Which one?

99 answers on picking the right glue, bit, grit, blade, paint, screw or lubricant for a material. Each page gives the physical reason behind the recommendation, because that transfers to materials not listed here and a brand name does not.

Three that save the most trouble

• Polypropylene and polyethylene resist almost every adhesive, because their surface energy is too low for glue to wet them. This is not a product problem — it is physics, and it needs a specific primer rather than a stronger glue.
• WD-40 is a water displacer and penetrant, not a lubricant. It evaporates and can wash away the grease that was doing the work, which is why it eventually makes locks worse rather than better.
• Never use a hammer drill on tile. Percussion shatters it. Rotary mode with a spear-point or diamond bit, and keep it cool.

Glue and adhesive

• Which glue works on plastic? It depends entirely on which plastic — identify it first, because solvent cement is unbeatable on some and useless on others.
• Which glue works on polypropylene and polyethylene? Ordinary adhesives cannot wet these plastics at all. Use a polyolefin primer with cyanoacrylate, an MMA structural adhesive, or weld the plastic.
• Which glue works on wood? PVA wood glue for anything indoors; a water-resistant grade (Type I / D4) or polyurethane for anything that gets wet.
• Which glue works on metal? Two-part epoxy for anything structural, cyanoacrylate for small dry parts, and MMA where the surface cannot be properly prepared.
• Which glue works on ceramic? Two-part epoxy for anything that will be handled or loaded, cyanoacrylate for a clean break on a display piece — and neither is dishwasher-proof.
• Which glue works on shoes? A flexible shoe repair adhesive — polyurethane or a neoprene contact cement — never superglue, which cracks within a day of walking.
• Which glue works on fabric? A washable fabric adhesive or a fusible bonding web — and never superglue, which reacts with cotton violently enough to burn.
• Which glue works on glass? UV-cure glass adhesive for an invisible joint, clear epoxy where it must hold load, and neutral-cure silicone where it must stay flexible or wet.
• Which glue works on PVC pipe? PVC solvent cement with its matching primer — and PVC, CPVC and ABS cements are not interchangeable.
• Which adhesive should I use for tiles? A cement-based thin-set in almost every case; ready-mixed tub adhesive only on small dry walls, never on floors or in showers.
• Which glue works on a phone screen? A pre-cut adhesive gasket, or a flexible B-7000-type adhesive around the frame — superglue destroys screens and is the classic mistake.
• Which glue works on rubber? Contact cement for large flexible areas and rubber-toughened cyanoacrylate for small ones — but silicone and EPDM need a primer or they will not bond at all.
• Which glue is waterproof for outdoor use? Polyurethane or epoxy for rigid joints, MS polymer where the joint has to move — and check the water-resistance class rather than the word "waterproof".
• Which glue works on acrylic? A solvent cement run into the joint by capillary action — not a tube adhesive, which will always look like a repair.
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Drill bit

• Which drill bit should I use for tile? A spear-point carbide or diamond bit in rotary mode only — hammer action shatters tile, every time.
• Which drill bit should I use for metal? An HSS twist drill, ideally with a 135° split point, run slowly with firm pressure and cutting fluid.
• Which drill bit should I use for concrete? An SDS-plus carbide bit in a rotary hammer — a normal hammer drill will get there eventually and blunt several bits doing it.
• Which drill bit should I use for masonry? A carbide-tipped masonry bit in hammer mode for brick and block; step up to an SDS rotary hammer above about 10 mm.
• Which drill bit should I use for porcelain tile? A diamond core bit, cooled with water, at low speed — carbide spear points do not cut porcelain.
• Which drill bit should I use for stainless steel? A cobalt bit at low speed with heavy constant pressure and cutting fluid — and never let it stop cutting.
• Which drill bit should I use for wood? A brad point bit for clean holes up to about 13 mm; an auger for depth and a Forstner for a flat bottom.
• Which drill bit should I use for plasterboard? Almost none — an ordinary HSS or brad point bit in rotary mode, and the real question is which fixing goes in the hole.
• Which drill bit should I use for glass? A spear-point carbide or a diamond bit, run slowly under water — and toughened glass cannot be drilled at all.
• Which drill bit should I use for plastic? An HSS bit ground to a shallower rake, or a plastic-specific bit, at low speed with a backing board — acrylic especially will crack.
• Which drill bit will go through hardened steel? Solid carbide in a rigid setup, or soften the spot first — HSS and cobalt cannot cut anything much above 50 HRC.
• Which drill bit should I use for aluminium? A sharp HSS bit at high speed with a wax or paraffin lubricant — the problem is aluminium sticking to the bit, not hardness.
• Which bit should I use for large holes in wood? Spade for speed and roughness, auger for depth, Forstner for a clean flat bottom, hole saw for big diameters in thin stock.

