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Composite decking drills much like wood, but its plastic-and-wood fibers can grab a dull bit, melt from excess heat, or leave a ragged exit hole. For most deck-board work, a sharp twist bit is the practical choice. The right size and technique depend on whether you’re making clearance holes for screws, pilot holes near an edge, or larger holes for cables and hardware.
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Choose the bit for the hole
For ordinary screw holes, use a sharp brad-point or standard twist bit sized to the screw and the manufacturer’s fastening instructions. A brad-point bit starts accurately and tends to wander less on the board’s smooth surface. A quality high-speed-steel (HSS) twist bit costs less and is usually sufficient for occasional work; a cobalt bit is rarely necessary unless you also drill a lot of metal.
For larger round openings, use a sharp hole saw or an auger-style bit only if its cutting geometry is intended for wood or plastic. A spade bit is inexpensive and fast, but it can tear the top surface, grab at breakthrough, and leave a rough hole. If appearance matters, a hole saw generally gives a cleaner edge. For a run of holes, consider a brad-point bit set with the sizes you actually need.
Bit types at a glance
| Bit type | Best use | Trade-off |
|---|---|---|
| Brad-point | Accurate small and medium holes | Can clog with melted debris if pushed too hard |
| HSS twist | General-purpose pilot and clearance holes | May wander more than a brad-point on a slick board |
| Spade | Fast, rough larger holes | More likely to splinter, grab, or leave a ragged exit |
| Hole saw | Cleaner larger openings | Slower; the center pilot and teeth need careful control |
Match the hole to the fastener
Don’t assume every deck screw needs a large pilot hole. Many composite-decking systems are designed for specific screws and hidden fasteners, and some boards have installation rules about predrilling. Check the board and fastener instructions first. Where a pilot hole is required, its diameter should follow the screw maker’s guidance; a hole that is too small can split or distort the board, while one that is too large can weaken the screw’s grip.
Near board ends or edges, predrilling is especially useful because the remaining material is limited. Keep the drill perpendicular and use a depth stop, or wrap tape around the bit as a visible depth marker. If you are drilling through a board into a joist, confirm the joist location before drilling and keep the bit clear of hidden wiring or other services.
Drill without melting or tearing
Set the drill to low or medium speed and use steady, moderate pressure. High speed is not automatically faster: friction can soften the plastic in the composite, smear debris around the bit, and make the cutting edges stop removing material. If the bit starts squealing, the hole looks glossy or smeared, or debris packs into the flutes, ease off, withdraw the bit, and let it cool. Clear the hole before continuing.
Let the bit cut rather than forcing it. A cordless drill with a clutch is useful for screw driving, but for drilling, use the drill setting rather than a low clutch number. A standard cordless drill is normally enough; a hammer drill’s hammer action is for masonry and should be switched off. An impact driver can drill with a compatible hex-shank bit, but its repeated impacts give less control and can damage the board or bit. It is not the first choice for clean holes.
For a hole saw or spade bit, clamp the board or support it firmly. Reduce pressure as the bit approaches the underside. If both sides are accessible, drilling partway from one side and finishing from the other can reduce breakout. A sacrificial backing board also helps, though it must be held tight against the exit side.
What to buy
For a few screw holes, a basic, sharp HSS bit in the required diameter is fine. There is little benefit in buying a premium multi-material set for one short deck repair. If you expect to drill many accurate holes in composite, choose brad-point bits in common sizes and replace them when they start rubbing instead of cutting. For larger openings, buy a hole saw matched to the diameter and thickness of the board; a cheap, dull saw can overheat and leave a poor edge. Search for a wood-and-plastic hole saw kit if you need several sizes, but check that the kit includes the diameter required.
Bit length matters too. Use the shortest bit that reaches the work; long bits flex more and make it harder to hold a square hole. A hex-shank bit can be convenient for quick changes, but a round-shank bit held in a drill chuck works just as well for steady, controlled drilling.
Common mistakes to avoid
Don’t use a worn bit and compensate by leaning harder. That adds heat without improving the cut. Don’t start a large bit at full speed on a smooth board, where it can skate; mark the center, use a small starter hole if appropriate, and keep the drill square. Avoid drilling immediately beside a board edge unless the fastening plan calls for it, and don’t leave plastic-and-wood chips packed in the hole, where they can obstruct a screw or fastener.
Wear eye protection and keep hands clear of the bit’s path. Composite dust and chips can be irritating, so clear them with a brush or vacuum rather than blowing them toward your face. With a sharp bit, modest speed, and the correct pilot size, composite decking needs no special-purpose drill—just a bit suited to the hole and enough patience to avoid overheating the board.