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How to avoid cupping and end splitting in timber benchtops

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Megan Parameshwaran October 7th, 2020

We sometimes get asked the question “why has my hardwood panel split?” or “my timber benchtop is cupping, what do I do?” and the answer is generally quite simple. However, this blog isn’t here to give you just answers, it’s purpose is to give you advice so that you can prevent any splitting or cupping to begin with.

Before we explain why your panel has changed, it is important to understand that timber naturally expands and contracts with variations to atmospheric conditions (e.g. temperature and humidity) and most importantly, wood moves in width and thickness, not length. This is an ordinary characteristic of timber which you will find in all solid wood products available.

Cupping example

Cupping is the result of one side being exposed to larger moisture variations than the other. ‘Cupping’ is not a fault of a solid timber product. It is a result of storage and handling. It is imperative that after purchasing your benchtop you store it flat, protected from the weather, wind and direct heat and not exposed to extreme changes in humidity. The panels are to be full wrapped in plastic until it is required.

End splitting is the result of moisture content changes which are more rapid at the exposed end grain of timber – the stress created by this movement can result in splitting. A preventative measure is to fix the panel so that you allow it to expand and contract.

Splitting example

Cupping and splitting are both completely avoidable. The main aim is to seal, fix or protect your timber products so that it allows the product to expand and contract naturally or prevent any moisture changes.

Now on to the easy part… prevention.

To prevent your timber product from cupping, you must do one or all of the following:
– Coat it immediately with an adequate moisture barrier on all sides. Note that bees wax or other oils are not a moisture barrier. Bees wax allows the timber to breathe and expand or contract, which means that the timber panel should be restrained in a flat plane while allowing movement in width.
– Fix in a method that restrains timber in a flat plane, while allowing movement in width. See fixing diagram below for reference.
– When fixing, make an oversized or elongated hole in the cross rail. Make sure your holes are big enough and that your screws are placed in the holes so that the top has room to shrink

Lastly, how to troubleshoot your timber product (if you did not take the preventative measures above):
Cupping: any cupping is temporary and can be corrected by wrapping the panel in plastic and storing it on a flat, dry surface away from wind, rain or direct heat. To avoid future cupping, it needs to be envelope (top, bottom and sides) sealed with at least two coats of sealant coating.
End splitting: this one is a much harder to ‘fix’ as splits cannot simply join again. Prevention is best for end splitting, so ensure you envelope seal your product once purchased and fix it to best practice standards!

For more information and troubleshooting issues, read our full benchtop installation guide.