Caulking gun: setting it up and changing the bit or blade

Learn to load, prime and control a caulking gun so sealant comes out smoothly, not in blobs.

CG-01Learn the parts of the gunA caulking gun has a frame, a long metal plunger rod that runs through the middle, and a trigger that pushes the rod forward a little each squeeze. There's also a thumb release lever near the back handle - pressing this lets you pull the rod all the way out freely. Find this lever now, because you'll use it constantly.

CG-02Load the cartridgeA cartridge is the plastic or cardboard tube of sealant (also called mastic or caulk). Press the thumb release lever and pull the plunger rod all the way back. Drop the cartridge into the cradle nozzle-first, then push the rod forward gently until the flat plate at its tip touches the back of the cartridge. It should sit snugly, not loose and not jammed.

1 each · Sealant cartridge

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CG-03Cut the nozzle to sizeThe nozzle is the tapered plastic tip. Cut it at an angle, about 45 degrees, with a craft knife or sharp scissors. Start small - a 3-5mm hole gives a thin bead. Cut more off later if you need a wider bead, but you can't undo a cut that's too big.

CG-04Break the inner sealInside the nozzle there's often a foil or plastic seal that stops the sealant drying out in the tube. Push a long nail, a piece of wire, or the pointed spike built into many craft knife handles down through the cut nozzle to puncture it. If you skip this, nothing will come out no matter how hard you squeeze the trigger.

CG-05Prime the gun before you startPoint the nozzle at some scrap card or paper, not your project, and squeeze the trigger several times until sealant actually appears at the tip. This takes up the slack in the mechanism. The beginner mistake is starting straight on the job - the first few centimetres come out thin and patchy because the gun wasn't primed.

CG-06Control the flow while you workSqueeze the trigger steadily and move the gun along the gap at a smooth pace - don't stop mid-bead if you can help it. The ratchet mechanism inside keeps pressure on the sealant even after you let go of the trigger, so it keeps oozing out for a second or two. The moment you finish a bead, press the thumb release lever - this drops the pressure instantly and stops the ooze, which is what stops you leaving a blob at the end of every line.

CG-07Know you've got it rightYou've set it up correctly if the bead comes out as one continuous, even ribbon with no air gaps, spitting, or sudden bursts. When you release the thumb lever the flow should stop within a second, not keep dribbling. If sealant keeps coming after you've released the lever, the pressure has built up too far - squeeze less next time and release the lever sooner.

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