Is this dry rot?

[Tim Watts]

GRP sheet with some pebbles/sand stuck on to soften the visual impact?

Sheet of ali with roofing felt?

[Martin Brown]

How about 5mm PVC foam on an aluminium or mild steel frame?

Available in a rang of colours and can be worked like wood. Obviously it would need additional strengthening if you intend to walk on it.

If price is no object then a stone mason can cut you a piece of slate to match the void (or look for a marble/slate counter top in junkyards).

[Tricky Dicky]

I would suggest the main reason water got under was the lack of an effectiv e drip around the edge of your board. If your pump/filter gives any heat th is will have condensed onto the underside - fungus heaven! I would use OSB cover it with mineral felt the type with the adhesive already on so it just needs heating from the top with a torch to make I stick. Cut your felt a g ood 100mm+ oversize. Heat the part on the flat part of the roof, but not th e overhang, to make it adhere. The next bit you may require a gauntlet to w ithstand a little heat. Heat along the very edge of the roof to make the fe lt a little more flexible and pull the overhang down, you will probably get a few ripples but not to worry. To complete the drip, re- heat the overhan g but his time fold the first 40-50mm back on itself under the roof. A few vertical cuts in the overhang will make the folding under easier and enable you to follow the curve doing it in short sections.

Richard

[Tim Streater]

I'm still waiting for MeowMix to confirm what he meant. Am I going to wait forever?

[Roger Mills]

You could be right. There *is* an overhang - but that is mostly taken up with the ivy which has attached itself to the outside of the brickwork. It may even be the ivy which is bringing the moisture in.

I don't think it does. The (water) pump itself is submerged in the pond and the filter is entirely passive - apart from housing a low wattage UV lamp. The air pump might produce a *bit* of heat, I suppose - but not that much.

As in the case of the current lid and its predecessor, it will need lots of cuts in the edge of the felt to allow it to follow the curved shape.

What are the relative merits of OSB vs WPB? I think the first lid was OSB and that lasted longer than the second one (WPB). I was expecting WPB to last longer than OSB.

[Dave Liquorice]

There are various grades of both. I'd be wary of "WPB" from a DIY shed. There was(is?) a bit of 18 mm WBP ply that was leaning against a wall outside bottom edge on the ground, last time I looked at it after being there for several years it was still solid. Not seen it for a while but it may now be enveloped in undergrowth... That would have been a good grade of WBP ply.

I think you'll be hard pushed to beat a bit of high grade OSB or WBP for the size and strength you want. Stone or paving is just going to be to damn heavy. With the board just make sure you have good ventilation under it and where it would rest on the wall top and have a good drip edge to stop water getting underneath in the first place.

[Andrew Gabriel]

Dry rot spores are already in everyone's house. Mostly, the conditions are wrong for germination and growth.

(Doesn't look like dry rot to me anyway, but difficult to tell. Looks more like some man-made insulation!)

[Roger Mills]

I can assure you that it appeared of its own volition!