I began my intended garage layout in late Summer/Autumn last year, and only got as far as building the baseboard, which is a 'U' shape in the rear half of my double length/width garage, utilising 9mm ply. Unfortunately I didn't then get around to sealing the bare ply before the onset of winter, and my garage is no place for spending time in during freezing weather, so it got left. As Winter progressed, the baseboard, or at least most of it, began to turn black with mould, not actually 'growing', but quite badly staining the ply, due to the inherent dampness in the UK climate. Until the weather began to improve, there was little point in attempting cleaning as it would just repeat the mould process, so I left it as it was until yesterday morning, when I made a start on getting it sorted. First job was to clean off/kill the mould, so a strong bleach and water solution was applied with a cloth, followed by a further wipe down with a fresh cloth and clean water. This improved things, though still left some dark marks in the ply, but at least I had the basis for a start on sealing the ply. Leaving the garage doors wide open for a couple of hours quickly dried the ply ready for the paint. During the Winter, I'd researched products suitable for sealing the ply, and it seemed that professional decorators swear by a paint product called "Zinsser B-I-N", which is a primer/sealer used for walls/ceilings etc which have been watermark stained, as anyone who's had that happen will know that umpteen coats of 'normal' paint can be applied and the stain will often reappear. It's not a paint like most others as it's Shellac based, pongs a bit since it seems it has a 'Meths' content (which is the recommended brush cleaner), and is white in colour. Since it has a Meths content, it dries in about 20 minutes and is recoatable in 45 minutes, so I was able to get 2 full coats on in the afternoon, leaving a really nice smooth clean surface to which I shall now be able to apply an oil based final coat of a brown earth coloured paint ready for some tracklaying to begin in due course. A 1 litre tin of this Zinsser isn't cheap (£18.53 at Toolstation, £1 cheaper than Screwfix) but given it's reputation amongst decorators, it'll be worth it and hopefully I can now make progress with the layout. Keith.