A Professional Guide
Have you noticed large gaps appearing around your skirting boards, window frames, brickwork or concrete paths?
While they may not seem like a major problem at first, unsealed gaps can allow water, draughts, insects and even rodents into your home. In Melbourne's changing climate, where buildings naturally expand and contract throughout the seasons, sealing larger gaps correctly is essential to protect your property and improve energy efficiency.
Although small gaps are relatively easy to seal, larger gaps require the correct preparation, materials and technique. Simply filling a wide gap with silicone often results in sagging, shrinking or cracking, leading to an ineffective seal that won't last.
Here's how the professionals approach sealing large gaps.
What You'll Need
Before you begin, make sure you have the right equipment.
- Premium quality silicone or polyurethane sealant suitable for the application
- Foam backer rod (available in various diameters)
- Heavy-duty caulking gun
- Utility knife
- Scraper or stiff brush
- Masking tape
- Finishing tool or spatula
- Spray bottle with a mild soapy water solution
Using quality materials from the beginning will produce a stronger, neater and longer-lasting result.
Step 1 – Prepare the Surface
Preparation is one of the most important parts of any caulking job.
Remove all existing silicone, loose material, dirt and dust using a scraper or stiff brush. Wipe the area clean and allow it to dry completely before applying any sealant.
Applying silicone over damp or dirty surfaces reduces adhesion and can lead to mould growth or premature failure.
Step 2 – Install a Foam Backer Rod
For gaps wider than approximately 6mm, a foam backer rod is highly recommended.
Choose a backer rod slightly larger than the gap so it fits snugly when compressed. Push it into the joint until it sits just below the surface, leaving enough depth for the sealant.
A backer rod provides support, reduces the amount of sealant required and helps create a stronger, more flexible joint.
Step 3 – Apply the Sealant Correctly
Cut the nozzle of the sealant tube at a 45-degree angle to suit the width of the gap.
Apply a steady, even bead over the backer rod, ensuring the sealant makes good contact with both sides of the joint.
Avoid applying too much at once, as excessive sealant can sag before curing.
Step 4 – Finish the Joint
Lightly spray the sealant with a mild soapy water solution before smoothing it with a finishing tool or gloved finger.
If you've used masking tape, remove it immediately while the sealant is still wet to achieve clean, straight lines.
Allow the sealant to cure according to the manufacturer's instructions before exposing it to water or heavy use.
Common Caulking Mistakes
Not Using a Backer Rod
Trying to fill a large gap entirely with silicone wastes product and often results in sagging or cracking once cured.
Choosing the Wrong Sealant
Different applications require different products. External joints, bathrooms and high-moisture areas should always use premium weatherproof sealants designed for those conditions.
Poor Surface Preparation
Dust, moisture and old silicone prevent proper adhesion and significantly reduce the lifespan of the seal.
Rushing the Application
Working too quickly can leave air pockets or uneven joints, allowing water to penetrate over time.
When It's Best to Call a Professional
While smaller household gaps are often suitable for DIY repairs, larger expansion joints, commercial projects, pool surrounds and extensive weatherproofing are best left to experienced professionals.
Professional caulkers have the equipment, knowledge and products needed to deliver straight, durable and long-lasting finishes that stand up to Melbourne's changing weather conditions.
At Professional Caulking Group, we provide high-quality residential and commercial caulking services throughout Melbourne. Whether you need new construction caulking, remedial sealing or weatherproofing, our experienced team delivers neat, reliable workmanship every time.
🚨 Emergency Repair Services Melbourne
If you’ve noticed leaking water, damp walls, or signs of damage, it’s important to act fast.
Contact Professional Caulking Group for emergency leak repair in Melbourne — quick action now can prevent costly repairs later.