How To Seal a Sink

How do you seal around a sink or basin?

A proper seal around a sink prevents water penetration, makes the area easier to clean, and keeps the cabinet underneath from swelling and discolouring. The method is short: clean and dry the joint, remove any existing silicone, gun a steady bead of Selleys No Mould at 45 degrees, smooth it with a damp finger or rounded spatula, and clean up with mineral turps before the product cures.

Fifteen minutes of work. What determines whether it lasts is preparation — contaminants will prevent a decent bond, and a sink surround collects exactly the contaminants that stop silicone sticking: detergent film, cooking oil, hand cream, toothpaste.

What you need

• Selleys No Mould
• A caulking gun
• A utility knife — a small, sharp blade makes cleaning edges safe and easy
• A rounded spatula
• A clean rag
• Mineral turpentine
• Masking or painters tape

Step 1 — Prepare the joint

Clean your workspace so that it is free from dust and debris. If necessary, cut away or remove any existing silicone. Contaminants will prevent a decent bond, so wipe over the area with some mineral turps.

If the old bead is stubborn, Selleys Sealant Remover handles it: cut the sealant back to a layer less than 5 mm deep, spread at least a 5 mm thick layer of remover evenly over it, leave it at least 10 minutes, then scrape it off and clean residue with mineral turpentine. See how to remove old sealant for the detail.

If there is any mould in the old joint, spray Selleys Rapid Mould Killer into the gap first to kill residual mould, then dry the area thoroughly. Sealing over live mould does not work — an established colony can penetrate a new seal even where the new product contains mould inhibitors.

Then let it dry. The gap between a basin and a benchtop holds water for longer than the surfaces around it, and silicone does not bond reliably to a damp surface.

Step 2 — Mask, if you want a clean line

For neater joints, mask both sides before applying the sealant, and remove the tape before the sealant skins. On a benchtop this is worth doing: a bead against a laminate or stone surface shows every wobble, and tape gives you a straight edge without needing a steady hand.

Step 3 — Load the gun

Load the Selleys No Mould cartridge into your caulking gun. Cut the cartridge tip, fit the nozzle, and cut it at a 45 degree angle sized to the joint. Cut it smaller than you think — you can widen it, but you cannot go back.

If you have not used a gun before, see how to use a caulking gun.

Step 4 — Run the bead

Hold the sealant tip at a 45 degree angle and apply the silicone evenly and with a steady hand. When you reach the end of the area you want to seal, release the lever to stop the flow of silicone.

Push the sealant into the joint rather than laying it over the surface. A bead that merely sits on top has almost no depth of bond and peels away; one pressed into the gap grips both faces and flexes with the small movements a benchtop and basin make.

Do the whole run in one pass. Joins in a bead are weak points and they show.

Step 5 — Smooth it

Use a damp finger or rounded spatula to wipe off any excess product and leave a smooth, clean finish.

Do this promptly. No Mould's published skin time is 20 minutes, and Selleys' own directions for the product are to tool with a spatula dipped in detergent water within 10 minutes of application. Past that, the surface has begun to set and smoothing tears it rather than shaping it.

Pull the masking tape off as soon as the bead is smoothed, before the sealant skins.

Step 6 — Clean up

Clean up any excess and your tools with mineral turps before the product cures. Cured silicone has to be cut off mechanically, and doing that against a stone or laminate benchtop is a job worth avoiding.

Curing — when can the sink be used?

Selleys No Mould contains Speed Seal technology. Its technical data sheet states that the sealant is waterproof and shower ready 1 hour after application, and that the semi-cured sealant must not be touched until fully cured — at least 48 hours.

Property	Typical result
Technology	Acetic cure silicone sealant
Skin time	20 minutes
Curing rate	2 mm / 24 hours
Waterproof	1 hour after application
Full cure	At least 48 hours
Joint movement capability	±25% (ISO 9047)
Elongation	Approx. 400% (ASTM D412 modified)
Packaging	290 mL cartridge or 100 mL tube; transparent or white

Indicative data only, not intended for the preparation of specifications.

What the difference between those two numbers means: silicone cures from the outside in. At one hour the skin is firm enough to keep water out, which is why the sink can go back into normal use. Underneath, the material is still curing at about 2 mm a day, which is why the 48 hour figure exists. Normal use is fine during that window; touching, wiping or scrubbing the bead is not.

