Eroded sandstone window sills

[rhamson]

Hello, I'm in the middle of repainting our sandstone window sills on our 1910 house, and looking for some advice on what to do about the currently unpainted undersides of the ground floor sills - they are slightly eroded all the way along, plus one end is particularly damaged (see photos). I'm just trying to work out what is needed in terms of breathability etc and what will protect the house best. The first floor sills are already painted underneath and seem in better condition.

Should I paint the underneath on the ground floor sills too to protect against further erosion (Sandtex masonry paint)? And/or would it be best to patch up with some masonry filler first (I have Toupret), either just the very damaged end or all the way along (and can I use the Toupret for the pointing underneath too)? OR would either of these risk causing more damp by reducing the breathability of the stone?

Grateful for any advice!

 

[rhamson]

Bump

 

[opps]

I would coat the underside with dilute SBR. You can apply masonry paint over that if you want.

To get a clean edge, wrap a length of timber in polythene, then clamp it to the window sill, and fill. Once the filler had dried, you can unclamp the timber. The polythene will prevent the timber from sticking to the filler.





The above is a sill that I filled with 2 pack filler. I often use Toupret Murex as well- it is faster to sand (and cheaper). It glossing I find that 2 pack gives a better quality of finish. That sill took half day (including painting).

If you have the grey Toupret, that will be fine but it is much softer. It is however very easy to hand sand.

Try to ensure that the under "lip" only goes back by about 5mm, it will reduce the risk of water tracking back to the wall when it rains.

 

[Ivor Windybottom]

They look like they're very soft stone, so any filler will probably fall off eventually.

Have you priced up replacing them? That would surely be the best option. Then you'd have a drip strip ready-cut into the underside and wouldn't need to paint them ever. Bare stone always looks much better than painted.

 

[^woody^]

Use an epoxy repair product specifically made for sandstone.

You'll need to reform a drip detail to the bottom edge of the cill to prevent water lingering or tracking back the wall.

 

[Wayners]

I've seen a box made around sill and another concrete sill cast. Also seen old sill removed and soldier bricks along to create another sill

 

[Ivor Windybottom]

There's very good evidence in those photos that whatever stone was used at the time, it's definitely not strong enough. I can't imagine anything sticking to it for too long before it falls off. The equivalent of super-glueing to a loaf of bread. Whatever you stick to it, it's only stuck as well as it is to itself, which is evidently not very well.

New stone would look really good. Might be worth a phone around, probably the sort of thing where phoning a manufacturer may result in a very different price to getting someone in to replace them. Buy them then pay someone to fit them, cut out the markup.

 

[^woody^]

Adhesives have moved on since the industrial revolution.

Lets also consider the cost of a pack of epoxy repair £15, with the all-in cost of a new cill .... 100x as much.

Perspective.

 

[Ivor Windybottom]

I doubt it's £1500. But I don't know.

Eopxy's good stuff. But it will only stick to the outer layer of sand particles which, by the look of the photos, is very likely to become detached from the next lot pretty soon.

It just looks like crap stone was used. Best to actually fix it. Perhaps a patch up and paint if selling, otherwise it should be worth doing properly.

 

[^woody^]

But I don't know.

Sandstone, like other "soft" stone is actually quite tough and cohesive - so it does not just start randomly disintegrating. It will take suitable adhesive products no problem.

The inherent weakness is erosion and spalling, and that's what needs to be dealt with.

The work involved in replacing cills to sash frames, especially at first floor levels is not inconsiderable.

 

[opps]

They look like they're very soft stone, so any filler will probably fall off eventually.

There's very good evidence in those photos that whatever stone was used at the time, it's definitely not strong enough. I can't imagine anything sticking to it for too long before it falls off. The equivalent of super-glueing to a loaf of bread. Whatever you stick to it, it's only stuck as well as it is to itself, which is evidently not very well.

I am guessing that you are not a decorator...

90% of my work is Victorian properties.

I have been filling sandstone sills for years.

Why is it that when I return to a customer's house after 20 years, the filler hasn't fallen off?

The sill in my earlier post was sandstone.

This is the latest one that I had to repair. I used an angle grinder to cut slots so that I could insert helifix bars (using anchor fix resin).



I additionally drilled holes at jaunty angles to insert the bars.

Here is it after- I used Toupret Murex to reskin the whole sill. It works out cheaper and quicker than using 2 pack filler, but I wouldn't use it for sills that need to be glossed.




For the benefit of anyone reading this in the future, sandstone sills should last hundreds(?) of years if maintained properly. It is often the case that the underside on the ground floor has been neglected, and possibly never painted. If you have one in that state, my advice, as a decorator, is to seal the underside with dilute SBR. You can then use masonry paint after.

Use dedicated exterior fillers, eg Toupret Murex (hard to sand by hand), Toupret Touprelith F (really easy to sand but if the window cleaners leans a ladder against it, it will bruise), 2 pack filler will give you the smoothest finish but you need powered sanders.

With regards to time... the above bay window would take 6 hours to fill with the soft exterior filler, 12 hours with the Murex, 16 hours or more with the 2 pack, but the quality of finish will be far higher.

