Is Microcement Actually Waterproof? What "100% Waterproof" Marketing Claims Leave Out

The short answer: what "100% waterproof" claims leave out is your waterproofing warranty. Even microcement sold as waterproof still has to be applied over a compliant waterproofing membrane (AS/NZS 4858) to meet Australian wet area requirements. But most membrane manufacturers only specify and warrant their membranes when they are covered with tiles. Apply microcement directly onto the membrane and you step outside that specification, and the membrane's waterproofing warranty goes with it.

That's why Ecoflor recommends applying our microcement in showers over existing, well-bonded tiles, with the compliant waterproofing membrane left undisturbed underneath.

Microcement itself is a decorative, water-shedding surface finish, not a waterproofing membrane. In an Australian wet area, the waterproofing is provided by a membrane complying with AS/NZS 4858, installed as part of a system to AS 3740. For showers, we recommend applying Ecoflor over existing tiles with that compliant membrane underneath, so the waterproofing warranty stays intact.

What "100% waterproof" claims leave out: the membrane warranty

Microcement is not a waterproofing membrane under AS/NZS 4858, whatever the label on the tub says. So every microcement shower in Australia, including those using products marketed as "waterproof", relies on a compliant membrane underneath to do the actual waterproofing.

The catch is what goes on top of that membrane. Waterproofing membranes are designed, tested and warranted as part of a tiled system: membrane, tile adhesive, then tiles. Most membrane manufacturers state in their data sheets that the membrane is to be covered with tiles, and some specifically exclude cement or render finishes. When microcement is applied directly onto the membrane, the membrane is no longer installed to its manufacturer's specification, and its waterproofing warranty is lost.

That's the part the marketing doesn't mention. A "100% waterproof" claim on a microcement product is not a waterproofing membrane warranty. If the shower leaks later, the homeowner can be left with a membrane its manufacturer won't stand behind, because it was covered with something it was never specified for.

How Ecoflor avoids the problem: apply over tiles

Applying Ecoflor over existing tiles keeps the waterproofing exactly as it was installed. The membrane stays covered by tiles, inside its manufacturer's specification and warranty, and Ecoflor bonds to the tiles rather than the membrane. You keep the waterproofing system that was built for the shower and change only the surface you see and touch.

Microcement is also a multi-layer system, not a single coat, and each layer plays a different role. The diagram below shows the full Ecoflor build-up over an existing tiled surface: a PrimeLock base coat, fibreglass mesh reinforcement, a second PrimeLock coat, then the Ecoflor 600 and 300 cement layers, the Ecoflor Micro Cement finish, and finally the Prymaren/Ecostar sealer combination with EcoGrip on top.

The Ecoflor microcement system build-up over tiles, the installation we recommend for showers.

Before applying Ecoflor over shower tiles

• No active leaks or signs of water damage, such as staining, mould, or swelling in adjoining walls, floors or cabinetry.
• Tiles firmly bonded, with no drummy, loose or cracked tiles.
• Grout and silicone intact, with no gaps at junctions or around taps and the waste.
• Movement joints at wall-to-floor and wall-to-wall junctions kept and finished with a flexible sealant, not bridged with microcement.
• If you're unsure about the condition of the existing waterproofing, have the shower checked by a licensed waterproofer first. Microcement won't fix a leaking shower, so any waterproofing issue needs to be repaired before you start.

The other problem with "fully sealed" as a selling point

A shower is not a sealed box. Waterproofing membranes, grout lines, junctions, and penetrations all have some tolerance for moisture getting past the first line of defence, which is why AS 3740 (Waterproofing of Domestic Wet Areas) specifies a full system, not a single layer, and why every wet-area build-up assumes some moisture will reach the substrate over time, especially at wall-to-floor junctions, wall-to-wall junctions, and tap or mixer penetrations.

