Wooden cill replacement onto stone cill

[flicg]

Hi there, I've got some technical questions around installation of a new cill. I've done 2 before, but think I could improve.
Very grateful for any answers to any of my questions
Pics / detail / questions here :

Replacement ground floor south facing cill · Monday, Sep 29 📸

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[Cubist]

I've been trying to get a clear understanding of the problems and challenges you are facing whilst also trying to grasp how your ideas in terms of the remediation would work would/could be implemented. Before going any further there are a couple members here who have direct and good experience of similar challenges (@Feltwell and @fernicarry) but I don't think I would be stealing any of their thunder if I were to say; -

• The holes you've found beneath the old cill/sash rail serve no useful purpose. In fact they are a direct threat to both the frame and the interior walls insofar that they are direct route that can and will be exploited by driven rain.
• Your original window frame was constructed of pine, possibly pitch pine, but it's hard to be absolutely sure of that. What is not a good idea, in my opinion, is to mix different wood species and classes in a single construction. Each of the woods will behave differently during the annual expansion and contraction cycles and there is a risk that differential movement will pull them apart - particularly if any joints are not very tight and sealed against water penetration. You would be wise to think in terms of using a readily available redwood pine window cill moulding of a suitable design and dimensions.
• Regardless you will need to ensure the rear face of the frame to which the new moulding would be mated is a clean and smooth as possible. That will be exceptionally difficult to do in situ so you would be wise to re-think how the new cill would be fixed to the extant frame and how any irregularities in the mating surfaces could be overcome whilst ensuring a watertight joint.
  • Hidden cabinet/furniture screws would be with considering as these would allow you to pull the new and old timbers together in a controlled manner.
  • In terms of the mating faces of the new and old timbers you could consider the use of PlumbersMait (a none setting putty) applied to both faces of old and new timber before they are pulled together and compressing the putty with the screws. Any excess can be cleaned off and the joint painted after a few days.
• When preparing the new, and old timber for that matter, make sure to thoroughly treat the end-grains of the timbers and seal all joints between the old and new timbers with PlumbersMait as discussed above.
• After fitting the new cill you should also consider how to best fill and close any remains gaps around the masonry and render where this closed to the frame originally.

Enough for now. Hopefully one of the guys I've mentioned will be along to offer some better advice.

 

[Cubist]

An afterthought. Be careful about using ordinary glaziers putty around that frame. As it dries it will become brittle and any movement resulting from expansion and contraction of the wood, will push it out.

 

[fernicarry]

You've taken a very different approach to how I've done it so this may not be a great deal of use to you.

When I've replaced cills I've replaced the whole thing as one piece. As @Cubist says a join will be a weak spot that's likely to open up again due to seasonal movement or continuing decay of the older piece. It looks like your horizontal join is still on the "outside" part of the cill so water that gets forced up between it and the bottom sash will find its way into any imperfections. The downside to replacing the whole thing is that you may damage the internal joinery especially the window board removing the old cill. I now cut a groove on the inside face of the cill to take a tongue on the back of the window board so that it gets mechanical support without needing any permanent fixings and the cill can in theory be removed without wrecking the window board.

You can get correct profile cill sections from ETP. I believe they have started doing sash sections in meranti if that's what you want. In the great scheme of things meranti isn't particularly durable as my storm doors will attest to. Its about the same as a durable soft wood like larch or douglas so a bit better than redwood but no where near as good as other hardwoods. Hard and soft is a biological distinction (flowering and non-flowering trees) not a absolute measure of durability.

The pulley stiles should be rebated into the cill. The cill itself extends one or two inches beyond the stile into the bottom of the weight pocket. The stiles will need to be cut back to do the repair in situ but as they usually need attention themselves this isn't a problem. This resulting join is a lot less vulnerable than if you butt the cill up against the stile and you don't need your protection pieces. Bonus points if you stop the groove for the parting bead in your pulley stile repair section at or just above the top face of the cill rather than running it all the way down into the rebate.

