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How to repair new deck with boards lifting?

Hello, I’m hoping for some advice. I am a novice when it comes to wood and decking so forgive my attempt to explain!

We had beautiful new blackbutt decking installed at the end of March replacing approx 100m2 old karri hardwood decking using existing frames. We were told to let the wood weather for several weeks before oiling. We rolled into autumn rain season and weren’t able to find a weather gap for oiling.

10 weeks after install, with the first rainy cold snap of autumn we noticed a few boards lifting and “humping” around the pool and the lower step, where space between deck and ground is shorter (approx 300mm). The deck higher from the ground is not doing this.

The carpenter who installed the decking said it’s because we didn’t oil the boards fast enough. He came and lifted a few boards up and said we have to wait to Spring but isn’t keen to discuss options.

The deck is getting worse, with almost all boards at lower areas lifting and rising, it’s hazardous to walk on and I’m wondering if there’s anything we can do now to help, and how we can save the deck?

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Comments

JacobZ

Hi @ryana,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Oh dear, I'm so sorry that this is happening to you.

What I believe is happening, due to the lack of oil to prevent water from soaking into the timber, the timber is absorbing water and expanding in all directions, causing the decking boards to cup and push on each other. As there is not enough space for the expanded boards to sit together, the force is pushing them up.

It looks like your carpenter used angled nails into the sides of the boards to fix them in place. This is likely a good thing because nails can pull out, whereas if they had used screws, the boards wouldn't pull up from the frame and would instead crack around the screws.

Unfortunately, the only remedies I can think of, because you can't shrink the timber back down to its original dimensions, are to remove the decking boards and either plane their sides to allow their reinstallation with space between, or to remove a board, then use the space it has created to reinstall the boards with adequate spacing between them for expansion.

Unfortunately, there is no easy fix to this problem. The boards will need to be lifted and then reinstalled. When reinstalled, the decking boards would need to be oiled as soon as possible.

Out of curiosity, do you have any photos of the deck when it was first installed? How wide were the gaps between the boards on installation?

Allow me to tag our experienced members @Dave-1 and @Nailbag for their thoughts.

Jacob

Nailbag

Hi @ryana

I pretty much agree with what @JacobZ has mentioned, though you wouldn't need to plane all the boards. Just re-position them side by side and only the end boards will need to be trimmed. You could do this now and just rest them there for a couple of months as they would move much at all in this state. Long term-wise I think it would be wiser as @JacobZ said to consider leaving a small gap to prevent future issues.

As far as fastening the boards down, you would need to hire a nailer to replicate the secret nailing the carpenter did if he's not doing the job. Otherwise, screwing them down is the only other option.

Nailbag

ryana

https://www.workshop.bunnings.com.au/discussion/comment/54529#Comment_54529

Thank you @JacobZ @Nailbag for the detailed replies, much appreciated! I suspected (worried) that might be the only course of action. It seems we got some bad advice that weathering new blackbutt timber can take up to 6 months.

I have attached photos of the deck when first installed to show the gaps. The higher deck closest to the house is not showing any signs of cupping or lifting, despite not being oiled and same exposure to rain. It’s only the decking low to the ground that’s lifting and cupping. It seems the gaps were sufficient for expansion up top but not for the lower deck.

Will oiling the top of the boards after relaying be enough to prevent this in future or should we oil the underneath too before nailing back in?

Also one more question if I can - do you know how to undo secret side screws? I’m keen to space these out asap. There is no screw head visible from the top, some boards have come away completely on their own, so I have been resting these on top for now.

Thanks again! Ann

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/89518#Comment_89518

Hi @ryana

The lower deck is getting more uprising ground moisture being closer than the top deck, which would explain why that level is only affected.

If you're lifting all the lower level boards you might as well put one coat on the underside. But for now rest them in place until spring as recommended.

You will have to pry up and out at least one board to see exactly how they are fastened, but I am confident they are nailed not screwed as they wouldn't peak lift like some have. Once that board is up just pry against the joist under and up on each board. Then cut the sticking out brads with one of these.

Nailbag

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/89518#Comment_89518

Good Evening @ryana

😕 Oh man, stressful and a pain, I feel for you.

Those last photos of the deck show Id be happy with the boards and layout. There is a resonable gap between the boards and they look right.

I would actually go the route of lifting them and reinstalling them, making sure you have a gap again. The first photos show the timbers forcing each other up but I dont really see any cupping so no plaining will hopefully be needed 🙂

I would actually start one end of your deck and lift the existing boards, redo the spacing and put them down, then I would oil each section as you roll along, making sure that you keep doing it within a month type deal so the age wont really show.

As to undoing the secret side screws, mmmmm I havnt had experience with that type of screw so will tag @JacobZ and @Nailbag as I am sure they probarly have 🙂

Dave

EricL

https://www.workshop.bunnings.com.au/discussion/comment/89518#Comment_89518

Hello @ryana

It's great that you've received excellent advice from @Nailbag and @Dave-1. I totally agree with the recommendation to undercoat the panels and as Nailbag has suggested to lift one of the panels out to see how secret screws are fixed in place. My best advice is to maximize the gaps if possible, between the panels for full ventilation.

If you have any other questions we can help with, please let us know.

Eric

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