External window sill - cause of cracks?

[lizziecupcakes]

Hi all
I noticed our external window sills have some cracks in them. I haven’t tried to take a piece off since it’s also winter and raining a lot now.

I can’t tell what the window sills are made of, and want to fix these maybe in early spring.

There’s no obvious damp or water ingress issues coming into the house.

My main concern is that it will get worse and eventually cause damp issues and maybe even affect our newish sash windows put in by the previous owner (2019). They are made of wood too and good condition so far.

I’m not sure if it’s just the paint layer that’s cracking off, but it looks a tad bit deeper than that I think, but I’m not certain.

These sills are also white while the rest of the house has black-grey ones that are in good condition (just minor paint flaking), so I think the previous owner had work done on these when the windows were fitted in, or maybe just got them painted years back… unsure really.

Is it possible to fix these myself?

Thank you!

 

[lizziecupcakes]

 

[fernicarry]

Not entirely certain but I’d say the lower sill is stone or concrete. It might even be painted PVC as it’s a very regular shape for something of any age. What does it look like end on? Only way to tell is probably to remove some paint.

The bit you really want to take care of is the join between it and the timber cill. You don’t want water being blown in between. The mastic there doesn’t look like it’s in brilliant condition so might be worth renewing. You should also check all the way round where the window case meets the masonry for any gaps and cracks.

 

[lizziecupcakes]

Thank you @fernicarry - I’ll have another look when the rain clears.

Do you know which tradesperson I should contact to have a look at this?

 

[stuart45]

It looks to me like it's the paint that's cracking.

 

[lizziecupcakes]

Thanks @stuart45 - how do I take it off and fix this?

 

[stuart45]

I'd use a scraper to remove the loose paint for a better look.

 

[lizziecupcakes]

Thanks all. Just another question, these are the windows to the other side (these sills don’t have cracks at all). I’ve noticed after the rain stops there’s pooling of water in the bottom corners of the windows in the bricks.

Thankfully, There is no damp inside the house.

I imagine the water is getting between the fine line cracks between the sill and the bricks. The other side doesn’t have that greying patch (I think the window sill on this side leans a bit to the right so water drips off that edge more)

Is there a way to seal these edges - i’m not sure if there’s some type of outdoor waterproof caulking I can use?

Thank you

 

[stuart45]

It doesn't look a very good cill from the photo. How much fall is there to shed the water?

 

[lizziecupcakes]

I have no idea tbh. I don’t think very much. How could I measure this?

I think they look pretty straight.

Is the greying on the brick a problem? I was just sure if this will make things worse.

It’s always been there but I didn’t take much notice until I saw that water was in the bricks when the rest had dried off the house after rainfall.

 

[stuart45]

A boat level will tell you the fall. Should be around 12 mm. You could pour some water on it and see how it works.
It's better not the have the bricks constantly soaked. The freeze/thaw cycles might cause some spalling over time, plus if it's a solid wall you could get some penetrating damp.
Does it match the other cills on the house?

 

[Flyfisher]

I'd go with @stuart45's suggestion of pouring on some water and see what's happening, or go outside with an umbrella when it's pouring with rain.
Also, use a smallish level to check the side-to-side and back-to-front angles of the sill.

If the water run-off is only staining the brickwork one one side then it would suggest the sill is not level. If the fall is not too bad, I'd think about fitting some sort of 'upstand' to the side of the sill so that the water can't run over the side and has to run off the front of the sill and then miss the brickwork (assuming there is a drip groove underneath the sill). This would avoid removing and properly re-seating the whole sill, which would be a much bigger job.

The cracking looks like just the paint from the photos, but it can't be verified until the paint is removed, which needs to be done whatever is going on underneath.

Basically, remove all the cracked and loose paint with a scraper, check the sill levels in both dimensions, consider how to best control the flow of rainwater so that it all falls off the front of the sill (hopefully without having to re-seat the entire sill), ensure there's a drip groove underneath the front edge of the sill, add a suitable mastic seal between the sill and the window frame and repaint. Or something like that.

 

[stuart45]

These photos should give you an idea of what the cill should look like.

 

[lizziecupcakes]

Thank you so much. I'll have a look at this over the weekend - hoping it doesn't rain.
I think the suggestion of a suitable mastic seal between the sill and the window frame and repaint, sounds good.
Can you recommend a sealant, and suitable paint too?

Before measuring, I think it might be a little sloped to one side on that second photo, and the others (first photo) I think the cills are straight, so I think water is sitting there and eventially causing cracking of the paint.

Also, to answer your question, yes, all the cills are the same as these at the front, it's just the ones around the rest of the house had been painted charcoal black-grey. These are the only ones painted white. I think they were painted when the windows were put in (just my guess).

I'm not sure how to create a slope to run water down the front. Do you know how one would do this?

 

[stuart45]

You need to establish the type of material used for the cill first. For example timber would require a different type of paint to concrete. Stone is normally better off left unpainted.

