Marks or Stains on Timber
Iron Stain
Iron stain, is an unsightly blue–black or gray discoloration that is often incorrectly described as "mould" because of its frequently "spotty" appearance. Iron stain can occur on nearly all woods, however some timbers are particularly prone to iron stain because they contain large amounts of tannin-like extractives. The discolouration is usually caused by a chemical reaction between extractives and iron content in steel products, such as nails, screws, and other fasteners. Steel used in contact with wood must be protected from corrosion. This can be accomplished by using stainless steel or processes such as hot dip galvanising. Problems with iron contamination have also been associated with traces of iron left on wood from cutting, grinding or slicing; cleaning the surface with steel wool, wire brushes, or iron tools; using finishes stored in rusty containers; and using previous iron-containing or iron-contaminated finishes. Iron dust from metalworking and even plant fertilizers can be sources of iron along with many other potential sources that are often difficult to identify. Urine on wood floors will also hasten the reaction with iron and wood extractives, producing the typical iron stain discolouration. Unprotected timbers that get wet on or off site prior to fixing are particularly vunerable as the water soluable extractives are more readily mobilised to react with any iron contamination.
Testing For Iron Stain
A simple test can be used to determine whether wood discolouration is caused by iron. Apply undiluted WAO Stain Remover by scrubbing into the stained wood surface. If the solution removes the stain after approximately one hour, then iron is present on the wood. If the solution does not remove the stain, try applying bleach to the stained area. If it removes the stain, the discolouration was probably caused by surface mould or mildew. If the iron stain is spotty, try to view the stained wood under a 10x magnifying glass. ”Chunky” discoloration is usually a result of molten metal and looks like clinkers from a grinding operation. Stain that resembles slivers or flakes could be from steel wool. An even discolouration throughout the stain indicates that the iron was in solution when it contaminated the wood, probably in a contaminated finish or iron contaminated water.
Removing Iron Stain
It is easy for iron to contaminate wood, as there are so many possible sources of iron contamination on a building site that are often not initially recognised. For example removal of old rusted guttering, handrail construction, contact by steel capped boots, and merely striking wood with a hammer can cause iron stain on some timbers. WAO Stain Remover reacts with iron tannates to form a colorless complex. To remove iron discolouration scrub stained timbers with undiluted WAO Stain Remover and leave to soak for one hour. After one hour thoroughly wash the surface with fresh water (preferably with a power washer) to remove excess WAO Stain Remover. It is very important to rinse the WAO Stain Remover off thoroughly because if all sources of iron are not removed or protected from corrosion, staining will occur again. In other words, treatment with WAO Stain Remover is only a temporary solution if iron remains on or in the wood. In time, the residual unrinsed WAO/iron complex will break down, permitting the iron to react with the extractives to form a dark-coloured stain again.