Merbau, like most hardwoods, contains water-soluble extractives. When rain or irrigation moves through the timber, those extractives can wash onto nearby surfaces and leave brown stains that are hard to remove from unsealed brickwork, concrete and paving. You cannot switch this off, but you can plan for it: where the pack is put down, how the boards are coated, and where the water runs.
Why it happens
WoodSolutions' Domestic Timber Deck Design guide explains that most hardwood species contain water-soluble extractives that give colour and some natural decay resistance, and that these can be leached to the surface and washed onto other surfaces. Coating manufacturer Intergrain lists Merbau, with Spotted Gum and Jarrah, as tannin-rich and oily timbers that take longer to weather naturally (Intergrain, preparing a new timber deck).
Before delivery
- Choose where the pack goes. Do not have Merbau put down on light-coloured paving, a sealed driveway you care about, or render-adjacent paths. Tell us when you arrange delivery; see our delivery and collection guide.
- Store it flat, dry and covered, off the ground and clear of surfaces that could stain. Our timber storage guide covers the basics.
Before and during laying
- Coat every surface. To reduce bleeding and staining, WoodSolutions recommends seasoned timber and a water-repellent finish on all surfaces, including freshly cut ends, preferably before fixing.
- Prepare to the coating label. New timber carries surface tannin and oil that can stop coatings adhering. Intergrain notes natural weathering generally takes four to six weeks but depends on exposure and is not reliable, and uses a dedicated tannin and oil remover instead. Use the preparation product your chosen coating's manufacturer specifies, following its label.
- Keep metal off the boards. Iron filings from angle grinders, or metal left lying on the deck, react with moisture and timber extractives and cause dark stains (WoodSolutions).
In the first months
- Direct the run-off. Where you can, let water from the deck drain to garden beds or gravel rather than across paving.
- Protect what is below. If paving or concrete sits under or beside the deck, ask the paving or sealer supplier about sealing it first.
- Maintain the coating. Coatings wear with sun and foot traffic, and worn areas take up water again.
If staining happens
On the timber itself, our Merbau product pages note that an oxalic acid-based timber cleaner removes dirt, grease and tannin stains before recoating. For paving, concrete or render, ask the manufacturer of that surface or of the cleaning product what is suitable, and test a small hidden area first. Follow the label and wear the protective equipment it specifies.
FAQ
Does coating stop tannin bleed completely?
We do not claim that. A finish on all surfaces reduces it; planning where water runs matters as much.
Is tannin bleed a defect?
It is a characteristic of tannin-rich hardwoods such as Merbau. Your rights for goods that are faulty or not as described are covered in our refund policy and the Australian Consumer Law.
Which of your products does this affect?
All our Solid Merbau sizes; see Solid Merbau decking sizes.
Talk to us
If you are planning Merbau next to paving or render, tell us when you request a quote so delivery placement is part of the plan.
Sydney Timber Supply team
Guidance drawn from WoodSolutions Technical Design Guide 21, Domestic Timber Deck Design (revised October 2020), page 15; Intergrain; and our product care notes. Reviewed November 2026.