Once a relatively obscure tool, but now available from a good number of sources and with a wide range of prices.
What does it do?
Quickly cuts chases (i.e. slots) in solid walls, so that cables and pipes may be buried and hidden from view. This is a job that was traditionally done using a lump hammer and a bolster chisel. While this technique is still viable, a wall chaser is one of a number of alternative ways to do it, that take much of the hard work out of the task.
How else might I chase a wall?
The traditional approach is to use a hammer – usually a club hammer – and a cold chisel. This is useful for small jobs and in tight corners. It is also good for use on old soft or flaky plaster where use of of a power tool may damage the surrounding plaster. It has the advantage of requiring no (electrical) power supply. However on hard materials it can be extremely hard work, and not practical for anything but the shortest of chases.
The modern mechanised version of the hammer and chisel is an SDS drilling machine with a chiselling (also known as 'roto-stop') mode. This can drive a variety of chisel and gouge-type bits that can be used to cut chases in fairly hard materials. Special SDS-fitting tools are also available for cutting out large recesses for power socket back boxes etc. The SDS machine can carry out quite delicate chasing if a good quality machine is used with skill in suitable material (not too hard or too crumbling). Using a machine this way will create slightly more airborne dust than a hammer and chisel, however with some careful sheeting up, and plenty of vacuuming after, the level is tolerable even in an inhabited house.
An Angle Grinder equipped with a diamond masonry cutting disk will quickly cut narrow slots in even quite hard materials. Two slots cut a small distance apart leave a small fillet of wall material between which can be be broken out easily using a hand chisel or SDS tool. Whilst effective this technique produces massive amounts of heavy masonry dust in the air very quickly. A 9" (230mm) machine can create an impenetrable fog obscuring the work area and the rest of the room (and the rest of the house as well if you forgot to shut the door!). Even with doors shut it can permeate and settle on every surface and object in the house, and it is hard to clean up. Using a smaller (4" / 100mm) grinder with a vacuum cleaner nozzle following the cutting disk so as to catch the main stream of debris can reduce the distribution of dust significantly. Otherwise this technique should be reserved for building sites, uninhabited properties, or outside.
Another option is oscillatory cutting tools, such as the Fein Multimaster or the Arbortech Allsaw. The oscillatory motion applied to a suitable cutting blade makes a slit in a wall much like the cut made with an angle grinder, but the nature of the cutting action creates far less airborne dust, making them useful in inhabited properties. The Multimaster is capable of very fine delicate work, such as cutting a chase in ceramic tiles without causing damage to surrounding ones. However its actual depth of cut is limited and not usually sufficient to complete the job. The allsaw is a bigger more powerful machine with more depth of cut, but very expensive (circa £750).
For soft plaster walls an old hand saw can be used to cut a pair of slots that will allow a fillet to be knocked out later.
What types are there?
Wall chasers can be divided into two broad categories: disc based, and “others”. For the purposes of this document we will concentrate on the disc type. The “others” category includes a number of machines that are designed to function as an add on to conventional rotary drills or angle grinders. Typically they feature some sort of masonry bit and a carriage assembly that allows it to be plunged into the surface of the wall and then pulled along grinding away at the plaster creating masses of dust and a chase. Most reports suggest that these tools are relatively ineffective in anything but soft plaster, and generally suffer most of the drawbacks of the angle grinder approach while being slower and more expensive.
The disc based wall chasers also owe their heritage to the angle grinder, and in fact many of the tools are recognisably based on angle grinder parts. There are two critical areas of difference however. Firstly they are equipped with a different blade assembly that allows two cutting discs to be mounted at once – usually with a variable number of spacers between them, to create a pair of slits with user selectable spacing. Secondly they include a carriage assembly that allows the unit to be precisely dragged over a wall, cutting the slits at a precisely controlled depth, and at the same time facilitating dust extraction.
It is the capability for dust extraction that separates out the wall chaser as a vastly more suitable tool for the job than an angle grinder. The tools feature a carriage assembly or cowl that covers the cutting discs and mounting arbour. When plunged into the wall the cowl ensures that little of the dust is able to escape. However for this to function the chaser *must* be attached to a good vacuum extractor of some sort. Typically plaster dust will clog any filter based vacuum cleaner in very short order, and some form of cyclonic extraction is usually preferred. This can be a simple home made pre-filter on a normal “shop vac”, or an old cyclone vacuum cleaner (probably with its filters removed if it has them), or a more purpose made industrial type extractor designed for fine particle dust such as a chimney sweeps vacuum. Note that workshop chip collector type extractors are not usually well suited to this task since they often do not provide adequate filtration, and do not work well with the small bore hoses that are most useful with a wall chaser.
