Silicone Caulking vs Membrane Waterproofing: Which Do You Need

The contractor’s standing in your facility, pointing at the water damage. “You need waterproofing,” he says. 

Great. What kind? 

He shrugs. “Just waterproofing.” 

This happens daily on Perth job sites. Facility managers get quotes for “waterproofing” without knowing if they’re getting silicone caulking, membrane systems, or something else. Contractors toss around terms like they’re interchangeable. Everyone’s confused, and someone’s about to drop serious cash on the wrong fix. 

Here’s what most people miss: silicone caulking and membrane waterproofing are entirely different beasts, solving entirely different problems. Use caulking where you need a membrane? Water still gets in. Use a membrane where caulking works? You’ve just burned thousands for no reason. 

Let’s sort this out properly. 

What Silicone Caulking Does 

Silicone caulking seals joints, gaps, and seams. That’s the whole job. 

Window perimeters, expansion joints, pipe penetrations, control joints, door frames. Anywhere two materials meet and leave a gap, caulking fills it. The silicone stays flexible, moves with your building, keeps water from sneaking through those tight spots. 

Think targeted defence. Small problem areas that need sealing? Caulking nails them. Fast application, you see results immediately, relatively cheap per linear meter. 

Caulking doesn’t coat entire surfaces. It’s not built for that. It lives in the cracks and joints where water’s trying to weasel its way through. 

What Membrane Waterproofing Does 

Membrane waterproofing creates a continuous barrier over the entire surface. Bathrooms, balconies, roofs, wet areas, below-grade walls. Basically, anywhere water exposure is constant or hits a wide area. 

The membrane (which comes in liquid or sheet form) gets applied over the whole space. You end up with a seamless waterproof layer. No gaps, no weak spots, just one solid barrier between water and whatever’s underneath. 

This is an area of defence. Big surfaces exposed to water? Membrane’s what you need. Takes longer to put down, costs more upfront, but protects way more real estate. 

Membrane struggles in moving joints, though. That’s not what it’s made for. It protects surfaces, not seams. 

The Critical Difference 

When You Actually Need Caulking 

• Expansion joints in buildings – These move constantly. Membrane cracks when joints shift. Caulking stretches and bounces back without breaking a sweat. 

• Window and door perimeters – Those narrow gaps around frames need flexible sealing. Caulking fills them perfectly. Membrane would be massive overkill and couldn’t handle the movement anyway. 

• Pipe penetrations through walls – Small gaps where pipes enter buildings. Caulking seals them fast, handles any minor shifting from things heating up and cooling down. 

• Control joints in concrete – Concrete expands and contracts with temperature swings. Caulking in these joints stops water while letting the concrete do its thing. 

• Facade joints – Modern buildings have heaps of panel joints and architectural seams. Caulking seals these while dealing with wind movement and temperature changes. 

Bottom line: if you’re measuring protection needed in linear meters (not square meters), caulking’s usually your answer. 

When You Actually Need Membrane 

• Bathroom floors and walls – Entire surfaces constantly hit with water. Membrane under tiles creates a complete waterproof shield. Trying to caulk a bathroom floor? Yeah, don’t. 

• Balconies – The whole deck needs protection, not just the edges. Membrane covers everything, stops water getting through the substrate. 

• Flat or low-slope roofs – Water sits on these. Every single inch needs waterproofing. Membrane creates that continuous barrier, keeping your building dry. 

• Below-grade walls – Basements and retaining walls cop constant moisture from soil. Membrane on the outside creates a proper barrier against water pressure. 

• Planter boxes – The entire inside needs waterproofing to protect what’s underneath. Membrane handles the whole job. 

Simple rule: if water hits entire surfaces rather than just joints, membrane’s what you’re after. 

The Hybrid Truth (What Really Happens on Job Sites) 

Real buildings need both. That’s what nobody tells you upfront. 

Bathrooms get membrane on floors and walls, then caulking around fixtures, between wall panels, wherever materials change. Membrane does the heavy lifting, caulking tidies up the joints. 

Balconies get membrane on the deck, then caulking seals perimeter joints, door thresholds, any spots where something pokes through the membrane. 

Facility managers who think it’s either/or? They end up with half-done waterproofing. Both products earn their keep. Neither replaces the other. 

Expensive Mistakes People Keep Making 

Using caulking instead of membrane in wet areas – Someone tries cutting costs by just caulking shower corners. Water still gets through the substrate. Mould parties behind the tiles. Repair bill runs ten times what a proper membrane would’ve cost. 

Using membrane in expansion joints – Contractor slaps membrane across a building expansion joint. Joint moves like it’s designed to. Membrane tears. Water floods through. Now you’ve got membrane failure AND water damage to fix. 

Wrong caulking with membrane systems – Different membranes need specific, compatible caulking. Acrylic caulk with polyurethane membrane? They don’t stick right. Mismatched products create weak spots that fail. 

Skipping one product entirely – Membrane in bathroom, but fixtures not caulked properly. Or all balcony joints caulked, but no membrane on the deck. Incomplete waterproofing fails. Always. 

Why Material Compatibility Actually Matters 

This trips up contractors all the time. Waterproofing materials don’t all play nice together. 

Polyurethane membranes need polyurethane-compatible caulking. Acrylic membranes need acrylic-compatible caulking. Silicone caulking won’t stick to some membranes at all. 

Product data sheets exist for a reason. Manufacturer specs aren’t suggestions. Mix incompatible materials and you’re looking at failures popping up months or years down the track when fixing them costs stupid money. 

The Real Cost Question 

Facility managers see caulking quotes at $2,000 and membrane quotes at $8,000. Cheaper looks better, obviously? 

Wrong thinking. Real question: what actually fixes your problem? 

Caulking won’t save a bathroom floor needing membrane. Dropping $2,000 on caulking isn’t saving anything when water still leaks and you’re staring at $20,000 damage repair. 

Match your solution to your actual problem. Cheapest only matters when you’re comparing things that actually work for your situation. 

Questions to Ask Before Work Starts 

• “What exactly are you waterproofing—joints or surfaces?” – This tells you caulking versus membrane right off the bat. 

• “How much movement happens in this area?” – Lots of movement? Caulking. Minimal movement? Membrane works. 

• “What’s the water exposure like?” – Constant water? Membrane. Occasional water at joints? Caulking. 

• “Will this work with what’s already there?” – Critical question for renovations where new meets old systems. 

Here’s the Actual Bottom Line 

Silicone caulking seals joints and gaps. Membrane waterproofing protects surfaces. Different tools for different jobs. You need both. 

Buildings leak because someone picked the wrong fix. Caulking where membrane belonged. Membrane where caulking would’ve worked better. Half-finished systems missing one or the other. 

The choice isn’t caulking OR membrane. It’s caulking AND membrane, each doing what it’s actually good at. 

Waterproofing Perth has protected Perth buildings for over 25 years with both membrane systems and silicone caulking. We handle complete waterproofing for homes and commercial properties: bathrooms, balconies, roofs, wet areas with membrane systems, plus all the joint sealing and caulking that finishes the job properly. We’re GAPP approved practitioners using quality gear backed by 10-year application warranties and manufacturer guarantees up to 25 years. Call 08 9375 7948 for an inspection that tells you exactly what waterproofing each part of your building actually needs.