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Hi team, I am building an outdoor box seat with storage. It will be down in a sunken firepit (which has drainage) however my question is about material.
I was thinking of building a base with marine ply and facing it with aluminum and marine ply built seat faced with external cladding. Is this the best way to stop any water getting to the ply ?
Pictures is of area it’s going so it will have rain contact.
Also is thick marine ply enough or should I use treated pine for a frame first ?A Bunnings video I watched just uses mdf however that was inside but no pine frame as of such.
My second option was to build a seat on metal feet.
Hi @Bolton,
Marine ply, despite its name, isn’t fully waterproof and only performs slightly better than standard ply in wet conditions. To prevent water damage, it needs to be completely sealed on all sides and edges with multiple coats of exterior paint or sealant.
If durability is a concern, especially given the exposure to rain, you might consider constructing a frame from H3-treated pine and cladding it with Merbau decking. This would provide better longevity in outdoor conditions compared to relying solely on ply.
If you do use marine ply without a frame, make sure the lid is well-supported to prevent sagging over time. Also, just a note—if you’re planning to use the firepit while the bench is inside the sunken area, it’s worth reconsidering. That space was likely designed with safety clearances in mind, and adding flammable materials could pose a risk.
Please let me know if you have any questions.
Mitchell
