If you have some exterior slate flooring in your home, then you may want to consider adding some grouting to them, in order to keep them in place and prevent dirt from sliding into the cracks. These kinds of floors are often difficult to grout, as they are very sharp, and need to be smoothed down before you can do anything like grouting. Bear in mind that the slate is also very fragile, so don't be too rough when adding your grouting to the slate flooring.
Clear Up the Floor
Begin by cutting back the edges of your slates. You should do this using a wet saw, which will prevent the saw from catching fire due to the friction. You need to cut down through the slate flooring, so make sure that you wear all kinds of safety equipment, such as a helmet, safety glasses, and gloves. These will protect you from flying pieces of slate. When you have cut enough off the slate to make a gap, you should then brush the pieces into a secure spot, and dispose of them in the bin. Slate is exceptionally sharp, so don't touch it with your bare hands. Smooth down the slate using a sander.
When the floor is completely clean, you should take your sanded grout, and mix it around until it is completely firm. Sanded grout is necessary, as the extra grip provided by the sand will ensure that the grout doesn't slide off of your slate flooring. You should then take the grout trowel, and start spreading it between the grout. You need to make sure that the grout is spread evenly, as this will ensure that there are no gaps. Unlike with tiles or bricks, you cannot leave a smear of grout on the slate, since the latter is porous and will just dry out the grout.
Removing Excess Grout
You should apply the grout very carefully so that you can wipe away any small mistakes quickly. Use a damp cloth to take away these marks on the grout, by simply removing it as quickly as you can. You may find that you see a haze develop on the surface of your slate flooring as the grout dries, but this is normal, simply mop it off with a towel and sponge. When the first lot of grout dries, you should then add a second coat of the grout, taking as much care as before to ensure that you don't stain the slate.
Sealing the Grout
You then need to seal around the edges of the grout, to make sure that it doesn't get washed away. You should cover all of your slate with the sealant, making sure that all of the grout is covered. Leave this to dry, and then check that the sealant has covered all of the slate floorings, including the grout.