Yes, waterproofing an outdoor concrete step is a practical DIY job for most homeowners — provided you prepare the surface properly and choose the right product for NZ's variable climate. Done well, it can stop water ingress, prevent freeze-thaw cracking in colder regions, and extend the life of your concrete significantly.
Why Waterproofing Matters for Concrete Steps
Concrete is porous by nature. Water that soaks in can cause efflorescence (white salt deposits), surface spalling, and in colder parts of New Zealand, frost damage as water expands when it freezes. Steps near the house can also direct water toward foundations, which is worth keeping in mind under the NZ Building Code clause E1 (Surface Water).
A good waterproofing system keeps water on the surface and channels it away, rather than letting it soak through.
Assess the Situation First
Before buying anything, check:
- Cracks or structural damage — hairline cracks can be sealed, but large or moving cracks may indicate a structural issue that needs a professional eye.
- Existing coatings — if the step has been painted or sealed before, you'll need a compatible product or may need to strip the old coating first.
- Drainage — make sure the step has a slight fall (a suitable slope (check product and council guidance for recommended fall ratios)) so water runs off rather than pools. Poor drainage is often the root cause of ingress.
- Source of water — is water coming from above (rain), from the side (a garden bed), or wicking up from below? Each needs a different approach.
Choosing the Right Waterproofing Product
For a single outdoor concrete step, you have several good options available at NZ hardware stores:
| Product Type | Best For | Notes | |---|---|---|| | Penetrating sealer (silane/siloxane) | General water repellency, keeps natural look | Soaks in, invisible finish, breathable | | Acrylic or polyurethane coating | Decorative finish + protection | Adds colour/sheen, may be slippery when wet — choose a non-slip additive | | Cementitious waterproofing | Damp-proofing, wicking issues | Brushed on like paint, bonds well to concrete | | Epoxy coating | Heavy-duty, high-traffic areas | Very durable but less flexible; surface prep is critical |
For most outdoor steps, a penetrating silane/siloxane sealer or a polyurethane coating with a non-slip aggregate is the most practical choice. Products from Sika and Ardex are well regarded in the NZ trade, and both Bunnings and Mitre 10 stock a range of concrete sealers suitable for this job.
Always read the product datasheet — application temperatures, recoat times, and coverage rates vary, and NZ humidity can affect cure times.
Step-by-Step: How to Waterproof a Concrete Step
1. Clean the Surface Thoroughly
Remove all dirt, moss, algae, oil, and loose material. A pressure washer works well; follow up with a concrete cleaner or diluted sugar soap if there's grease or staining. Allow the surface to dry completely — most sealers require the concrete to be dry (check the datasheet, as some cementitious products prefer a damp surface).
2. Repair Cracks and Holes
Fill hairline cracks with a flexible polyurethane or epoxy crack filler. For larger voids, use a concrete patching compound. Allow repairs to cure fully before sealing.
3. Etch if Required
Some coatings require the concrete to be lightly etched with diluted hydrochloric (muriatic) acid to open the pores. If you do this, wear gloves, eye protection, and work in a well-ventilated area. Refer to WorkSafe NZ guidance on handling hazardous substances. Rinse thoroughly and allow to dry.
4. Apply the Waterproofing Product
Follow the manufacturer's instructions exactly. Most sealers are applied by brush, roller, or low-pressure sprayer. Apply in thin, even coats — two thin coats are almost always better than one thick one. Work the product into the surface rather than leaving it sitting on top.
5. Add Non-Slip Texture if Needed
If using a film-forming coating, broadcast fine non-slip aggregate (silica sand or aluminium oxide) into the wet first coat, or use a product with non-slip additive already included. Wet concrete coatings can be dangerously slippery — this step is important for safety.
6. Allow Full Cure Before Use
Most products need 24–48 hours before foot traffic and longer before they reach full hardness. Avoid applying if rain is forecast within the cure window.
Safety Note
Always wear appropriate PPE — gloves, safety glasses, and a dust mask when grinding or sanding. Keep children and pets away from the work area until the product has fully cured. Check the product's Safety Data Sheet (SDS), available from the manufacturer's website.
When to Call a Professional
Consider hiring a qualified waterproofer if:
- The step is part of a larger waterproofing system (e.g., a deck, balcony, or tanking situation) — these may require a building consent or need to meet specific NZ Building Code requirements such as clause E2 (External Moisture).
- There are structural cracks or signs of subsidence.
- Water is wicking up from below (rising damp), which needs specialist diagnosis.
- The step is tiled — grout and tile waterproofing membranes under tiles are best left to a professional to ensure compliance.
- You're a landlord — under the Healthy Homes Standards, moisture management is a legal obligation and professional documentation may be needed.
You can find qualified local waterproofers and concreters on tradedirectory.co.nz.
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SiteWise
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