Blue Stain, Color Problem at the Wood.

Blue stain is a problem in the wood that degrades the wood quality. Blue stain appears as dark spots or lines (usually in the blue or black color) at the surface of the wood. The stain may be very thin and exist at the top surface of the wood, but it can also be very strong and thick and come deep from inside the timber. Blue stain is not a problem for wood if the wood is used for structural uses. Blue stain does not affect the strength of wood, but it disrupts the appearance and color of the wood. Blue stain will be a problem in the finishing process, especially when the light or natural wood color is needed. The blue stain will be a problem for products that need the aesthetic function from the wood, such as furniture, floors, doors, windows, wall panels, and architectural products that need good appearance.

blue stain at the wood

Blue stain is mainly caused by a special fungus that is called the wood staining fungi. The fungi will not affect the wood's strength, but they will make the dark stain on the wood and affect the appearance of the wood. There are two species of fungi that are recognized as the blue stain causes: aureobasidium pullulans and hormoma dematodies. The fungi grow during the tree cutting, sawmilling, and drying process. The risk of the fungi attacking is higher when the environment is wet and humid. 

Here are some ways to handle the blue stain problem.

• Proper process and storage of the timber.

The fungi that caused the blue stain grow in the media that are wet. The wood staining fungi grow when the wood is still wet, either on logs or at the wood boards at the wood processing. If we can control the wood processing to make the wood dry fast and minimize the wet condition, then we can minimize the fungi problem. The well-integrated wood processing from the harvesting to the drying is the best way to prevent the fungi attack. Keep the wood log or board in the dry and well-circulated air and do the wood drying in the proper schedule. Some anti-fungal chemicals can be applied to protect the wood from the fungi. The chemical is usually applied together with the anti-insect chemical to keep the wood quality. The antifungal chemical is highly recommended to handle the wood when the condition is wet and humid. The antifungal is also needed when we deal with some species of wood that are susceptible to the fungi, such as mango, rubber wood, etc. 

• The proper finishing selection.

If the blue stain already exists in wood products, then it is quite difficult to remove it. It will lower the wood quality and restrict the uses of the wood. It will ruin the appearance, especially if we need the aesthetic value for the product. We can still use the wood to make the product in which the dark blue stain is not disturbing the appearance. We can use the wood for the interior part of the products with dark wood color or solid color (paint finish).

The thin blue stain may be able to be hidden with the sap stain or equalizer stain during the finishing process. But it will darken the final finishing color, and then it cannot be done in the light color or natural wood color finish. If the blue stain is thick, bold, and strong, then we can only use it for products with dark color. or solid color finish. The dark finish, such as black or dark brown, may be able to cover and hide the blue stain.
If the blue is too strong and thick, then solid color or the pint finish could be the only option. The stain to make solid color will cover and block the entire wood. With this finish, any color of the underneath is not a problem.

• Bleaching

Bleaching is a process of the oxidation process to whiten the wood color. The bleaching process is necessary when we need to develop a light color in the wood with dark base color. The bleaching is usually done for the dark wood, such as rosewood, walnut, or crotch mahogany, to lighten the wood color while we want to keep the performance of the wood grain (see our previous article: wood bleaching). The bleaching process also works to lighten the blue stain. We can whiten and lighten the blue, black, or dark color at the blue stain with the bleaching process. The process needed is very similar to the bleaching process for dark wood. We may need the strong bleach chemical with several applications to get the white wood color according to the strength of the blue stain color.