As per my earlier post- if any of the paint has flaked off, use something like SBR to prime it. It is a cheap product, Approx £20 for L (and you need to dilute it, meaning that a much smaller quantity, if available will suffice0.

Please, for the love of Mike, never use PVA to seal exterior masonry. PVA when wet re-emulsifies. SBR will not/ should not.

Sorry, I have hijacked my own reply, but as a decorator, I can tell any one that has sandstone sills, you don't need you pay thousands of pounds to rip them out (baring exception circumstances).

In my opinion @Ivor Windybottom doesn't come across as a credible source of advice with regards to this thread, he may, or may not have an arena where he is knowledgeable....

My advice is offered up as a professional decorator that attempts to provide a high quality of finish.

Ultimately, follow the advice that has been offered...

 

[Ivor Windybottom]

For that amount of work you must charge a few quid. Looks very good, but that photo was ten minutes after you'd finished.

There are often multiple ways of doing things, there isn't always one right answer. I'd start with the best option (replace), then look at other options if the cost is prohibitive. Best to aim for the stars initially, even if you do then decide to set your sights lower.

From a quick google, price doesn't look like too much of an obstacle...

NATURAL STONE WINDOW CILLS/SILLS MADE BY JOWETT STONE STARTING FROM £180.00 (#C) | eBay

These are natural stone cills, not cast stone cills. New Natural Stone Heads / Cills all made by Jowett Stone. We can cut them down to any specific sizes. It does not include chamfering. It is one of the products that we specialize in.

www.ebay.co.uk

Even less if you're happy with fake stone, which often looks pretty good anyway. Definitely better than painted.

(Cue nit-picking about wrong sort, wrong end of the country, bla bla etc). Just an indicative example, nothing else.

As I said, also depends on whether keeping or selling the house. If selling then it's obvious, fill and paint.

 

[rhamson]

Thank you everyone for the responses! This is our house for the long term, and we do want to preserve as much that is original as possible - plus have plenty that needs money spending on elsewhere. The house has been reasonably neglected since the late 80s, so the sills possibly haven't been painted since then!

I am guessing that you are not a decorator...

90% of my work is Victorian properties.

I have been filling sandstone sills for years.

Why is it that when I return to a customer's house after 20 years, the filler hasn't fallen off?

The sill in my earlier post was sandstone.

This is the latest one that I had to repair. I used an angle grinder to cut slots so that I could insert helifix bars (using anchor fix resin).

View attachment 316486

I additionally drilled holes at jaunty angles to insert the bars.

Here is it after- I used Toupret Murex to reskin the whole sill. It works out cheaper and quicker than using 2 pack filler, but I wouldn't use it for sills that need to be glossed.


View attachment 316488

For the benefit of anyone reading this in the future, sandstone sills should last hundreds(?) of years if maintained properly. It is often the case that the underside on the ground floor has been neglected, and possibly never painted. If you have one in that state, my advice, as a decorator, is to seal the underside with dilute SBR. You can then use masonry paint after.

Use dedicated exterior fillers, eg Toupret Murex (hard to sand by hand), Toupret Touprelith F (really easy to sand but if the window cleaners leans a ladder against it, it will bruise), 2 pack filler will give you the smoothest finish but you need powered sanders.

With regards to time... the above bay window would take 6 hours to fill with the soft exterior filler, 12 hours with the Murex, 16 hours or more with the 2 pack, but the quality of finish will be far higher.

As per my earlier post- if any of the paint has flaked off, use something like SBR to prime it. It is a cheap product, Approx £20 for L (and you need to dilute it, meaning that a much smaller quantity, if available will suffice0.

Please, for the love of Mike, never use PVA to seal exterior masonry. PVA when wet re-emulsifies. SBR will not/ should not.

Sorry, I have hijacked my own reply, but as a decorator, I can tell any one that has sandstone sills, you don't need you pay thousands of pounds to rip them out (baring exception circumstances).

In my opinion @Ivor Windybottom doesn't come across as a credible source of advice with regards to this thread, he may, or may not have an arena where he is knowledgeable....

My advice is offered up as a professional decorator that attempts to provide a high quality of finish.

Ultimately, follow the advice that has been offered...

Many thanks @opps for the detailed post, I'm sure that will be helpful for others in future as well with this issue!

Use an epoxy repair product specifically made for sandstone.

You'll need to reform a drip detail to the bottom edge of the cill to prevent water lingering or tracking back the wall.

@^woody^ thanks for responses, would you use the repair product to build up a bit of a lip/ridge on the bottom edge, do you mean?

 

[opps]

@^woody^ is talking about a little curved groove on the underside. As the water runs down the from the front of the sill, when it it gets to the groove, rather than running back to the wall, it drips down (hence the name drip groove).

Sometimes people use an angle grinder to create a square profile channel- they often look pretty rough though.

On sills that have no existing drip channel, and which are on the first floor, I often use some wedges to tilt the timber that I use to create the straight underside front edge. I then backfill the underside. The underside then tilts downwards from the wall to the front face, thereby ensuring that drips cannot track back to the brickwork.