Help - advice on Mold on Plywood

[MeoMeo]

Hiya friends,

Doing a build (https://www.diynot.com/diy/threads/garden-retreat.514649/) and recently found there is mold on the plywood. Plywood is 18mm and was given a coat of wood preserver (https://www.wood-finishes-direct.com/product/barrettine-premier-wood-preservative) before I put on the covers for the winter. Unfortunately, water managed to get in from somewhere.

I am not sure what to do next and can do with your expert advice/help.

Thx!

 

[JohnD]

if it has been wet through the winter, there is a considerable chance of delamination. Even nominally WBP grade will do this in a week or two. post some pics, especially of the edges.

 

[MeoMeo]

Posted the pics here:
https://www.diynot.com/diy/threads/garden-retreat.514649
Thx

 

[MeoMeo]

@JohnD Noticed this evening the top layer of a few boards are 'flaking off'. I'm fearing this delamination you mentioned has happened

 

[Gerrydelasel]

Plywood cannot be left outdoors in the UK Climate. I'm amazed that people think it can. Just look around you at anything made from plywood; billboards, hoarding, blocked-up windows... if it's been there for more than a few weeks you'll see it's always rotting and delaminating. Use plywood for temporary outdoor structures only.

 

[cwhaley]

Plywood cannot be left outdoors in the UK Climate. I'm amazed that people think it can. Just look around you at anything made from plywood; billboards, hoarding, blocked-up windows... if it's been there for more than a few weeks you'll see it's always rotting and delaminating. Use plywood for temporary outdoor structures only.

That's not true. I was given a large shed for free but it needed a new roof. I laid 3 x 18mm plywood sheets on the roof and covered with thick roofing felt. That was nearly 3 years ago and the ply is bone dry and solid. My dad also used the same spec ply on a roof for a gazebo and that was nearly 10 years ago and still absolutely fine.

As long as it's protected from the rain it'll be fine.

 

[Gerrydelasel]

That's not true.
As long as it's protected from the rain it'll be fine.

That was exactly my point. If it's protected from rain on one side and sitting above dry air on the other, then it's not outdoors, it's part of an indoor structure.

 

[cwhaley]

That was exactly my point. If it's protected from rain on one side and sitting above dry air on the other, then it's not outdoors, it's part of an indoor structure.

No worries. I was just clearing up the fact that ply can be used indoors and outdoors if protected. Your comment reads as if you're telling people not to use it other than for temporary use. The underside of the roof overhang on my shed is exposed 24/7 but the roofing felt above it keeps rain off the top -- it is outside but protected.

 

[opps]

Plywood cannot be left outdoors in the UK Climate. I'm amazed that people think it can. Just look around you at anything made from plywood; billboards, hoarding, blocked-up windows... if it's been there for more than a few weeks you'll see it's always rotting and delaminating. Use plywood for temporary outdoor structures only.

My "temporary" backgate is now 18 years old. It is a sheet of 18mm WBP plywood. It did get a coat of waterbased fence paint (one side only) but, well that was 18 years ago.

TBH I only expected it to last a couple of years but there is no delamination, so I have no plans to replace it.

Given that the wind tends to come in from the west, it is slightly protected by the garage that it butts up to but under normal circumstances (ie) rain that isn't driven by the wind, the gate gets wet.