How To Use a Caulking Gun

How do you use a caulking gun?

Whether you have a shower that needs resealing or some gaps to fill, a caulking gun is likely to be part of your arsenal. If the thought of using one makes you nervous, there are four steps to have you caulking like a pro: understand the gun, prepare the cartridge, apply the product, and finish the joint.

Nothing about it is difficult. What catches people out is that a caulking gun does not stop instantly when you stop squeezing, and that sealant is only workable for a few minutes after it leaves the nozzle. Both are dealt with below.

Before you start

Look at the type of cartridge product you are using, because sealants and glues want different preparation.

If you are waterproofing a joint with a sealant, or filling a gap before painting, do some preparation first: mask up 5 mm either side of the joint. This makes sure you get the neatest possible finish afterwards, and it is the single easiest way to make a first attempt look like a professional one.

If you are using a glue, you do not have to worry about masking — just make sure the surfaces are clean and dry. Check the cartridge of the glue you are using for more information.

Step 1 — Become one with the caulking gun

Each caulking gun typically has four parts:

• A barrel or cradle that holds the cartridge.
• A plunger rod that pushes the product out.
• A large trigger for extruding the product.
• A small trigger that releases the plunger rod so you can remove the cartridge.

That small release trigger is the one worth finding before you start rather than during. Squeezing it mid-bead is what stops the flow; forgetting it exists is what causes product to keep oozing out after you have finished a run.

Step 2 — Prepare the cartridge

Cut the tip off the cartridge. Secateurs work very well for this and are safer than knives — the tip is a small, awkward plastic cone and a slipping blade has nowhere good to go.

Then cut the nozzle to the width of the joint, or to your desired bead size, on a 45 degree angle. Cut it smaller than you think you need: you can always trim the nozzle further back to widen the bead, but you cannot make the opening smaller again.

Insert the cartridge into the gun. You will need to ensure the plunger rod is pulled all the way out first, or the cartridge will not seat.

Why 45 degrees

The angled cut lets you hold the gun at a comfortable angle to the work while keeping the nozzle opening flat against the joint. That is what pushes product into the gap rather than laying it across the surface — and depth of bond, not width of bead, is what makes a seal last.

Step 3 — Apply the product

If this is your first time using a caulking gun, get some practice by gunning the product onto some cardboard to get a feel for how it comes out. Products vary enormously in viscosity, and thirty seconds of practice tells you more than any instruction.

When you are ready, apply the product into the joint. Gun in a forwards direction, making sure the product is pushed in as you go.

You will find that when you have to release the trigger to pull again, you may get a little blob appear. This is normal. It can be smoothed out after application when you smooth your sealant; glues will just get squished flat when the surfaces are brought together.

Getting an even bead

Steady pressure and steady speed. Moving too slowly builds a fat bead; too quickly leaves a starved one. Aim to complete a whole joint in one pass — joins in a bead are weak points and they show.

Work in sections you can finish before the sealant skins. That window is short: most Selleys silicones want tooling within 5 to 10 minutes of application, and No Mould's published skin time is 20 minutes. On a long run, that means completing and smoothing one length before starting the next, not running the whole bathroom and then coming back to tidy up.

Step 4 — Finish off your joint

You are now ready to finish off your joint. Soapy water often works well for this, but the manufacturer of the product will recommend the best way to finish their sealants or fillers — check the pack, because the recommendation differs between products. A spatula dipped in detergent water is the common instruction across the Selleys silicone range; some products call for mineral turps instead.

Pull the masking tape off as soon as the bead is smoothed, before the sealant skins. Tape removed after skinning drags the edge of the bead with it.

Glues are finished differently: bring the surfaces together and clamp them in place until they dry.

What to do with the leftover product

An opened cartridge does not have to be thrown away. You can store it for longer by simply leaving the nozzle on the cartridge filled with product. When you need to use it again, just clear the nozzle using a screw or a nail.

Typically, products will last 3 to 6 months when stored like this in a cool, dry location.

The product in the nozzle cures into a plug, and that plug is what keeps air away from everything behind it. Pull the plug out next time and the cartridge is usable. Individual products have their own shelf life and storage requirements too — several Selleys silicones specify storage below 30 °C and use within 6 months of opening, so check the pack for anything you want to keep.

