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How to apply decorators caulk in a thin skirting gap

Updated: 21 October 2026

You are about to run a bead along new skirting or an architrave, and the first attempt usually floods the joint or skins before you have smoothed it. This is how to apply decorators caulk as a thin, paintable line on a joint that is already sound and dry. It is the first bead, not a repair for paint that has already split. That failure is on [paint cracking over caulk](/hub/painting-supplies/decorators-caulk/sub/decorators-caulk-painting-and-cracking). Which tube to buy is on the [decorators caulk comparison](/hub/painting-supplies/decorators-caulk). A qualifying purchase can earn us a commission at no extra cost to you.

You are about to run a bead along new skirting or an architrave, and the first attempt usually floods the joint or skins before you have smoothed it.

Our top picks

Soudal Soudal white twin

Best overall

Soudal Soudal white twin
8.3/10about £6.18
View offer
Everbuild Caulk Once white twin

Rank 2

Everbuild Caulk Once white twin
8.6/10about £5.38
View offer
Siroflex SX Siroflex 310 ml

Best value

Siroflex SX Siroflex 310 ml
7.3/10about £4.99
View offer
On this page
  1. 1.Prepare the joint
  2. 2.Cut, load, and run the bead
  3. 3.Tool and clean
  4. 4.When you can paint

Prepare the joint

Scrape out old caulk, dust, and loose paint so the bead has two firm edges. The joint wants to be clean and dry. Toolstation's skirting guide adds a mist coat on new plaster before the finish bead, because bare plaster drinks water out of acrylic. If the wall is new, mist-coat or prime first, then caulk, then paint. A hairline at the top of a skirting board is a fair DIY bead. Wider than about 3 mm, that same guide says you may need a backing fill first. That 3 mm line is a how-to, not a British Standard. Soudal listings here state 10 mm as a maximum width, not a depth. If the crack keeps opening, or the plaster is damp, stop. The cartridge itself is on the decorators caulk buying guide.

Cut, load, and run the bead

Cut the nozzle at about 45 degrees, only slightly wider than the gap. Sika's Caulk Once sheet and Evo-Stik both say that. A wide opening turns a 2 mm shadow gap into a ridge. If the cartridge arrives with no nozzle, which UK reviews report on the Caulk Once twin and the SX single, fit a spare or send it back. That is a delivery fault, not a technique. Pierce the inner seal and keep the gun moving. Release the plunger at the end of a run or the corner floods. On Caulk Once, Sika says tool within 20 minutes, so do not run a whole room in one bead. The one-hour paint claim and the 15 minute listing field are separated on best decorators caulk.
Soudal Soudal white twin

Testsieger

Soudal Soudal white twin
8.3/10about £6.18
View offer

Tool and clean

Smooth once, with a wetted spatula or a damp tool, while the bead is workable. Sika says not to saturate it. Evo-Stik allows a soapy finger and tells you not to lick it. A tool in a kit does not rescue a gun frame that snaps. Wipe excess with water while the acrylic is uncured. Soap and water is the clean-up on the SX bullet. Once it has skinned, wiping smears the architrave. Do not sand the cured bead. If a ridge is already hard, cut it out and run a thinner bead. A second skim, where Toolstation says one is normal, is still a thin bead, not a second sausage.

When you can paint

Paint when the product's window and the depth of the bead both allow it. Sika says overpaint Caulk Once in 1 hour once it has skinned, and full cure in 3 to 5 days. Homebuilding's practical wait is at least 24 hours. Bostik's rule of thumb is about 1 mm of cure in 24 hours. A 1 mm bead can take paint on the one-hour line. A 6 mm plug cannot. The Amazon field of full cure in 15 minutes is the tack figure repeated. Do not paint at 15 minutes. The SX listing gives no skin time, so you cannot claim a one-hour window from that page. If a thin coat later crazes, do not lay a thicker bead over the split. This is not a lab test.

Common questions

Do I caulk before or after the mist coat?
On new plaster, mist-coat or prime first, then caulk, then the finish paint. Toolstation's skirting guide puts the mist coat before the bead because bare plaster pulls water out of the acrylic. On a previously painted, sound wall you can caulk the gap and then paint over the bead once the window allows. Do not caulk onto dusty bare gypsum and expect the line to stay put.
Finger or a tool?
A wetted spatula or a purpose-made smoother gives a cleaner line and keeps the bead from being flooded. A soapy finger can work on a short run if you do not soak the joint. Do not lick your finger. Evo-Stik warns against that because of bacteria. One pass is enough. Going back and forth drags caulk onto the face of the skirting.
Can I wipe it with water?
Yes, while it is still wet. Water, or soap and water, is the clean-up for these acrylics, and Sika says not to saturate the bead as you tool it. After the skin has formed, a wet cloth smears the surface instead of lifting the excess. Silicone does not clean up the same way, which is another reason the tube in the gun should be decorator's acrylic.
What if the tube has no nozzle?
You cannot run a controlled bead from an open thread. UK reviews on the Caulk Once twin and the SX cartridge both mention nozzles missing from the delivery. Fit a spare nozzle from another cartridge of the same thread, or return the tube. Cutting a random cap to fit is how the bead width gets away from you on the first metre of skirting.
When is this no longer a DIY bead?
Stop when the crack keeps opening, when the surround is damp or leaking, or when the gap is a deep void rather than a few millimetres at a skirting edge. A tenancy that limits decoration is also a stop. A neat bead will not pin a moving lintel or a wet frame. Those jobs need someone who can treat the cause, not another cartridge.

Related pages

Paint scraper comparison

Decorators caulk

Best decorators caulk for white skirting and frames

Decorators caulk buying guide: joint, gap and pack

Paint cracking over caulk on skirting and architrave

Decorators caulk vs silicone: painted trim or a bath

Sources

Public UK sources used for this comparison. Listing prices, stars and review counts are the amazon.co.uk figures saved for this set on 19 October 2026.

  1. Sika Caulk Once product data sheet (retrieved 19 October 2026)
  2. Bostik SX Decorators Premium Paintable Caulk technical data sheet (retrieved 19 October 2026)
  3. Bostik UK, decorator's caulk uses and drying time (retrieved 19 October 2026)
  4. Homebuilding, silicone vs caulk (retrieved 19 October 2026)
  5. Homebuilding, painting caulk (retrieved 19 October 2026)
  6. GOV.UK, Construction Products Regulation in Great Britain (retrieved 19 October 2026)
  7. Decorators Forum UK, paint cracking over caulk (retrieved 19 October 2026)
  8. Screwfix, No Nonsense decorator's caulk 310 ml (retrieved 19 October 2026)