shape) hole in a tile, drill a hole in the middle of the bit to be removed (using a masonry drill with no hammer action), fit the saw blade through the hole, saw to the edge of the area to be removed, and follow round the periphery.

Adhesive Spreader; 6mm square notches every 6mm, *not* v notched. Do not use the "blob" method i.e. 4 or 5 blobs of adhesive on the back of the tile and shove it onto the wall. Typically this only gives 25% contact where 80% is provided by spreading on the wall with a notched trowel. Blobs also increase the risk that water will get behind the tiles and cause damage.  The notched trowel should be held at about sixty degrees to the wall, so that the adhesive is pressed firmly into the substrate, but the ribs of adhesive are sufficiently generous.  For permanently wet or exterior areas, you should use solid bedding, i.e. spread the adhesive to a depth of 3mm, and lightly comb with the trowel before applying with the trowel. If the adhesive is of the "thick bed" variety, the adhesive can be spread thicker, to take up any surface irregularity. When you apply the tiles a sliding or twisting action will maximise the contact area you achieve.

Beating Block; Particularly for floor tiles to get a well bedded, flat tiled surface. A piece of 2x4 about 10" long (50x100x250mm) works quite well with the wide face used on the tiles. You may want to put a "waist" in this if you have small hands.

Grouter; A sponge is popular, although a soft-faced float is another option. A small rounded end stick is another useful tool for finishing the grout lines.

How do I prepare the surface?

Walls;

Papered; strip back to plaster.

Painted; The paint must be well fixed, and of the gloss type. Ideally strip back to plaster, but you can simply wash well with sugar soap and abrade with sandpaper before priming.

Plaster/plasterboard; The plaster must be sound, and well stuck to the wall behind. Prime with PVA bonding agent diluted 4:1, allow to dry overnight. On highly trowelled surfaces sand before priming. Again do not use cement- based (powder) adhesives on plaster as in the presence of moisture the two can react with each other to form ettringite which will result in bond failure.

Concrete/render; As for plaster, but cement-based adhesives are suitable. The surface should be cleaned of any mould release oil by mechanical roughening or acid etching if the concrete is cast, and any laitence must be removed.

Tiled; Abrade with coarse sandpaper, prime with a waterproof primer. Obviously the existing tiles must be well fixed.

Timber; Must be reasonably rigid - 1/2" marine ply recommended. PVA bonding agent diluted 4:1 left to dry overnight

Floors;

Concrete; Any laitence (the fine material which tends to congregate on the surface of the concrete) must be mechanically removed e.g. by a kango hammer with a toothed blade. If greasy (e.g. a garage) contact an adhesive manufacturer. Prime with PVA 4:1.

Floor boards; 12mm marine ply screwed down at 140mm centres. (1/2" at 6" in old money) Prime with a waterproof primer.

What if I have just ripped up my floorboards, and I want tiled floors? Do I have to put down floorboards again?

Get 18mm ply, WBP (Water and Boil Proof) minimum, marine or flooring grade are suitable. Paint at least the edges and (soon to be) underside with Cement Particle Board (CPB) sealer paint. Let the paint cure as recommended by the manufacturer. Screw the boards down at 6" (150mm) centres along the joists, with noggins inserted under the joins between the boards, which should then be screwed down to the noggins. Allow a fortnight for the whole job to stabilize. Then use a cement-based thickbed adhesive with a flexibilising polymer additive to fix the tiles.

And finally two rare types of floor, both to my knowledge only found on ground floors and in cellars;

Asphalt; Check it is flooring grade asphalt. It will be *very* hard and brittle, and was often pigmented brown, brick red, or chrome oxide green. Remove all polish, use a waterproof primer, and tile as per concrete floors.

Magnesite; Only likely in old houses (pre about 1920). Normally coloured coral pink or verdigris. A small lump, when held in a gas flame will glow brightly, like a gas mantle, at the edges, whereas asphalt will burn with a smoky flame and a tarry odour. Magnesite needs complete removal, and replacement with 3:1 sand/cement screed. Then tile as per concrete. Magnesite was often made with sawdust as a filler, and when the tiling traps any water vapour this rots, expanding the magnesite and ruining the tiling job.