 

[Cubist]

Ooooh, this ones interesting ... but not the cill itself so much. Any of you guys ever been interesting in the forensic sciences and in particular 'blood splatter analysis'?

What's captured my attention is the stains in the brickwork. The absorbed water pattern itself is rather odd but the black and white stains below the cills edge are, to my eye, more revealing. The black stuff is clearly airborne sooty grime from the cities air brought down during any rain and the white most likely is particles of pulverised paint from cill itself and window frame. The soot and paint particles are then being washed along the surface of the cill to the photographed side where it then runs down the wall. Based on this I would guess that the wind typically blows from the left and toward the right of this window frame and, due to the speed of the wind and/or the poor fall of cill, large amounts of grubby water is being driven toward that corner. To my mind this would explain why this section of the masonry has not dried out as quickly as rest of the wall and why this more sodden area seems to have reached a height of 150mm, or thereabouts, above the top face of the cill.

In terms of repairs. Your fingers and ears are your best tools to determine whether the cills are wood or stone. Wood will feel nearer to body temperature than stone regardless of the paint. A rap of the knuckles, or a using a stick, will produce a very dull sound from stone but a a slightly resonant/echoy one from wood. Regardless, the repairs are best conducted after the spring rains are done and as per the methods suggested by @Flyfisher and @stuart45 above. If though you are particularly worried about water penetration to the interior than an emergency temporary fix for the caulking can be applied using a product called PlumbersMait - come back to us if you decide to go down this route though.

 

[lizziecupcakes]

Thanks so much!! Today, I spent time with it and it feels like stone, but I'll give it another tap and feel test. It feels cold to touch, and on tapping, there wasn't a hollowness. I don't know if it's stone or not tbf, but I am mainly worried about my sash windows absorbing water.

I looked at the paint layer more, and it looks mainly of paint cracking off. I consulted a lovely lime expert today and he suggested I flake it off, sand and repaint.

I think you're right @Cubist regarding the rain. I've noticed that when it does rain, it seems to hit the window hard, suggesting it's being forced that way. It's so icky that grey-black stuff. And I also wiped down the cills today and the paint was coming off on the sponge. Do you know how I could remove that horrible discolouration? I also noticed it on my neighbours too, but theirs is subtle.

I think maybe the previous person who worked on the cills used the wrong paint.

I think I would like to do the temporary measure of using PlumbersMait , just because we are in rainy season and I'm nervous about any water getting to the windows (made of wood - sash). I'm not sure if this will eventually crack off and I can do the whole job properly during spring or summer (2027???).

I also wanted to ask if anyone can suggest a good cill paint (white), one that doesn't come off.

I really like the cills but I'm a bit annoyed that they are straight and there isn't a slope. I guess it'll look pretty when I eventually place flowers there (but I said i'd do that last summer and it didn't happen).

Oh and guess what?? Me and my partner are planning on growing our own lawn (or garden grass area is patchy and uneven) and we will add fencing to the back too, so i'm looking forward to mixing cement for the posts in a month or so

I feel so much better knowing the main bedroom is pretty much done - walls repaired, wallpapered, ceiling done, floors done, albeit none of it perfect. It's a massive sense of achievement and satisfaction!!

 

[Cubist]

PlumbersMait is available from most hardware stores and is used typically to seal the joints of bathroom sanitaryware. Its a putty like material that never completely sets and therefore can remain flexible for many years - this flexibility allows it to move in response expansion or contraction of the surrounding materials while maintaining a water tight hold on their surfaces. That though, is also its greatest disadvantage as you cannot directly handle it even with butyl or similar gloves - never wear decent clothing or touch your hair while using it - its not dangerous but you'll make a dreadful mess, have to bin your clothes and cut your hair if you do. A good strong putty knife is the most effective tool to use, after first cleaning out the old caulk where necessary, to firmly press small amounts of the putty into the joint, When you've filled the opening you can smooth the surface using the knife with a little oil on the knifes blade. it will take a long time - weeks/months - but eventually a skin form that will accept a paint if you choose.

Regarding the cills; I'm not convinced they are stone as I can see what may be the grain structure of a timber in the paint - but my eyes could be being deceived by a very poor paint job. Removing the old paint should be straightforward but do be careful near the glass if you choose to use a heat gun. Best too to strip the paint before you replace or refresh the caulking. Theres a variant of @Flyfisher idea that occurred to me that you could try easily enough to re-direct/divert the bulk of any driven rainwater off the face of the cill. A narrow strip of say 5mm thick wood arranged at 45 degrees to the window and pinned or glued to the cill around 100mm from the end would do the trick - at least for experimental purposes. Sadly short of moving house you're not going to beat the sooty deposits but replacing the paint will produce a longer term solution for the white 'blood splatter' you're seeing presently. No particular suggestions re the new paint until you know whether the cills are wood or stone. That said I think some of the problem is due to a previous owners use of an inferior quality paint products.

Oh, and there are several products available from the hardware stores that you could try to clean up the brickwork, check out the Sika products.