Side-Bonding 101

There are plenty of waterborne finishing products on the market that claim to prevent Side-Bonding, but what is this process, and why should you pick a premium “non-sidebonding” finish over a cheaper one?

Avoiding the effects of Side-Bonding

Ever had unsightly and unexpected gaps or cracks and splits appear in wood flooring?  If so, you are familiar with the nightmarish effects of Side-Bonding.

This problem occurs during the refinishing process when waterborne finishes and lacquers flow in between boards and glue the wood together. Due to the high durability and adhesion of modern floor finishes, this gluing-effect is often stronger than the wood fibres holding the boards together. As the wood naturally expands and contracts depending on the room climate and humidity, this causes huge stresses across entire sections of the floor until it finally cracks at the weakest point– usually right at the most visible point or in the middle of a walkway!

And it gets worse – the bigger the floor, the bigger the problem. Each board may individually shrink just a fraction of a Millimetre, but multiply that by 100+ boards side-bonded together and you have a crack Centimetres wide that is trying to appear (accumulative shrinkage), potentially across the whole length of your floor.

accumulative shrinkage2
Accumulative shrinkage in action. Small stresses in individual boards create huge tension in the floor when fused together by Side-Bonding.


In addition to low-quality primers and lacquers, Side-Bonding can also result through the installation process when too much adhesive is used. As the floor goes down, the excess adhesive is pushed up into the cracks between the boards and causes the same problem of sticking them together in a way that does not allow for adequate growth or shrinkage over time.


Preventing Side-Bonding

Due to the nature of Side-Bonding, special care and thought must be given to the type of finishing system that will be applied to larger floors like gyms, halls and offices, as well as ensuring that there are suitable controls in place to maintain a stable environment (temperature and humidity) over time. As seasons pass, the wood floors will grow and shrink because wood is a hydroscopic material and it’s important to have a sealing system that can cope with the stresses and strains this will cause.

Installation with adhesives:

A simple step to preventing Side-Bonding is to use the correct notched trowel when applying adhesive to the subfloor. This will help ensure an even, uniform coverage – minimising problems that can occur later. There are all kinds of grades for adhesive trowels available to control the application rate of adhesive as recommended by the manufacturer.

Filling Gaps

Another sensible step in reducing the risk of Side-Bonding is to use a high-quality filling product like Lecol 7500 to fill gaps in the floor and prevent primers and finishes flowing between the wood flooring in the first place. It seems counter-intuitive to fill the gaps as the wood has less room to expand and contract, but the filler will compress when the floor expands and release when the floor shrinks. After initial sanding has taken place, mix some of the wood dust (taking care to wear suitable respiratory safety gear) with filler and trowel across the entire surface to fill smaller cracks and gaps in the floor. The best part? You can guarantee a colour-match as the dust has come from the wood you are sanding! Reclaimed Pine Slivers are also an excellent option for filling wider spaces between boards.



Primers and Lacquers:

Picking a waterborne finishing system suitable for the floor type and species is the most effective step to avoiding Side-Bonding. Many manufacturers have Primers and Finishes developed specifically designed to work together on different floor types, making the process much easier.

Two-Component finished are the standard for approaching larger areas because of their durability and slip resistance, but the gluing effect can be even stronger. Extra care must be taken to fill gaps and use the correct primer. Specific sports systems are available from manufactures and usually have more elastic properties to cope with the field expansion and contraction of large areas like gymnasiums.

While it is possible and sometimes tempting to mix & match Primers and Finishes of different brands, it is always strongly recommended to work within one manufacturer’s system from start to finish as individual chemical properties of each could cause unpredictable results during application and/or over an extended period time (chemical reaction, discolouration, delimitation, premature wear, softening & maintenance issues).

Temperature & Humidity

In an ideal world (for floor sanding professionals at least!) room conditions would be constantly maintained throughout the life of the floor. In the real world this is not always possible but there are still steps that can be taken to get ahead of issues before they occur, allowing your floor the best possible chance to last a life time.

School Halls and Gym floors generally get work carried out during the summer when humidity is higher. Some gapping is likely to occur as the temperature drops and heating systems are turned. However, during much colder climates or extended cold periods it is worth advising the client on steps they can take to maintain their floor at a reasonable temperature if the building is likely to be unoccupied for any duration over winter. At the very least, offering this advice and guidance will help prevent angry call-backs if the worse should happen!


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