External filler for render and window sill

[Martin Pentreath]

Hi,

I'm planning to do a bit of exterior redecoration. We have a bay window which is a triumph of the victorian cowboys who built this place. Its foundations are (I think) two courses of bricks sitting on nice London clay. Consequently it's not very stable. The last time it cracked up it was shored up using helical bars. They're better than nothing, but there is still some movement, and things have cracked up a bit since the last repaint (about six years ago).

Anyway, as the options seem to be either underpinning it, or just filling the cracks every few years, I'm opting for the second. So the question is what's the best thing/technique to use to fill it. Here are two photos:
http://imageshack.us/g/254/imag0181g.jpg/
One shows the cracked rendered plinth. The other one shows a crack in the sill - it sounds pretty hollow underneath and I suspect when I give it a whack a large chunk of it will fall away leaving a big hole.

Cheers!

Martin

[Ian Jackson]

In message <147d4c9d-1e3f-4c03...@googlegroups.com>,
Martin Pentreath <martin_p...@hotmail.com> writes

How old is the house? If it's been there a long time, and there's no
sign that anything will collapse, I would be tempted to repair things
with something flexible, so at least the cracks won't reappear (or at
least so they will only appear at the junction of the flexible and
non-flexible parts - so you will know where they are).
--
Ian

[Martin Pentreath]

On Wednesday, August 29, 2012 12:55:54 PM UTC+1, Ian Jackson wrote:
>
> How old is the house? If it's been there a long time, and there's no
>
> sign that anything will collapse, I would be tempted to repair things
>
> with something flexible, so at least the cracks won't reappear (or at
>
> least so they will only appear at the junction of the flexible and
>
> non-flexible parts - so you will know where they are).
>
> --
>
> Ian

Hi Ian,

The house was built around 1880. But anyway, there aren't any structural problems with the rest of it - it's just the bay window that has no foundations. So really I'd already decided that it's just a filler job. I'm wondering what the best filler is to use for this, and particularly for the sill, which I think will be left with a gaping hole after I've removed the bit that's cracked away.

[Ian Jackson]

In message <923a119b-2d05-472b...@googlegroups.com>,
Martin Pentreath <martin_p...@hotmail.com> writes

Having done, in the past, a fair number of body repairs on my
ever-rusting bangers, I'd be tempted to use up some of my car repair
materials (fibreglass matting, resin and paste). I suppose 'Plastic
Padding' is maybe the most appropriate (especially the flexible type).
However, there are probably better 'genuine' building materials for the
job - which others will advise on.
--
Ian

[The Natural Philosopher]

One thing I discovered about 'genuine building materials' is that they
have only one overriding advantage. They are cheap.

One would be far better off with - say - a house made of GRP lined with
PU foam, and self colored gel coat on the outside, than rendered.
Especially if it were epoxy and not polyester. Bolts would be better
than nails.


Beams of Titanium would be far better than wood. etc.

I leave you to draw the obvious conclusions.


--
Ineptocracy

(in-ep-toc’-ra-cy) – a system of government where the least capable to
lead are elected by the least capable of producing, and where the
members of society least likely to sustain themselves or succeed, are
rewarded with goods and services paid for by the confiscated wealth of a
diminishing number of producers.

[stuart noble]

Nothing better than car body filler IME, preferably a cheap 3.5 litre
job from a trade outlet. £15 ish IIRC

[Andrew Philips]

If it were me, I'd crack off any loose portions of the sill and fill the resultant hole with mortar - a weakish mix, certainly not as strong as 1:3, more like 1:5 perhaps? Maybe use a little watered down PVA (50:50? - or you can mix in a little neat cement with the pva to make a bonding slurry - to be used sparingly) to better bond the infill mortar to the inside of the hole you'll end up making in the sill.

The bay wall itself - same thing really - except it's difficult to do keyhole surgery on these things so cut the crack wider and deeper using a chisel and fill as for the sill. Remember you can't put on too much render on a vertical surface in one go - half an inch would be OK.

If you really, really wanted to do something more permanent, the only thing I can see that might work for the bay wall would be to knock off all the render back to the brickwork, fix expanded metal mesh to the wall with appropriate fixings then render over that. You then have metal mesh reinforced render which ought to hold together much better than plain render, when under strain.