I have a flat roof outside my window, and I want to make it into a tiled patio what should I do?

Firstly, consult a Structural Engineer that the roof will take the weight of the patio. (see below) then put down 500 gauge building polythene, and on top of this 2" of 3:1 sand cement with weldmesh halfway down. Allow to cure, damping down if necessary in hot weather. Tile as for an internal concrete floor, but using frost resistant tiles. NOTE: this will not make a leaky flat roof waterproof, in fact I recommend the roof be inspected by a roofer, and if necessary, maintenance carried out.

The grouting in my ten-year-old tiling has become grotty. What can I do about it?

You can buy a tool for raking out the grout, or you can make one from a 2" length of (old will do) hacksaw blade screwed into a wooden handle.

(ASCII art approx to scale) 

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##############___ <----------- Blade 
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Try to use all the teeth at once. It is a bit laborious, but not as bad as a re-tile. There are also products for re-colouring grout, but in my opinion, they are really only of use if you intend to sell the premises, and want a bit of a makeover.
 

How do I bond slate?

You should wipe the slate absolutely clean on the side you intend to bond. Slate is formed from shale, which is formed from clay sediment, which in turn is formed from the felspars in rocks. Clay minerals have crystals in the form of plates (often hexagonal, I am using the word plate in the geometrical sense), and when they settle down, they are randomly orientated, so that clay is actually more water by volume than clay. Think of a packet of crisps. There is more air by volume than crisp. Under the weight of superposed sediments the clay is squeezed so that there is less  water. If the sediment becomes uplifted, then it appears as shale. If however the shale is subject to extreme pressure and moderate temperature, it becomes slate. The pressure makes all the clay crystals align perpendicular to the greatest stress, and this is what makes slate cleave so nicely, however when the slate is cleft, some of the surface crtstals may become loosened and compromise the bond. Hence the wipe. Because of it's easy cleavage, slate is one of the trickier materials to stick to a floor. I recommend using a polymer additive in your cement-based adhesive, as a belt-and-braces measure. You will also need one of those diamond blade cutters, which will go through slate quite nicely. For grout, a cement-based grout. Most people prefer the grout lines to be unobtrusive, so you may be able to obtain black grout, or use black pigment to match the slate. This should be available from the place you buy the adhesive.
 

How can I fix into a tiled wall?

Ideally put some tape on the tile. This stops the drill from "skating" all over your nice, shiny tile. Then drill through the tile without hammer action. when you are through the tile engage the hammer action, and drill the rest of the hole. Then try to get the rawlplug itself deep enough into the hole so that it is not in the tile. This is to avoid the risk of cracking the tile.

Are there any tips for applying mosaic?

Line up the sheets of mosaic before you put any adhesive on the job. It is much easier trimming the sheets without adhesive all over them. Some mosaics are held together with brown paper, on the top side, do not use these upside-down. After the adhesive has set (24 hours normally) soak the paper, which is stuck with water-soluble adhesive, and strip the paper. Patience is a virtue here, let the water do its work. Remember that grouting mosaic will be time consuming. If you feel creative, make your own mosaic by breaking up assorted tiles, and arrange them either in a random pattern or to make a picture. Quite often there is an odds-and-ends bin in tile outlets, including broken tiles, which will be cheap and ideal for this sort of project.

Talking of makeovers, can I paint on top of my tiles?

Yes, Clean the tiles with hot water and sugar soap until they are squeaky clean, and abrade lightly with fine wet-and-dry sandpaper. Then paint as per (e.g.) metal, with a good quality oil-based gloss on top of primer.

International Disclaimer;
The above is based on current practice in the UK, other countries have rather different products and techniques.

Copyright notice: With the growth of the net, copyright law has become very complicated. You may reproduce this FAQ in any form from stone tablets to putting it on your homepage. You may distribute it to absolutely anyone. You may even add your own bits to it. However, if you remove my name from it, or try to pass it off as your own work, I will be very, very angry with you.

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John Schmitt <john49@mdx.ac.uk>

Last updated 06/06/00