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Sagging Finlock (concrete) gutters - fixable?

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Alec Waters

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Feb 24, 2004, 11:44:50 AM2/24/04
to
Hi all,

I have Finlock gutters at my house (this kind:
http://www.finlock-concretegutters.co.uk/), and they're sagging over the
windows. This movement of the blocks has caused damage to both the
plaster on the inside walls, and the rendering outside. There's almost
certainly water damage to the brickwork between the two :(

How easy is this to fix? I'm not proposing that I do it myself, I just
want to get some idea of the magnitude of the task.

Has anyone had this repair carried out in the past?

thanks,
alec
--

Peter Taylor

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Feb 24, 2004, 2:14:22 PM2/24/04
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Alec wrote

Hi Alec. It's a fairly major problem I'm afraid. Finlock gutters were a "good
idea at the time" in the 50s and early 60s. The concrete gutter sections were
laid directly on the top of the cavity external wall to form a continuous
combined precast concrete gutter/fascia/wall plate and, where passing over
window openings, the "lintel trough" was filled with concrete with a couple of
steel reinforcing bars to make a beam. The water trough part was sealed with
aluminium foil and bitumen. The trouble is that even tiny amounts of movement
(due to thermal expansion, shrinkage or minor settlement/subsidence/heave) cause
cracking and open joints and then the gutter starts to leak. For many years
Finlock offered a fairly cheap relining service, but a better and more effective
way of sealing them these days is to provide a separate rigid sheet aluminium
liner which is unaffected by movement. As for the sagging, this is quite
unusual and I can't say why it has happened in your case - sounds like there may
be a problem with the reinforcement. One thing's for sure - it's not a simple
repair.

If you can live with the sagging then it might be worthwhile just providing new
aluminium liners (e.g.
http://www.rainwatergoods.co.uk/finlock_concrete_gutter_liners.htm), but
otherwise it really is not worth rebuilding the sagging sections. Even after
you've done it and had the gutter relined to stop the leaks, there will still be
a serious cold bridge situation and virtually always this causes severe
condensation problems. The extra cost involved in removing the Finlock sections
altogether is much more worthwhile IMO, although if your house is a semi that
might be a problem unless your neighbour does it as well.

You will need to remove some of the roof tiling and support the wall plate under
the rafters before you can do anything about the sagging lintels. If you
rebuild them and form new beams you will probably need to remove the windows.
Alternatively you could remove all the Finlock sections altogether, build up
the cavity wall to plate level with bricks and blocks, and provide new steel
lintels over the windows. You will need to extend all the rafter feet and
provide a new fascia, soffit and gutter, and also plaster and decorate all the
tops of the walls internally. It's also a good opportunity to sort out cavity
wall and roof insulation.

I would suggest you get a few quotes from builders. Ideally give them a short
specification or schedule of all the work required - this will make sure they
all price on the same basis and prevent any nasty "extras" later.

Sorry to be the bearer of bad news. Good luck with it.
Peter

Alec Waters

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Mar 1, 2004, 7:49:45 AM3/1/04
to Peter Taylor
Hi Peter,

Thanks for the reply!

> As for the sagging, this is quite unusual and I can't say why it has
> happened in your case - sounds like there may be a problem with the
> reinforcement. One thing's for sure - it's not a simple repair.

Here's what the Finlock people said on the matter:

> Thank you for your recent enquiry regarding sagging guttering. This
> is a very common problem where original Crittal or timber windows
> have been replaced with UPVc that has little or no structural
> integrity. The gutter should have been installed with reinforcing at
> the time of construction, but in many cases, this was not done. The
> result being the guttering sags and creates a problem with the
> replacement window.
>
> There are two remedies that we are aware of. Both will require the
> services of a competent builder.
>
> Method one.
>
> Using small structural props, jack up the blocks to original line.
> Hack off plaster to inner surface of the blocks and insert 150 X 100
> X 10 stainless steel angle, sufficiently long enough to provide at
> least 150 bearing to reveal brickwork on both sides. Dry pack angle
> into place by ramming sand and cement. This angle supports the rear
> lower edge of the blocks and takes the weight off of the window and
> relies on the cantilever effect of the roof to keep the blocks level.
>
>
> Method two.
>
> Provide localised temporary support to the roof plate using something
> like a Strong arm ACROW Prop or gallows props. Remove the collapsed
> blocks over the window opening and one either side. Provide temporary
> frame in place of window and replace the blocks with new. Provide
> either reinforcing bar cage or small universal beam and place in the
> rear trough of the gutter block. Cast in with strong mix of concrete
> and allow to cure. Remove temporary frame and replace original
> window. Remove props. Reinforcing cage or universal beam should be
> long enough to provide 150 bearing to both sides of opening.
>
> In both cases, it will be necessary to reline the blocks to maintain
> continuance of rainwater disposal.

