Is decorators caulk waterproof? Caulk vs silicone
On this page
Decorators caulk is a flexible acrylic filler for sealing gaps before painting, along skirting, architrave, coving and where timber meets wall. Once dry it is paintable and water-resistant, and some are sold as waterproof, but it is not a sealant for constant wet areas. For a bath, shower, basin or worktop, use silicone, not caulk. The simple rule: caulk takes paint and suits dry gaps; silicone is waterproof for wet areas but will not take paint.
Is decorators caulk waterproof?
Mostly the honest answer is water-resistant, not fully waterproof. A good acrylic caulk like our Soudal decorators caulk dries colourfast and water-resistant and is sold as waterproof, which is fine for the odd splash and for painted interior trim. What it is not is a sealant for standing water or constant wetting, the seal around a bath, a shower tray, a sink or a worktop. That is a job for silicone. Caulk shrinks a little and is not made to flex under a permanent water line, so used there it cracks and lets water behind.
What is decorators caulk for?
Caulk is what turns a rough gap into a crisp painted line. It is for the interior joints a painter fills before painting:
- Along the top of skirting boards and down architrave
- Around coving and cornice
- Where timber meets a wall, door linings, window boards
- Fine cracks and gaps in plaster before decorating
It stays slightly flexible so it does not crack as the trim moves, and it takes paint straight over the top. It comes in 290 to 300ml cartridges for a sealant gun, and in boxes of 24 for bigger jobs.
Caulk or silicone: which do you need?
They look similar in the gun but they are for opposite jobs:
| Decorators caulk | Silicone | |
|---|---|---|
| Base | Acrylic | Silicone |
| Paint over it? | Yes | No |
| Waterproof? | Water-resistant | Fully waterproof |
| Use it for | Dry interior gaps before painting | Baths, showers, sinks, wet areas |
| Movement | Light movement | High movement joints |
So: painting a gap, use caulk; sealing water, use silicone. The one that catches people out is trying to paint over silicone, paint will not stick to it, so silicone goes on last, after painting, in its own colour.
Can you paint over decorators caulk?
Yes, that is the whole point of it. Let the caulk skin over and dry (usually an hour or two for touch-dry, longer in a deep bead), then paint straight over with emulsion or trim paint. Paint it too soon and the paint can crack as the caulk finishes drying underneath, so give it time. This paintability is exactly why you cannot swap silicone in, silicone stays unpainted forever.
How to apply decorators caulk
- Cut the nozzle small at an angle for a fine bead, you can always cut more off.
- Run a steady bead along the gap with a sealant gun, filling it in one pass.
- Smooth it with a wet finger or a caulking tool before it skins, pushing it into the gap and wiping the excess.
- Let it dry, then paint. Fill anything wider than about 5mm in two passes rather than one thick bead.
Common mistakes to avoid
- Caulk around a bath or shower. It is not built for standing water. Use silicone in wet areas.
- Trying to paint over silicone. Paint will not take. Caulk for anything you will paint.
- Painting caulk too soon. Let it dry or the paint cracks over it.
- One thick bead in a big gap. It shrinks and sinks. Fill wide gaps in two passes.
- Not smoothing the bead. Tool it with a wet finger for a clean line, unsmooth caulk looks rough through paint.
The short version
Decorators caulk is a paintable acrylic filler for dry interior gaps, skirting, architrave, coving and trim, and it is water-resistant but not a wet-area sealant. Use silicone for baths, showers and sinks, and remember you cannot paint over it. Grab caulk from the decorators caulk range, or silicone from the sealants and silicones range.
By Steve, Builders Hardware Direct. Steve runs the BHD trade counter and has spent years supplying caulk, sealants and decorating sundries to painters and builders across South Wales. Not sure which to use? Call the counter on 01269 267030 or order online for fast UK delivery.
