Replacing sash window's sill

[theallan]

Hi all,

Looking for a little advice about replacing the sill on a sash window. The sill is rotten and when it rains, water is seeping between it and the side stop (I think that's the right terminology) - then running down behind the lathe and plaster. Attached are a couple of photos of it.

The issue I'm having is that the current sill extends behind the stone surround, so I can't just cut it and slip a new one in. So what I'm thinking is cutting out the old one, making a new one, and this cutting it at 45deg in the middle so I can slide each half in behind the stone - a biscuit joint, or a dowel, plus waterproof glue and oil based paint would then mean that cut wouldn't be any weaker than the joints.

Does that sound like a reasonable plan, or are you all going to throw porridge at me? Taking the sides off completely is beyond my ability I think (that would be time to call someone in who has more experience).

Thanks!
Allan

 

[thetyreman]

I'm no expert but that silicone bead can't help, it may be trapping moisture in and the reason it has rotted, also maintaining the paint is critical to prevent rot, I wonder if it'd be possible to splice in a new piece without having the remove it? depends how bad the rot is.

 

[Trevanion]

I'm not massively well versed in sash restoration as I've always sort of thought of it as a totally pointless exercise beyond a certain point as it suddenly stops being value for money especially if you're paying a "specialist" so I tend to advise people against it once it's beyond a bit of light patching, filler and paint job. That Cill would be very difficult if not impossible to pull off cleanly without pulling the whole window out, to be honest (That probably goes for most sash windows actually). The cill extends probably a good three inches behind the reveal if it's a weight counterbalanced sash and not a spring balance or plain peg, then the pulley stiles are usually trenched an inch deep into the cill, wedged, glued and nailed in place into the cill which makes removal of the cill very awkward in the opening, even more so if you're trying to put a new one on!

I can tell you right away that that mitre joint you're proposing will open with time if you use natural timber, you might get away with it in Accoya but not in anything else.

I'd say if you want to repair it properly you'll have to pull the window out of the opening completely, no point getting someone to do it for you as you may as well opt for a new window in Accoya by that point as it'll be far better value for money and you won't be in the same place in a couple of years when patchwork starts showing up and rot starts again. Like Tyreman said, the run of silicone at the very front edge is a window killer as water will work it's way in around the edges of the window opening and get being the silicone but cannot get out.

 

[owen]

It looks like the sash has some rot too. I'd make a whole new window.

 

[Doug71]

Repaired more sash windows then I care to remember, I try and avoid it these days.

Your method of mitring in a new cill is actually the traditional way of doing it, I haven't done one like that for probably 20 years though and don't plan on doing it again!

For a quick easy fix to get a few more years out of your window I would just chisel* the front off the cill back to the rebate where the bottom sash fits, just behind the parting bead (probably 75mm?). A new piece can then be put in, screwed through it's front in to the remaining back half of the cill (sink and plug the screws, stick on with fix all or similar). You will still need to cut it in using a mitre to do it properly but looks like the front linings are rotten anyway so you could just cut it full length and slide it in under them. It's always tricky when the windows are in from the back because you can't do much with the front linings.

Then a bit of wood hardener, 2 part filler, caulk and paint, window will be good for another few years =D>

* a wood chisel attachment for an SDS drill with rotation stop makes light work of this.

https://www.tooled-up.com/makita-sds-pl ... od/244387/

 

[Mike Jordan]

Windows fitted in reveal like that are normally held in place by folding wedges at the ends of the cill and head and are easy to remove. I suggest you prize off one of the architraves and see, repairing the window on the bench is much easier.
Your first move should be to check if the bottoms of the Pully stiles are rotten, if so the window is scrap I'm afraid.

 

[eezageeza]

You might find this a useful read :

http://www.periodproperty.co.uk/forum/v ... =1&t=16963

 

[theallan]

Wow - thank you everyone! Amazing feedback. Time to do a bit more investigation about the state of the rest of the window then.

I think the wood on the upper and lower sash are okay - but they are definitely in need of being stripped and repainted. Will find out about the state of the pully stiles. Hopefully they are okay... While not a listened building, it is a conservation area, so a whole new window, I believe, would require planning permission (even matching the original style - which is all that they would accept anyway).

