How do you clean oak frames that have become stained or marked? There are several different ways oak frames and fittings can become tarnished. Some of these are a by product of production and installation, others will arise naturally over time. Understanding the source of the problem allows the owner to use the appropriate response. This will save wasted time and money and prevent damaging the wood in an effort to remedy the issue. There are professional companies that clean oak frames, but these can be expensive to use. Why waste money on professional help if you can solve the problem yourself?
Why does oak go black? Oak timber naturally contains Tannins. These are a natural chemical that provide the protective waterproof quality oak is famed for. Being acidic, they can react with iron and water to produce chemicals that stain the wood. In green oak, the tannins will naturally leak out as the timber dries and this can leave brown stains on the surface.
Sources of staining and tarnishing
Production and Delivery
When oak is cut using iron based tools (including steel tools), this can leave traces of metal on the wood itself. This will react with the tannins in the wood to produce bluish black marks. Handling in the workshop and during transport can leave dirty scuff marks on the wood and small dents. If oak is air dried using oak sticks to separate the timber the double dose of tannins can stain the boards up to 10mm deep. Softwood or poplar should be used instead to avoid this.
The use of ferrous tools (those containing iron) during construction will have the same result as during production, if the frame is left exposed to rain, brown tide marks can be left towards the bottom of the frame. These are caused by the water soluble tannins being washed down by rain. Also, it is virtually impossible for workers not to transfer some dirt to the timber as they assemble the frame. Oak can also develop dark stains if left in contact with wet plaster. Any oak surface that may be in prolonged contact with plaster should be masked off for protection.
External fittings of frames exposed to the weather can also develop brown oak tannin stains towards their base. Ferrous fixings such as nails or hinges will also cause staining over time. This can be avoided by using brass fixings (rare and expensive), or marine grade 316 or A4 stainless steel fixings. These will not react with water, avoiding the problem all together.
Soot and smoke
For oak beam fireplaces or those with an oak beam mantel, soot and smoke are an unavoidable issue. This can be minimised with regular cleaning, but any staining that has built up over time is easily remedied.
Damp and fungal damage
Prolonged contact with damp can cause water staining and potentially rot oak timbers. The presence of damp can also encourage the growth of fungi that can stain the wood.
How to clean tarnished oak
Minor surface staining and general scuff marks can be removed by light sanding. If the timber already has a smooth sanded finish a fine grade sandpaper and electric sander should be used. This will ensure an even, consistent finish. General dirt from handling can be scrubbed off with soap and water, but wire wool or brushes should be avoided. These will roughen the surface and can leave traces of metal in the wood. This will react with the tannins and cause further staining. Jet washing should be avoided. It is largely innefective and the timber will take a long time to dry out. Sandblasting with non – silicone material can be used for rough or heavily tarnished timber. This will emphasise the grain and remove deep milling lines but can damage detailing. Persistent black staining that still remains should be treated with Oxalic Acid to bleach the wood.
Soot and fire debris
This can be prevented to some degree by weekly cleaning with a soft cloth or brush. Oak polish can be used but should be sprayed onto the cloth and not the surface of the wood. Too much polish will leave a surface layer that will actually trap soot. If a deep clean is required, wash the wood with an oil based cleaner and apply oak frame oil. Water should not be used as soot contains oil and this will just smear the dirt around, creating more mess. For minor cleaning, a dry sponge or eraser sponge will remove built upsoot. Any smears left can be removed by rubbing a small amount of rubbing alcohol on with a cloth. Traditionally a mix of two parts water to one of vinegar was used and this can be effective in the absence of rubbing alcohol.
Fungal staining and damp
Firstly, locate the source of the damp problem and treat this to avoid further build up. Allow the wood to dry naturally and make sure it is not rotten or needs to be replaced. Mould or mildew remover can then be applied to kill any surface fungus on the wood. If any black staining remains it should be treated with Oxalic Acid.
How to remove dark stains from oak wood
Black staining that lies beneath the surface of the wood is impossible to remove by scrubbing or sanding. It should be treated with Oxalic Acid, a bleaching agent (made from rhubarb) that will not damage the wood itself. As with any chemical, it can be dangerous if used incorrectly and the following steps should be followed:
- Always read the Safety Data Sheets (SDS) on the manufacturers website thoroughly before starting work.
- Always wear a safety mask, goggles and latex gloves. This is a corrosive substance that can cause great harm to the user if not protected. Ensure the work area is adequately ventilated to avoid breathing in dangerous fumes.
- Ensure the correct Oxalic Acid to water ratio is used. The acid is supplied as crystals that are mixed with water or methylated spirits. Methylated spirits evaporate quicker than water, speeding up drying time, but are not essential. Sixty grammes of crystals should be added to one pint of liquid and stirred until they dissolve. Adding more crystals will not make a stronger solution, they simply won’t dissolve. Use a metal container for mixing as the acid will dissolve plastic ones.
- Apply the solution with a paintbrush, avoiding drips, and leave for one to two hours. If staining persists, apply more solution and leave for longer.
- Once the staining is gone, wash off any surface residue with water or methylated spirits and leave to dry.
- Dispose of used containers, paintbrushes and used gloves in a safe and responsible manner.
Hardwoods Group are specialists in the design and construction of oak framed buildings. We carry an extensive range, assembled in our workshop and delivered ready to build. We also offer a bespoke design service. If you have a unique design in mind, we can make it a reality. Contact us today to discuss your needs, we will be happy to help.
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