Can You Apply Another Bead of Silicone After the First Dries?
Can you apply a second bead of silicone over the first, a day later?
No. Selleys does not recommend putting another layer of silicone over an existing bead, because it may not adhere to the original silicone very well. The right approach is to cut out the previous bead and reapply a fresh one to the correct depth, making sure it is properly adhered to the edges of the area being sealed.
This comes up constantly in showers, and usually for the same reason: the first bead did not look right, or a small section pulled away, and adding a second layer looks like a five minute fix. It is not — it is a joint that will fail again, usually along the seam between the two layers, and then you have twice as much material to cut out.
Why fresh silicone does not bond to cured silicone
A silicone sealant cures by reacting with moisture in the air to form a rubber. Once that reaction is complete the surface is chemically finished — there is very little left for a new bead to react with. Fresh silicone laid on top grips the cured surface weakly, mechanically rather than chemically, and that weak seam becomes the failure point the first time the joint moves.
The other half of the problem is depth. A properly performing bead has to be seated into the joint and bonded to both faces, so that when the joint moves the bead stretches across it. A second layer sitting on top of an old one is bonded to silicone, not to the tile and the tray. It cannot do the job the joint needs done, however thick it is.
Do it properly instead
- Cut the old bead out completely. Run a blade down both edges to break the bond with each face, then lift the length of silicone away in as long a piece as you can.
- Remove the residue. A thin film always stays behind, keyed into the grout and glaze. Apply Selleys Sealant Remover at least 5mm thick over the remaining silicone, leave it at least 10 minutes to soften — a second application may be needed on stubborn residue — then work a scraper backwards and forwards to lift it. Clean up residue and tools immediately with mineral turpentine.
- Treat any mould. Before applying new sealant, Selleys recommends spraying Selleys Rapid Mould Killer into the gap to kill any residual mould.
- Clean and dry the joint. Thoroughly clean the surface where the sealant will be applied with turps, and dry it. Silicone will not bond reliably to a damp surface.
- Apply the new bead to the correct depth. Cut the nozzle at 45°, fit it, place the cartridge in a caulking gun and apply with steady pressure, ensuring the sealant is pushed into the joint rather than laid across the surface.
- Tool it. With No Mould, tool with a spatula dipped in detergent water within 10 minutes of application. With Wet Area Silicone, within 5 to 10 minutes.
- Clean up with turps before the product skins, and leave the bead undisturbed while it cures.
Cure times, so you know what you are waiting for
| No Mould (acetic cure) | Skin time 20 minutes. Shower ready 1 hour after application. Must not be touched until fully cured — at least 48 hours. Cure rate 2mm per 24 hours. |
| Wet Area Silicone (neutral cure) | Skin time 5 to 10 minutes. Shower can be used 24 hours after application. Cures in 72 hours. Cure rate approximately 2mm per 24 hours. |
Indicative data only, not intended for the preparation of specifications.
Note the pattern in both: a usable seal arrives well before a full cure. Twenty-four hours after your first bead — the point at which most people consider adding a second — the original is still curing. Resist the urge to help it along with more product.
Where the sealant remover is safe to use
Selleys Sealant Remover can be used on ceramic tiles, porcelain, glass, grout, most metals and brass, laminate, most plastics, masonry, coated timber and most painted surfaces. Do not leave it on porous materials or acrylic-painted surfaces for extended periods, as it may cause damage. It will not remove staining caused by old penetrated silicone oils.
Safety: doing it properly means solvent in the smallest room in the house
The answer above is to cut the old bead out and start again, and step 2 is the part with the serious classification attached.
Selleys Sealant Remover is classified Danger, Poison Schedule S5, and is more than 60% petroleum naphtha — a thickened hydrocarbon solvent:
- H304 — may be fatal if swallowed and enters airways (aspiration hazard, Category 1)
- H226 — flammable liquid and vapour; Dangerous Goods Class 3, UN 1133, Packing Group II
- H336 — may cause drowsiness or dizziness
- H315 — causes skin irritation
Read step 2 again with H336 in mind: a layer at least 5mm thick over the whole bead, left at least ten minutes, "a second application may be needed on stubborn residue". That is a lot of solvent paste evaporating in a tiled recess with a door and often no window, while you crouch inside it. Drowsiness in a shower recess, on a step or a stool, is a fall as well as a symptom. Open the door and window, run the exhaust fan, and step out between applications.