Common mistakes worth avoiding

• Cutting the nozzle too big. The most common error, and irreversible. Start small.
• Laying the bead on the surface instead of into the joint. A bead sitting on top has almost no depth of bond and peels away.
• Tooling too late. Once the surface has skinned, smoothing tears it rather than shaping it.
• Skipping the masking. Two minutes of tape saves ten minutes of cleaning and produces a better line than a steady hand does.
• Sealing a joint you intend to paint. Silicone sealants across the range are not paintable, and painting must be completed 7 days before the sealant is applied. If the joint has to be painted, use a paintable gap filler instead.
• Not cleaning up before the product skins. Cured silicone has to be cut off mechanically. A minute with turps now saves a great deal of scraping later.

Choosing what goes in the gun

The gun is the easy part; the product decides the result. For wet areas, a wet area silicone such as Selleys Wet Area Silicone gives a waterproof, mould resistant seal that will not shrink, crack or peel away. For interior gaps that will be painted, a gap filler is the right family. See types of caulk for how the categories differ.

If you are removing an old bead before laying a new one, Selleys Sealant Remover takes the elbow grease out of removing old and unwanted sealant — silicone, acrylic, SMP/hybrid or polyurethane — with a single application, for showers, baths, spas, sinks, vanities and splashbacks.

Safety: the gun is harmless, the products in it are not all the same

This page is where most people start, so it is worth saying once: what goes in the gun varies enormously in hazard, and the cartridge does not tell you at a glance. Read the label's signal word before you cut the nozzle. A wet area silicone is usually a Warning product — eye irritation, skin sensitisation. Some solvent-borne sealants and adhesives are Danger and are classified flammable liquids for transport.

The product named above for stripping an old bead is one of the serious ones. Selleys Sealant Remover carries the signal word Danger and Poison Schedule S5, with H304 (may be fatal if swallowed and enters airways), H226 (flammable liquid and vapour), H336 (may cause drowsiness or dizziness) and H315 (causes skin irritation). It is Dangerous Goods Class 3, UN 1133, Packing Group II.

It is used in exactly the rooms that hold vapour. This page lists its jobs as showers, baths, spas, sinks, vanities and splashbacks. Every one of those is a small enclosed space, and the method leaves a thick layer sitting and evaporating for at least ten minutes before you scrape. Open the window and run the exhaust fan for the duration, and turn off any gas appliance or pilot in the room first — H226 vapour is denser than air and travels along the floor rather than rising out of the window you opened.

H304 changes how you store it. A resealed tub of solvent in a cupboard with cleaning products is the classic way this product ends up swallowed. Keep it in its own labelled container, lid on between applications, out of reach of children. If any is swallowed, the product's first aid is explicit: rinse the mouth, give water, and do not induce vomiting.

The practical habits that cover most of it. Nitrile gloves whenever you tool a bead with a finger — several silicones carry skin sensitisation, which is permanent once acquired and is built up by casual repeated contact rather than one exposure. Safety glasses when you cut a nozzle or work overhead. And the page's own tip about secateurs is a safety point as much as a neatness one.

Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.

Common questions about using a caulking gun

What angle do I cut the nozzle at?

45 degrees, sized to the width of the joint or your desired bead size.

What is the best tool for cutting the cartridge tip?

Secateurs — they work very well and are safer than knives.

Why won't the cartridge fit in the gun?

The plunger rod needs to be pulled all the way out first.

How do I stop the product flowing?

Release the trigger. Most guns also have a small trigger that releases the plunger rod, which stops residual pressure pushing more product out.

I get a blob every time I re-grip. Is that normal?

Yes. It can be smoothed out when you finish the joint; with glues it just gets squished flat when the surfaces come together.

What do I smooth the bead with?

Soapy water often works well, but check the pack — the manufacturer will recommend the best way to finish their own sealant or filler.

Do I need to mask?

For a sealant or a gap being filled before painting, yes — 5 mm either side. For glues, no; just make sure the surfaces are clean and dry.

How do I stop an opened cartridge going hard?

Leave the nozzle on, filled with product. Clear it with a screw or nail next time.

How long will an opened cartridge keep?

Typically 3 to 6 months when stored that way in a cool, dry location. Check the individual product's own storage advice as well.

How much practice do I need?

A few beads on cardboard is enough to get a feel for how the product comes out before you touch the real joint.

What if I make a mess of the bead?

Clean it up with the solvent the pack specifies before the product skins, and start again. Once cured, it has to be cut out — see how to replace old silicone.