Wrapping greenhouse/shed floor bearers in plastic to protect against rotting?

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Yana

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I've bought a wooden greenhouse / shed combo and have painted the floor bearers of both with three coats of sadolin wood protection. I've painted the floor boards as well (you get the theme here that I am a painting addict) and sure that someone mentioned that they then over-wrapped the bearers in plastic to further protect them against rotting.
The base that I have prepared is an area of non-slip paving slabs........ Not sure if that makes any difference ......  That have been bedded into hardcore and cement and is really flat.
I don't want to have to dismantle the whole thing to replace the bearers so am trying everything I can think of to prolong the life of the wood.
Thanks
Yana
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mumofstig

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I wouldn't wrap the wood - I find it makes it sweat, rather than dry out when it's warm.
Could you get some dampproof course stuff from the builders merchant and use that? The type of stuff they use under door frames.
this kind of thing

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Diary comments
https://chat.allotment-garden.org/index.php?topic=56565.msg666947#msg666947

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John

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My understanding is that it is important to allow the wood to breathe and to dry if it does get wet. So airflow under the shed is a must. Wrapping in plastic - I think that would be a mistake as it will cause condensation and produce a nice humid environment for rot.
3 coats of Sadolin? Well done! :)
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Yana

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I wouldn't wrap the wood - I find it makes it sweat, rather than dry out when it's warm.
Could you get some dampproof course stuff from the builders merchant and use that? The type of stuff they use under door frames.
this kind of thing
Thanks MoS I do have some of that. Do I stand the floor bearers on this?

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Yana

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My understanding is that it is important to allow the wood to breathe and to dry if it does get wet. So airflow under the shed is a must. Wrapping in plastic - I think that would be a mistake as it will cause condensation and produce a nice humid environment for rot.
3 coats of Sadolin? Well done! :)
I am a bit of a paint-a-holic John. How does the saying go........ 'If it isn't screwed down, paint it' or something like that.

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mumofstig

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Quote
Thanks MoS I do have some of that. Do I stand the floor bearers on this?

Yes, it certainly won't do any harm  :D

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aelf

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It's a good idea to have some sort of waterproof barrier between the ground and the bottom of the floor bearers. My shed is on old flagstones. If you like painting  :), you could always paint the bottom of the floor bearers with bitumen  to waterproof them, leaving the other 3 sides unpainted to allow the wood to breathe...
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Stree

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If the rot starts anywhere it will start on the ends because the fibrous ends of the timber are exposed.
in situations like this I usually hammer the end grain until it becomes shiny, then its more or less sealed. You could varnish over as well.
Another, but more expensive way is to get some of the shrink wrap used for posts and apply that to the ends.
As for the DPC, I would use it under the bearing bricks/blocks and also between the bearing surface and the timber.
As stated on an earlier post, airflow is important to keep the timber in optimum condition.
So if you want to rat proof, use wire mesh or grill round the sides, laid flat and buried at the foot ala chicken runs. That or bricks with a few airbricks built in.

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Yana

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It's a good idea to have some sort of waterproof barrier between the ground and the bottom of the floor bearers. My shed is on old flagstones. If you like painting  :), you could always paint the bottom of the floor bearers with bitumen  to waterproof them, leaving the other 3 sides unpainted to allow the wood to breathe...

This seems like a good idea to waterproof the timber with bitumen. The more painting the better!

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Stree

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Yana, Aelf is actually telling you that more painting is NOT necessarily better........ re-read the post you quoted.
If you seal the wood completely then it cannot breathe, if it cannot breathe it will deteriorate, moisture will find a way in but not out. If you must use paintable substances all over then just bitumen the bottom of the bearer and use a micro-porous preservative on the other three sides. That will be perfectly adequate.

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Yana

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Yana, Aelf is actually telling you that more painting is NOT necessarily better........ re-read the post you quoted.
If you seal the wood completely then it cannot breathe, if it cannot breathe it will deteriorate, moisture will find a way in but not out. If you must use paintable substances all over then just bitumen the bottom of the bearer and use a micro-porous preservative on the other three sides. That will be perfectly adequate.

Thanks for pointing that out Stree. I saw the word 'paint' and didn't read the rest properly. Too late now as I've already painted them so will build everything and see how it goes.

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BobE

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Treated timber bearers layed onto slabs are going to last 10-20 years.  Then perhaps you would need to raise the shed enough to slide in new bearers for another 10-20 years.
If you bought Tanalised bearers they, on dry slabs would last 20 years and no need to paint them.

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Welsh Merf

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My understanding is that it is important to allow the wood to breathe and to dry if it does get wet. So airflow under the shed is a must. Wrapping in plastic - I think that would be a mistake as it will cause condensation and produce a nice humid environment for rot.
3 coats of Sadolin? Well done! :)

I totally agree with John. I put my shed on three railway sleepers, which allows plenty of air to circulate.
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