Raised Bed Construction

[Andyc84]

Hello,

I have been given a load of old (in good condition) scaffolding planks, 1.5 x 9 inch, in 4 meter lengths.
I intend to put a waterproof membrane between the wood and the raised soil to stop the soil leaking out and to retain moisture in the bed, and to keep moisture off the boards.

My question is, what is a suitable treatment to try and prevent rot in the boards?

I know the best thing to do would be to used tanilised timber, but seeing as this is free, I was hoping it would last a few years and then I could replace with treated timer.
I will be using 4x4 treated posts to secure the boards to and to fix in place in the ground.

 

[jay679]

Personally, I wouldn't bother. Those planks will have spent their entire lives outdoors in all weathers. The membrane will prevent wet soil standing against them. They will certainly last a good few years as is. If you definately want to treat them, then anything from the sheds thats plant friendly will do, but be aware that if the planks have a lot of cement stains, ground in cement and plaster etc, then you are unlikely to achieve an even finish.

 

[Andyc84]

I was hoping that would be the answer... to me they don't look like they have been used really, no marks or stains, just weathered, so was hoping not to treat as the wood looks nice.

If they will last a few years on their own, I will save myself the effort.

Quick second question, is a 4x4 post overkill and will a 2x2 be sufficient, longest gap between posts will be 1.4m

 

[jay679]

How high do you intend making them? if only 1 plank width tall, then 2x2 should be fine, any higher, then I would go for 4x4.

 

[Andyc84]

The intention was 2 planks total, so soil behind would be about 16-17 inches deep.

I guess a 4x4 it is then

 

[Deleted2797112]

Personally, I wouldn't bother. Those planks will have spent their entire lives outdoors in all weathers. The membrane will prevent wet soil standing against them. They will certainly last a good few years as is. If you definately want to treat them, then anything from the sheds thats plant friendly will do, but be aware that if the planks have a lot of cement stains, ground in cement and plaster etc, then you are unlikely to achieve an even finish.

^^^^ This. I have a pair of old scaffold boards that I used on my allotment and now in my garden to spread my weight when I have to walk on beds/borders. They've been in use for more than 10 years and are showing no signs of rot. They live outdoors, either sitting flat on the soil or propped up on their edge.

 

[Andyc84]

Well then, I hope not to have to replace them for a few more years then

 

[rjm2k]

You could staple some DPM against the inside, its fairly cheap

 

[Andyc84]

Great idea, and it'll save me a few quid! Thanks for the help everyone

 

[Andyc84]

Further question on this item,

I have now built the frames out of the boards and posts and they are looking really good,

I am wondering about colouring them with Ronseal fence and shed paint. I would only do this on the external face and I am using DPM between the boards and soil.

my question is, is this a bad idea due to contaminating the soil, or will I be ok?

I know I will have to repaint again and again, but the lady of the house wants the timeber to be the same colour as the fence so it matches...

 

[Deluks]

If its the water based stuff, it should be fine. If it's oil based, don't make a mess.

 

[Andyc84]

Its the water based stuff, but with a "special wax" to help prevent colour fade...

I will be brush applying and will be putting down a bit of dust sheet to stop me painting the gravel I have down.

Thanks for the response.