How to make outdoor timber waterproof for a garden bed?

[rickychan]

Sorry for the dumb question. This is my first time to post here in Bunnings Workshop. I just bought a house and wanna to do some enhancement myself. The first thing I am want to build is a small garden bed and rack for some small plants as a weekend project. I am considering to use treated pine like this one. 

https://www.bunnings.com.au/70-x-35mm-outdoor-framing-h3-treated-pine-2-4m_p8032103

Does anyone know how to make this timber waterproof? Is there any recommended product that I can buy from Bunnings? 

Any help is appreciated. Thanks in advance. 

[MitchellMc]

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

The 70 x 35mm Outdoor Framing H3 Treated Pine is suitable for above-ground use where it's not in contact with soil, so it might be fine for your rack. It's already resistant to decay, but you could paint it to provide an additional layer of protection.

Regarding the timber for the garden bed, you really need to use one that is H4-treated, which means it's suitable for use on and in the ground and in contact with soil. H4-treated timber is typically in sleeper form. For a garden bed where you're growing vegetables, you might wish to use a non-CCA-treated sleeper.

Here's a helpful guide: How to build a raised garden bed. Also, here are our Top 10 most popular raised garden beds for inspiration.

Please let me know if you have any questions.

Mitchell
 

[rickychan]

Thank you so much @MitchellMc . I am new to this area and have not known about the difference between H3 and H4-treated pine. It's good to know that H4-treated pine is a suitable type of pine that can be used on and in the ground. May I confirm if the following one is non-CCA-treated sleeper? 
https://www.bunnings.com.au/200-x-50mm-3-0m-sleeper-h4-treated-pine-sienna-micropro_p0077935

Also, it's good to know that treated pine is already decay-resistant. If I still want to paint the outside of the garden bed, which type of paint do you recommend? 

Thanks in advance. 
Ricky

[MitchellMc]

Hi @rickychan,

Our Sienna Mircropro sleepers are not CCA-treated, so they will be perfect for your garden bed. 

You can paint their exteriors with external paint, such as Dulux Weathershield. However, moisture enters the sleepers from the soil behind them, which doesn't create a conducive environment for paint adhesion. To prevent the sleepers from becoming waterlogged, you might like to add a layer of Builder's plastic to the internal side of the garden bed.

Mitchell

[rickychan]

Thank you so much, @MitchellMc. Much appreciated. I will check these options.