Sash Window Sill Repair

[jungle_jim01]

So i'm in the middle of repairing my wooden sash window and i've noticed that the sill is shorter than it should be. Obviously at some point the ends have rotted, the ends have been chopped and the space filled with cement. I've managed to remove the cement but i'm wondering how to proceed. I'm considering using wood blocks to match into the ends as the rest of the sill is relatively ok. However i was just wondering about replacing the sill...does anyone know where i could source one?

Also the sill has a fillet of cement underneath which fills the gap between the wood sill and the stone. With a small amount of force, the wood moves slightly clear of the fillet. Should i remove the fillet or is there something i can use to seal between it and the window. Does anyone know how the original sill would have been bedded in? lime mortar?

Thanks for everyone's advice

 

[jungle_jim01]

should the fillet underneath the sill be 'burnt sand mastic'?

 

[jungle_jim01]

The sill's popped out nice and easy (wasn't stuck at all) so i'm thinking about a full replacement but not too sure what to do about the cement fillet underneath. Should i chisel it out and replace with burnt sand mastic? or leave in and just try and seal around the sill? It's about 15mm thick so quite a chunk.

 

[jungle_jim01]

The sill's popped out nice and easy (wasn't stuck at all) so i'm thinking about a full replacement but not too sure what to do about the cement fillet underneath. Should i chisel it out and replace with burnt sand mastic? or leave in and just try and seal around the sill? It's about 15mm thick so quite a chunk.

 

[Hudson]

I'd of gone for cement removal followed by the burnt sand mastic filler only a 15mm gap maybe too big as you say. Therefore I'd probably be tempted to leave the cement in place so long as it's even and flush with the frame.

 

[Feltwell]

15mm is a bit big for mastic - it needs filling with mortar first, then the line between the mortar and cill sealing with mastic.

Ideally lime mortar, but I doubt your cement is doing any harm there so I'd be inclined to leave it alone if it's sound and well stuck.

Burnt sand mastic is dead easy to make up - don't bother with posh mixes. I use cheap B&Q boiled linseed oil and kiln-dried paving sand from the local builder's merchant. Mix it up until it looks about right (sticky but not runny), put it on a with a "leaf and trowel" (sometimes called a plasterer's small tool - make up your own jokes!) - and then don't worry when 2 weeks later it still hasn't set. It will, it just takes time.

 

[Hudson]

cheers feltwell, I'm doing this at the moment and wasn't sure if I had the mix right or if the stuff was ever going to dry. I had to pad the vertical voids out with newspaper too so the filler had something to sit against and didn't keep collapsing in on it's self. Do you think it's ok to do this?
thanks.

 

[Feltwell]

cheers feltwell, I'm doing this at the moment and wasn't sure if I had the mix right or if the stuff was ever going to dry. I had to pad the vertical voids out with newspaper too so the filler had something to sit against and didn't keep collapsing in on it's self. Do you think it's ok to do this?
thanks.

I'd say fill large gaps with mortar. If they're really big then pack them out with some slate or bits of roofing tile or whatever you have that's handy, then point with mortar over the top.

Only my opinion though!

 

[jungle_jim01]

thanks for the replies. been a long week and i'm still a bit confused about how this should all fit together. should the sill be loose from the rest of the window or is there some way it fixes with the frame? if it's loose then i think i'll chip away a little of the cement, sit the sill on the remaining cement ledge then seal in with burnt sand mastic...but a little puzzled about how to make it stick...whats to stop the sill from coming loose?...i must be missing something obvious.

 

[jungle_jim01]

The more i read online the more confused i get...my window doesn't quite look like other's i've seen. Here's a photo for folks to ponder over?? any thoughts would be appreciated. cheers

 

[Feltwell]

Most (and note most, not necessarily all!) box sashes are built in such a way that the only way to replace the cill is to remove the whole sash box from the wall - not as bad as it sounds, although you'd probably need to do some making good on the plaster inside the room.

In your case the ends of the cill where it joins on to the sides of the sash box have rotted away. Machining up a new cill is not a big job, any decent joinery company should be able to do this for you if given a pattern to work to.

Only you can decide if you think it's worth taking the whole box out of the wall. If you do, then if your woodwork skills aren't great you could give the whole thing to a joinery company to repair and if necessary splice new sections into the bottoms of the boxes, so that a new cill can be properly attached. This will be the best and most long lasting repair, especially if you replace all the rotten bits with hardwood.

