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Question

I have a new Tallow wood deck replacement almost completed that has extensive black marking. The builder is attempting to sand the marks out but I expect the marking will continue. I intend on applying a clear oil finish. What is the correct procedure to achieve the best finish with the least amount of black marking? Does the timber need to be weathered for an amount of time before cleaning and applying the finish?

Woodsolutions Answer +

Black marks on new hardwood suggest that the problem is 'iron staining', ie. metal particles falling on the deck and reacting with tannin in the wood when it gets wet. The recommended treatment is oxalic acid, or a proprietary timber cleaning product that contains oxalic acid. The US Department of Agriculture's Forest Service has a helpful data sheet on the subject. It can be dowloaded via this link https://www.srs.fs.usda.gov/pubs/48449. Treating the timber with an oxalic acid solution is likely to be easier and more effective than the builder trying to sand the marks out. You may be able to stop further staining if you can find the source of the metal contamination and eliminate it. It could arise from cutting metal nearby, for example working on guttering or other metal items. Your builder can find a product with an oxalic acid base by checking the labels of deck cleaning products, or reviewing their Material Safety Data Sheets. 

Iron stain

Answered on 15-04-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

I made a refectory table for my Daughter out of recycled oregon which was sealed with hardened shellac. The table was stripped back to raw timber to change it's appearance to a "modern" natural look. Unfortunately, before my Daughter got to sealing the timber, she left a bag on her table with a bottle of "rejuvenating shampoo - blue in colour" in it, regrettably, the cap dislodged and the contents spilled onto the table resulting in a surface stain blue in colour. Can you advise if there is a product that may remove the stain? I have used Oxalic acid previously on beach timber.

Woodsolutions Answer +

If the blue stain of the shampoo has penetrated through the shellac sealer and soaked into the wood it will be difficult to remove. Oxalic acid is very useful to remove stains from wood, particularly 'iron stains', ie. stains caused by the chemical reaction of tannins in the wood mixing with traces of metal. We feel oxalic acid is unlikely to work on a strong colour that may have soaked in to some depth, but perhaps it's worth a try. Remember to follow up by neutralizing the acid after treatment. It's possible to bleach wood with a stronger bleach than oxalic acid, but then you will lose the natural wood look that you are trying to achieve and you would have to restore some colour with a wood stain. Bleaching can also be tricky unless you have some experience, since it can result in a patchy appearance. If oxalic acid doesn't work we suggest you try an orbital sander. That will be the least risky strategy.

Stain removal

Answered on 12-04-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

Question

We have a large spotted Gum deck along the Western side of the house which was installed around 8 months ago. It has been left natural and allowed to grey off. It’s now at a point where we really like the look of the weathering and want to seal it so that it remains the same. What product would you recommend that we use to seal the timber. I don’t want it to change appearance from what it looks like now as I know some sealers with allow the timber to weather a bit more, while others give the timber that wet look.

Woodsolutions Answer +

We don't endorse any particular finishes since we don't have the resources to test them. However, it sounds as if Feat Watson's "Weathered Grey" might achieve the result you are looking for. Make sure you see it on a sample of timber before purchasing. You could, of course, just leave the decking the way it is if that's the look you want. Spotted gum stands up to the weather well without a finish, although applying a finish will help to avoid the fine surface cracks that occur in weathered wood. 

Weathered wood

Answered on 29-03-2021
Please note that our answer is based on the best advice available at the time. If the National Construction Code, Australian Standards or local requirements have been subsequently amended, our answer may no longer be correct in all details. For more information, please read our disclaimer.

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