Sealing grout and natural stone tiles is one of the most important — and most overlooked — steps in any tiling job. Without a good sealer, grout soaks up moisture, cooking oils, soap scum, and dirt, while porous stones like marble, travertine, and slate can stain almost instantly. The good news is that sealing is a straightforward DIY task if you follow the right process.
Why Sealing Matters in New Zealand Homes
New Zealand's climate varies enormously — from the humid, wet conditions of Auckland and Northland to the cold, damp winters of the South Island. High humidity accelerates mould growth in grout lines, and in wet areas like bathrooms and kitchens, unsealed grout can deteriorate quickly. The NZ Building Code (specifically clause E3 — Internal Moisture) requires wet areas to be waterproofed and protected from moisture damage, and while sealing grout isn't a substitute for proper waterproofing membranes, it is an important layer of protection. BRANZ also recommends regular maintenance of tiled surfaces to extend their lifespan.
Understanding the Difference: Grout Sealer vs Stone Sealer
Not all sealers are the same, and using the wrong one can cause problems.
- Grout sealers are designed to penetrate the porous surface of cement-based grout and repel water and stains. They come in two main types:
- Penetrating (impregnating) sealers — soak into the grout and don't change its appearance. Best for most applications.
- Topical (coating) sealers — sit on the surface and can add a sheen. Can peel over time in high-traffic areas.
- Natural stone sealers are also typically penetrating sealers, but formulated for denser, more varied surfaces like marble, travertine, limestone, slate, and sandstone. Some stones (like granite) are very dense and may need little or no sealing; others (like travertine) are highly porous and need sealing before grouting as well as after.
| Surface Type | Sealer Type | Frequency (approx.) |
|---|---|---|
| Cement grout (wet areas) | Penetrating grout sealer | Every 1–2 years |
| Cement grout (dry areas) | Penetrating grout sealer | Every 2–3 years |
| Marble / Limestone | Penetrating stone sealer | Every 1–2 years |
| Travertine | Penetrating stone sealer | Annually or more |
| Slate | Penetrating stone sealer | Every 1–2 years |
| Granite | Check absorbency first | Often 3–5 years |
What You'll Need
Step-by-Step: How to Seal Grout
1. Clean thoroughly first
Grout must be completely clean and dry before sealing. Use a neutral pH cleaner — avoid acidic cleaners (like vinegar) on natural stone as they etch the surface. Scrub grout lines with a stiff brush, rinse well, and allow to dry for at least 24–48 hours. New grout should cure for a minimum of 48–72 hours (check the manufacturer's instructions) before sealing.
2. Test absorbency
Drop a few beads of water onto the grout or stone. If it soaks in within a few minutes, sealing is needed. If it beads up, the existing sealer may still be working.
3. Apply the sealer
Work in small sections. Apply the sealer along grout lines using an applicator brush or bottle, keeping it off glazed ceramic tiles where possible (it won't absorb and can leave a haze). For natural stone, apply evenly across the whole surface with a cloth or applicator pad.
4. Allow to penetrate, then wipe off excess
Follow the product's dwell time (usually 5–15 minutes). Before it dries completely, wipe off any excess sealer with a clean cloth. Sealer left to dry on the surface can leave a cloudy haze that's difficult to remove.
5. Apply a second coat if needed
Highly porous stones like travertine often benefit from a second coat applied after the first has been absorbed (usually 10–20 minutes later).
6. Allow full cure time
Avoid wetting the surface for at least 24 hours, or as directed by the product. Full cure may take several days.
Choosing the Right Product
Look for products from reputable suppliers. Ardex and Mapei both offer professional-grade sealers used widely in the NZ trade. Sika also has suitable products for wet area protection. Your local tile shop or trade supplier can advise on the best match for your specific stone type.
Common Mistakes to Avoid
- Sealing dirty or damp grout — the sealer locks in stains and moisture
- Letting sealer dry on glazed tiles — causes a stubborn haze
- Using acidic cleaners on natural stone — etches and damages the surface
- Skipping the water bead test — you may not need to reseal as often as you think
- Using a topical sealer in a shower — these can peel and trap moisture underneath
When to Call a Professional
Sealing is generally safe DIY work, but there are situations where a qualified tiler is the better choice:
- If tiles are lifting, grout is cracking, or there are signs of water damage behind the wall — these point to deeper waterproofing issues that need professional assessment
- If you're retiling a wet area from scratch, waterproofing membranes must comply with NZ Building Code clause E3, and this work is best left to an experienced tiler
- If you're unsure what type of stone you have, a professional can identify it and recommend the correct sealer
You can find qualified, local tilers on tradedirectory.co.nz who can assess your tiles and carry out any remedial work to a professional standard.