I don't really know what these entail (I mean I can sort-of "guess", but
I don't "know" if you see what I mean.). They both sound pretty major
though.

alec
--

Peter Taylor

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Mar 1, 2004, 11:57:47 AM3/1/04
to
Alec Waters wrote

> Hi Peter,
>
> Thanks for the reply!
>
> > As for the sagging, this is quite unusual and I can't say why it has
> > happened in your case - sounds like there may be a problem with the
> > reinforcement. One thing's for sure - it's not a simple repair.
>
> Here's what the Finlock people said on the matter:
>
> > Thank you for your recent enquiry regarding sagging guttering. This
> > is a very common problem where original Crittal or timber windows
> > have been replaced with UPVc that has little or no structural
> > integrity. The gutter should have been installed with reinforcing at
> > the time of construction, but in many cases, this was not done. The
> > result being the guttering sags and creates a problem with the
> > replacement window.

Well, that makes sense - never seen it myself though. Just goes to show how
much of an expert I am then, doesn't it? :o)

> > There are two remedies that we are aware of. Both will require the
> > services of a competent builder.
> >
> > Method one.
> >
> > Using small structural props, jack up the blocks to original line.
> > Hack off plaster to inner surface of the blocks and insert 150 X 100
> > X 10 stainless steel angle, sufficiently long enough to provide at
> > least 150 bearing to reveal brickwork on both sides. Dry pack angle
> > into place by ramming sand and cement. This angle supports the rear
> > lower edge of the blocks and takes the weight off of the window and
> > relies on the cantilever effect of the roof to keep the blocks level.

I don't understand the bit about cantilever effect. As far as I can tell, this
method involves only supporting the inner edge over the window opening. The
outer edge (the gutter) and the roof load is still not properly supported.

> > Method two.
> >
> > Provide localised temporary support to the roof plate using something

> > like a Strong arm ACROW Prop or gallows props.....

I think they must mean Strongboy prop heads.

> > Remove the collapsed
> > blocks over the window opening and one either side. Provide temporary
> > frame in place of window and replace the blocks with new. Provide
> > either reinforcing bar cage or small universal beam and place in the
> > rear trough of the gutter block. Cast in with strong mix of concrete
> > and allow to cure. Remove temporary frame and replace original
> > window. Remove props. Reinforcing cage or universal beam should be
> > long enough to provide 150 bearing to both sides of opening.

This is exactly what I envisaged.

> > In both cases, it will be necessary to reline the blocks to maintain
> > continuance of rainwater disposal.

As I said, a separate aluminium liner would be better.

> I don't really know what these entail (I mean I can sort-of "guess", but
> I don't "know" if you see what I mean.). They both sound pretty major
> though.

Method 1 sounds like a bodge structurally, unless I'm missing something. It
will still be quite expensive (guess about £2.5 - £3K for a semi + the gutter
lining). Method 2 is better but involves an extensive amount of work and
disruption, involving removal of windows. In both cases you'll still end up
with a major cold bridge with a high possibility of damage to decorations and
plaster due to condensation or gutter leaks.

Personally, I don't think Method 2 is worthwhile. If at all possible I would
recommend you go the whole hog and remove the Finlock stuff altogether and put
in a proper fascia and gutter. Ask around and get yourself a good builder and
see what he has to say Alec, and then if necessary come back here.

One last point - were the windows replaced with uPVC prior to this damage
occurring? If so, maybe the window company should have recognised the need to
support the Finlock before they removed the old windows.

good luck
Peter

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