Repair of window sill

[ajbaker]

After all of the reading I have done regarding the repair of my property, I have seen very little relating to window sills.

Due to the previous owner making the sill 'look nice' with gloss paint that begain pealing recently, and a less than careful contractor using the window to get materials in and out of the house, my window sill had to be taken back to bare brick.

I removed a very thin layer of plaster that I can only assume was a modern skim coat, and the layer of gloss emulsion.

My question is how I should I prepare and finish it? Would it have originally been rendered with lime mortar and then lime washed? Would it have been left as it is now, or am I overlooking something really obvious?!

Pictures attached for reference. Also, the house is an early Victorian terrace.

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[Lime]

Window sills are often overlooked when assessing a house for repair or renovation.
Sills play a very important part in keeping the walls dry.
Rain running off a window needs to be directed off the wall otherwise it will soak into the wall and become damp.
Your stone (?) sill shows all the usual problems:-

A large crack that is all but impossible to seal.
A poor joint between the wooden sill and the stone.
(the wooden sill does not look in good condition either)
The water bar (if fitted) that should be under the wooden sill compromised by the crack.
A slight slope to the side.
A broken drip outer edge. (probably with a poor underside and damaged/no groove)
No raised section on either side of the sill to prevent water entering the wall directly.
Cement pointing under and around the sill.
A protuding lower wall directly under the sill edge that is probably dripped upon.

Each of these problems can cause the surrounding wall to be damp.
Some can be remedied easily some can't without a replacement sill.

Almost certainly this sill will require regular attention as much of the weathering protection that can be applied will be superficial.
Window sills take a great deal of water run off from the vertical impervious window so that the wear and tear is great.
I don't think there is a permanent solution apart from replacement.

Sorry to be so gloomy.

 

[ajbaker]

Gloomy indeed. Many thanks for the insightful advice anyway - I'm amazed you managed to spot so much from two limited pictures.

At the moment I am not looking for a permanent solution specifically; more so the most appropriate protection for the coming winter at least.

A poor joint between the wooden sill and the stone.

Is it a good idea to try and fill this with wood, mortar, or a sealant?

A broken drip outer edge. (probably with a poor underside and damaged/no groove)

Sorry, not sure what you mean by this?

No raised section on either side of the sill to prevent water entering the wall directly.

Could this be achieved with a little lime mortar?

Cement pointing under and around the sill.

The lower quarter or third of the property has a lot of cement pointing. This is one of the items on the agenda next summer, but only if it can be removed without too much damage to the brick.

A protuding lower wall directly under the sill edge that is probably dripped upon.

Are you referring to the cement render or is the picture deceiving you to imagine the brick protrudes the sill?

So, everything considered, what are the pressing priorities for the nest few weeks to provide as much protection as possible for the coming winter?

 

[Nemesis]

What is the sill actually composed of? You say brick...

 

[ajbaker]

Sorry, you are right. Thanks for pointing out my mistake in the first post. Stone.

 

[Nemesis]

Without poking too hard - is the wood OK which sits on it? Don't panic if not - ours is a bit soft too but the house hasn't fallen down yet... and is the angle of slope on the stone sill enough to shed water? Hard to tell in a pic.

 

[Lime]

The sill's condition is quite typical of many older houses, as I said they tend to get overlooked.
I take your point that winter will soon be here and address the problems accordingly.

Quote:
A poor joint between the wooden sill and the stone.

Is it a good idea to try and fill this with wood, mortar, or a sealant?

The joint needs to be cleaned out.
You may find the wood is poor in places.
I would use a modern silicone sealant that has a high modulus to allow for any movement and has good adhesion.
Originally the joint would have relied on the slope of the stone sill and a physical water barrier further (1"-3") under the wood.

Quote:
A broken drip outer edge. (probably with a poor underside and damaged/no groove)

Sorry, not sure what you mean by this?

In your first picture the lower front of the sill is ragged.
This is the drip edge.
Behind it and under the sill there should be a water stop such as a groove the prevents water running back towards the wall.

Quote:
No raised section on either side of the sill to prevent water entering the wall directly.

Could this be achieved with a little lime mortar?

Yes it could if it is possible to get a suitable key on the sill.
However I'm not sure (looking closely at the picture again) whether you have a raised section or not.
In the first picture where there is some paint under the brick but over the sill, is that mortar or part of the sill?

Quote:
A protuding lower wall directly under the sill edge that is probably dripped upon.

Are you referring to the cement render or is the picture deceiving you to imagine the brick protrudes the sill?

The cement render.

Also the mortar directly under the sill where it meets the wall is often neglected.
Have a look and ensure it is sound.

 

[monkey writer]

You may find the wood is poor in places.
I would use a modern silicone sealant that has a high modulus to allow for any movement and has good adhesion.

Can you recommend a suitable sealant? Also do you know of a good epoxy resin for making the wooden part of the sill good?

 

[Lime]

You may find the wood is poor in places.
I would use a modern silicone sealant that has a high modulus to allow for any movement and has good adhesion.

Can you recommend a suitable sealant? Also do you know of a good epoxy resin for making the wooden part of the sill good?

Not really, any exterior high modulus silicone sealant will do.
As long as a good key is made on the stone sill and applied under the wood continuously from end to end water should be prevented from entering.

Making the wooden sill good is difficult. Often the underside of the wood is badly rotted further in.
I have tried many variations over the years.
Cutting out the rotten section completely and replacing it works best if done properly but it is not easy.
Usually if a hard filler is used after a short time it will break away from the wood and allow water to get in.

On my present house I took the complete window frames out, replaced everything that was suspect and reinstalled them.
It is surprising how little actually holds the frames in!
In most cases it is 3 or 4 large clout nails hammered in at an angle through the wood into the brickwork.
Careful use of a good hacksaw blade (by itself) in between where the plaster and box meet to cut the nails allows removal with little or no disturbance to the room.