Walk into any DIY shop and you will see decorators’ caulk and silicone side by side, often in identical tubes. It is easy to think they do the same job. They don’t. Caulk is made for painting over in dry areas. Silicone is made for wet areas and movement. Using one where the other belongs is one of the most common reasons joints crack, go mouldy or leak. This guide explains where each belongs.
What decorators’ caulk is
Decorators’ caulk is usually acrylic. It is water-based, easy to smooth with a wet finger, and can be painted once it is dry. It fills gaps neatly so paintwork looks continuous.
It is flexible enough for small, steady gaps in dry areas. It is not designed for constant water, and many caulks can be damaged by water before they are fully dry.
What silicone is
Silicone sealant cures to a flexible rubber. It stretches and recovers as surfaces move, and it is waterproof once cured. Sanitary silicones contain anti-fungal additives for bathrooms and kitchens.
Silicone can’t be painted. Paint won’t stick to it, so any paint over silicone will peel. It also doesn’t stick well to old silicone, so it must go onto clean surfaces.
Where each belongs
| Joint | Use |
|---|---|
| Skirting to wall | Caulk |
| Architraves and door frames to wall | Caulk |
| Ceiling to wall, coving | Caulk |
| Inside window frame to plaster, painted | Caulk |
| Bath, shower or basin to wall | Sanitary silicone |
| Kitchen worktop to wall | Sanitary silicone |
| Shower screen to tile or tray | Sanitary silicone |
| External window and door frames | An exterior sealant suited to the frame and wall |
Painted skirting in a dry room is caulk. Skirting on a tiled bathroom or kitchen floor that gets mopped is better sealed with silicone. Our guide to sealing skirting and floor joints covers this.
Need it done properly? Mr Mastic covers the South East, London and Scotland, with a one-year guarantee on every job. Call or email for a quick quote.
What goes wrong with the wrong one
Caulk around a bath or shower softens, cracks and goes mouldy because it isn’t made for constant water. Water then gets behind it.
Silicone on painted woodwork can’t be painted over. Paint peels off it, leaving a shiny line that stands out.
Caulk outside may not cope with weather and larger movement, so it can crack and let in water.
Caulk over silicone, or silicone over caulk, doesn’t bond properly. Old material has to come out first.
Fixing a joint sealed with the wrong product
The fix is the same in most cases. Cut out the wrong product completely, clean off any residue, let the joint dry and apply the right one. On a bathroom or kitchen, that is a straightforward reseal with anti-fungal sanitary silicone. For a deeper look at sealant types, including hybrid and polyurethane sealants, see our guide to mastic vs silicone.
Hybrid and polyurethane sealants
Between caulk and silicone sits a third group: polyurethane and hybrid (MS polymer) sealants. Many of these are flexible, weather-resistant and paintable, and they bond to a wide range of surfaces. They are often used outside on frames, cladding and movement joints, where a painted finish is wanted or silicone isn’t suitable.
They are not a replacement for sanitary silicone in a shower, but they show that the right product depends on the joint, the surfaces and whether it will be painted.
Quick answers
Can I paint silicone?
No. Paint won’t stick to it. If a joint needs painting, use a paintable product such as decorators’ caulk, where it is suitable.
Is caulk waterproof?
Some caulks resist splashes once cured, but they aren’t made for joints that are wet every day. Use sanitary silicone around baths and showers.
Can I put caulk around a kitchen worktop?
It isn’t recommended. Worktop joints get wet and need a sanitary silicone.
Related services
More advice
- Mastic vs Silicone: What’s the Difference?
- Sealing Between Floors and Skirting Boards
- Coloured Sealant and Colour Matching
- All advice
This guide is general information about sealant work. It isn’t legal, fire-safety or structural advice; for those, speak to a qualified professional.