How To Avoid Cupping & End Splitting In Timber Benchtops

Cupping in evenly kiln dried, laminated timber products 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 poor storage and handling.

It is imperative that after purchasing a laminated timber panel, like a benchtop, it is stored flat off the ground, protected from the weather, wind and direct heat and not exposed to extreme changes in humidity. ASH laminated panels are fully wrapped in protective plastic and they should remain fully wrapped or resealed after opening until they are ready to be installed/machined/coated.

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 that you will find in any solid wood products sold anywhere.

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 at the end.

Splitting in timber sometimes occurs between rigid mechanical fixings. If a laminated panel, (particularly a wide panel), is restrained by multiple mechanical fixings across the width, as a panel contracts to equalise with its environment, the contraction is limited to between rigid fixings. If the panel is not given the ability to contract evenly across the entire width, a split can occur between the rigid fixings.

A preventative measure is to coat the product such that moisture is slowed/prevented from leaving the panel, and fix the panel such that you allow it to expand and contract.

The best solution to timber splitting and cupping is to prevent it in the first place. It is recommended the following steps be taken to preserve the quality and stability of your high value, appearance grade, ASH laminated products:

• Leave the product fully wrapped until ready to use/install.
• Store on a flat, elevated, dry surface (not concrete), out of the weather elements like wind, heat and rain.
• Once unwrapped, coat the timber immediately with an adequate moisture barrier, evenly on all sides. Note: beeswax or other oils do not offer a moisture barrier. These allow 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 the timber in a flat plane while allowing movement in width. See the 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.

Should your product have suffered cupping or splitting, here are some troubleshooting tips if preventative measures weren’t adequate:

• Cupping: any cupping is temporary and can be corrected by wrapping the timber panel in plastic and then storing it on a flat, dry surface away from any wind, rain or direct heat. To avoid future cupping problems, the timber needs to be envelope-sealed (top, bottom and sides) with at least two coats of sealant coating.
• End splitting and splitting caused by rigid fixings: unfortunately this is a much harder problem to ‘fix’ as splits in timber cannot simply join again. Prevention is the best for solution for splitting, so make sure you envelope seal your timber once purchased and fix it in accordance with best practice.
  • If splits were caused by rigid fixings, immediately replace rigid fixings with ones that allow movement across the width. Before any patch work for splitting can be undertaken, assess the likelihood of further contraction. You may need to measure the moisture content of the timber and compare against the long-term equilibrium moisture content (EMC) of the environment.
  • If further contraction is likely in the long-term scenario, fill the crack with an epoxy (or other chosen filler) and adequately coat all faces and ends of timber to prevent/limit further moisture loss. Likelihood of success in this situation is directly proportional to the coating’s ability to prevent further moisture loss.
  • If expansion is likely in the long-term scenario, you may wish to wait and observe until the panel has expanded and the crack has reduced. Once at a more stable position or closer to being closed (which ever is first), fill the crack with an epoxy (or similar) and coat all faces and ends of timber to prevent/limit further moisture loss.

Timber cupping and splitting are both issues that are completely avoidable. The main aim when working with laminated timber products is to seal, fix and protect your timber products so that it allows the timber to expand and contract naturally. The prevention, where possible, of any moisture changes wherever you are storing or installing your products will help avoid issues.