Wood coatings, also sustainable

by Vanesa Restrepo

Wood continues to be the most versatile construction material and, par excellence, the most appropriate for the construction of furniture and the manufacture of doors, kitchens, bathrooms, balconies and floors. Its durability is high and depends, to a large extent, on the type of coating that is applied to immunize, waterproof and protect it.

Considering that in Latin America the proportion of forests for logging is higher than metal deposits and that wood is also recognized as synonymous with quality in furniture and base construction, we can affirm that the sector has a promising future, which directly benefits the paint sector.

All wood used in construction or architecture must be protected, because being a natural element is vulnerable to the onslaught of the climate. That means specific coatings will be used to prevent surface contact with water, dust and other components that may affect it. But for this to happen, the chain of protection (which includes the coatings sector) must follow instructions to the letter.

Initially a selection of the type of wood is made, according to the construction or the furniture that is going to be manufactured. There are nobler, more resistant and better malleable woods, so the application should be considered from before the logging. The cutting of the wood will always be done preserving the native forests, the fauna of the place and minimizing the environmental impact through planting of new species of forests.

Subsequently, it is passed to the separation part that includes debarking, drying, immunization through biocides that prevent the attack of termites and other pests and the machining or cutting of the pieces according to their final purpose.

It is at this moment of the work in which the formulators and applicators of paints and coatings intervene, who have the purpose of protecting the furniture or the construction from the changes of climate and the effects of use that may affect it.

The Mission: To Protect
At the first stage it should be verified that the drying of the wood is adequate. According to Jaime Adolfo Pineda, technical director of coatings for wood and metals at the company Amtex S.A of Colombia, the wood should be dried until it obtains its hygroscopic balance, that is, it is in
balance with the humidity of the environment that surrounds it.  That is, that the moisture content is ± 1 – 1.5 above the average maximum moisture content.

This hygroscopic character of wood can only be used through water-based formulations, since this component is absorbed and embedded by the wood, while the solvent can be embedded by capillarity, but will never be absorbed.

Similarly, within the wood market the natural beauty of this product is well appreciated, so coatings are rarely used to cover the grains of the wood. In that sense, the market has seen a growth in the application of laisures (stain in English), which are practically transparent layers but retain the protective capacity of traditional coatings.

These formulations are composed of an aqueous-type resin, some pigments, dispersants, thickeners, preservatives, biocide and insecticides, hydroregulators, waxes, paraffins, silicones and other components that adjust the pH and act as UV protective filters.

For woods very rich in tannins and oils, Jaime Adolfo Pineda advises cleaning the surface with alcohol and not using thinner or active solvents because they dissolve the exudates. It also recommends the use of brush, roller, rag (stump), as they allow the highest transfer of product.

According to the application, guns can also be used, either airmix, airless or cup, at an ambient temperature >10°C during application and drying, with relative humidity between 60 – 80% (not exclusive) and do not apply the product when there is rain. In hot environments and surfaces, the application area should be moistened and the drying time will be between 30 and 60 minutes for initial layers, and two to three hours for repainting.

Laisures can be applied without problems in woods treated with water-soluble salts, although it must be considered that the green color of this material influences the final hue.

Powder coatings
The use of powder coating for wood protection has grown at a slow pace in Latin America. Powder paints of the conventional type (hybrids, polyesters, epoxies) are cured in convection ovens, are produced in all colors, shines and textures in qualities of hybrids (epoxy-polyester), pure polyesters (cured with TGIC or Primid) and epoxy cured with different belting agents, according to Hugo Haas, of the company Pulverlux.

Paints chemically and mechanically resist a wide variety of agents used in bathrooms, kitchens and furniture, such as solvents, detergents, cleaners, aerosols, perfumes, etc. In the same way, they have great resistance to abrasion, shocks and wear typical of use.

The application of these coatings is done through electrostatic equipment by "corona" process and cured in conventional convection furnaces heated by hot air, gas or electricity at temperatures ranging between 120 and 140 ° C.

There is another type of powder paints for wood: those that cure by a mixed process of red (IR) and ultraviolet (UV) infrared radiation. These types of applications have gained ground in the market, but their use is conditioned on the customer owning the corresponding curing installation. Considering that they are high-cost facilities, we can say that their use is limited to large companies that are intensive consumers of these paints.

The system is based on formulations with special unsaturated polyesters containing photoinitiators that are the ones that cause the curing reaction through the entire paint film and in very short times.

Environmental care
The new laisures and liquid paints do not emit polluting elements, thanks to the fact that most of them are formulated in water-based. In any case, it is recommended that before applying these products it is verified that they have low levels of toluenes and benzenes, since in excess they can be harmful to health.

The manufacturer must also be asked for the technical sheet and the content specifications of Volatile Organic Compounds or VOCs, the calculation of which is made through the following formula:

VOC (gr. / lt.) = (100 – NV) x ( D ) x ( 2.64 )

where:
– NV= % of Non-Volatiles (solids)
– D= Paint density in kg./gallon
2.64= Constant to convert to gr. / lt.

By international standard the VOC is expressed in units of grams / liter (gr./ lt.)

Finally, as far as possible, the use of powder paint for wood will reduce contaminants, allow greater reuse of the material and extend the useful life of furniture or architectural pieces.