I began testing Hilti's DCH 300 – a 12-inch electric concrete cutter – last fall. After several months of hard use, I can report that, for certain tasks, it is a viable alternative to the two-stroke gas cut-off saws I'd used in the past.
Gas-powered saws can get the job done, but cutting masonry with them is dirty, nasty work. If you cut dry, the dust goes everywhere; and if you cut wet, there's all that slurry to clean up. And then there are the exhaust fumes, which make it impractical to use these tools indoors. Moreover, gas-powered saws can be temperamental – and if someone forgets to put oil in the fuel, you may find yourself the proud owner of a $1,000 doorstop.
The DCH 300 is electric, so it's reliable and produces no fumes, and it has a hose port that can be connected to a dust-collecting vacuum. Though designed to cut concrete and masonry, the saw can be used to cut metal if it's equipped with a fiber-reinforced abrasive blade. Lots of companies make electric cut-off saws; what's unusual about this one is the cutting capacity, which at 4-3/4 inches deep is comparable to that of a 12-inch gas model or an electric tool with a 14-inch blade.
On the Job
My crew and I used the saw in the regular course of our work, which consists mostly of building decks and remodeling. On the first couple of jobs, we used it to cut through concrete patios so we could pour footings for new wood decks. Most recently, we used it to cut through a basement slab so we could relocate a bathroom drain.
Unlike circular saws and many electric cut-off saws, this model does not have a base plate. Instead, it has two rubber rollers at the front of the blade housing. The operator can plunge-cut slabs by pivoting down from the rollers and cross-cut masonry units by rolling in from the edge. The ergonomics are very good: At just under 21 pounds, the DCH 300 is lighter and easier to handle than many gas-powered saws, and the way the trigger curves around the inside of the D-shaped handle makes it comfortable to use on both horizontal and vertical surfaces.
The manual explicitly says not to cut curves with this saw, but I tried anyway because I wanted to see if it would work for the kinds of cuts made when installing concrete pavers. I make these cuts all the time with my gas cut-off saw but had trouble doing them with the DCH 300. They're possible with a gas cut-off saw because you cut on the pull, and the back of the blade is exposed so you can see your cut line. This is not the case with the Hilti saw: You cut on the push, and the front of the blade is hidden within the housing.
The DCH 300 can be used with or without a vacuum. Used without one, it produces the same clouds of dust as a gas model; but used with one, the cutting is nearly dustless. We ended up always using a vacuum with this tool, and – except for the first plunge into the work – almost no dust was released into the surrounding area. This was great for both indoor and outside work, because it allowed us to keep a cleaner job site and kept the neighbors happy. Also, there are no combustion fumes, so we could use the saw in the basement of an occupied home without asphyxiating ourselves or the homeowners.
The dust collection gets better the deeper you cut, because the kerf channels dust to the collection port. To get the most dust, you should plunge once at the beginning of the cut and then move the saw forward to the other end. We made the mistake of missing the beginning of the cut line, and then we had to move the saw backward and plunge again. At that point, dust spewed out of the front of the kerf because it extended beyond the blade housing.
It's best to use a vacuum designed for collecting masonry dust, since the fine particles or wet slurry generated by a diamond blade will clog or foul most machines. We used the Hilti VC40-U, which contains a device that, every 30 seconds or so, reverses the flow of air through the filter to keep it from clogging with dust. We didn't use the machine for wet-cutting, but it can be equipped with a plastic collection bag and used for that application.
The VC40-U is designed to be dragged around real-world job sites: It's low to the ground and hard to tip, with large rubber wheels in back and locking metal swivel casters in front. It's one of the better vacuums I've used – very well-made, and its suction never fades. I liked being able to choose between three different collection options: fleece bags, paper bags, and inexpensive plastic liners that can be used wet or dry.