Do I need to use a core drill or hammer drill?
How to install a pipe through a block wall? Contractors, tradesmen, and homeowners have used many methods to run pipe through concrete block walls since building with precast cement products began back in the early 1900s. This according to Ball State University and a thesis paper I found online on their site about the history of the cement block. Sometimes, but not always, to get the best results required one may be required to core drill.
But if the cost is a consideration, or the hole is in a place that can not be seen such as above ceiling level or below grade, and if indeed the cement block wall is hollow you may consider other methods.
Hammer drilling
One such method for holes 5-inches in size and under is to take a hammer drill with a masonry bit drill and make an outline of the size hole you are trying to make where you think the hollow cell of the block is located and drill small holes all the way around the outline as close as you can make them while at the same time making sure to drill straight and level all the way through the wall. We call this perforating the wall. When the outline drilling is completed you should be able to take a hammer and knock out the center, leaving a hole to pass your pipe through. Do not be disappointed if it does not come out perfect, or if a bit of chipping or tapping with the hammer is needed to knock out all the debris.
Almost Core Drilling
Another method that is similar to dry core drilling is to use one of the newly carbide-tipped hole saws that have come out on the market at the beginning of 2019. Often in sizes of 1" to 6" at your local Lowes, Home Depot, or hardware store. With these type bits your don't hammer drill but use the drilling mode of your drill and cut relatively quick through a hollow block wall
Core Drilling
But if cement block is reinforced with 5000 psi. concrete and filled with rebar, and you need a professional-looking hole then core drilling may be the answer. Core drilling bits are engineered with embedded diamonds that allow the bit to cut both metal and concrete. Core drill rigs and motors and all the accessories that are needed to go with them are expensive tools and not something that the average person will want to invest in, but they can be rented from many places.
Setting up a core drill is where the magic happens. Most core drills are heavy and must be anchored to the wall being drilled. If the wall you are drilling is poured and reinforced with rebar you can use wedge anchors to mount the rig. If the wall is hollow then the best anchors to use are sleeve anchors, and do not be afraid to use more than one, a core drill rig coming off the wall while you are drilling is not something anyone wants to have happened. You will also need water and a way to pump and connect to the water inlet to keep the diamond-tipped core bit cool during the core drilling process. When finally set up. Start the drill. Do not force the core drill; just apply steady downward pressure on the feed handle, letting the bit do the work. Diamonds are indestructible, but the diamond teeth can break away from the metal barrel they are mounted on so be aware. Apply even pressure throughout the drilling process. Never force down when cutting rebar, which usually produces black or metallic-looking slurry instead of the milky white slurry when cutting concrete.
When running any pipe through a core drill hole make sure to select a core drill bit one size larger than the pipe being installed, especially if your pipe has to be sleeved. Which is one pipe inside another pipe. A hole larger than the outside diameter of the pipe will give you a little wiggle room in case the hole does not line up perfectly with where the pipe has to go. Once you have the pipe installed, you will want to seal up space around the pipe. If the holes were drilled through interior CMU block walls, you might need to use an expanding foam, but if the holes were drilled through an exterior wall, or needs a sleeve, use a masonry water seal mix found at most hardware stores to patch the hole and seal out moisture and humidity. The foam is even tough enough to keep out household pests.