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Filling spaces between decking boards?

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Filling spaces between decking boards?

Hi. I want to fill gaps between merbau decking boards (black filling preferably) and was wondering what the easiest thing to do would be. I looked at filler rod, but they all say it's just a pre-silicone thing. Is there a product out there that doesn't require caulking and won't come out easily? 

It won't be under foot traffic, and needs to be waterproof :smile:


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Re: Filling spaces between decking boards?

Hey @Deano84, thanks for posting this question. Anything that you use to fill between the space will need to be flexible enough to allow for the expansion of the the decking otherwise you will likely end up with warped decking boards.


The gap between them is intentional to try to prevent this warping.


The only products that I can think of are foam based that may allow for this expansion but no guarantees some like.


But this is not high traffic wearing, anything rubber will not allow expansion. 


I hope that helps some.



Bunnings Team Member
Bunnings Team Member

Re: Filling spaces between decking boards?

Welcome to the Bunnings Workshop community @Deano84. It's brilliant to have you join us, and many thanks for your question about sealing decking.

Where are you planning for the water to go that falls on the deck? The gaps between the boards allow it to flow away. If you trap it on the deck's surface, you'll see premature rot and decay, especially if the water sits in the grooves above your seal. 


You could use a flexible polyurethane sealer like Sikaflex 11FC. It's similar to what you'd see on a boat. There are concerns like those mentioned by @CSParnell.


Are you planning on using the area under the deck? You might consider adding roof sheeting under the deck and capturing the water that falls through the boards. The water can then be directed to a guttering system and taken away. You can clad over that sheeting with Aquacheck if you're fully enclosing the area.


Please let us know if you have further questions.




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Re: Filling spaces between decking boards?

Thanks mate, i'm actually encasing a couple of concrete planters with palms in them with the merbau at a pub hotel. I've had plants in pots there before but they are killed pretty quickly by patrons pouring the drinks into the pots. This is why I wanted to seal between the gaps. The palm trunks would be coming out of a hole in the top part of the casing. 

It's the only thing I could think of to theft proof and murder proof the plants. I'm also accepting alternative ideas haha

Bunnings Team Member
Bunnings Team Member

Re: Filling spaces between decking boards?

Hi @Deano84


Would it be possible for you to post a photo of the area? This will give our members a chance to assess its layout. We can then make recommendations on how to proceed. However, I am in agreement with my colleague's suggestion of using roof sheeting under the deck to prevent spills from going under the deck. This will at least keep the look of your deck and prevent drink puddles from forming on the deck itself.


If you need further assistance, please let us know.




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