How to prepare treated Pine for staining?

[JRM2023]

Hey all,

I’ve recently bought several 2.4M sleepers with the intention to stain them with Cabot’s Deck and Exterior Stain water based New Jarrah colour. It’s been difficult to find information on what the preparation work is for treated pine.

I’ve been letting the timber dry out in my garage for the last two weeks, do I need to wait until it’s fully dried out or can I apply the stain soon?

Is it necessary or recommended to use a new timber prep followed by deck clean? 

After staining can I use a decking oil or linseed oil over the top for added protection? 

I’m planning to use this for a raised veggie garden. I’ve read a lot of conflicting reports about using the CCA treated pine and its safety regarding leaching into soil. I plan to line the garden bed with thick Geofabric material. 

Cheers for any and all advice 

[EricL]

Hello @JRM2023 

Thanks for sharing your question about preparing treated pine for staining. Please do not use CCA treated timber for your vegetable garden. Instead, I suggest using MicroPro Sienna Sleepers or ACQ treated sleepers. If you still have your docket, I recommend exchanging them for the sleepers I suggested. 

But before going, I suggest calling your local store for stock and availability. These sleepers are safe to use in vegetable gardens as they do not leach chromium or arsenic into the soil.

If you wish to add further protection to your garden soil, you can line the interior surface of the sleeper with builder's plastic. This will provide an extra barrier to prevent the soil from touching the sleeper.

In regards to staining, I suggest building your vegetable garden and leaving the sleepers to season in the sun for about eight to twelve weeks. This should be enough time to dry off the surface of the sleeper and allow you to stain it in your preferred finish. 

I don't recommend washing the sleeper in timber prep as it is geared more towards oiled timber panels. There is a bit of a selection when it comes to staining or oiling your sleeper. Some decking oils have stains included such as jarrah, merbau, walnut and teak. I suggest visiting your local store and having a look at the sample board in the paint department to give you a better idea of the finishes available.  

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

Eric

[JRM2023]

Thanks for getting back to me Eric. 

I also appreciate the concern with the use of CCA treated pine. The Sienna sleepers are still an option for me as I haven’t altered the CCA ones I have in any way yet, but the extra cost will blow out my budget for this project at the moment. If I could get your opinion on some safeguards, it would be much appreciated. 

If I stain and then oil the CCA sleepers, would that add a layer of protection against the leaching? Furthermore, double lining the inside with builder’s plastic and then using the Geofab would nearly eliminate all soil contact with the timber edges. After implementing these, would it make a difference? 

Would planting root vegetables 8+ inches from the edge and other vegetables 6 inches away be enough to prevent any leaching? 

Are the tannins and oils that get removed by new timber prep detrimental to the functionality of timber treatment?

Thanks again,

[EricL]

Hello @JRM2023 

I'm afraid that despite the safeguards that you put into place, it will only take one point of failure from the builder's plastic to contaminate the soil. The Geofab is just a sediment filter and will not prevent chemical contamination. You can stain the sleeper and it will still continue to leach out the chemicals pumped into it. 

I understand that you are on a budget, but perhaps you can delay the other vegetable garden beds until you have enough money to buy the MicroPro Sienna/ACQ sleepers. It is a safer alternative, and you won't be taking your chances with the CCA treated sleepers. 

Using the timber prep will have the same effect it has on Merbau deck panelling and that it will strip the surface of oil and tannin thereby preparing the surface for staining. If left unstained for too long a period, then it does become detrimental to the surface of the sleeper. However, because the sleeper is so much thicker than a standard decking panel the oil, tannin and preservatives inside will continue to leach out and might push the stain off the surface. Hence, I recommend just seasoning it out in the weather.   

Let me tag our experienced member @Adam_W for his recommendations.

If you need further assistance, please let me know.

Eric