The question that actually matters isn't "can water get behind the finish." Over the life of a bathroom, in some quantity, it usually will. The question is what happens to that moisture once it's there. If the finish above it is genuinely and completely vapour-impermeable, that moisture has nowhere to go. It sits at the interface, and it stays there until it either finds a crack or builds enough pressure to lift the bond.

This is a well-documented mechanism, not a theory. Research into osmotic blistering of waterproofing membranes (published via IIBEC) has measured field blister pressures exceeding 326 kPa, enough to physically lift bonded material off its substrate. Technical literature from major waterproofing manufacturers describes the same failure in simpler terms: trapped moisture vapour and air expand, especially under heat, and that expansion drives toward the surface until something gives. Independent microcement industry guidance confirms it happens in this exact product category too, attributing shower delamination and blistering directly to trapped moisture at junctions and penetrations where "the membrane isn't properly integrated."

Why Ecoflor doesn't build its system around total impermeability

Ecoflor's approach is the opposite. Rather than trying to make every layer a perfect vapour seal, the Ecoflor microcement and sealer system is designed to let moisture that does find its way in continue to move, so it can dry out through the surface rather than getting trapped behind it.

That's not just a design philosophy. Ecoflor's sealer, Ecostar 2K HD, has been independently tested to a recognised international standard for water vapour transmission and verified as allowing a measured rate of vapour movement rather than acting as a total seal (full lab results available on request). It's also been separately tested for resistance to sustained humidity and condensation (UNI EN ISO 6270-1): 120 hours of continuous one-sided condensation exposure at 38°C and 100% relative humidity, with a result of zero blistering, zero cracking, and zero flaking. That's a different test to the vapour transmission figures above, since it measures how the coating holds up under sustained surface condensation rather than moisture specifically trapped behind an installed system, but it points the same direction: a coating engineered to cope with sustained moisture exposure rather than simply trying to exclude it entirely.

That matters most at exactly the failure points described above. If a small amount of moisture does get behind the surface at a joint, a penetration, or a fitting, a vapour-permeable system gives it a path to dry out. A fully impermeable one doesn't. It just accumulates pressure until it fails.

Frequently asked questions

What do "100% waterproof" microcement claims leave out?

The waterproofing warranty. Microcement still needs a compliant waterproofing membrane underneath, and most membrane manufacturers only warrant their membranes when covered with tiles. Applying microcement directly onto the membrane takes it outside the manufacturer's specification, and the membrane's waterproofing warranty is lost.

Is microcement waterproof?

Microcement itself is a decorative, water-shedding surface finish, not a waterproofing membrane. In an Australian wet area, the waterproofing is provided by a membrane complying with AS/NZS 4858, installed as part of a system to AS 3740. For showers, we recommend applying Ecoflor over existing tiles with that compliant membrane underneath, so the membrane stays within its manufacturer's specification and its waterproofing warranty stays intact.

Can microcement be applied directly onto a waterproofing membrane?

We don't recommend it in showers. It takes the membrane outside its manufacturer's specification and voids its waterproofing warranty. This applies to any microcement, including products marketed as waterproof.

Does Ecoflor microcement need a waterproofing membrane underneath?

Yes. In showers and other wet areas, Ecoflor should be applied over existing, well-bonded tiles with a compliant waterproofing membrane underneath. Ecoflor is a decorative finish, not a standalone waterproofing layer.

What causes microcement to delaminate or blister in a shower?

The most common cause is moisture trapped behind the surface, usually entering at wall-to-floor junctions, wall-to-wall junctions, or around tap and mixer penetrations. If the finish above that trapped moisture is fully vapour-impermeable, the moisture has no way to escape and builds pressure until it lifts the bond.

Is Ecoflor's sealer vapour permeable?

Yes. Ecostar 2K HD, Ecoflor's sealer, has been independently lab tested for water vapour transmission and shown to allow a measured rate of vapour movement rather than fully blocking it, and separately tested for resistance to blistering, cracking and flaking under sustained humidity and condensation exposure.