First mark out your chase, and use a suitable scanner to establish that the chase does not cross any pipework or wiring that may already be buried – you won’t get much warning when you chop through a live wire or your central heating pipes!
Ear defenders are a must, and a dust mask would be a good idea. The tool will need to be set to the correct chase width (on many tools this involves removing the discs and changing the order of discs and spacers on an arbour – more spacers between the discs giving wider cuts). Next the depth of cut is selected. Usually this is achieved by setting the amount of disc that protrudes from the cowl – although some tools may implement a plunging action with a preset depth stop.
To cut the chase, turn on the extractor and then the chaser. Plunge it into the wall at the start of the chase. Getting it plunged into the wall quickly and neatly is also a good way to minimise the dust escape on machines that do not have a plunging mechanism. The carriage assembly will have wheels or rollers that should make it easy to drag in a straight (ish) line. As you slide the tool along the wall it cuts the slits at the edges of the chase. When you reach the end of the chase, turn the chaser off and remove from the wall.
Once your chase has been cut, you will need to break out the remaining fillet of wall. In plaster this can usually be done easily using an electricians style bolster chisel (these have a wide, thin, and tough blade). Push the bade into one of the slots and then push the handle to the side – in effect applying leverage to the fillet of plaster. Typically this will then break out in a sizeable chunk leaving a nice neat chase with clean edges. More robust material may require the use of a narrow chisel in a SDS drill.
In addition to controlling the dust problem these machines will work fast. In plaster they can produce the chase for a cable drop from a ceiling to a light switch in less than ten seconds. The width of the chase makes no difference to the speed of cut, although deeper cuts require more time. Use the note of the motor to gauge the feed rate. Feeding too fast will just accelerate the wear rate on the discs and the machine.
Several sizes of machine are available. The difference is the diameter of disc used. Ones that user 115mm discs may prove to have insufficient depth of cut for many applications, hence 125mm or 150mm models are more common. The biggest machines that take 230mm discs are handy for burying big pipes in wall, but are very heavy to handle, and obvious care must be taken to not cut too deeply into a wall hence weakening it, or even accidentally cutting right through thin blockwork.
Look for a machine with good ergonomics – some handle about as well as bagpipes! A good range of adjustment's desirable, as is a dust exhaust port that is sensibly positioned and preferably can be rotated so that the vacuum pipe can be angled in a number of different directions. Especially on the larger machines, a soft start feature is well worth having since they will otherwise give a substantial “kick” at start-up due to the relatively large mass of spinning discs, arbour, and spacers. An ability to plunge into a wall while keeping the dust collection cowl flat against the wall during the process will also help minimise dust escape. If the plunge mechanism can be set to a preset depth limit then even better.
Many of the comments about angle grinder quality apply here, although the resistance of the switch gear to dust ingress is slightly less critical since less dust will escape. The main difference between the “pro” level machines and lower budget tools will be endurance. The pro level tools are designed to be run for long periods and used frequently without undue wear on the tool. Buying a better quality tool may be advisable if you plan to chase very hard materials like concrete or engineering brick.
The extra enclosure of a chaser makes them somewhat safer than an angle grinder. Also the carriage assembly means that the tool is not being used “freehand” in quite the same way. However it is important to maintain respect for these tools since they harness a large amount of rotational energy, and diamond cutting discs will create a nasty gash or burn if they touch you. Also note that the extra mass of the disc assembly will mean the tool takes longer to spin down after turning off. Hence, care must be taken to ensure it has actually stopped before putting it down. For prolonged use a pair of anti-vibration gloves will also help reduce fatigue. Respiratory protection is also advisable when doing lots of chasing, since even with all the dust control facilities offered, some will still escape.
Second hand tools
Nothing special to look for other than making sure the blade changing spanner is present, the cable is undamaged, and the switch works correctly. Since these tools have not been readily available for that long, you may however find bargains on the second hand market hard to find. eBay will usually offer a selection of new budget tools.