Professional Guide

Best Flexible Filler for Making Good: 2025 Expert Review

Oli at OR Electrics

Fully Qualified Electrician (18th Edition)

Published 18 December 2025

One of the biggest worries my customers have isn't about the wiring itself—it's about the mess. When we chase cables into solid brick walls, which is common in Leeds' Victorian properties, it creates dust and channels that need 'making good'.

Standard filler is fine for a pinhole, but for electrical chases or gaps around socket boxes, it often cracks. Walls vibrate when doors slam, and houses shift with the seasons. If the filler is too rigid, you'll see a hairline crack appear around your new switch plate within weeks.

That is why choosing the best flexible filler is essential. In this review, I'm sharing the products I keep in the van to ensure a seamless finish that stays put, whether I'm patching up after a rewire or just swapping a faceplate.

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Specs vs. The Real World

The Spec: "One Coat Application"

The Theory

"Manufacturers claim you can fill deep holes in a single pass to save time."

The Reality

If you fill a deep cable chase in one go, the filler will slump or crack as it dries. It is always better to build it up in layers, allowing each to dry properly.

The Spec: "Ready to Paint in 30 Minutes"

The Theory

"Quick-drying formulas let you decorate immediately."

The Reality

Whilst the surface skin might feel dry, deep filler holds moisture. Painting too soon traps that moisture, causing the paint to bubble later. Patience is key.

My Top 3 Recommendations

Three options to cover different needs and budgets

Ronseal Smooth Finish Flexible Filler 330G

Budget Pick

Ronseal

This is a brilliant little tube to have handy for minor touch-ups. It's affordable, incredibly flexible, and ideal for running a bead around a newly installed socket where the plaster might have chipped slightly.

Price£4.99 (at the time of writing)

BrandRonseal

Key FeatureFlexible acrylic polymers

The Good

Very flexible, moves with the wall preventing cracks
Smooth finish requires minimal sanding
Tube format is easy to handle for small jobs

The Bad

Not suitable for deep filling large chases
Can be tricky to get out of the tube when nearly empty

Installer Tip:

If you've just fitted a switch and there is a hairline gap between the plate and the wall, run a small bead of this around the edge and smooth it with a wet finger. It frames the accessory perfectly.

Priced at £4.99 at the time of writing

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Tetrion TWF600/TWF606 Woodfil 600g Flexible Wood Filler

Quality Pick

Tetrion

Whilst marketed as a wood filler, this Tetrion product is excellent when sockets are mounted into high skirting boards—common in older Leeds terraces. It's durable, fills deeper holes well, and sets hard enough to hold a screw if needed.

Price£7.33 (at the time of writing)

BrandTetrion

TypeReady Mixed / Flexible

The Good

Extremely durable and long-lasting
Ready mixed formulation saves time
Fast drying (sandable in 20 mins)

The Bad

Harder to sand than lightweight foam fillers
Stronger smell than water-based acrylics

Installer Tip:

If you are moving a socket on a skirting board and need to fill the old screw holes, this is the product to use. It won't shrink back into the hole like standard polyfilla.

Priced at £7.33 at the time of writing

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Everbuild FLEX-EBD Flexible Decorators Filler 290 ml

Problem-Solving Pick

Everbuild

This is essentially decorators caulk, and it is a lifesaver for long runs. If I've installed surface trunking or a new consumer unit against an uneven stone wall, this filler bridges the gap cleanly and stays flexible permanently.

Price£4.92 (at the time of writing)

BrandEverbuild

ApplicationCartridge Gun

The Good

Excellent slump resistance
Can be overpainted without sanding
Permanently flexible – ideal for corners and junctions

The Bad

Cannot be sanded (it roughens up)
Not designed for filling holes in the middle of a wall

Installer Tip:

Do not try to sand this product. Apply it, then immediately smooth it with a wet profiling tool or your finger. Once it cures, it's rubbery, so you need to get the finish right whilst it is wet.

Priced at £4.92 at the time of writing

Check Price on Amazon

Frequently Asked Questions

Why does filler crack around my light switches?

Cracking around switches is usually caused by vibration or the different expansion rates of materials. Using a rigid filler on a wall that moves slightly (like lath and plaster) causes it to snap. Flexible filler absorbs this movement.

Can I use flexible filler over deep electrical chases?

For deep chases (where we've cut into the brick), you should first use a bonding plaster or hardwall to fill the bulk of the depth. Use the flexible filler only for the top few millimetres to get a smooth, paintable finish.

What is the difference between caulk and filler?

Filler is generally for holes and can be sanded flat. Caulk (like the Everbuild option) is flexible and rubbery, used for sealing gaps in corners or skirting. You cannot sand caulk, so it is strictly for gaps, not flat wall repairs.

Does OR Electrics handle the plastering after a job?

We ensure all chases are safe and filled to a 'bonding' level or a rough finish. For a perfect décor-ready finish, we typically recommend a professional plasterer, though for smaller jobs (swapping sockets), we utilise these fillers to leave a neat edge.

Is it safe to fill over cables?

Yes, provided the cables are installed in safe zones or protected by capping/conduit as per BS 7671 regulations. We never plaster directly over bare cables without mechanical protection or proper clipping.

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