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The devil is in the details

What can affect the lifespan of the lacquer finish on your hardwood floor?
Richard Aylen makes a detailed examination.

I WANT to look at what causes the surface treatment on a wooden floor to wear out, perhaps in a little more detail than normal, and moving away from the well-worn paths of maintenance faults and the simple definition of ‘wear-and-tear’.

In this way we might find some more ways to make the lacquer last longer and retain its appearance from day to day. This may also help us understand the cause of problems that arise.

With only a few exceptions wooden floors need some kind of surface protection and lacquers are by far the most popular option. The technology used to create floor lacquers has changed immeasurably over the years. Chemical companies are always trying to develop new technologies to enable us to make coatings that are more durable and easier to use.

At the same time legislators who deal with hazardous substances will increasingly restrict the use of selected substances, creating further changes in the industry. However, one aspect of floor lacquers always remains… by one way or another they’ll wear out.

The surface treatment on any wood floor is a sacrificial layer that needs to be replaced from time to time – the process starts as soon as the first pair of feet comes into contact with the floor.
However, this is the key to one of the most impressive qualities of a solid hardwood floor – its longevity.

Periodically recoating the wood keeps it protected, and in the longer term a solid wood floor can be refurbished many times by scrub and reseal or sand and reseal if the sacrificial layer has been worn away.

Which factors cause lacquer to wear out?
The main ways the floor seal will wear out are:

  • • Abrasion
  • • Fracturing and cracking
  • • Chemical attack and other contamination

Abrasion: This is the effect of friction on the floor where harder substances eg grit and soles of shoes can wear away the lacquer because the lacquer, relatively speaking, is softer. This is why we use barrier mats at entrance doorways and felt pads on furniture legs.

Barrier mats: Alongside the cleaning regime, one of the best ways to reduce the amount of abrasive material that reaches the floor is an effective barrier mat system (and maintaining it properly).
Some buildings may need special consideration when choosing barrier mats.

A fully paved town centre location may not generate a lot of loose grit so the barrier mat may not have to work so hard. Contrast this with a rural location with gravel paths and other paved areas, and the possibility of wind-blown grit, then a more effective barrier may be needed.

No barrier mat is 100% effective and so the floor (and mat) cleaning regime will need to be tailored to suit the limitations of the mat. Sometimes the need for temporary measures can arise. One such case that came to me recently was a town centre office surrounded by ongoing construction works and their dark coloured floor was covered in a layer of light coloured building dust since they had opened for business.

As part of the natural wear process the lacquer coating becomes thinner and it may begin to look a little dull. This is the time to reseal the floor. If left for too long the seal becomes porous or wears away completely.

Dirt and water will get into the wood, seen as grey or black coloured patches. Cosmetically this is unsightly but for a solid hardwood floor this is not regarded as damage because it can be completely refurbished by sanding and resealing.

Cracking: Manufacturers of some types of lacquer eg UV-cured and some ‘new technology’ products make impressive claims for high abrasion resistance. However, they can also be very brittle (and some are very difficult, if not impossible to sand and reseal).

This means an extremely hard lacquer may not necessarily have a long life because it can crack under a point load or sharp edge. Cracks will allow dirt and water to contaminate the timber and the lacquer will fail.

Other lacquers provide a coating that is more flexible – so it’s ‘tough’ rather than ‘hard’, for example a 100% polyurethane crosslinked two-pack water-based product. This may not offer such high levels of abrasion resistance, but counter-intuitively these products can last longer.

Stiletto heels demonstrate this well. With a tough but flexible lacquer the stiletto heel will probably make an indentation in the timber floor, but the lacquer will bend rather than crack.

Therefore, the floor is still fully protected. A brittle but ‘diamond hard’ coating is far more likely to crack and after a short time you will see the heel indentations appearing as small black circles where the lacquer has fractured, and dirt has got into the timber. Longer term these fractures will cause the lacquer to deteriorate even faster.

Chemical attack and other contamination: My intention is not to focus in detail on maintenance faults as it is generally accepted that poor maintenance can significantly shorten the life of the lacquer. Over-wetting the floor can undermine the coating causing it to peel. Any cleaning pad has to be of the right type – not too abrasive, and it should be used only when necessary.

Contamination may occur when the client uses a cleaning product that is not intended for use on sealed timber. The cleaner may chemically attack the lacquer causing it to soften. This can make it porous, prone to staining, reduce its scratch and scuff resistance and shorten its life.

