Grout is used to fill the gaps between the tiles. Most capable DIY persons should have no trouble grouting to a good standard so long as they follow the basic steps. That said though, it's amazing how common it is too see badly grouted DIY tiling projects so take care. Done well grouting can make even a rough tiling job look fairly good. Done badly, grouting can make even the best tiling look awful.
Buying The Right Grout

For both floor and wall tiling projects, I would recommend buying a powdered grout which requires you too mix it with water. These types of grout are cement based and will set chemically as opposed to ready mixed which relies on evaporation.
Powdered grout can be bought either sanded or non sanded. The sanded grouts are for wider grout joints (and nearly all floor installations would use this type) and would typically be for grout joints from 3mm upwards (check manufacturers instructions).
Non sanded grout is usually only for wall tile installations and for grout joints of less than 3mm grout joint widths (again check your specific manufacturers instructions).
So typically you'll be using non sanded on wall tiles, and sanded on floor tiles and those wall tile installations where you've used a plus 3mm grout joint (for example a kitchen wall tile installation in a more rustic / country style).
There are specialist grouts available in a huge range of colours but this is certainly the more specialised. More typically, the choice is white or ivory for walls, and white, beige/sandstone or grey for floors.
It's also possible to buy grouts which have polymer additives in them (or you can even buy a bottle of additive which is used at mixing). Polymer modified grouts are recommended to achieve a more robust, waterproof and flexible grout finish. Recommended for power shower enclosures, and an absolute must for tile installations on a wood background (background movement requires flexibility in the grout to avoid it cracking). Bear in mind that these type of grouts are harder to wash off since the polymers additives are almost glue like and if you let this type of grout dry for too long, you'll have a struggle to remove it from the tile surface.
Mixing

Don'be scared of the mixing process. It's really not difficult. Obviously the grout you buy will have instructions on mixing and proportions which you should follow. But as a general guide, the grout should be mixed with just enough water to make it into a smooth paste without any visible dry powder. You are usually aiming for the minimum amount of water needed to achieve a smooth paste. The most common mistake a novice would make would probably be too use too much water. This can weaken the grout itself, makes it more messy to apply and can make it take too long to dry enough to wash out.
So avoid using too much water. Follow the manufacturers instructions and you won't have any problems.
Powdered grouts set via a chemical reaction and a particular grout will only be usable/workable for a certain period after mixing. Roughly this would be 20-40 minutes depending on temperature and the brand of grout being used. Check the usages instructions and only mix sufficient grout to be used comfortably within the pot life of the grout. If in doubt, mix in small batches until you get more confident about how much you can use in one go.
Application

Use a rubber float to spread the grout across the tiles and work the grout into the grout joints (gaps between the tiles). Apply pressure to the grout float and ensure you work the grout fully into the depth of the gaps / grout joints. This is most easily done by holding the grout float at an angle to the tiles of approximately 30 degrees.
Work small areas at a time. It's crucial that you only spread grout over an area that can be washed off before the grout sets too much. If the grout dries more than necessary, washing off becomes more difficult.

The size of the area to be worked varies depending on conditions. The following is a list of thing which will affect drying times

• the background beneath the tile (more absorbent backgrounds will draw the moisture out of the grout quicker causing it to dry quicker in the joints)
• the ambient temperature (a warmer atmosphere will dry the grout quicker)
• any breeze (If you've got the kitchen door open on a hot windy day, then beware. The grout will dry much faster than normal ! )
• the particular brand of grout
• how wet/dry the grout was mixed (wetter mix delays drying process)
• how long it has been since the grout was mixed (longer since it was mixed, the quicker it will dry)

Once of you've worked the grout in, remove the excess from the surface of the tile by holding the grout float at a now more steep angle (just under 90 degrees) to the tile and sweep the float diagonally across the tiles. Working diagonal to the grout joints reduces the chances of digging the float into the joint and disturbing it.
The technique of spreading the grout is essentially the same whether it is a wall or a floor tile application.
Washing Off

A decent size bucket of clean water, and a good size (ie a typical size used for car washing) clean sponge is all you need to effectively clean grout from tiles. You certainly don't need any shaping tools which are promoted to the DIY tiler, and trying to shape the joints by hand or with some tool should be avoided.
It's simply a question of wiping the tile surface clean with the sponge (working diagonally across the tiles) and rinsing the sponge frequently to ensure you don't leave excessive grout residue.
Ideally, before you wash the grout off it should have firmed up in the joints (if you wash too soon before it's firmed somewhat then it's easy to actually wash the grout out of the joint). This is where some judgement / experience is useful, but trial and error should get you there, but err on the side of washing too soon and reapply grout if necessary as opposed to being faced with dried out grout on the surface of the tile.
You'll see the excess grout on the surface of the tile dry out fairly quick, and you mustn't allow it to totally dry and harden else it will be very difficult to remove.
One very important point : Wear latex gloves or washing up gloves when you are spreading and washing off grout. The cement in the grout will burn your skin if you don't. Trust me, I've tried grouting without gloves and it's very painful once the small holes in your skin appear on your finger tips !
Dust Off

Once you've fully washed off the tiles and the surface has dried you will be left with a grout haze on the surface of the tile (ie the last residue). This is best removed by dusting off with a clean dry cloth.
Safety point: wear a dust mask for this since you can get a lot of grout dust in the air which is harmful to breathe in.

And finally

Stand back and admire your tile installation. You will no doubt be glowing with pride and glad you chose tile instead of some inferior alternative ! ...

great post dave.

unless its polymer modified still wet in the joints and dry on the surface
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but a good one Dave

Can I add one other item that will affect grout drying time Dave.Porosity of the tile itself. I hate those tiles which have at least one glazed edge. So you can end up with adjacent glazed edges(no suction) and the next joint could be two unglazed edges (plenty suction). Washing off then becomes a pain as one joint is setting off rapidly and the other washes out as you attempt to clean off.

That's why it is wise to keep checking the joints for setting up........

make sure the glazed edges are all the same way up or down

Originally Posted by pjc

make sure the glazed edges are all the same way up or down

It has got to the stage where I try to ensure that tiles are always fitted the same way, I have found many tiles that have 1 (or 2) edge chamfered slightly and the other side square, this can cause havoc with trying to get grout line the same if you have chamfer to chamfer or square to square in various places.

Grumpy

Great post

Does anyone have any clue where I can get Non-Sanded Grout in London? Online is even an option, I just need to find some!

Thanks in advance