Cutting chases in walls is not just a question of putting them where you want in any haphazard way. There are guidelines to follow to make the installation of electrical cables as safe as possible for you and anyone else entering your home. It is as well to note at this point that if you are chasing walls for the installation of a new circuit that this work may be covered by Part P of the building regulations . This can be checked out by clicking on the link.
Simple rules are:
- Vertical chases should not be any deeper than one third of the total wall thickness.
- In a cavity wall, vertical chases should be no deeper than one third of the thickness of the skin they are being placed in.
- No chases, horizontal or vertical, should be made back to back.
- Horizontal chases should be no deeper than one sixth of the thickness of the wall thickness.
- In a cavity wall horizontal chases should be no deeper than one sixth of the thickness of the skin they are in.
- Chases must go from a to b in a straight line and diagonal chases should not be used.
Common sense really. If the chase is too deep it will impair the stability of the wall. If chases are back to back, there is no wall! It must always be remembered that the person doing the electrical work may not be the same person who wants to hang a picture on that wall or put a serving hatch or window in it. All chases therefore should be sensibly placed to give everyone a chance of working out where they are in relation to lights, switches, sockets and appliance points.
Cutting a chase is a simple job and most electricians will own a chasing tool. The chasing tool can be seen on the left and its basically an angle grinder with two parallel blades. The depth of the blades can be set, a hoover hose plugged into the end and off you go. They are still dusty, even with the hoover, but the time they save is worth the cleaning up afterwards.
You can see the blades in the image set to a single chase as are most cutters. When the chase lines are cut you will need a hammer and bolster to chop out the middle but this is really easy as long as the chase blades are not set too far apart. You can also see a hammer and an assortment of chisels in the image. It is now possible to buy a chasing tool which fits onto your electric drill. This should be available in the store below, from Neweys Online or from your local DIY store.
Filling a chase when the conduit and cables are in is a matter of personal taste. Because of the depth we prefer to use a mix of sand and cement to make the chase really hard when it is set. This gives any future DIY enthusiast or builder a clue something is there should they try to hammer nails into the wall. We mix the mortar at 3 soft sand to 1 sharp to 1 cement giving a strong mix which is still a little flexible. We then paint the chase with undiluted PVA adhesive to give the mortar the best chance of adhering to the conduit in the chase. The mortar is pushed well into the chase and the chase is filled. A trowel is then placed on both sides of the wall, straddling the chase and this is pulled upwards to cut off any surplus mortar.
The chase is then left for 30 minutes or so, when we use a pointing trowel to cut the surface back about 3mm to allow it to be finished off with skim plaster. See our projects on plastering by looking to the left under the related projects section. Skim plastering is not necessary when filling chases on walls to be tiled after fitting pipes etc for concealed showers.
Chases can also be filled with a plaster called patching plaster or One Coat plaster. This can usually be applied in coats up to 50mm thick but despite what it says on the packet, it will sag at this thickness so if you have a deep chase, build the fill up in layers. If using One Coat plaster make sure you wet the chase really well before applying it. The plaster will dry out really quickly and crack badly if its moisture content is not maintained.