The other option is to take out what's left of your cill and the cement mortar out, put a new cill in and accept that some filling against the sash box will be needed and that you may have to repair again in a few years. As to how you fix the cill in - you won't be doing it as originally intended, so any method that will hold it secure. Could you cut some grooves in the top of the cill and the bottom sides of the sash box and use some L shaped metal brackets, then fill over them to hide them?

Edit - just seen your picture, yes that is a bit odd. What are your other windows like? It's difficult to see from your picture, when the bottom sash slides down does it sit in front of the bit marked "window frame"? If so it looks like whole thing has rotted away in years gone by and someone has done a bodge repair. If so I'd be tempted to take whole box out, remove the cement fillet, and get a joinery company to make and splice in a new wooden cill.

 

[Penners]

Jim - like Feltwell I'm having trouble understanding from your photo how your sash window is constructed. Could you possibly post another photo showing the same detail, but with the window closed? And just pull the camera back a little so we can see more of the general construction principles.

By the way, I sincerely hope you'll make the bed neatly before you take the next picture!

:wink:

 

[jungle_jim01]

:lol:

Thanks for the detailed replies...i've actually removed the sliding sash windows to strip and paint. The bottom one sits just behind where i've labelled the frame. I agree it would appear to botch job. First off i looked at the other windows in the house...the sills are very different to this one. Luckily my girlfriend is pretty handy with woodwork so she's doing the joinery etc but i'm just a tad nervous about removing the frame!! :?

 

[jungle_jim01]

Just been and had a closer look again with the window...wish i took a photo before i removed the window! I think the bottom (inner) window sits flush on top of the wood. I'll upload some photos later (once i've made the bed!)

 

[Feltwell]

Edit - just seen your picture, yes that is a bit odd. What are your other windows like? It's difficult to see from your picture, when the bottom sash slides down does it sit in front of the bit marked "window frame"? If so it looks like whole thing has rotted away in years gone by and someone has done a bodge repair. If so I'd be tempted to take whole box out, remove the cement fillet, and get a joinery company to make and splice in a new wooden cill.

Having a blonde moment

The top sash sits on the outside, not the bottom one.

So - the question should have been - if you pulled the top (when closed) outer sash all the way down to the bottom, does it sit in front of the bit marked "window frame"?

As Penners says, more pictures taken a little further back would help.

 

[jungle_jim01]

Currently working on the top window so can't check where it fits in yet but here's a couple of shots of the bottom window, which sits ontop of the frame. You can see the cement a bit more clearly here. (also featuring Sarah...a tad camera shy!...but doing a great job on the woodwork) I'm thinking of leaving the cement in and shaping a larger piece or wood to fit onto it for the sill. I'm thinking of shaping something to extend over the cement so that the sill is almost flush wit the stone in front of the cement. Should at least look ok and do the job for a few years i hope.

 

[Feltwell]

It looks like the bottom of the sash boxes on the sides have rotted out, as has the front part of the cill. Someone's just chopped the rotten front half off the cill in-situ, leaving the back half behind.

How to repair is totally up to you. Longest-lasting repair would be to remove the whole box sash, splice in new timber on the sides and fit a complete new cill, but I realise that can seem a bit daunting. Ultimately whatever you do is likely to be a marked improvement on how it is now and at least sort it for a few years.

 

[Feltwell]

Are you going to draught-proof the window while you're at it? Well worth doing - makes the window slide a lot more smoothly as well I've found. I replaced the staff and parting beads with ones with brush pile strips built in, and routed a groove in the meeting rail for another brush pile carrier (there are other ways of doing it as well).

I've used Reddiseals products myself, the other main supplier is Mightons who others on here have used to good effect. Search the forum, there are lots of old posts on this.

 

[Delta]

I may be missing the point... but looking at the pictures the sash boxes, or rather the area underneath the current wood, where I think they should extend to, is actually below the sill. In my (limited) experience, the sill has slots cut in, like open ended mortices, that the vertical box lining slots in to. Certainly with mine the sill extends under the boxes, the full width of the aperture. From the pictures, it is almost as though the cement in the middle, that sits prod of the stone(?) cill is a later fudge, otherwise why do the boxes (when repaired) go down below it?

 

[worms]

I may be missing the point...

Me too! I have no sash windows, so really shouldn't comment, but in the pictures, the bottom sash seems so far forward that it looks as if it is running in the top sash slot. If you imagine it being a couple of inches back, then the lower sill doesn't look quite so bad.