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Since the mid 80’s, granite has been a very popular stone for countertops, especially in the United States. Granite’s popularity has exploded over the last 20 years or so as cutting processes have improved, supply from other countries has increased, and the shipping process has been streamlined.
With many homes in the US boasting granite features, many people are looking for ways to add improvements like a filtered water system to the kitchen sink, but are afraid of drilling the necessary holes.
With the proper tools and preparation in place, learning how to drill granite is not a difficult task, and DIY may save you money over hiring a professional.
How to Drill Into Granite
Assemble all the tools first so you do not tear apart your sink, then find that you have missed one of the tools necessary for this project.
Drill or Angle Saw
A small battery powered home drill may not boast enough power to drill through granite. While high speeds are not necessary, the top RPM (Revolutions Per Minute) of a drill are normally a good indicator of how much overall power they have.
Look for a drill that advertises at least 1,800 RPM, with over 2,500 RPM being preferable.
Some of the most powerful drills can be hammer drills, but do not use these for drilling in granite! The added hammer action causes too much impact, and can cause cracks even if you did everything else correctly.
There are many diamond hole saws made to connect directly to an angle grinder without an attachment, and because of the high power of an angle grinder, this might be a better option if looking to purchase a new tool.
Diamond Bit or Diamond Core Hole Saw
Depending on the project you are undertaking, you may only need a small hole drilled, in that case use a normal drilling bit. If the hole you need to drill into the granite countertop is larger than standard drill bit sizes, you may need to buy or rent a diamond hole saw.
Hole saws look like a round cup that extends from your drill or angle grinder. They come in different attachment setups, so make sure that you purchase the correct hole saw for your drill or angle grinder.
Avoid cheap sets when trying to drill through granite, as the hardness of granite may cause poorly made hole saws to snap off at the base.
A piece of plywood or other thin wood is very helpful in keeping the drill bit from skittering on the smooth granite surface.
An extra piece of granite, sometimes provided when a countertop is installed, can help the underneath side of the granite from having rough edges.
Spray Water Bottle
Drill bits can get very hot when drilling through hard surfaces like granite. A spray bottle filled with water can help cool down and lubricate the bit while it is cutting.
Some drill bits are not meant to be used with water. Be sure to check the manufacturer’s instructions to be sure if you should drill with water or dry.
Alignment jig (Optional but recommended)
When drilling through thin slabs of granite, the angle isn’t as important, but you should always ensure that the drill goes completely perpendicular to the stone. An alignment jig mounts the drill in a perfectly vertical position, taking away any worries about drilling granite at an angle.
Eye protection is a must when you drill into granite. The hard pieces of granite may cause serious, irreparable harm to your eyes. If drilling without using water, wearing a dust mask will also help keep granite particles out of your lungs.
This is one of the benefits of cooling with water while drilling granite; the water will cut down the amount of dust in the air.
After the hole has been drilled in the granite, a diamond file can help you even out any rough edges. For a high polish, a diamond polishing pad can come in handy as well.
A Helping Hand
Having a partner along when you drill into granite is very helpful. They will be able to spray water on the drill bit while you are cutting so you will not need to take breaks. If you are drilling without water, they can also handle a shop vac to remove dust and debris from the cutting area.
Preparing to Drill Granite
- Measure hole – If inserting a purchased product refer to manufacturer’s instructions on the hole diameter.
- Clamp wood block – A wood block clamped above the drilling area will help the drill start in the right place and keep the bit from skipping across the hard granite, scratching your countertop in the process.
- Clamp stone counter scrap – Underneath the area being drilled, clamp a piece of scrap stone. This will help the bit continue drilling after it has gone through the initial granite, and will create a more finished edge.
2 clamps are recommended for the wood and stone scraps, one on each side of the granite hole being drilled. Be sure there is enough space for the drill to fit in between.
- Mark area – Using a grease pencil or permanent marker, place a center mark for a small diameter hole, or if necessary, mark the entire area for a wide diameter.
- Clamp alignment jig – If using an alignment jig, clamp it to the counter and attach the drill following the jig manufacturer’s instructions.
Drilling Into Granite
- Align your drill perpendicular to material to be cut, using an alignment jig if one is available.
- Line up the bit with your marks.
- Drill through the scrap wood.
- Continue drilling into the granite, approx. 1/4″, to set your guide, then remove the drill.
- You can remove the wood at this point.
- Using the initial cut as a guide, continue drilling at low speed with a slow and steady pace.
- Have someone with a water bottle spraying the bit and cutting area at all times.
- If not using water, have a partner with a shop vac removing the dust and debris from your work area. Take breaks if the drill bit is getting too hot.
- If granite is over 1/2″, stop at the 1/2″ point to clean hole and cool down the bit with water.
- Drill until you reach the scrap stone.
- Cool down your bit with water if drilling another hole.
Finishing the Granite Drilled Hole
First, remove any clamps and alignment helpers. Remove any debris from the interior of the drilled hole, and clean up the surrounding area of any slurry or dust that has accumulated.
Tip: To keep the water and slurry from making too much of a mess, create a raised barrier around the drilling area with artist’s clay.
Using a diamond file, smooth out any rough edges that have appeared. Check for any chips or cracks. If an extremely smooth surface is needed, as can be the case when drilling for mounting screws, use a diamond polishing pad to remove any scratches from the top and bottom surfaces.
Although not extremely brittle, care must be taken when drilling into granite to make sure the stone is not cracked or otherwise damaged. Something to consider, is that professionals will already have tools and experience that you may not.
If you are not familiar with using power tools, outsourcing may be the way to go.
However, if you are confident with tools like a drill or angle grinder, you can drill into granite on your own when outfitted with the right equipment and knowledge.