Sealant Guns: Skeleton, Sausage, and Smooth-Rod Explained
What a sealant gun does, why thrust ratio matters, the difference between skeleton, sausage, and smooth-rod, and how to lay a clean bead. Buy from £4 upwards.
A homeowner finishes a tiled splashback behind a new range cooker. The tiles are crisp, the grout is even, the worktop sits flat. They reach for the silicone tube to seal between worktop and tiles. Half the joint comes out as a thick rope, the other half as a thin trickle. They try to smooth it with a finger and the bead tears. Two hours later, the joint is patchy, the worktop has silicone smears around it, and the only fix is a scraper, a solvent rag, and starting again.
The sealant gun decides whether a silicone bead reads as fitted finish or DIY mess. The 4 pound sealant gun in the bargain bucket at the merchant is a common sight on homeowner job sites and a common reason for the result above. A 15 pound sealant gun lays a consistent bead, takes the same effort as smearing peanut butter on bread, and lasts ten projects. The choice is whether to skip the 11 pound difference and pay it back in time and re-work.
What a sealant gun is
A sealant gun (also called a caulking gun, mastic gun, or cartridge gun) is a hand tool that holds a 310ml standard cartridge of silicone, acrylic, polyurethane, or epoxy adhesive, and forces the contents out through the cartridge nozzle by pushing a plunger against the cartridge piston. You squeeze the trigger, the plunger advances, and a measured bead of sealant comes out the nozzle.
The simplest model is the skeleton gun, an open metal frame with a half-circle cradle that holds the cartridge and a notched rod that pushes the plunger. The trigger is a ratchet that advances the rod one click per squeeze. Skeleton guns cost 3 to 6 pounds, work fine on the cheapest acrylic decorator's caulk, and are the most common sealant gun in UK homeowner toolboxes.
The next step up is the smooth-rod gun, where the plunger advances continuously without ratchet clicks. The smooth-rod design produces a more even bead because the trigger pressure translates directly into plunger force without the start-stop of a ratchet. Smooth-rod guns cost 10 to 25 pounds and are the trade default for serious silicone work.
Beyond that are sausage guns (for foil-pack sealant rather than rigid cartridges), pneumatic and battery-powered guns (for production work), and specialist guns for two-part adhesives. For homeowner extension work, smooth-rod with a 310ml cartridge cradle is the right choice.
| Type | Approx price | Best for |
|---|---|---|
| Skeleton (cheap budget) | £3-6 | Decorator's caulk, occasional use, one-off jobs |
| Skeleton with high thrust ratio | £8-15 | Silicone, regular use, kitchen and bathroom seals |
| Smooth-rod (drip-free) | £12-25 | Trade-quality silicone work, the homeowner default for kitchens |
| Sausage gun | £15-30 | Tradesperson use with foil-pack sealant; less waste, cheaper sealant |
| Pneumatic / battery powered | £60-200+ | Production silicone work, hardly justified for one kitchen |
Thrust ratio: the spec that matters
This is the specification beginners don't know exists. Thrust ratio is the mechanical advantage of the trigger relative to the plunger force. A 12:1 thrust ratio means one pound of trigger force produces twelve pounds of plunger force. Higher ratios mean less effort, more even beads, and the ability to push thicker sealants.
Decorator's caulk is thin and pumps fine through any gun. A 4:1 ratio handles caulk easily. Silicone is much thicker, particularly low-modulus silicones designed for kitchen and bathroom seals. Pumping silicone through a low-thrust skeleton gun is hard physical work. Your hand fatigues, your trigger pressure varies, and the bead comes out uneven.
For silicone work, the minimum useful thrust ratio is 12:1. Trade guns are typically 18:1 or higher. The Newborn 250 series (a US brand widely sold in the UK) and the Cox Constructor 600 are both 18:1. Spend the 8 pound difference between a 4:1 cheap gun and a 12:1 mid-range gun and the silicone work becomes easier.
