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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)
##############
##############___ <----------- Blade
##############
##############
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.
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.
To the index
John Schmitt <john49@mdx.ac.uk>
Last updated 18/04/00
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