Large Gap Filler Kit — Multi-Room (gaps over 5mm)

Some gaps aren’t small fixes.

They run along an entire wall.
Across multiple window frames.
Or through several rooms that have all shifted over time.

The Big Gap Box Kit is built for larger internal gap repairs where standard filler will fail, and you’ve got more than one joint to fix.

Why Bigger Gaps Need A Proper System

Wide or deep gaps can’t just be pumped full and forgotten.

If you overload a joint with filler:

• It sinks into the cavity

• It cracks as it cures

• It wastes product

• It fails again

Gap filler is designed to bridge a small joint, not fill empty space.

This kit gives you the correct products to seal larger internal gaps properly and cleanly.

When To Add Backing Rod

If your gap is larger than 5mm wide or deep, we strongly recommend adding closed-cell foam backing rod(available as an optional extra).

Backing rod:

• Controls sealant depth

• Reduces cracking and shrinkage

• Saves product

• Creates a stronger joint

For smaller gaps under 5mm, you can usually seal directly.
For anything larger, backing rod sets the joint up properly before sealing.

Built For Bigger Jobs

This is the scaled-up version of our Little Big Gap Kit.

You get:

• 500ml Prep-It for proper surface preparation

• 500ml Smooth-It for clean tooling of polyurethane

• 2 x Tubes of Paintable Polyurethane Gap Filler for extended coverage

• Double the clean-up materials so you’re not reusing dirty cloths

It’s designed so you don’t run out halfway through the job.

Ideal For

• Multiple drafty window frames

• Long skirting runs pulling away

• Large internal expansion joints

• Renovation prep across several rooms

• Bigger internal gaps that require flexibility

The Kit Includes

• 500ml Prep-It Surface Cleaner

• 500ml Smooth-It Lubricant

• 2 x Tubes of Paintable Polyurethane Gap Filler

• Gap Sealant Applicator for a sharp finish

• 2 x Sponges

• 2 x Microfibre Cloths

• 2 x Timber Applicators

• Paper Towels

• Easy-to-follow instructions