I want to protect the wood of a deck with water-based products. What materials should I use and in what order?

For an outdoor wooden building to last as long as possible, the right wood must be chosen, properly constructed and protected against sun and weather. Each of these aspects is equally important. No point in choosing the right wood if water splashes on it. Also, you haven't done anything if you've invested a lot of money to build it right, but you're using randomly chosen finishing materials or because a friend told you it hit the kitchen table and still looks good 20 years later.

I was recently asked what the materials and steps are to finish a softwood deck using a water-based system. The owner of the deck had chosen this system because he did not want the smell and flammability assumed by solvent-based products. I think the subject may be of interest to many of you, professional or amateur, so I will expand on it below.

Water and sun, the enemies of outdoor wood

Outside, the wood must be protected from sun and water. The sun attacks the surface of the wood and changes its colour, and persistent water can cause it to rot. That's why a quality finish needs to deflect the sun's rays, keep water out and allow it to drain away. Find here the most important rules for outdoor timber construction.

Your ally in the fight against the sun are the pigments contained in the products. That's why there are no perfectly transparent and colourless outdoor varnishes. Pigments suspended in the varnish or lacquer reflect and deflect the sun's rays. The more pigment, the better. That's why paints have the highest outdoor resistance.

Wood has grown with water and has an affinity for it. That's why it needs to be covered with materials that keep water out. If given the chance, it will absorb water which will lead to it rotting over time. Water that puddles, that doesn't drain away creates the conditions for mould formation. That's how the black colour visible on the fences and fences in the countryside appears. If it is not removed and has favourable conditions for growth (damp), mould will eventually lead to wood rot. In addition to products that allow water to drain away quickly, construction solutions must be adopted that do not allow water to stagnate and allow air to circulate to dry out the moisture left after rainfall.

What is contained in a waterborne exterior finishing system and what is the order of application

To have the best resistance over time it is best to use professional products. That is, those systems made specifically to protect wood outdoors. I say systems because it's not just one product applied in successive layers but several products which, applied correctly, provide long-lasting protection for the wood.

A complete outdoor water-based system includes insulator, impregnator, primer and varnish or paint. On the market, especially in DIY stores, there are products that say they contain all of the above, those 3-in-1 laziness. They certainly contain some of each of them, but that miracle product that does everything well that each of the products mentioned does doesn't exist. It's a compromise made in favor of lighter application, but this comes with decreased strength over time. Quality translated into increased durability is achieved by using the complete system and following the application technology.

Isolatoris used when the wood to be coated is tannic (oak, acacia, meranti, mahogany). We have seen here what can happen if such wood is not insulated before painting. It is the first coat that is applied. Softwood, as is the case with the terrace from which we started, does not need insulation. There are situations, however, when the knots contain resin that could affect the colour of an open finish. In this case the knots can also replaced by branches or isolated. Find here node isolation solutions.

Impregnants (some also call them lazures, but different from the above) are solutions for staining and protecting wood. They contain mixtures of dyes and pigments that are resistant to direct light and UV radiation and sometimes insect-fungicidal substances. They are applied as a first coat on wood when there is no risk of colour change or over the insulation layer. If the wood is painted there is no need for a first coat of impregnating agent to colour it. In this case, the impregnating agent should only be used if it contains insect-fungicidal substances.

Some firms have on offer waxed impregnants for exterior use. They are different from ordinary wax-containing impregnants. They are used where durability is not the primary requirement and are the only product that is applied in 2-3 coats. Such a finish should be re-applied annually, maximum after 2 years, if the season has not been rainy, there have been no persistent winds and the air is not salty.

Grundul is applied over the impregnant. It is not a mandatory step, but in my opinion, it is easier to work with the primer-lacquer system than applying 2-3 coats of lacquer and for this reason the results are much better. The primer gives consistency to the film and sands more easily, allowing for smoother surfaces. The alternative is a varnish/paint so formulated that several coats can be applied in succession. In the case of an opaque finish using paint, the use of primer also reduces costs.

Lacquer/paint is the final coat that is applied over the sanded and stripped primer. These are materials that come into direct contact with the sun and weathering and therefore contain pigments, and the film spread is very good so that water drains off very quickly and easily. Exterior primers, varnishes and paints have good elasticity which allows the wood to vary dimensionally without the finish coat cracking.

I have, for more than 20 years, had laminated oak framed windows finished with a full hydrodilution system. In all that time, they have only once been surface sanded and another coat of varnish applied as a preventative treatment. It still looks perfect and this was due to the good quality finishing materials, the correct application of the whole system and the well-chosen construction solution.

Recommendations for a durable finish

Below, some of the things you need to pay attention to in order to have a protected wood for a long time:

• Wood sanding - prepare the wood properly before applying the first coat. Sanding correctly ensures adhesion of subsequent coats, easier sanding between coats and a pleasing appearance.
• sand between layers - in addition to the unpleasant appearance, the high grain of the wood can contribute to a decrease in strength over time as it is a pathway for moisture to penetrate. It also contributes to increased surface roughness and slower water run-off.
• do not dilute the primer/varnish/paint more than 5% - water will be absorbed into the wood and cause the grain to rise even more. Usually such products are ready to use. Even though they appear very thick, there is an apparent viscosity that allows for vertical application without spillage (thixotropic products - find here explanation).
• don't apply very thick layers - even if the materials are elastic, a very thick layer is likely to crack over time and thus compromise protection.
• opt for matt finishes - the gloss is less resistant to the sun. The matting agent in the varnish also helps to deflect UV rays.
• check the appearance of surfaces from time to time, especially before cold periods with persistent moisture. If you notice the slightest crack, sand lightly and apply another thin coat of varnish. Don't wait for water to penetrate under the film because then protection is compromised. Everything must be removed and the finish re-done.
• use maintenance products - they are easy to apply and prolong the life of the finish.

I hope you find the above information useful. If you have any additions or questions, please leave them in the space below. I will certainly reply.