Sandpaper grit

• Which sandpaper grit for bare wood before finishing? 80 to 120 to 150 on softwood, finishing at 180 or 220 on hardwood — and stop there, because over-sanding ruins stain.
• Which sandpaper grit removes paint? 40 to 80 grit open-coat aluminium oxide or ceramic — but test for lead paint before sanding anything painted before the 1990s.
• Which sandpaper grit removes rust? 60 to 80 grit to strip scale, 120 to 180 to blend — then prime the same day, because bare steel flash rusts within hours.
• Which sandpaper grit between coats of paint or varnish? 220 to 320 grit with almost no pressure — you are knocking off dust nibs, not removing the coat.
• Which sandpaper grit for plasterboard and filler? 120 to 150 grit to level joint compound and 220 for the final pass, ideally on a mesh with a vacuum attached.
• Which sandpaper grit for plastic? Start at 320-600 wet for scratches, work up to 2000, then finish with a plastic polish — and keep it cool.
• Which sandpaper grit for car body filler? 80 grit to shape, 180 to refine, 320 before primer and 400-600 on the primer before paint.
• Which sandpaper grit for a final finish? 400 to 600 dry, or 800 to 2000 wet on a fully cured film, followed by a polishing compound.
• Which sandpaper should I use for wet sanding? Silicon carbide wet-or-dry paper, water with a drop of detergent, a rigid block, and 800 grit upwards.

Blade

• Which blade cuts metal? A bi-metal or carbide-tooth blade with at least three teeth in the cut — that tooth-count rule matters more than the machine.
• Which blade cuts tile? A continuous-rim diamond blade with water — and cut wet, because dry cutting tile produces respirable silica dust.
• Which circular saw blade for wood? 24 teeth for ripping and framing, 40 for general work, 60-80 for a clean crosscut finish.
• Which blade cuts plywood without tearout? A sharp 60-80 tooth blade, a scoring pass, tape on the line, and the good face oriented for the tool you are using.
• Which blade cuts brick? A segmented-rim diamond blade, cut wet or with on-tool extraction — brick and mortar dust is a serious silica hazard.
• Which blade cuts laminate? A triple-chip or negative-hook blade for worktops, and a reverse-tooth jigsaw blade for laminate flooring cut face up.
• Which blade cuts acrylic? A triple-chip negative-hook blade on a table saw, or score-and-snap for thin sheet — and keep the feed steady so it does not melt.
• Which blade cuts glass? None — a tungsten carbide scoring wheel, one firm pass with oil, then snap it. And toughened glass cannot be cut at all.
• Which blade cuts plasterboard? A utility knife for straight cuts and a jab saw or multi-tool for cutouts — a circular saw is the wrong tool entirely.
• Which blade cuts plastic pipe? A fine 24 TPI hacksaw or a proper pipe cutter — and deburr the inside afterwards, which is the step people skip.

Paint

• Which paint goes over previously painted wood? Clean it, key it and spot-prime bare areas — and find out first whether the existing paint is oil or water based.
• Which paint should I use on bare wood? Knotting solution on the knots, a wood primer, then your topcoat — and prime end grain twice.
• Which paint sticks to plastic? Any paint, provided an adhesion promoter goes on first — and on polypropylene or polyethylene, the promoter is not optional.
• Which paint should I use in a kitchen? A scrubbable acrylic eggshell or satin on the walls — and for cabinets, degrease, prime and use a proper cabinet enamel.
• Which paint should I use in a bathroom? A moisture-resistant acrylic in a satin or eggshell sheen with a mould inhibitor — but ventilation, not paint, is the actual fix.
• Which paint should I use on metal? Remove the rust, apply a rust-inhibiting primer the same day, then an alkyd or a direct-to-metal acrylic.
• Which paint should I use on a ceiling? A flat matt emulsion — and if there is a water stain or nicotine, seal it with a shellac-based stain block first.
• Which paint can I use on tiles? Tile paint over an epoxy or adhesion primer on a thoroughly degreased and abraded glaze — and expect a limited life in a shower.
• Which paint should I use on a fence? A penetrating stain or fence treatment rather than a film-forming paint — and let new pressure-treated timber weather first.
• Which paint should I use on a floor? Two-pack epoxy on concrete after a moisture test and a proper grind; floor-grade varnish or floor paint on timber.
• Which paint should I use on radiators? A radiator enamel — water-based acrylic ones no longer yellow, which ordinary gloss on a hot surface always will.
• Which paint should I use on exterior masonry? A breathable mineral or masonry paint — and on an old solid wall, breathability matters more than any durability claim.
• Which paint sticks to galvanised metal? A mordant wash, a self-etch primer or a purpose-made acrylic primer for galvanising — ordinary oil-based primer peels off in sheets.
• Which paint can I use on uPVC? A uPVC-specific paint or an adhesion promoter with an acrylic topcoat — and avoid dark colours, which can distort the frame.

