What Sealant Do I Need? Silicone vs Acrylic vs Polyurethane Explained (Australian Guide)

By The DIYers — backed by 30 years of building experience

Standing in the hardware aisle wondering "what sealant do I need?" You're not alone. Most DIY mistakes happen because people grab the wrong tube. Bathroom silicone gets used outside. Gap filler ends up in showers. Cheap interior sealant gets destroyed by the Australian sun.

This guide answers the most common questions about sealants in plain English — so you buy the right product the first time.

What This Guide Covers

  • Silicone vs acrylic vs polyurethane — what's the difference?
  • Indoor vs outdoor sealant
  • Wet area sealant vs structural joint sealant
  • What movement capability means
  • When to use neutral cure silicone
  • What works best in Australian conditions

If you're searching things like best sealant for bathroom, can I use silicone outside?, what is the difference between caulk and sealant?, or what sealant for concrete joints? — you're in the right place.

Silicone vs Acrylic vs Polyurethane: What's The Difference?

Silicone Sealant — Best for Wet Areas

Best for: Bathrooms, kitchens, wet areas, waterproofing
Can you paint over it? No

If you're asking "what sealant for a shower?" — the answer is silicone.

Silicone sealant is waterproof, flexible and resistant to mould. It's designed for areas exposed to constant moisture, including showers and baths, basins and sinks, splashbacks, and around windows. It stays flexible long term, making it ideal for areas that expand and contract with temperature changes.

If water is involved, silicone is the correct choice.

The DIYers Wet Area Reseal Kit uses Sikaflex Kitchen and Bathroom silicone — a professional-grade product trusted by tradies for over 30 years. The kit includes everything you need: the sealant, all tools, prep sprays, and a QR code linking to easy step-by-step video instructions. No guesswork, no wasted product, no second trips to the hardware store.

Acrylic Sealant (Gap Filler) — Best for Interior Gaps

Best for: Interior gaps before painting
Waterproof? No

If you're searching "what sealant can I paint over?" — this is it.

Acrylic sealant (often called gap filler or no more gaps) is used for cosmetic interior gaps such as skirting boards, architraves, cornices, and small plaster cracks. It dries firm and can be painted over. That's why painters use it.

It is not suitable for showers, external use, or heavy movement joints. Using acrylic in a wet area will fail.

The DIYers Skirting Board Kit uses Sikaflex Gap Filler — formulated for clean, paintable lines on interior trim. Like all DIYers kits, it includes the tools, prep sprays, and QR-code video instructions so the job gets done right first time.

Polyurethane Sealant — Best for Structural and Exterior Joints

Best for: Exterior gaps, cladding, movement
Waterproof? Yes
Paintable? Yes

If you're searching "best sealant for large cracks" or "what sealant for window gaps?" — you're looking for polyurethane.

Polyurethane sealant is strong, flexible and designed for joints that move. It handles heavier movement than most silicones and bonds aggressively to most surfaces. It's not as easy to tool as silicone, but it's the right product for serious exterior joints.

The DIYers Window Draught Seal Kit uses Sikaflex Pro — ideal for sealing around windows and exterior gaps to stop draughts and moisture. Everything is included: the sealant, all tools, prep sprays, and QR-code instructions.

Indoor vs Outdoor Sealant: What Should You Use?

A common question is "can I use interior sealant outside?" — the short answer is no.

  • Indoor dry areas: Use acrylic gap filler for gaps you want to paint
  • Indoor wet areas: Use mould-resistant silicone sealant
  • Outdoor use: Use exterior grade silicone (neutral cure preferred) or polyurethane for concrete and structural joints

Australia's UV exposure and heat cycles destroy cheap interior products fast. Always choose a sealant labelled for exterior use if it's exposed to sun and weather.

Wet Areas vs Structural Joints: They're Not The Same

A common mistake is confusing waterproofing with movement sealing. They are different problems requiring different products.

For wet areas — showers, baths, sinks, splashbacks — your goal is stopping water penetration. Use silicone. It stays flexible and resists mould growth.

For structural joints — driveways, concrete expansion joints, brick movement joints — your goal is accommodating movement. Use polyurethane.

What Does Movement Capability Mean?

If you've seen something like "movement capability ±25%" and wondered what it means — here's the simple version.

If a joint is 10mm wide, a ±25% sealant can stretch to 12.5mm or compress to 7.5mm without tearing or failing. In Australia, temperature swings can be extreme. Concrete and metal expand significantly in summer heat. Using a low-movement sealant in a high-movement joint will lead to cracking and failure.

If movement is expected, choose a sealant with a higher movement rating.

When Should You Use Neutral Cure Silicone?

People often ask "neutral cure vs acetic cure silicone — what's the difference?"

Neutral cure silicone should be used when sealing natural stone (marble, granite), metals, concrete, mirrors, and outdoor window frames. Acetic cure silicone releases acid while curing (that vinegar smell). That acid can corrode metal, stain stone, and damage sensitive materials.

If you're unsure, neutral cure is generally the safer option for exterior work.

Best Sealant for Australian Conditions

Australian climate isn't mild. We deal with high UV exposure, extreme summer heat, rapid temperature changes, and coastal salt air. That means:

  • Exterior sealants must be UV resistant
  • Movement capability matters more here than in milder climates
  • Interior acrylic should never be used outside
  • Neutral cure is safer for metal and coastal environments

Cheap sealant might look fine on day one. It won't look fine after a summer in Queensland or a year in coastal NSW. All DIYers kits use Sikaflex products — a professional brand specifically suited to Australian conditions.

Quick Answer: What Sealant Do I Need?

Situation Use This The DIYers Kit
Re-sealing a shower or bath Silicone (wet area) Wet Area Reseal Kit
Skirting boards, cornices, interior gaps Acrylic gap filler Skirting Board Kit
Sealing windows, stopping draughts Exterior sealant / polyurethane Window Draught Seal Kit
Concrete joints, driveways Polyurethane Window Draught Seal Kit

Why The DIYers Kits?

Every kit from The DIYers includes the right Sikaflex sealant for the job, all the tools you need, prep sprays, and a QR code linking to clear step-by-step video instructions. You don't need to be a tradie. You just need the right kit.

Final Advice

Choosing the right sealant comes down to four questions:

  1. Is it exposed to water?
  2. Will the joint move?
  3. Is it inside or outside?
  4. What material are you sealing?

Answer those correctly and you won't be redoing the job in 12 months. Still unsure? Browse The DIYers kits — each one is built around a specific job, so you always know you're getting the right product.