I usually pack the new cill up on plastic spacers or wooden wedges to get it at the right height and degree of levelness so that the meeting rails line up perfectly. You'll notice if the meeting rails aren't right but you are unlikely to notice that the cill isn't level. Recently I've been putting a strip of expanding foam tape (not can or gun foam) along the bottom of the cill towards the front edge before finally sitting it into position. This should on its own provide a permanently weather tight seal. I also use a gun mastic (Soudal 215LM) along the front edge and then burnt sand mastic. I've also been known to pack the underside of the cill with lime mortar from the inside. Can't have enough layers of protection IMO.

Here's one I made earlier... (pictures are probably of a dry assembly as I always paint the inaccessible bits before final assembly)

 

[flicg]

Thanks for your time and the other member tags. I have updated the project text in my link as things evolve.

The holes you've found beneath the old cill/sash rail serve no useful purpose. In fact they are a direct threat to both the frame and the interior walls insofar that they are direct route that can and will be exploited by driven rain.

Well, the cill will be sealed all round but I am inclined to agree with you. Any thoughts on what to use? Would you pack the empty ends of the frames sides with the same thing or not?

• Your original window frame was constructed of pine, possibly pitch pine, but it's hard to be absolutely sure of that. What is not a good idea, in my opinion, is to mix different wood species and classes in a single construction. Each of the woods will behave differently during the annual expansion and contraction cycles and there is a risk that differential movement will pull them apart - particularly if any joints are not very tight and sealed against water penetration. You would be wise to think in terms of using a readily available redwood pine window cill moulding of a suitable design and dimensions.

Points taken. We've got meranti today for better or worse but I'll bear this mind for the future.

• Regardless you will need to ensure the rear face of the frame to which the new moulding would be mated is a clean and smooth as possible. That will be exceptionally difficult to do in situ so you would be wise to re-think how the new cill would be fixed to the extant frame and how any irregularities in the mating surfaces could be overcome whilst ensuring a watertight joint.
  • Hidden cabinet/furniture screws would be with considering as these would allow you to pull the new and old timbers together in a controlled manner.
  • In terms of the mating faces of the new and old timbers you could consider the use of PlumbersMait (a none setting putty) applied to both faces of old and new timber before they are pulled together and compressing the putty with the screws. Any excess can be cleaned off and the joint painted after a few days.

Yes, I'm glad you've weighted this key issue. Currently leaning towards a polymer adhesive designed for wood to do most of that work. Like the idea of the internal screws. Thanks for that. Better than headless nails.

• When preparing the new, and old timber for that matter, make sure to thoroughly treat the end-grains of the timbers

Indeed.
Thank you

 

[flicg]

An afterthought. Be careful about using ordinary glaziers putty around that frame. As it dries it will become brittle and any movement resulting from expansion and contraction of the wood, will push it out.

Yes, probably not going with that now but still not sure what to do there.

 

[flicg]

When I've replaced cills I've replaced the whole thing as one piece.

Hi and thanks for your time / ideas. Yes, not sure our skills extend to that.

You can get correct profile cill sections from ETP. I believe they have started doing sash sections in meranti if that's what you want. In the great scheme of things meranti isn't particularly durable as my storm doors will attest to. Its about the same as a durable soft wood like larch or douglas so a bit better than redwood but no where near as good as other hardwoods. Hard and soft is a biological distinction (flowering and non-flowering trees) not a absolute measure of durability.

Meranti's what we've got today. We were pointed to MGM and that's what they had and this is quite urgent as to be away shortly. But I will bear in mind your points for the future.

I will have to come back to you on the other points as there are terms I don't know and I will have to look them up. I am not a proper DIY-er and all of the DIY I do with my friend is in Spanish so I only know the names for tools in both languages, not the design or structure-related stuff! For that I normally just point!