Hi there, I purchased some merbau pre-stained deck boards for this project from Bunnings and found that after rain the stain leaked and has damaged the render and the lawn. Is this normal? I applied a clear coat on the top of the boards and this has stopped the damage to that surface but every time is rains the board stain runs and I don’t know what to do. I’m not keen to remove them and reseal them but surely the pre stained boards can be used without this happening?
Welcome to the Bunnings Workshop community @Maiters. It's wonderful to have you join us, and many thanks for your question about Merbau decking boards.
I'm sorry so to see you are experiencing this issue.
Merbau timber contains a large number of tannins which is what is bleeding out of the timber. It requires a period of being weathered (up to two months) for the tannins to be stripped out of it naturally. This process can be accelerated by using products like Cabot's New Timber Prep. Anytime Merbau is used around a surface where the tannin could bleed out and onto it, it is best to pretreat and strip the tannins before installing.
The boards you have are likely pre-oiled, which means they have a coating of oil to protect them during the delivery process. They then need to be prepared and stripped of tannins before being sealed. I suggest you grab some of the New Timber Prep and scrub the boards down as per instructions. Unfortunately, you won't be able to access the underside of the boards, and these will continue to leech out tannins for a couple of months. You can periodically wet the boards to accelerate the process. Once the timber has ceased leeching, you can oil it to provide nourishment and protection. At that point, you can re-paint the render to cover the tannin marks.
I apologise for this inconvenience. Please let me know if you have any questions.