Decking Mistakes - Here's some big ones!

Rotted Decking Boards

We often come across Decking failures. Even qualified Trades can make mistakes when it comes to deck building. Partly, this is due to conflicting recommendations from different material suppliers of timber, fasteners, oils and finishes. Attempts to save money, time and poor workmanship can also contribute to decking failure. Recently we came across a real contender for the winner in the "biggest Decking stuff up" category.

This Deck was laid only a few years ago using 140 x 22mm Merbau which is a good choice of timber. Here's the problem. It was laid on a concrete slab. This can be done but in a very specific way to avoid the monumental fail that ocurred here.

Incorrect screw used

This is what the builder did:

1. He fixed 25mm battons to the concrete. This is ridiculous as it meant that he could only use very short screws to fix the decking. He used 38mm screws. the correct screw length for this size decking is 65mm, so already he is well under spec

2. Timber decks need ventilation. Laid so close to the ground, the moisture would have an adverse affect, causing the timber to "cup". With the inadequate screw embedment, many of the boards had separated fully from the battons.

3. the deck was not finished with an oil or protective coating, allowing the water and moisture to exacerbate the problem

4. He did not use a joist protector. This is a water barrier that should be used between the deck boards and the joists, or in this case 25mm battons!

So, what should have he done when building a deck over a concrete slab. Here is one method that would ensure a longer life:

1. Fix 45mm treated battons to the concrete. If possible raise them off the concrete by 5mm, using plastic packers.

2. Use a joist protector membrane

3. Use a composite decking board. These look like timber but are not. They can handle extreme conditions and moisture

4. If you prefer timber, Use Merbau, Give it 1 coat of a high quality oil baseed finish prior to laying and then a second coat immediately after laying. Cutek extreme finish is very good in this instance.