Allan

 

[Mike Jordan]

If you fit a new window it has been my policy to hang on to the old one until the conservation officer has inspected the new . Some of the COs think they know all about cased frames when the opposite is the truth.

 

[thomashenry]

I've made a few replacement box sash frames in my time and in each case, I don't know how it would have been possible to properly replace the cill leaving the frame in situ.

If it were me, I'd bite the bullet, remove the whole thing, and made a new sash box up, reusing the non rotten parts of the frame, which will probably be the inner face linings, top rail, and maybe the outer face linings. Normally I find that if the sill is rotten, the bottom of the pulley stiles are too. If not - you are in luck and the job is that much easier again. Can reuse the pulleys too. A sash box is a fairly easy thing to knock up, no fancy joinery required. Don't use any bloody silicone when you drop the new box into place!

I've rarely encountered sashes that need replacing or significant repair - full strip down with heat gun and sand paper, then reglue any loose joints, and you should be good to repaint them and go. The bottom rail on the bottom sash is the only place that ever seems to take a beating, but only once have I needed to replace that.

Contrary to what is posted above, from the picture your sashes look fine to me, just need a bit of TLC.

 

[thomashenry]

Windows fitted in reveal like that are normally held in place by folding wedges at the ends of the cill and head and are easy to remove. I suggest you prize off one of the architraves and see, repairing the window on the bench is much easier.
Your first move should be to check if the bottoms of the Pully stiles are rotten, if so the window is scrap I'm afraid.

Can still re-use the inner linings, top stile etc, when making up a replacement sash box.

 

[Mike Jordan]

I don't think it's an economic move to totally dismantle the window to salvage the inner linings. A new window is quicker and obviously better. Likewise grafting pieces into the Pully stiles is not a sensible repair, just a bodge.

 

[thomashenry]

I don't think it's an economic move to totally dismantle the window to salvage the inner linings. A new window is quicker and obviously better. Likewise grafting pieces into the Pully stiles is not a sensible repair, just a bodge.

Takes all of 30 mins to take the box frame out and dismantle. I see no reason to not re-use the good parts, what's the point in milling new wood to the same size when you already have exactly the parts you need.

"Obviosuly better" - why?

 

[Mike Jordan]

If you can strip the window down and remove the nails without damage, it's still covered in paint and nail holes. There is no premium or pleasure in using old timber.
Most box frames are made of pine, even the unsorted grade is cheap to buy and nicer to work.

 

[thomashenry]

If you can strip the window down and remove the nails without damage, it's still covered in paint and nail holes. There is no premium or pleasure in using old timber.
Most box frames are made of pine, even the unsorted grade is cheap to buy and nicer to work.

All my sash windows are stripped and unpainted internally, the old pine linings look lovely. I suppose that's subjective though. For me without any power tools though, what's not subjective is that it's much easier and cheaper to use existing timber that's exactly the right size, than it is to get hold of nice pieces in the awkard size that the linings are.

For me there is definitely a premium and pleasure in using old timber, but this is personal preference.

 

[theallan]

> Don't use any bloody silicone when you drop the new box into place

Haha. The number of things in this house which I've found that were fixed with silicone... Slates, carpet, and of course the windows. Previous owner must have had a great time "fixing" stuff.

 

[bohngy]

I had a go at this last summer. On my own place, before anyone accuses me of being a cowboy!

• 
  - I cut out the old sill and the lower faces of the interior the sash box.
  - Then made a replacement sill and slid (hammered) it into place, from the inside of the room.
  - I made sure the 'wings' of the sill were the correct thickness to ensure the sash box wouldn't sag down.
  
  
  
  - I then cut blocks that I dropped down the inside of the sash pockets and glued them into place. This tightened up the existing parts of the sash box against the cheeks of the sill. From drawings ive seen, the parts of the sash box that sit on the sill go in a rebate and a groove, so the blocks allowed me to maintain a 'correct' profile/joinery for the sill, once everything had beed glued together
  
  

I certainly wouldn't advocate taking the window out... well, not in my place. The brickwork is so shonky that I don't think it would take the trauma of window removal!