Screw

• Which screw and pilot hole should I use for wood? A pilot hole matching the screw's core diameter in the lower piece and a clearance hole in the upper one — that is what makes a joint tight.
• Which screw should I use for decking? Stainless steel — 304 inland, 316 near the coast — or a screw specifically rated for modern treated timber, which eats ordinary zinc plating.
• Which screw should I use in masonry? A concrete screw into a precisely sized hole, or a plug and screw — and hollow block needs a different anchor entirely.
• Which screw should I use for plasterboard? Coarse-thread bugle-head drywall screws into timber studs, fine-thread into metal studs — and never use them for anything structural.
• Which screw should I use in MDF? A straight-shank MDF screw with a parallel thread, always into a pilot hole — the edge splits without one.
• Which screw should I use for sheet metal? A self-drilling (Tek) screw with a drill point matched to the material thickness, or a self-tapping screw into a correctly sized pilot hole.
• Which screw should I use in chipboard? A twin-thread chipboard screw with an unthreaded shank under the head, so it pulls the joint together instead of bursting the board.
• Which screw should I use in plastic? A thread-forming screw designed for plastic, or a heat-set threaded insert where the joint will be undone more than once.
• Which screw should I use for roofing sheets? A hex-head screw with a bonded EPDM washer, driven until the washer just spreads — no further.
• How do I drive brass screws without snapping them? Cut the thread with a steel screw of the same size first, wax the brass one, and use a driver that fits the slot exactly.

Cable and wire

• Which extension lead should I use for a heavy load? One with a conductor rated for the full load, and always fully unwound — a coiled cable reel can be derated to a fraction of its rating.
• Which cable size is used for socket circuits? Typically 2.5 mm² for a UK ring final on a 32 A device, or 12 AWG on a US 20 A branch circuit — subject to the code and the installation method.
• Which wire size should I use for a 12 V circuit? Size it for voltage drop, not current — at 12 V a small drop is a large percentage, so the cable is far thicker than the amps suggest.
• Which cable size is used for a lighting circuit? Typically 1.0 or 1.5 mm² twin and earth in the UK, or 14 AWG on a 15 A circuit in the US — but the code and the installation method decide.
• Which cable should I use outdoors or underground? Steel wire armoured cable, or a direct-burial type, at the required depth with RCD or GFCI protection — never ordinary indoor cable.
• Which cable size does an electric shower need? Commonly 6 or 10 mm² depending on the shower rating, the run length and the installation method — and it is notifiable work in most jurisdictions.
• Which speaker cable should I use? 16 AWG for short runs and 14 AWG beyond about 15 metres or into low-impedance speakers — and make sure it is copper, not copper-clad aluminium.

Pipe

• Which pipe should I use for hot and cold water? Copper or PEX for most installations — PEX is faster and more freeze-tolerant, copper is more robust and takes heat without question.
• Which pipe should I use for waste and drainage? Solvent-weld or push-fit PVC-u or polypropylene, at the right diameter and fall — and ABS and PVC cements are not interchangeable.
• Which pipe should I use for central heating? Copper, or a barrier-grade plastic pipe — non-barrier plastic lets oxygen into the system and corrodes it from the inside.
• Which pipe should I use for a boiler condensate drain? Plastic, never copper, at a generous diameter with continuous fall — and insulate any external run, because frozen condensate is the classic winter breakdown.
• Which pipe is used for gas? Steel, copper of the right grade, or yellow MDPE underground — and in most jurisdictions only a registered installer may do the work.
• Which pipe should I use for a buried water supply? Blue MDPE for potable water, in one continuous length at the required depth, with no joints under a building.
• Which pipe should I use for compressed air? Copper, steel, stainless or a purpose-rated aluminium or HDPE air system — never PVC, which fails explosively.
• Which pipe should I use for irrigation? Low-density polyethylene tubing with barbed fittings for drip lines, and PVC or MDPE for buried mains.

Lubricant

• Which lubricant should I use on a bike chain? Wet lube for wet conditions, dry lube for dry and dusty ones, wax if you want the cleanest and lowest-friction option — and not a general penetrant.
• Which lubricant should I use on a lock? A dry lubricant — powdered graphite or a PTFE spray. Oil and general penetrating sprays gum locks up and are the classic way to ruin one.
• Which lubricant stops a squeaky door hinge? A drop of light machine oil or a smear of white lithium grease on the pin — and lift the pin out to clean it, which is usually the actual fix.
• Which penetrating fluid frees a seized bolt? A dedicated penetrant or a 50/50 acetone and automatic transmission fluid mix, plus time, heat cycles and shock — and anti-seize on reassembly.
• What should I put on a squeaky floorboard? Talc, graphite or powdered soapstone worked into the joint as a stopgap — the real fix is screwing the board down to the joist.
• What should I put on a sticky drawer? Paraffin wax or beeswax on wooden runners, dry PTFE on metal ones — and never oil on wood.
• Which lubricant is safe on rubber seals? Silicone grease on most rubbers, and a PTFE or fluorosilicone product on silicone rubber itself — petroleum products swell and destroy natural rubber and EPDM.
• Which lubricant should I use on a garage door? White lithium grease or a garage-door lubricant on rollers, hinges, springs and bearings — and not on the track, which should be clean and dry.