H226 and the bathroom. Packing Group II is a real flammability rating, and bathroom ignition sources are close: a gas hot water pilot on the other side of the wall, a fan heater, a heat lamp. Turn them off before the tub is opened. The mineral turpentine in the same step is flammable too.
H304 is the one to respect in a family bathroom. The product is a light beige paste in a 375g screw-top tub and it looks like filler. Put the lid back on between applications, keep it out of reach, and never decant it. If any is swallowed, do not induce vomiting — vomiting is the mechanism that gets a light hydrocarbon into the lungs. Rinse the mouth, give a glass of water and seek medical advice immediately.
Do step 2 and step 3 separately. Strip, ventilate the recess properly, then treat the mould, then ventilate again — rather than having solvent paste and a mould spray working in the same enclosed space at the same time.
The new bead is a much lower rung. No Mould carries Warning with H319 (serious eye irritation), skin irritation Category 2 and skin sensitisation Category 1; Wet Area Silicone carries Warning with H319 and H317. Sensitisation is permanent once acquired and built by repeated casual contact, so tool step 6 with the spatula rather than a bare finger. And cut and scrape as much of the old bead as you can before the remover comes out — it is designed for a residual film under 5mm.
Poisons Information Centre — 131 126 in Australia, 0800 764 766 in New Zealand.
Common questions
Can I put a second bead over the first?
No. It may not adhere well to the original silicone. Cut the previous bead out and reapply a fresh one.
What if I only need to fix a short section?
Cut out that section back to sound, well-adhered sealant and rebuild it. Joins in a bead are weak points, so make the overlap clean and press the new material firmly into the joint.
Does it help if the new silicone is the same product?
No. The issue is that cured silicone is a poor substrate for fresh silicone, regardless of brand or type.
How do I get the last of the old silicone off?
Selleys Sealant Remover, spread at least 5mm thick, left at least 10 minutes, then scraped off with a forward and backward motion. Clean up with mineral turpentine.
Do I have to kill the mould first?
Yes. Selleys recommends spraying Rapid Mould Killer into the gap before applying new sealant, to kill residual mould.
How long before I can use the shower?
One hour with No Mould, 24 hours with Wet Area Silicone. In both cases do not touch the bead until it has fully cured.
How long is a full cure?
At least 48 hours for No Mould; 72 hours for Wet Area Silicone. Both cure at roughly 2mm per 24 hours, so a deep bead takes longer.
Why did the first bead fail?
Usually the joint was not clean or fully dry, or the bead was laid on the surface rather than pushed into the joint, so it had almost no depth of bond.
How thick should the new bead be?
Deep enough to contact both faces of the joint properly. The instruction is to reapply to the correct depth, well adhered to the edges of the area being sealed.
Is there a full guide?
Yes — how to replace old silicone and how to remove old sealant.
Can I put a second bead over the first?
No. It may not adhere well to the original silicone. Cut the previous bead out and reapply a fresh one.
What if I only need to fix a short section?
Cut out that section back to sound, well-adhered sealant and rebuild it. Joins in a bead are weak points, so make the overlap clean and press the new material firmly into the joint.
Does it help if the new silicone is the same product?
No. The issue is that cured silicone is a poor substrate for fresh silicone, regardless of brand or type.
How do I get the last of the old silicone off?
Selleys Sealant Remover, spread at least 5mm thick, left at least 10 minutes, then scraped off with a forward and backward motion. Clean up with mineral turpentine.
Do I have to kill the mould first?
Yes. Selleys recommends spraying Rapid Mould Killer into the gap before applying new sealant, to kill residual mould.
How long before I can use the shower?
One hour with No Mould, 24 hours with Wet Area Silicone. In both cases do not touch the bead until it has fully cured.
How long is a full cure?
At least 48 hours for No Mould; 72 hours for Wet Area Silicone. Both cure at roughly 2mm per 24 hours, so a deep bead takes longer.
Why did the first bead fail?
Usually the joint was not clean or fully dry, or the bead was laid on the surface rather than pushed into the joint, so it had almost no depth of bond.
How thick should the new bead be?
Deep enough to contact both faces of the joint properly. The instruction is to reapply to the correct depth, well adhered to the edges of the area being sealed.
Is there a full guide?
Yes — how to replace old silicone and how to remove old sealant .