However, it’s not always a case of using the wrong cleaning product. Some lacquers may be affected by alcohol and heavy deposits of spilled drinks. If left for a long time this can dull the finish.

More severe localised damage can be caused by the alcohol in hand sanitisers – something that in current times may be seen on unprotected floors beneath hand sanitisation points in medical and other similar facilities.

Adhesion – a spectrum
We often talk about ‘good’ and ‘poor’ adhesion, as if the adhesion is either 100% perfect or a complete failure. In practice though it is quite common for the adhesion to be not quite perfect, but good enough for the floor to be sufficiently protected.

There are standard tests such as the crosshatch test under ISO 2409:2013 that are used throughout the coatings industry but there are no universally defined limits for lacquer coatings for floors as far as I know.

The level of adhesion between coats can affect the life span of the seal. If the adhesion is at the lower end of the spectrum the floor may be OK for some time but will deteriorate quite quickly as the effects of wear-and-tear take their toll, and the bond between individual coats begins to fail.

You can also find floors that will take foot traffic well but if scratches or high point loads occur localised peeling will become evident.

One point in favour of using primers, lacquers and staining products from a single manufacturer is that the manufacturer will guarantee good adhesion between all companion products being used.
There’s always a risk of poor adhesion when combining products from different manufacturers because they may not have been tested thoroughly in combination with one another. A manufacturer will ensure that if they make product changes there’ll still be compatibility with their other products. This safety net will not exist when products are selected from different manufacturers.

Adhesion is also related to the next topic.

Excessive over-coating
I talked in my last column about not treating a wood floor with kid gloves and in fact it is possible to cause a problem with a lacquer finish simply by applying too many coats. It may be strange to think that you can have too much lacquer on the floor (can you really protect the floor too much?) but if taken to excess this can be a direct cause of peeling.

Any wooden floor will expand and shrink, and on a micro level the lacquer needs to stretch in sympathy. When this happens, the lacquer develops ‘micro-cracks’- invisible to the eye, and not to be confused with cracking through brittleness referred to earlier. These micro-cracks are normal and have no effect on the durability of the lacquer, but they contribute to its elasticity.

But if you apply more and more coats to a floor the stronger and less flexible the coating becomes. With excessive coating thickness, movement of the wood puts stress upon the adhesion between the layers of stain, primer, lacquer etc. If the coating is too strong then the adhesion will fail, and peeling will occur at the weakest layer.

The next and final part of this column takes a broad look at the composition of lacquer itself.

Hand-in-hand: quality and durability
We’ve already touched upon some specific properties of the lacquer that limit or enhance durability but in a more general way lacquers can be classified by durability according to their composition.

Based on the idea that diamond hard abrasion resistance isn’t necessarily the key to a long lasting finish my personal preference is for a tough but flexible lacquer. This type of coating is likely to suit most people’s needs as a good quality one will have sufficient abrasion resistance but will be highly resistant to cracking.

So, here’s a brief rundown of the main types of lacquer available. I’ve only included water-based products as those that are organic solvent based are becoming less acceptable due to site restrictions and health and safety considerations.

  1. Acrylic-based lacquers: These were among the first water-based products to be developed and offered a basic level of durability and good flexibility. They are low cost and often used today for floors in residential buildings where foot traffic levels are relatively low.
  2. Polyurethane/acrylic mixes: Polyurethane binders are generally more expensive than acrylic but more durable so a combination of the two is a good way of boosting durability without increasing cost too much. Broadly an acrylic/PU mix will be suitable for heavy duty domestic or light duty commercial floors.
  3. 100% Polyurethane: The most durable water based lacquer, for commercial high traffic floors, but higher in price. Durability can be further increased with the addition of a hardener.
    The three types above are usually of the ‘tough but flexible’ type mentioned earlier.
    This may not necessarily be the case for those lacquers which have mineral additives and claim to have enhanced abrasion resistance.

    UV-cured lacquers: These are mainly used for factory applied coatings and can be of the more brittle type. Some time ago onsite UV lacquering systems were introduced here in the UK, but I believe the uptake by contractors has been slow owing to the relative complexity of the process.

    While some of the ways a lacquer coat can fail are relatively complex, the issues that bring about failure are usually quite uncomplicated – ie, choosing the wrong products, poor maintenance, too many coats etc. I hope this column will give some guidance over and above the basic issues of application and maintenance, and if things should go wrong, what has been discussed here may be useful for diagnosing issues onsite.
    Richard Aylen is technical manager, Junckers
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