How to stop timber stair treads cracking?

swong1

Hello Bunnings! 

We have a new set of outdoor stairs installed end of March. It is now mid of July.

The stair treads are Hwd F14 Sawns.

Some treads are stained (first coat with oil based decking oil and second & third coats with water based exterior stain Cabot's).

Some treads aren't stained yet.

So it has been 3.5 months since the stairs were installed, I can see that the wooden treads are starting to split and crack. One of them has a very fine split right through to the bottom. A couple of the woods have holes 3cm deep. 

Is this a common encounter for this type of hardwood to crack/split in just 3.5 months. have we bought the wrong type of wooden treads for outdoor? What can I do to prevent them from continuing to split so quickly?

 

JacobZ

Hi @swong1,

Thank you for reaching out.

The timber you've used, which is F14 hardwood — is a type of structural hardwood that's often rough-sawn rather than smooth. This kind of wood is commonly used in building, but not always finished to a high level, so things like surface imperfections, small splits (called checks), and cracking are pretty normal, especially in outdoor conditions.

Because it's outside, the timber is exposed to sun, rain, and temperature changes, which cause it to expand and contract. If the timber wasn't sealed properly on all sides, or if some parts were left unstained for a while, water will get into the timber, and that can make the splitting worse.

To prevent further cracking, I would recommend resealing all sides of the timber. Can you advise what specific products you have used? 

We need to ensure that the stain is fit for purpose, as not all stains are rated for exterior applications. You can use a product such as Cabot's Merbau Water Based Deck And Exterior Timber Stain if yours is not for exterior use. Your stain should be applied to all sides of the steps, not just the top face. This will ensure water does not get into the timber, causing it to expand and contract and split any further.

You haven’t bought the wrong timber—it’s fairly common for rough-sawn hardwoods like this to develop cracks over time. It just needs a bit of protection and maintenance to keep it looking good.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob