Painted Shiplap rotting at the bottom edge (1)

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Hi I built a workshop 15 years ago and painted it with Sadolin Superdec. I have painted 1 side of it every year (it's a big shed)
and I have been pleased that most of the paint is nice and firm with no problems.
But..
on the front and one side where it's much more exposed to driving rain etc I have a problem with some of the bottom edges rotting and the paint peeling off.
I am in the process of ripping these off and replacing them as I've tried patching them up but it just doesn't work.
The problem seems to be water getting into the overlap and rotting that from the inside.
I had slapped lots of paint up in this joint and mostly this has been ok but obviously not where they are exposed.

I am thinking of using a bead of 'something' along the rebate as I assemble the new boards.
Could anyone suggest a good product to use here please?

Thanks

Mike
 
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If you can dry it out maybe a resin based wood repair system like timbabuild ehb60, it's slightly flexible but sands well and takes stain.

Blup
 
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Thanks I have tried a resin wood hardener on the bad patches but they still keep coming back every year.
But I was mainly asking for when i replace these boards with new ones?

Mike
 
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Maybe consider replacing the bottom-most boards with recycled plastic or composite shiplap? One name is Cladco, but there will be others. It certainly won't rot any time soon
 
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Thanks but strangely enough it's not just the bottom ones that are affected. in fact they are mostly ok.
I don't really understand why most are OK just thing it must be that some of them are warped and have created a gap that water gets into.
 
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photo would help

I've had rotting cladding before, and when I fitted new, I cut some spare ones that could be swapped in if necessary. the boards are held to battens with brass screws so easy to remove.

the bottom ones had multiple additional coats of spirit based preserver before the decorative stain, back, front and edges, before fitting.

One section has a dwarf wall to space it off the paving, and another has a metal "skirting"

seem to be doing well

are you bad ones exposed to water by splash, or a leaking gutter?
 
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photo would help

I've had rotting cladding before, and when I fitted new, I cut some spare ones that could be swapped in if necessary. the boards are held to battens with brass screws so easy to remove.

the bottom ones had multiple additional coats of spirit based preserver before the decorative stain, back, front and edges, before fitting.

One section has a dwarf wall to space it off the paving, and another has a metal "skirting"

seem to be doing well

are you bad ones exposed to water by splash, or a leaking gutter?
There is a field behind to the North side. and a hedge protects most of it but there is a 10 foot section that is exposed to the wind and rain. that is where I get the problem. I think the rain must be getting forced up under the boards. I can't see how they would rot otherwise.
The gutter is ok and seems to work properly.
I am just looking for a sealant that wont crack to fill any gaps between the boards.

Thanks
 
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have tried fixing the problem before and tried what you suggest but paint always starts peeling again.
I am now using brand new wood. and just hope anyone can suggest a good sealant
 
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Timber will naturally expand and contract with humidity

I do not think sealant is the answer.

Use wood preserver and your protective stain on the boards, all round, before you fit them. Then there will be no untreated surface to attract damp.
 
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OK Thanks !
I always thought that leaving the back unpainted left the wood able to dry out
But I'm obviously wrong about that !
as its just the bottom edge maybe I can paint the first couple of inches at the back?
thanks again
 

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