Filling a large gap in wood?

Hi All,
For reasons I won't go into now I've been left to try to deal with a bathroom floor and to make it ready to have some vinyl laid (round 'Mum's').
A 6mm ply sheet has been laid but is a <insert varying distance here (averaging 20 mm probably)> gap from the wall / skirting [1] and I'm either going to have to take it all up and replace with a sheet that's actually cut to fir that actual bathroom (?) or try to fill said gap (so ~20mm x 6mm by ~8m) between the edge of the ply and the wall / tiles with something?
As it is such a narrow (and varying width) strip I'. thinking of applying some sort of liquid 'filler' (rather than an infill strip of some sort) and it probably needs to be sufficiently stable / stuck_to_the_floorboards so it doesn't lift when the flooring is stuck down?
I was thinking something along the lines of Gripfill but I know the real (solvent) stuff might be a bugger to get flat, and smooth and something like a cement, might not be strong enough in that thickness to stay down / together?
So, I'm really keen to know if there is anything that would be ideal for this purpose please as I really don't want to be taking the new toilet and hand basin up again (but actually want to).
Cheers, T i m
[1] I'm going to take the one length of conventional skirting that has been 'fitted' away and carry the tiles down to the floor on the two walls that are tiled. I was thinking of using some uPVC (5mm x ~60mm?) as a trim round the bottom of the shower tray (to hide the concrete base) and carrying it round as a mini skirting on the walls?
https://www.angelplastics.co.uk/Images/Images_Large/60mm%20arch%20ww.jpg
(or in black to match her cabinet work top).
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Assuming I had matching spare ply to hand, I'd saw a strip to fill the gap.
Quite possibly I'd saw the existing piece _narrower_, such that my infill was about 2" wide. That's easier to work with than a really narrow strip, especially if it's tapering.
I wouldn't mess with gripfill or liquids. I'd buy more ply than do that.
Another way is to just buy more ply and do it again. I can always find a use for a large piece of the mis-cut plywood somewhere in the workshop.
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On 03/10/2012 12:39, Andy Dingley wrote:

Polyfilla. It's what the pros use and presumably nobody's going to be tip toeing along the edges. Gripfil would make a fine old mess.
That Toolstation Deep Fill stuff in a tub dries really quickly if that's important
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On 03/10/2012 13:14, stuart noble wrote:

Would the vinyl just bridge over that gap? As you say, nobody will be walking on that bit. Having said that, I used polyfilla once in quite a high traffic area - it worked a treat.
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I have to replace some vinyl tiles where the small gap (in high traffic area) has made the tiles crack. I was thinking of using car body filler. Would Polyfilla work there?
Jonathan
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I have an access panel under the shower tray with a similar kind of gap (a favourite residence of spiders, which some people aren't keen on). I was thinking of using silicone on a bit of plastic (ice cream tub) for support - easy to cut through. Wondering whether acrylic or similar filler might do instead (have a pot of it, from Aldi I think). Is it easy to get out should access be needed?
Theo
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On 03/10/2012 12:39, Andy Dingley wrote:

Agreed.
First question is whether the joists are perpendicular to the wall, or parallel. If perpendicular:
Don't take up the old piece yet. Get your strip (actually I would probably work with 4 - 6 inches) and scribe it to fit the wavy wall. Ideally, have the side opposite the wall as an original edge, so it will be dead straight. Cut to fit with a jigsaw. Then lay it in position against the wall, and mark the "overlap" line on the existing board. Now, you only have to cut a straight line along the existing ply and remove the unwanted bit. You may be able to do this without removing the existing sheet using a circular saw set to the exact depth, as long as you are sure there are 1) no nails or screws and 2) no wires or pipes which you are likely to hit.
If parallel, it may be a bit more awkward. There is probably a joist fairly close to the wall. It may be worth screwing a piece of (say) 2 x 2 alongside it, so that you have a bearing area about twice as wide as normal. Then you can still use an "insert" as described above, but you want the join line to run along the middle of the joist, and have the overhanging piece screwed down firmly. If the gap between the joist and the wall is only an inch or two you should get away with the overhang although there is still a bit of a risk if (say) a chair is placed with legs up against the wall. One "fix" in this case is to add another support along the wall attached to the studding or brickwork. Another is to make your inserted board start at the next joist away from the wall.
6 mm is a bit on the thin side for floorboard although you can get away with it if bridging an unloaded gap (for example behind a loo or wash-basin).
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On Wed, 03 Oct 2012 13:16:04 +0100, newshound