Tip
The cheapest skeleton guns at builders' merchants typically don't print the thrust ratio. If the price is under 5 pounds and the spec sheet doesn't mention thrust, assume 4:1 or 6:1 and accept that it'll struggle with silicone. Spend 10 to 15 pounds on a known brand (Cox, Newborn, Albion) and the ratio is printed on the packaging.
Skeleton versus smooth-rod: the drip difference
The other specification that matters is whether the gun has a thumb release that retracts the plunger immediately when you stop squeezing.
A skeleton gun continues to push the plunger after you release the trigger because the ratchet rod has no easy back-step. The pressure inside the cartridge keeps pushing sealant out the nozzle for several seconds after you stop pressing. This is what causes the dribble of silicone that lands on the wrong piece of timber, drops on your shoe, or tracks across a finished tile.
A smooth-rod gun has a thumb release at the back of the gun. Press the thumb release and the rod retracts, the pressure on the cartridge drops, and the sealant flow stops immediately. Smooth-rod guns are also called drip-free or no-drip guns for this reason. The difference is real and cumulative: across a long bead, a smooth-rod gun produces a clean cut-off at the end of every section, where a skeleton gun produces a tail.
For one-off occasional use, a skeleton with thumb release is enough. For a kitchen extension where you'll be running silicone around sinks, hobs, worktop joints, and worktop-to-wall joints, a smooth-rod is worth the 10 to 15 pound difference.
How to lay a clean silicone bead
The technique is the same whether you're using 3 pound acrylic caulk or 15 pound specialist silicone. The difference between a clean bead and a mess is preparation and angle.
Prepare the joint
The two surfaces being sealed must be clean, dry, and free of dust. Wipe with a clean rag and methylated spirit, then let it dry. Old silicone must be removed completely with a sealant remover (Hippo, Soudal Stop & Seal Remover) and a sharp knife. Silicone does not bond to old silicone.
Mask both sides of the joint
Apply low-tack masking tape to both surfaces, leaving a gap the width of the bead you want to lay. The tape gives a clean cut line and protects the surrounding surfaces from smears. Apply the tape so it'll lift cleanly without dragging silicone with it.
Cut the cartridge nozzle at 45 degrees
Cut the plastic nozzle at a 45 degree angle, with the opening sized to match the joint width. A 5mm joint needs a 5mm opening. Most cartridges have moulded grading marks on the nozzle. Test on cardboard first to check the bead width before committing to the joint.
Pierce the foil seal inside the cartridge
Most cartridges have a metal foil seal inside the threaded neck. Push a long thin object (the wire from a clothes hanger, or the spike that comes with most sealant guns) down through the nozzle to break the seal. Without this step the sealant won't come out at all.
Hold the gun at 45 degrees and pull, don't push
Lay the nozzle into the joint at 45 degrees to the surface. Pull the gun along the joint rather than pushing it. Pulling drags the bead behind the nozzle and produces a cleaner finish. Pushing rolls the bead up in front of the nozzle, traps air, and looks lumpy.
Move at constant speed with constant trigger pressure
The bead size is determined by speed (move slow for thicker beads, fast for thinner) and pressure (more squeeze for more sealant). Keep both constant along the joint. Smooth-rod guns make this much easier because the trigger pressure translates directly to bead size.
Tool the bead immediately
A wet finger, a small spatula, or a dedicated silicone tool (Fugi sticks are the trade default at around 4 pounds) smooths the bead into the joint and produces a concave finish. Tooling needs to happen within 5 to 10 minutes of laying the bead, before the silicone skins over.
Lift the masking tape while the bead is still wet
Remove the tape immediately after tooling, before the silicone skins. Pulling the tape after the silicone has skinned tears the bead. Pull at 45 degrees to the joint, away from the bead.
Tip
A spritz of soapy water (washing up liquid in a fine spray bottle) on the bead before tooling acts as a release agent. The wet finger or spatula glides without dragging the silicone. This is the trade trick that produces the trade finish and most guides don't mention it.
