How to Remove Bore Water Stains from Concrete

If your driveway, paths or pool surround have orange or brown staining near the sprinklers, it’s almost certainly bore water. It’s one of the most common concrete problems in Perth.

Light staining can usually be removed with the right product, while years of build-up, especially on honed concrete, may need to be honed out.

What causes bore water stains?

Much of Perth’s groundwater carries dissolved iron and other minerals. When bore water reticulation sprays onto concrete, the water evaporates and the iron oxidises, leaving a rusty orange or brown deposit. Every watering cycle adds another layer, which is why the staining usually forms in arcs or fans matching the sprinkler pattern.

Unsealed concrete, or concrete whose sealer has worn out, is worst affected, because the stained water soaks into the surface rather than sitting on top.

Stop the source first

There’s no point removing stains if they’ll be back in a month. Before treating the concrete:

• Adjust or replace sprinkler heads so they don’t spray onto hard surfaces.
• Consider an iron filter or bore stain treatment system on the bore.
• Seal the concrete once it’s clean, so future overspray is easier to remove.

Removing light to moderate staining

Fresh or light bore stains often respond to a dedicated bore water or rust stain remover. These products are designed to dissolve iron deposits.

1. Rinse the area and let it dry if the product calls for it.
2. Test the product on a small, inconspicuous spot first, especially on coloured concrete, honed concrete or near pool tiles and plants.
3. Apply as directed and let it dwell for the time specified. Don’t let it dry on the surface.
4. Rinse thoroughly with clean water. Stubborn areas may need a second application.
5. Let the surface dry fully, then seal it.

Always follow the product’s safety directions and protect nearby plants, metal fittings and painted surfaces. Many of these products are acid-based, so treat them with care on honed concrete, where they can dull the finish.

When chemical treatment won’t fix it

Bore staining that has built up over many years can soak well into the concrete. You may lighten it chemically but not remove it completely. Signs you’re at this point:

• The stain fades after treatment but a clear shadow remains
• Repeated treatments make little difference
• On honed concrete, treatment has left the surface dull or uneven

Honed concrete

Re-honing removes the stained top layer and restores an even finish. This is often the most reliable fix for heavy bore staining on honed surfaces. How deep the stain goes determines how much needs to be removed, so we assess it on site before quoting.

Exposed aggregate

Some of the staining sits in the stones themselves, particularly lighter, porous stones. Chemical treatment is usually the first step here. Grinding exposed aggregate is possible but changes the finish from a washed stone look to a flat honed aggregate look, so it’s a decision about the finish, not just the stain. See Concrete Stains That Need Honing Out, Not Chemicals.

Preventing it coming back

• Keep reticulation off hard surfaces.
• Keep the concrete sealed. A sound sealer stops the iron soaking in and makes overspray easy to wash off.
• Rinse fresh overspray with mains water before it builds up.
• Check the sealer each year with a water bead test.

For the full cleaning and resealing process, see Cleaning and Resealing Honed and Exposed Aggregate Concrete.

Frequently asked questions