Why coir doormats cause tannin stains
Coir doormats are made from coconut fibre. Because it’s a natural material, it naturally contains tannins (plant compounds). When the mat gets wet, those tannins can leach out and the brown water can soak into whatever the mat is sitting on. Porous surfaces are the main troublemakers, because they absorb the liquid instead of letting it sit on top.
We’ve been UV printing on doormats for 10 years and keep refining our methods. Most tannin marks can be improved with the right approach. The key is using a cleaner that targets organic staining, and not jumping straight to harsh acids that can damage finishes.
Prevent it first (the easiest fix)
Coir is a natural fibre and it contains tannins. When the mat gets wet, those tannins can leach out, and the brown moisture can soak into porous surfaces. The main goal is simple: keep the mat dry, and don’t let it sit wet on the same spot.
1) Use an undermat (choose the type that matches your entry)
An undermat helps in two ways, it reduces slipping, and it changes how water sits under the coir. If you can, choose an undermat that’s slightly larger than the coir mat, so any runoff isn’t sitting right at the edges.
Open-style rubber undermat (ring or honeycomb)
This is a popular choice because it lifts the coir slightly and improves airflow, which helps the mat dry faster after rain or washing. Faster drying usually means less time for tannins to keep leaching.
On very porous, pale surfaces (like unsealed concrete or light sandstone), tannin-rich water that drains through can still stain. That’s why the drying routine below matters.
Doormat tray (solid base with a raised lip)
If you’ve got a stain-prone surface and you want the most protection, a tray can keep tannin runoff off the concrete or stone. The trade-off is that a tray can hold moisture under the mat if you never lift it, so you still need to dry the mat properly.
Non-slip rubber underlay (more solid style)
These are great for grip on smooth floors, but avoid anything that traps water underneath for long periods. If water can’t drain or evaporate, the mat stays wet longer, and that’s when leaching is more likely.
A simple rule of thumb:
- If your surface is porous and light-coloured, a tray is often the safer option.
- If your surface is less porous or sealed, an open rubber undermat plus good drying habits usually works well.
2) Keep your doormat dry
Keep the doormat dry. When coir gets wet, tannins can leach out and that’s when staining is most likely.
Keeping the mat out of harsh, direct sun and away from constant wet weather also helps it look better for longer. With printed doormats, less sun exposure and less soaking means the design stays fresher over time, and the coir fibres themselves tend to wear more slowly.
3) If the mat gets wet, move it to dry somewhere safe
If the mat gets wet, move it to dry somewhere safe.
Don’t dry it on the driveway, the porch slab, or your sandstone landing. Pick a spot that won’t stain (like a gravel area), let it dry fully, then put it back.
If you’re choosing a printed mat for your entry, our personalised doormats are UV printed in our Sydney workshop.
Before you clean, do this quick check
- Work out what surface you’re cleaning. Concrete and sandstone behave very differently to marble.
- Patch test first. Choose a small corner spot.
- Don’t mix chemicals. If you try one product, rinse thoroughly before trying another.
If you’re unsure whether your stone is marble or travertine (acid sensitive), treat it as sensitive until you confirm, because acids can etch and dull these stones.
Best first method for most homes
For tannin staining on porous outdoor surfaces, our first pick is usually an oxygen bleach product based on sodium percarbonate (often sold as Napisan type soakers). Sodium percarbonate breaks down in water to release hydrogen peroxide, which helps lift organic stains.
The oxygen bleach paste method
This is the method many homeowners and tradies reach for on concrete-style surfaces, because it’s effective and generally lower risk than acid washing.
- Pre-wet the area. Lightly hose the stained section and a border around it. This helps reduce patchiness.
- Mix a paste. Add a small amount of hot water to the powder until it’s a spreadable paste (think thick yoghurt).
- Apply and cover. Spread it over the stain and slightly beyond the edges. For better results, cover with plastic film so it stays damp.
- Wait 30 to 60 minutes. Don’t let it bake dry in the sun.
- Scrub gently. Use a stiff nylon brush.
- Rinse very well. Hose thoroughly so residue doesn’t dry back in.
- Repeat if needed. Older stains often take a few rounds.
If you’re cleaning near garden beds, rinse plants with clean water first and after, and keep the paste contained.
Surface guide (what changes by floor type)
Concrete, exposed aggregate and concrete pavers
These surfaces are porous, so tannins soak in. The oxygen bleach paste method is a strong first step. If your concrete is unsealed, expect to repeat. If it’s sealed, stains tend to sit closer to the surface and lift faster.
Tip: if you’re tempted to pressure wash, do it after the stain has lightened, not as step one.
Sandstone and other porous natural stone
Sandstone can stain easily and deeply, and strong cleaners can cause uneven colour if you spot clean too aggressively. Some stain removal guides recommend using poultice-style methods (paste left in place to draw the stain out), which fits well with the oxygen bleach paste approach.
If your sandstone is pale or high value, do a careful patch test and consider a stone professional if the stain is old.
Marble and travertine (acid sensitive stone)
These are calcium-based stones and they can be etched by acids. That includes many “natural” acids like vinegar, and it includes oxalic acid if used incorrectly.
If your entry is marble or travertine, start with the mildest option and patch test. If you see dulling, stop. Etching is damage, not a stain, and it usually needs polishing to fix.
Timber decking and coated timber
A wet mat can hold moisture against timber and coatings. If there’s staining, oxygen bleach products are often used for organic marks on outdoor timber, but they can lighten the surface, so patch testing matters.
Also check that the mat isn’t blocking drainage. A rubber undermat with holes helps here too.
Last resort for old, stubborn stains
If you’ve tried oxygen bleach a few times and the stain is still hanging on (especially if it’s been there for years), oxalic acid is sometimes used for tannin-related staining. We treat it as a last resort because it needs more care, and it can be risky on acid sensitive stone like marble and travertine.
If you go down this path, follow the product directions closely, use proper PPE, and test first. If your surface is stone, it’s often worth calling a stone restoration pro before you start.
FAQs (researched and practical)
1) Will the stain fade on its own?
Sometimes it lightens a bit, but on porous surfaces it often needs cleaning to fully lift.
2) Can oxygen bleach lighten or patch my concrete?
It can slightly brighten the treated area, especially on unsealed concrete. Pre-wetting and treating a wider border helps it blend.
3) Can I just pressure wash the stain out?
Pressure washing alone often won’t remove the colour. It’s better after the stain has been chemically lifted.
4) Is oxalic acid safe on all surfaces?
No. Avoid it on marble and travertine, and be cautious on any natural stone. Always patch test.
5) How do I stop it happening again?
Keep the mat dry, lift it to dry if it gets wet, and use an undermat or tray that suits your surface so the mat isn’t sitting wet in one spot.
DIY cleaning disclaimer
The cleaning methods above are general suggestions only. Every surface is different, and products can react in unexpected ways depending on sealers, finishes, age, and porosity. Always patch test first, follow the product label directions and safety advice, and consider a professional if you’re unsure. Any cleaning you do is at your own risk, and we can’t accept responsibility for damage, discolouration, or injury resulting from DIY stain removal.