Caulking

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In Britain the word caulking covers two products that are not interchangeable, and most failed sealant jobs are really a failure to tell them apart. Decorator's caulk is a paintable, water-based acrylic used to close the shrinkage gaps in a room: the line where skirting meets the wall, the joint around architrave and door linings, the gap along a coving or a picture rail, and the hairline where a plasterboard ceiling meets a masonry wall. It is designed to be painted over and it tolerates only small amounts of movement.

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Silicone sealant is a different animal. It stays flexible, it does not accept paint, and it is what belongs around a bath, a shower tray, a basin, a worktop and a window frame - anywhere water sits or a joint moves. Sanitary grades contain a fungicide to slow the black mould that otherwise colonises a shower seal within a year or two. Using caulk where silicone belongs produces a joint that goes brown, splits and lets water through; using silicone where caulk belongs produces a line that cannot be painted and shows forever.

The third thing worth saying up front is that sealant is a finishing material, not a waterproofing system. A bead around a bath is there to close a designed joint, not to hold back water escaping from a badly fitted shower tray or a failing tile bed. If a seal keeps failing in the same place, something behind it is moving or leaking.

Decorator's caulk, silicone and the joints each belongs in

Decorator's caulk: skirting-to-wall, architrave-to-wall, coving joints and internal angles that will be painted afterwards.
Sanitary silicone: baths, shower trays, basins, around a WC pan and along the back of a kitchen worktop, where water and mould are the issue.
Low-modulus neutral-cure silicone: external window and door perimeters, where the joint moves seasonally and the substrate may be sensitive.
Frame sealant and expanding foam: the structural gap behind a window or door frame, which is then closed with a finishing bead rather than left exposed.
Hybrid polymer sealants: high movement joints, wet areas that need painting, and situations where silicone will not adhere well.
Intumescent mastic: sealing service penetrations where fire resistance matters, which is a specialist product and a specialist judgement, particularly in flats.
Sealant strip and tape: a fast cover-up for a failed bath seal that almost always traps water behind it, and rarely a real repair.

Why a bead fails, and what makes one last

Three things decide the life of a sealed joint: adhesion, joint geometry and movement. Adhesion fails when the surface is dusty, greasy, damp, or still carrying traces of the old silicone - and silicone bonds very poorly to itself once cured, which is why a fresh bead smeared over an old one lifts within months. Removing every trace of the previous sealant is most of the work and most of the reason a professional bead outlasts a DIY one.

Geometry matters because a sealant needs to be able to stretch. A bead that is deep and narrow, or one that has stuck to three sides of a joint instead of two, cannot deform and tears instead. That is what a backer rod is for in a wide joint, and why gouging sealant hard into a gap is worse than laying it in and tooling it once.

Movement is the reason the bath seal fails and the skirting line does not. A steel or acrylic bath deflects when it is filled and someone gets in, and the joint opens by a millimetre or two every time. Sealing a bath empty and then filling it is the old trick for a reason: it sets the joint at close to its loaded position rather than its unloaded one.

When a seal has stopped doing its job

Black spotting in the sealant that no longer comes off with cleaning, which means the mould is in the material rather than on it.
A bead that has lifted at one edge, however slightly, because water is already tracking behind it.
Splits or crazing along the length of a bead, which usually means it was applied too thin or onto a moving joint.
A soft or discoloured patch on the floor or ceiling below a bath or shower, which is a leak rather than a sealant question.
Caulk at the skirting line that has shrunk into a visible crack, normal after the first heating season and easily re-run.
Sealant around a window that has gone chalky and hard, which is the end of its working life rather than a cosmetic problem.
A smell of damp in a bathroom cupboard or under a basin, which often precedes any visible failure of the seal.

How a sealant joint is replaced properly

The old bead is cut out completely with a sharp blade and a sealant remover, not simply trimmed back.
The joint is cleaned, degreased and allowed to dry fully, because silicone will not bond to a damp surface.
Adjacent surfaces are masked so the tooled edge is straight and the sealant does not smear into grout or paint.
A backer rod is used in any joint deep enough that the sealant would otherwise stick to three sides.
A bath is filled with water before sealing where the guidance for that product allows it, so the joint is formed under load.
The bead is laid in one continuous pass and tooled once; repeated tooling drags the skin and leaves a rough finish.
The masking comes off immediately while the sealant is wet, and the joint is left undisturbed for the full cure time, not the touch-dry time.

The seal that keeps failing is telling you something else

A bath or shower seal that fails repeatedly in the same spot is usually a movement or support problem. A bath on adjustable feet without a proper cradle, a shower tray bedded on an uneven floor, or a panel that is screwed tight on one side and loose on the other will all open the joint every time they are used. Re-sealing that joint a fourth time is buying a few months; packing, supporting or re-bedding the unit fixes it.

Black mould that comes back quickly is a ventilation question rather than a sealant question. Bathrooms generate a great deal of moisture in a short time, and if it is not extracted it condenses on the coldest surfaces, which include the tile-to-bath junction. Sanitary sealants contain a fungicide that slows this, but nothing in a cartridge will out-run a bathroom with no working extract fan and a window that is never opened - which is why this often ends up as a ventilation job.