Firstly, can I just that everyone for their prompt and informative replies. Lots of ideas there! I'll try to comment on all the idea vi a reply here.

Agreed as well. However. The toilet is currently set on a 'plinth' of Gripfill and I'd rather not do that again unless I really have to.

Both. The area in question so far is one narrow end of the bath room and the one with the WC, basin and a bit of skirting board (now removed).

Right, so the joists run the length of the room so this would apply to (left to right) the length of wall covering the airing cupboard, rectangular shower tray and some small floor standing cabinets (cabinets about 1.2m wide total and 200 mm short of the shower) and the main / blank / to_be_painted wall opposite.

Understood. I believe I've done similar with carpet tiles.

Understood. Question here if I may. Would it be 'better' to cut this joint at 45 Deg (beveled), like an expansion joint on a railway track? Not so easy to do unless you cater for the length difference before cutting (moving the new bit away from the wall by the length of the overlap)? If this would be considered to be 'overkill, do you normally have such panels touching or would you leave a gap (and if so, how big)?

I could cut the new on top of the old with the same cut?

Understood. One of these parallel sides was under the bath and many of the floorboards stop quite a bit short of the wall (joggled and probably 1 in 3 and by no more than 20mm worse case). Whist most of this area will be under said cupboards, this is the area I'm most like to see covered with at least this 6mm ply.

Understood. I may need to make things clear here. This 6mm exterior ply is only being used to provide a 'flat' surface for the vinyl covering. The floorboards are old fashioned real wood planks, firmly cut_nailed or screwed to some pretty substantial joists. Apart from the 'holes' mentioned above, this ply is regularly screwed to the floorboards (to but not through).

Understood. There is a section on the long / clear wall where the (3?) floorboards have been cut away from a joist and I'll be supporting that before the floorboards there are replaced. The boards themselves probably still span 3 - 4 joists.

I may have explained that better above.
So, I think I may end up using a mix_an_match of the suggestions offered. I note one floorboard (that was under the tap end of the bath) that looks to be slightly soft / rotten so I'll cut the ply back as suggested, replace the floorboard (probably 3-4 joist spaces long with only a 1 joist spacing looking bad).
I'll do the same with the section to be under the cupboards and up to the shower (a 200mm length will be visible and currently sports a floorboards with 200mm 'gap' against the wall. Visible because the ply is 25mm short of the wall at that point).
Around the shower tray and the more awkward bits behind the WC and basin / pedestal (minus the section to do the bad floorboard) I might use a filler (Toolstation 'deep' stuff?).
I might do the trim and insert back along the clear wall as I can get to all of it fairly easily and it's the bit most likely to take a chair / steps leg one day.
As only half the room had been done, hopefully *I* can do the rest without any gaps. ;-)
It looks like I might also be doing the rest of the laminate flooring down the hall (kitchen already done) but that is another story! ;-)
Thanks again all who replied!
Cheers, T i m
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On 03/10/12 21:46, T i m wrote:

using car body filler you could have it curving slightly up, so that the vinyl covering curves up at the edges, and any water spillage doesnt seep down the edge...
im thinking of doing this, is it a good idea?
[g]
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On 03/10/2012 12:13, T i m wrote:

Have you considered resin-based fillers, as used to repair car bodywork? You can buy small quantities as Plastic Padding or Isopon (can you still get that?) - but for larger quantities you need to buy resin and powder separately, and mix your own.
--
Cheers,
Roger
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