Stone Sills

[d_cavalier@hotmail.com]

Hi,

This site has been tremendously helpful whilst restoring my house, so thanks to all for the contributions, it's really great.

On my latest 'challenge': I have some stone sills in need of redecorating. I think the sills might be limestone - this is a victorian house in London, but am not entirely sure.

I noticed that on the underside of some of the sills there has been damage to the stone. I've attached some pictures (i) top of sill; ii) bottom of sill; iii) bottom of sill with paint removed - this is actually a different sill to i/ii), but they are all pretty similar.

When removing the paint in iii), the first 1-2mm of stone crumbled badly before getting back to hard stone. I was wondering whether this is due to trapped moisture from many years of modern paints, and if so what the best remedy might be? The decorators I've had around so far suggest filling with a cement based toupret filler, but cement and limestone sounds like a bad idea to me, not least because it has the potential to once more trap moisture.

Any advice much appreciated.

 

[88v8]

Hello and welcome.

Ideally, there should be no moisture in the sills. The house has a dpm so the walls should be dry, the paint envelope should keep water at bay.
However, pant cracks, water gets in.

The first thing I notice in that second pictureslice is that the drip under the sill has been filled up with paint. That should all be removed with stripper.

Is there other stonework in the facade? How do you intend to decorate, that is to say, do you intend to cover everything with uniform white, for instance?

The best thing for stonework would be a limewash, as that is breathable, and the lime content will bind the stone. It would need all the existing paint and cement repair stripping off, limewash will not adhere over paint. Existing cement repairs would have to be replaced with lime, limewash is not durable over cement as it cannot sink in.
Many decorators have no experience of limewash, but could be a DIY job.

However, if the rest of the façade is going to be covered in modern paint, the limewash will stand out, shall we say, also it will need redoing in a few years, it has not the longevity of a plastic paint.

The other approach is to use filler, then an alkali resist primer, then modern paint. Eventually it will crack again, more limestone will flake off, etc.
Nothing is forever.

Is the façade brick or stucco? Is it all painted? Are you terraced? Are they all slathered in paint? Little point in being a saint in a terrace of sinners.
What is your overall decorative approach? Do you have original windows, are you seeking a period ambience, or do you just want to keep the weather out?

Ivor

 

[d_cavalier@hotmail.com]

Thanks Ivor,

The first thing I notice in that second pictureslice is that the drip under the sill has been filled up with paint. That should all be removed with stripper.

Yes, and that looks to be the case on all the sills. Is there a preferred chemical stripper for removing the paint from the stone to restore the drip groove (I'm guessing a heat gun on stone is ill advised?)

Is there other stonework in the facade? How do you intend to decorate, that is to say, do you intend to cover everything with uniform white, for instance?

Yes, there are 4 bays and the stone mullions are painted white, I had intended to get the whole front façade painted, masonry paint on the bay surrounds and perhaps something higher sheen for the sills (all white).

Is the façade brick or stucco? Is it all painted? Are you terraced? Are they all slathered in paint? Little point in being a saint in a terrace of sinners.
What is your overall decorative approach? Do you have original windows, are you seeking a period ambience, or do you just want to keep the weather out?

The house is brick and detached, all stone work is painted but not the bricks. I'm mainly looking to keep the weather out, and not do anything that might encourage further deterioration of the stonework.
To strip all the stonework in order to limewash would be quite a job, and probably beyond me unfortunately. When you suggest filling and repainting with modern paint (accepting that it's not a perfect solution) I assume some fillers are more appropriate than others (e.g. https://www.lime-mortars.co.uk/stone-restoration/stone-repair-mortar)?

 

[88v8]

The Klingstrip family is the usual weapon of choice, but it depends what paint you are removing.
http://www.stripperspaintremovers.com/I_want_to_remove.htm
Try a small tub first, see how you get on.

I don't think you'd do any harm with a heat gun.... on low setting. I am always wary of heat guns adjacent to things I don't want to strip, as one cannot see the notflame.

The problem with painting stone is that inevitably moisture gets in and is trapped by the paint, and degrades the stone. Then the damage is (badly) repaired and painted over and the cycle repeats. Much better that it were never painted, but you are where you are.

Hadn't seen that filler. I suspect it's just an expensive way of buying lime mortar, but not at all a bad idea. Better than 50lb bags of lime and having to source the right type and colour of sand. I presume it wil come with instructions - if not, the stone needs to be slightly damp when applied - a hand mister is fine - and the repair should be misted for a day or so.

All white. We have all the colours of the rainbow at our disposal. Do you not remember the streetscape when people painted their houses in colours.
Green & cream, red & cream, two-tone yellow, brown & cream two-tone blue, white & cream.
In those days we had all-white underwear. Now we have colourful Y-fronts and the street is all white.
All white. Sigh.

Ivor