Choosing the right product for your benchtop

No Mould is an acetic cure silicone. Acetic cure suits glazed ceramic, porcelain, glass and stainless steel — most kitchen and bathroom sinks and most tiled surrounds.

If the joint runs against natural or engineered stone, use a neutral cure product instead — Selleys Wet Area Silicone, which is neutral cure and lists ceramic, glazed and porcelain fixtures, metal, copper and brass fittings, powder coated aluminium, plastic laminates, glass, stainless steel and concrete among its substrates. It cures in 72 hours rather than 48.

Limitations — where No Mould should not be used

• Not paintable. Complete any painting 7 days before applying the sealant.
• Not suitable for aquariums.
• Not suitable for food and drinking water contact. A bead around the outside of a sink is not in food contact; a bead inside a food preparation vessel would be.
• Not suitable for permanent water immersion.
• Not suitable for metals other than aluminium and stainless steel. Worth checking before sealing against a copper or brass sink — for those, the neutral cure Wet Area Silicone lists copper and brass fittings among its substrates.

Keeping the seal working

Keep the sealant cleaned regularly to avoid the build-up of soap scum. This is not housekeeping advice — it is a condition of the product's own mould performance. No Mould's technical data sheet qualifies its "stops mould growth" claim with the requirement that soap scum and dirt are regularly cleaned off, because those, not the silicone, are what mould feeds on.

Safety: the fifteen-minute job, and the one step that is not

Running the bead is the mild part. No Mould is a Warning-level product — skin and eye irritation and skin sensitisation — and mineral turps is a familiar solvent. The step that carries a serious classification is the optional one in step 1, for a stubborn old bead.

Selleys Sealant Remover is classified Danger, 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). Dangerous Goods Class 3, UN 1133, Packing Group II.

Keep it scoped to what it is for. This page is right that most of the preparation is cutting the old bead away and wiping with turps. The remover is for the residue that will not come off that way. Using it because it is on the shelf turns a fifteen-minute job into a solvent job, and the difference in what you are breathing is real.

Where the vapour goes at a sink. A basin or kitchen sink joint sits under an overhang, against a splashback, with a cupboard open below you. Those are three surfaces trapping air around your face, and the method holds the remover there for at least ten minutes. Open a window, run the rangehood or the exhaust fan, and do not put your head in the cupboard while it dwells. In a kitchen, turn a gas cooktop and its pilot off first — H226 vapour is heavier than air and moves along the benchtop and the floor.

H315 is the everyday one. The method is to spread a thick layer and scrape it, which puts your fingers in the product repeatedly. Nitrile gloves, not bare hands and not the kitchen gloves under the sink. Safety glasses, because you scrape back toward yourself at face height.

H304 means the tub never gets decanted into anything that looks like a drink container, and if any is swallowed the product's own first aid is do not induce vomiting — rinse the mouth, give water, get advice immediately.

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

Common questions about sealing a sink

How soon can I use the sink?

One hour after application with Selleys No Mould, at which point the bead is waterproof. Do not touch it until it has fully cured at 48 hours.

How long is full cure?

At least 48 hours for No Mould; 72 hours for Wet Area Silicone.

How long do I have to smooth the bead?

Tool it within 10 minutes of application. Its skin time is 20 minutes, after which smoothing tears the surface.

Should I use a finger or a tool?

Either — a damp finger or a rounded spatula. A spatula dipped in detergent water gives the most consistent concave finish, which is what sheds water instead of holding it.

Do I have to remove the old silicone?

Yes. Contaminants and old residue prevent a decent bond, and a fresh bead over an old one may not adhere well to the original silicone.

What colour should I choose?

No Mould is available transparent or white. Transparent is the safer choice against a patterned or coloured benchtop; white reads as part of the tile or grout line.

Cartridge or tube?

A 100 mL tube covers a single small basin. A 290 mL cartridge in a gun gives much better control on a long benchtop run.

Can I paint the bead?

No. Complete painting 7 days before sealing.

What if my benchtop is stone?

Use a neutral cure product — Selleys Wet Area Silicone — rather than an acetic cure one.

What removes silicone from my hands and tools?

Mineral turps, before the product cures. Once cured, it has to be cut or scraped off.

Is there a guide for a kitchen splashback join?

Yes — how to seal a kitchen splashback.