Is cement grout waterproof?
No. Cement grout is made from cement, sand and additives. Once it sets, it's full of tiny pores. In a shower it absorbs water every time you use it, stays damp, grows mould and gradually breaks down. That's why old shower grout goes dark, cracks and crumbles, and why water ends up behind the tiles.
Does sealing grout make it waterproof?
Not really. A grout sealer reduces how much water cement grout absorbs, but it wears off with cleaning and use and needs reapplying. It doesn't fill cracks, and it can't fix grout that's already breaking down.
Is epoxy grout waterproof?
Yes, epoxy grout itself is waterproof. It's made from epoxy resin and a hardener, so once it cures it's non-porous: water can't soak into it. It's also highly resistant to mould and staining, and it doesn't need sealing. That's why we only use epoxy grout (Mapei Kerapoxy) in showers and on balconies.
Then why do showers still need a membrane?
Even with epoxy grout, water can find its way behind tiles through cracked tiles, failed silicone, movement or penetrations like taps. The waterproof membrane under the tiles, required in Australian wet areas, is the safety net that stops that water reaching the walls, floor or ceiling. Good grout and silicone protect the membrane; they don't replace it.
Cement vs epoxy grout at a glance
| Cement grout | Epoxy grout | |
|---|---|---|
| Waterproof? | No, porous | Yes, non-porous |
| Needs sealing? | Yes, regularly | No |
| Mould and staining | Absorbs water and stains; mould grows in it | Highly resistant |
| Durability in showers | Breaks down over time | Far more durable |
| Cost to install | Cheaper | Costs more (material and labour) |
| Replaces the membrane? | No | No |
For the full comparison, see Epoxy vs Cement Grout
What this means for your shower
FAQs
Is grout waterproof once sealed?
Sealed cement grout absorbs less water for a while, but it isn't waterproof and the sealer wears off.
Is epoxy grout 100% waterproof?
Epoxy grout itself is non-porous, so water doesn't soak through it. But water can still get behind tiles through other gaps, which is why the membrane and good silicone matter too.
Do I need to seal epoxy grout?
No. Epoxy grout doesn't need sealing.
Can you put epoxy grout over old cement grout?
No. The old grout has to be removed first so the epoxy fills the full depth of the joint.
How long does epoxy grout last?
It's far more durable than cement grout and, cared for properly, lasts many years. Our epoxy regrouting carries a 10-Year Warranty on eligible epoxy re-grouting work, subject to terms.
Send photos for a fixed quote
Send a photo of the whole shower or balcony and a close-up of the grout. We assess the visible condition and explain whether regrouting and resealing are suitable.