What to buy
For one extension build, three purchase tiers cover the realistic options.
| Tier | Approx price | Models | Buy if... |
|---|---|---|---|
| Budget skeleton | £3-6 | Wickes own-brand skeleton gun, generic Screwfix sealant gun | You only need to lay decorator's caulk on skirting |
| Mid-range skeleton with thumb release | £8-15 | Stanley 0-12-007 ratchet gun, Faithfull FAISGSR ratchet gun, Roughneck 32-100 | You need silicone capability for kitchen and bathroom work, occasional use |
| Smooth-rod drip-free | £12-25 | Cox Constructor 600 (~£15-18), Newborn 250L (~£18-22), Albion B-line 625-1 (~£20) | You're doing serious silicone work and want a tool that lasts beyond one project |
| Premium battery-powered | £60-200+ | Makita CG100D, DeWalt DCE580, Cox Battery 600 | You're a professional installer or doing multiple kitchens |
For a single recommendation: the Cox Constructor 600 at around 15 pounds from Toolstation is the homeowner-accessible smooth-rod gun that the trade buys for second-fix kitchen work. 18:1 thrust ratio, smooth-rod drip-free design, takes a 310ml cartridge, and fits in a tool bag. If budget is tight, the Faithfull FAISGSR ratchet gun at around 8 pounds from Screwfix gives you most of the bead quality at half the price.
Skip the 3 pound skeleton guns at the merchant counter. The 5 pounds saved is what gets paid back in re-work and frustration on the first kitchen joint.
Cartridge types: what fits what
The standard UK cartridge is 310ml (sometimes labelled 300ml, the difference is rounding). Most homeowner guns hold this size. Two slightly different cartridge types exist:
Standard 310ml plastic cartridges are the dominant format. Almost any sealant gun handles these. The cartridge has a piston at the back end that the plunger pushes, and a threaded nozzle at the front.
Foil pack sausages (typically 400ml or 600ml) are used by tradespeople because the sealant is cheaper per ml and there's no rigid plastic to dispose of. Sausage guns are required; standard cartridge guns won't take them.
For a homeowner extension toolkit, standard 310ml cartridges are the right choice. Trade-volume sausage packs are unjustified for the number of joints you'll seal in one build.
Where you'll use it
Sealant guns earn their place at every finishing detail in a kitchen extension:
- Kitchen installation for the worktop-to-wall joint, sink rim, hob cutout, and any worktop-to-tile or worktop-to-glass interface
- Tiling for movement joints, wall-to-floor transitions, and silicone in shower areas
- Skirting and architrave for caulking the gap between skirting and wall, between architrave and frame, and at internal corners
- Decoration for caulking the joint between ceiling and wall, around door frames, and any other paint-line edge that needs bridging
- Snagging checklist for re-doing any silicone joints that have failed since first-fit
The gun lives in the toolbox through second fix and decoration. After final snagging, it goes back in the cupboard for the next project.
Common mistakes
Pushing the gun instead of pulling. Pushing rolls the bead in front of the nozzle and traps air. Pull the gun along the joint and the bead drags behind cleanly.
Cutting the nozzle straight across. A flat nozzle cut produces a square bead that doesn't tool well. Always 45 degrees.
Skipping the masking tape. Tape produces a clean cut line that no amount of finger-smoothing can match. Five minutes of taping saves twenty minutes of cleanup.
Tooling too late. Silicone skins in five to ten minutes. Tool immediately after laying the bead, while it's still wet. Skinned silicone tears rather than smooths.
Using old silicone. Silicone has a shelf life of around 12 to 18 months. Old cartridges go gluey and don't lay an even bead. Check the date code on the cartridge before opening.
Sealing onto a dirty or wet surface. Silicone bonds chemically to the substrate. Dust, grease, or moisture in the joint prevents the bond and the silicone peels off in weeks.
Trying to silicone over old silicone. New silicone will not bond to old silicone. Strip the old joint completely, clean with sealant remover, then re-seal.