Water appearing below a bathroom with the seal apparently intact is the case that needs opening up rather than sealing over. A leaking waste, a failed shower valve connection or water tracking through grout into a wall will all show at the ceiling below and none of them is solved by another bead. Sealant applied over a live leak traps moisture in the structure and makes the eventual repair worse.

Keeping seals alive between visits

Wipe shower and bath seals dry after use where you can; standing water is what feeds mould growth in the joint.
Run the extract fan during and for a while after a bath or shower rather than switching it off with the light.
Clean seals with a mild detergent rather than a harsh bleach gel, which degrades some sealants over time.
Re-run the caulk line at skirting and architrave when it opens after the first heating season, instead of filling it with paint.
Check external window and door beads once a year, as a failed perimeter seal lets water into the reveal long before it shows inside.
Never seal over a bead that is already lifting: water is behind it, and the new material will not bond to the old silicone.

What drives a caulking and sealing quote, and how LokalMatch fits in

Sealing is priced on removal and access far more than on the metres of bead. Stripping out old silicone from a tiled shower without damaging the grout is slow work, and a bathroom that needs the bath panel taken off, the screen removed or a worktop unloaded takes longer than a straight run along a skirting board. The other variables are how many joints there are, whether any of them need a backer rod, whether the room can be left undisturbed for a full cure, and whether a leak or a movement problem has to be dealt with before anything is sealed at all.

This is exactly the sort of job LokalMatch is built for: small, specific and hard to price over the phone. Photograph the joints, say which rooms they are in and what has already been tried, add your postcode, and handyman and bathroom-fitting businesses covering your area come back to you. Homeowners are never charged - pros pay for the requests they receive. LokalMatch does not do the sealing, does not set prices and does not vet, rank or recommend anybody, so the decision about who to use stays with you.

Caulking: frequently asked questions

What is the difference between decorator's caulk and silicone?

Decorator's caulk is a paintable acrylic filler for the small shrinkage gaps in a decorated room - skirting to wall, architrave joints, coving lines - and it tolerates only slight movement. Silicone stays flexible, resists water and cannot be painted, which makes it right for baths, showers, basins, worktops and window perimeters. Putting caulk where silicone belongs gives you a joint that goes brown and splits; putting silicone where caulk belongs gives you a line you can never paint over.

Why does my bath seal go black so quickly?

Because moisture sits in the joint and mould grows in it. Sanitary silicones include a fungicide that slows this, but they cannot keep up with a bathroom where steam is not extracted, and once the growth is inside the sealant film rather than on its surface, cleaning will not shift it. The durable fix is better extraction and drying the joint after use, combined with a properly removed and replaced bead rather than fresh silicone over old.

Can I seal over the old silicone?

No. Cured silicone bonds very poorly to itself, so a new bead laid over an old one lifts within months, and any water already behind the old seal is trapped where it can damage the substrate. Complete removal with a blade and a sealant remover, followed by cleaning and thorough drying, is most of the work and the reason a professional bead lasts. It is also the point at which a hidden leak usually becomes visible.

Should the bath be full when it is sealed?

It is a common and sensible approach with baths that flex. A steel or acrylic bath deflects when filled with water and a person, so a joint sealed with the bath empty is stretched every time it is used. Filling the bath before sealing forms the joint closer to its loaded position, so it is not being pulled open in normal use. Check the sealant manufacturer's instructions, as some products have specific guidance on this.

How long before I can use the shower again?

Go by the cure time on the cartridge rather than by touch. Sealant skins over in minutes and feels dry long before it has cured through, and using a shower too early pulls the joint apart while it is still weak. Most products want the joint kept dry and undisturbed for at least a day, and a deep bead takes longer than a shallow one. It is the single easiest way to waste a good sealing job.

Sources

Written by the LokalMatch editorial team. Last reviewed 21 September 2026. How we write and check our guides

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What affects the cost of caulking

Prices depend on the details of your project. We only publish price ranges when they’re backed by real LokalMatch quote data or reliable sources. Until then, here’s what usually changes the price:

Number and type of tasks
Time needed and any minimum visit charge
Materials and parts
Wall type and what's being mounted or hung
Height and access

How to compare handymen before you hire

Describe all the small jobs up front so the handyman can bring the right tools and give you a realistic estimate.
Ask whether they charge by the hour, by the job or with a minimum visit fee.
For anything involving wiring, gas or new plumbing, use a licensed trade instead of a general handyman.
Check that they carry liability insurance, especially for work on ladders or on the exterior.
Ask whether they supply materials or whether you should buy them ahead of time.

Questions to ask handymen before you hire

Do you charge by the hour or by the job, and is there a minimum?
Can you do all of the jobs on my list, or will some need a licensed trade?
Will you bring the materials, or should I buy them?
Are you insured if something is damaged while you're working?
How do you handle it if a job takes longer than expected?

Caulking permits and local rules

Some caulking work needs a permit or has to meet local bylaws. Rules vary by municipality, so ask your pro whether a permit is needed and who will apply for it — and check with your city or town if you’re unsure.

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