Sealing treated wood with cement wash

[ajmoran]

I'm building a raised vegetable bed with pressure treated timber.
Does anyone know whether a cement wash (portland cement+water) is any good at sealing the wood to prevent/considerably slow down the transmission of chemicals from the pressure treating to soil?

Some people use plastic for this, but there question marks about chemicals leaching out of plastic too. Apparently a cement wash is a known technique for treating the inside of metal drinking water tanks on boats so cement is not harmful to soil too?

Cheers
Andrew

 

[Mr Ed]

I have just done some raised beds;

http://thingswemake.wordpress.com/2009/ ... -building/

I am planning to rely on the preservative in the wood as previous experience has shown me that this will last a good while.

Ed

 

[wizer]

Ed I think Andrew is worrying (unnecessarily IMHO) about the preservatives leaching out of the wood and into the produce.

 

[Mr Ed]

I really must start reading things properly.

I think you're right Tom - I can't see the leaching of chemicals being an issue, although they used to think smoking fags and using asbestos were harmless too.......

Ed

 

[jasonB]

As the cement layer will be porus, I can't see it doing any good, any toxins that may leach out the wood will pass straight through.

Jason

 

[Steve Maskery]

they used to think smoking fags and using asbestos were harmless too.......

As were using fags and smoking asbestos.

Trilby and portmanteau.
S

 

[MikeG.]

Andrew,

a cement slurry can be used to colour a timber, but it does nothing to seal it. It changes the colour of oak instantly, and can make pine look slightly more attractive, but you would be wasting your time doing it for your stated aim, I'm afraid.

Mike

 

[ajmoran]

Thanks for the replies.
I think it will have to be either plastic or nothing at all then. Although random eco ideas welcome!

Cheers
Andrew

 

[wizer]

I've never heard of plastic leaching back into the soil at all? Fair enough there is an issue with plastic production if you're really concerned with the environment. Personally I wouldn't worry. I had 8 2m x 1m raised beds on my allotment and they were all made with pressure treated timbers and we're all still alive (just).

 

[BigShot]

When I made my planter recently (about 5 feet long and a foot wide internally) I lined it with the bags my compost came in.

With regards to chemicals leaching into the soil - I believe it can happen. I can't remember where I saw it, but when I was deciding whether or not to line the planter I read something about a study that showed chemicals leaching from the wood quite quickly when it was in direct contact with rich compost.
Whether that would then transfer to any food you grew in there I don't know.

It's not a cheap option, but pond liner will do the trick. Not all pond liners are equal, do your homework and you'll see which ones are suitable for different knids of pond (there's a difference between one for water plants and one for fish, for example) - the ones that are suitable for fish shouldn't leach when used in a raised bed or planter.
The one drawback?
It's rather pricey - hence me using compost bags instead.


EDIT:
Alternatively, don't make the beds from wood at all. Try your hand a bricklaying. They will be far more durable, can look pretty good and won't leach anything unpleaseant (whether or not treated timber would).


FURTHER EDIT:
Do you particularly need raised beds? As he just said, Wizer used them on his allotment - I have no plans to use them on mine. In fact, the 80-something (84 maybe) year old Italian who is 2 plots over from me won "best allotment" this summer. If I recall correctly it was something like a North West competition - can't be sure though.
He walks with a stick, slowly, but manages just fine with ground level beds.

Not knocking raised beds at all, they have their up sides, especially if you have back trouble, but they might not be necessary.

Good luck whatever you do though... I hope you get some good crops (I'm told it's time to put in onions and garlic by a few folk online and the above mentioned Italian - it's about time for some others too, not least overwinter green manure and a brassica called "green in snow" - there's more too I think - so get it done quick and you'll have a nice early crop when you're sowing more stuff next year!)

 

[ajmoran]

Thanks for the comments BigShot.
I completely agree with you on brick versus wood but my raised bed could also be described as a window box or green roof

It's intended to cover my windsurfing kit and hopefully the flower filled sight line out of the living room will be nice as well. And since it's in a sunny aspect runner beans out and up the wall should work good too.
It doesn't need to be leak proof so it's not a tanking job but I do want to stop or significantly slow down any potential chemical transmission. Pond liner is too expensive for this job but the compost bag idea sounds good.

Cheers
Andrew

(The blockwork will be rendered and the front clad with timber)

 

[wizer]

I like that idea

 

[Mr Ed]

I see, its more raised than I realised.

I would be abit wary about
a) damp migrating into the walls of the house
and
b) plants growing up and blocking the light coming through your window.

Certainly will save on the bending over though!

Ed

 

[ajmoran]

Ed,

The whole structure is 100mm away from the house, hopefully enough separation to prevent damp transmission.

And the window is huge - 2600mm by 1500mm, south south/west facing - so light reduction is welcome!

Cheers
Andrew

 

[dickm]

Not sure how the price compares, but you may find it cheaper to get standard black polythene damp proof membrane. I suspect pondliner is generally a rip-off.