Caulking gun: what it does and when to reach for it

Learn to load, cut, and use a caulking gun to lay a neat, even bead of sealant.

CG-01Know what the tool is forA caulking gun holds a cartridge of sealant (also called caulk) and squeezes it out in a controlled line, called a bead. You reach for it to fill gaps that need to flex or stay waterproof, like where a bath meets a tile wall, round a window frame, or along a skirting board where it meets the floor. It is not for structural gaps or holes bigger than about 5mm - those need filler or expanding foam instead.

CG-02Load the cartridgePull back the long metal rod at the back of the gun until the round plate at the front (the plunger) sits flat against the frame. Drop the sealant cartridge in nozzle-first, then push the rod forward gently until it just touches the back of the cartridge. Beginners often shove the rod in hard and crack the cartridge - just make contact, don't force it.

1 each · Sealant cartridge

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CG-03Cut the nozzle to the right sizeThe cartridge has a plastic nozzle with a pointed tip. Cut it at an angle, about 45 degrees, using a sharp knife or scissors. Cut close to the tip for a thin bead in a small gap, or further back for a wider gap - the hole should be roughly the same width as the gap you're filling. Cutting too much off is the classic mistake; you can always cut more, but you can't put plastic back on.

CG-04Pierce the inner sealInside the nozzle there's a foil or plastic seal stopping the sealant coming out. Push a long thin object, like a skewer or a straightened wire coat hanger, down through the cut nozzle to break it. Some guns have a built-in metal spike on the frame for exactly this job. If you skip this step, you'll squeeze the trigger and nothing will come out.

CG-05Lay the beadHold the gun at a steady 45-degree angle to the gap and squeeze the trigger with even pressure, moving the gun slowly along the join in one continuous pull. Pull the gun towards you rather than pushing it away - this gives you a smoother, more even line and lets you see where the sealant is going. Beginners tend to squeeze in short bursts, which leaves lumpy, uneven sections instead of one smooth bead.

CG-06Smooth the bead before it skins overWet your finger with soapy water (a squirt of washing-up liquid in a cup of water works well) and run it along the bead once, in one smooth motion, to press it into the gap and remove the ridge. Do this within a minute or two of applying it, before it starts to form a skin. Wipe your finger clean on a cloth after each pass rather than dragging the excess back and forth, which smears it.

1 each · Cloth or kitchen roll

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CG-07Check you've done it rightA good bead is continuous with no gaps or holes along its length, sits flush or very slightly concave against the surfaces either side, and has no smears or fingerprints on the surrounding tile, wood, or wall. If you see air bubbles, thin patches, or the bead has pulled away from one side, smooth it again while it's still soft, or scrape it off and start that section again.

CG-08Release the pressure and store the gunAfter the last pull of the trigger, sealant keeps oozing out for a second or two because the gun stays under pressure. Push the small release lever near the trigger (or twist the rod, depending on the gun) to drop the pressure immediately and stop the drip. Cap the nozzle or push a screw into it to stop the sealant curing inside, and store the gun with the cartridge still loaded if you'll use it again soon.

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