You're quite right, Rodders.
I think it's quite possible it happened mostly when the tree was alive.
One of the other skirtings in the room had a much smaller attack at roughly the same distance along the board. It's entirely possible they came from the same tree (I've seen that a few times with floorboards) - picked off the stack consecutively in the mill, planed/moulded, then re-stacked together, etc.
In both cases the tougher heartwood seems to have been too indigestible. There was some evidence of filler having been applied to surface damage before first painting, but it's hard to tell as I hot-air stripped them and have sanded back fairly agressively.
Regarding planting extra on the bottom, I don't always do it, but in this case there are several reasons.
I'm sure you know it was common to fit the boards to a rendered wall, then skim down to the tops to finish. It had a number of advantages for the builder, but almost none for those following on.
I think it must have been a PITA for the plasterers too - the builders could get away with using really low grade timber, and it must have moved around a lot on the walls. It must have been the plasterers' job to lose any warpage so that the plaster finished neatly in line with the top edge of the board, which could have ended up anywhere depending on the weather! A bell cast was almost inevitable, but in this room one wall is a bit extreme.
The main three boards in the room were all cupped and one was badly warped too (loads of wind). That wall is nastily belled out at the bottom (the one with the winding board). Unfortunately, that's also the wall you look along as you enter the room. Any strong vertical or horizontal lines on it (wallpaper, for example) will make the problem really obvious.
The wind on that board was right next to the door, where it met the architrave at right angles. I think they fitted the door end square (because it met the artchitrave) then forced the rest of it into line as much as possible. Someone should have rejected the board!
I couldn't possibly have fitted it back nicely without problems. I can't easily use the traditional method of wooden wedges between the bricks, as the walls are too ropey now to take a lot of knocking about, and anyway it wouldn't help. The moulded sections are thinner, so move around less. By planting some more on the bottom, I get a second bite at squaring up the straight part of the board (with a belt sander, carefuly applied), and the extra height takes me up over the bell cast, which can be cut back gently to a straighter finish. I'm trying a new approach for actual fitting: fixing 3x8 x 3/4" vertical strips of ply to the brick, packed out to be vertical and around 1-2mm below the finish level of most of the skim coat. I intend to screw the boards to that. Any packing should be simplified and I hope to get away without blocks/battens on the floorboards (REALLY hate those).
The final reason is that I've bottled it regarding the fitted wardrobes - time and skills shortages on my part. The person making them is arranging the mouldings to hit a particular point on the skirtings (a straight bit in the skirting moulding - you can see it in one of those pics). The crown moulding in turn has a straight bit that the picture rail hits centrally. The picture rails are the datum line, as theyare the most level thing in the room! So the height of the wardrobes has to be fixed, and the plinth and skirtings adjust to meet them. Also, because the house has moved about the floors aren't level (they never are).
So he gets to fit the plinths level, and the bottom scribe (a simple bullnose) becomes relatively easy, and there's no risk of 'missing' the target, because I have height to spare. I also get to hide some of the sag in the floors with a new scribe...
... what's not to like (apart from all the fiddling about, cussing, etc.)?
E.
PS: I'm actually planting on about 2 1/2" (because it's easier to cramp up) and cutting it back to the right height. I also cut out about 3.5ft of the wind on the worst board and replaced that too, and butt-joined an extra 6" on the bit for the chimney breast (as was), so there's enough clean wood to get a really neat scribe as that one'll really show.
