Blue stain at the wood.

Blue stain is 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 of the timber. Blue stain is not problem for wood if the wood is used for structural uses. Blue stain does not affect the strength of wood, but he disrupts the appearance and color of the wood. Blue stain will make problem in the finishing process, especially when the light or natural wood color is needed. The blue stain will be problem for products that need the aesthetic function from the wood such as: furniture, floor, door, window, wall panel, architectural product, etc. 

blue stain at the wood

Blue stain is mainly caused by special fungus that is called as the wood staining fungi. The fungi will not affect the wood strength but he will make the dark stain at the wood and affect the appearance of the wood. There two species of fungi that are recognized cause of the blue stain, aureobasidium pullulans and hormoma dematodies.  The fungi grow during the tree cutting, saw milling and drying process. The risk of the fungi attacked 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 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 attacked. Keep the wood log, or board at the dry and well circulated air and do the wood drying in the proper schedule. There some anti fungal chemical can be applied during to protect the wood from the fungi. The chemical is usually applied together with the anti insect chemical to keep the wood quality. The anti fungal chemical is highly recommended to handle the wood when the condition is wet and humid. The anti fungal is also needed when we deal with some species of wood are susceptible for the fungi such as : mango, rubber wood, etc. 

• The proper finishing.

If the blue stain already exists in wood products than it is quite difficult to remove it. It will lower the wood quality and restrict to the uses of the wood. It will ruin the appearance especially if we need the aesthetic value for the product. We still can use the wood to make the product at which the dark of the 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 hided with the sap stain or equalizer stain in during the finishing process. But it will darker the final finishing color, then it cannot be done to make light color or natural wood color finish. If the blue stain is thick, bold and strong, then we only can use it for product with dark final color. The dark finish such as black or dark brown color 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 color is not problem.

• Bleaching

Bleaching is a process the oxidation process to whiten the wood color. The bleaching process is necessary when we need to develop light color at the wood with dark base color. The bleaching usually is done for the dark wood as the 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 the 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.