Silicone vs decorator's caulk

Learn to tell silicone from decorator's caulk, and apply a neat, even bead of either.

SC-01Understand what each one is forSilicone sealant is flexible and waterproof. Use it anywhere water sits or splashes, like around a bath, shower tray, sink or worktop join. Decorator's caulk is a paintable filler for static gaps that never get wet, like where skirting meets a plastered wall, or a crack where a ceiling meets a wall. Caulk goes hard and can crack if used somewhere that moves or gets wet, and silicone can't be painted over neatly, so mixing them up is the classic beginner mistake.

SC-02Pick the right tube for the jobFor wet areas, buy a bathroom or kitchen silicone, usually white or clear, often with mould-resistant additive. For gaps you'll paint, buy 'decorator's caulk' in a tub or tube. Both come in cartridges that fit a sealant gun, a hand tool that squeezes the tube out at a controlled rate through a trigger.

1 each · Bathroom silicone sealant cartridge

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1 each · Decorator's caulk cartridge

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SC-03Prep the gap before you touch the gunThe surface must be clean, dry and free of dust, old sealant or grease, or the new bead won't stick and will peel off within weeks. Run masking tape along both edges of the gap, leaving only the joint exposed, to give you dead straight lines. This feels slow but it's what makes the difference between a scruffy bead and a professional-looking one.

1 roll · Masking tape

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SC-04Load the gun and cut the nozzle correctlyFit the cartridge into the sealant gun and pull the trigger gently until you feel resistance, that's the plunger meeting the tube. Snip the plastic nozzle tip at an angle with a knife or scissors, low down for a thin bead, higher up for a thicker one. Pierce the foil seal inside the nozzle with a thin nail or the gun's built-in spike before you start, or nothing will come out.

SC-05Run a steady bead along the gapHold the gun at a consistent 45 degree angle to the joint and squeeze the trigger with steady, even pressure while moving in one smooth, unbroken pass. Move at a pace that lays down a continuous line, not too fast (gaps) or too slow (blobs). The beginner mistake is stopping halfway through, which leaves a visible join in the line.

SC-06Smooth the bead before it skins overWet your finger (or a proper sealant smoothing tool) and run it along the bead in one single stroke, pushing the sealant slightly into the gap and wiping the excess onto a cloth as you go. Do this within a minute or two, before a skin forms on the surface. Don't go back over the same section twice, it drags and looks messy.

1 each · Cloth or kitchen roll

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SC-07Peel the tape and check your workPeel the masking tape away slowly at a 45 degree angle while the sealant is still soft, straight after smoothing, not once it's cured. Done right, you'll see a smooth, slightly concave line with crisp, straight edges and no gaps, smears or trapped air bubbles. Leave it untouched for the time stated on the cartridge, usually 24 hours, before it gets wet or painted.

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