Best exterior caulking material for wood sash windows/sills on unlisted 1800's sandstone property?

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Wrongfoot

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The sash windows and sills on the front (S face) of my house are showing largish shrinkage cracks, mostly with the sills shrinking away from the windows. I need to fill them and repaint. They're not original, but a 10-15yr old modern double glazed wood window, reasonable quality, softwood with a modern white paint finish, but no doubt bodged in with silicone and rawlplugs somewhat by the usual "do it in a day window fitters" used to fitting UPVC in a hurry. Everest ripped off the previous owners trading on past glories and providing an ok product at a luxury price.

Can't justify removal and replacement or would prefer not to replace the sills, The wood isn't rotten or fragile yet it's just behaving like a softwood does as it weathers and dries, cracks from 5-10mm between sill trim etc. and few end grain splits to fill before painting too. A a winter with those cracks letting water in will likely damage them so I need to get them maintained.

What filler / caulk would you recommend? Anything I should avoid? Should I shim in some timber strips into the cracks? Hoping for an effective but quick fix as I've a lot on but don't want to be doing it again next year. Hope you all don't mind offering some advice.
 

RobinBHM

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you could use MS polymer -a paintable silcone.

or maybe an acrylic putty like geocell, dry seal MP or alternatively sikaflex EBT
 

gcusick

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+1 for Sikaflex EBT

The other thing to look at is the state of the fixings between sill and frame. Last year, our window cleaner handed me the sill off one of our softwood windows; it “came away in his hand”! No great surprise to find that it had been attached with mild steel brads, which had simply rusted through.
 

Jacob

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Thanks.
I was thinking of that as a tried and tested traditional material, is it fine under modern paints or should I refinish with an oil based gloss?
Gloss is kiss of death. It peels and lets water in behind. It stays in good condition itself though, even when it's fallen off in shiny flakes.
Putty and linseed oil paint as Adam says.
Seems pricy but goes a very long way and is very easy to apply. Brouns & Co Linseed Paint and Oil or google Allback paint
Re your deteriorating cills, I'd give the wood a stiff wire brush down and prime with raw linseed oil, to dry a few days before puttying. They sound a bit doomed though, they might need a proper job doing in a year or so.
 
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Doug71

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I filled a couple of cracks in some external door panels a couple of years ago with some polymer type sealant, the panels couldn't float so came apart at the joint. Think it was Fix All I used as that's my got to sealant/adhesive. Filled the gap well and hasn't opened up again, it seems to stay slightly flexible, it doesn't dry hard like filler so you can't sand it.
 

XTX

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Just to add to Jacob's post, depending on the size and depth of the cracks, you could also fill them with Oakum (hemp impregnated with Stockholm tar), then the putty and linseed paint.

We use Oakum as a crack filler on very old properties, then a lime mortar over the top.
 

Jacob

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Just to add to Jacob's post, depending on the size and depth of the cracks, you could also fill them with Oakum (hemp impregnated with Stockholm tar), then the putty and linseed paint.

We use Oakum as a crack filler on very old properties, then a lime mortar over the top.
Yes another natural material which is amazingly durable in the right application, along with linseed oil and shellac. Linseed paint doesn't last forever but on a severely weathered item the longest lasting bits still in good condition will be over the shellac knotting.
 

johnny

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Epoxy Resin is the go-to wood repair for Architects working on timber conservation projects . Basically its a posh version of car body filla .
I have used Epoxy Resin filler on external wood renovation for over 30 years its a superb solution. You can drill file sand paint repairs and it has a super-fine composition to fill the tiniest of scratches and surface imperfections. How & When To Use An Epoxy Wood Filler - Old House Journal Magazine
 

Doug71

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I sometimes use the epoxy fillers, they are good, initially seem expensive but can save loads of time.

There are different versions with different setting times etc, this is what I use for smaller repairs.


This is the same type of thing but you don't need the special application gun


I'm picturing the traditionalists on here with their heads in their hands saying "Just stick some putty in".
 

Tuna808

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I use Tigerseal for my boats ,it’s a sealant adhesive,can be applied on wet surfaces……..I used it to seal my son’s exterior windows and it done the trick.
I’ve used it to seal joints under the waterline and 20 years later it’s still almost impossible to remove.
 

Jacob

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.........

I'm picturing the traditionalists on here with their heads in their hands saying "Just stick some putty in".
Usually after having tried many of the expensive and hi tec alternatives first, and also after asking themselves why so many trad methods are so incredibly durable. Not unusual to find 100 to 200 year old ordinary joinery in very good condition. It took me some time to discover linseed oil paint and have now more than 10 years of good experience. Have had modern paints peeling after 3 in spite of doing everything "properly" and carefully.
Tip - old putty left in the pot not good for glazing as it tends to be too stiff and lumpy, but it can be softened with a quick blast in a microwave, is ideal for bigger hole filling and can be painted immediately with linseed oil paint.
 
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johnnyb

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I'm a fan of repaircare tbh. it does need to be applied in the correct manner though. so it's a thin epoxy first then a choice of different setting time epoxies. the slowest is often the most effective btw.
hand applied oil based I like sandtex flexigloss or the satin version with owatrol oil added more in the undercoat than the top. even raw owatrol on slightly punky wood
 

johnnyb

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ps that's not to poo poo the traditional approach favoured by Jacob et al. just to say this may be less...finicky.(and much quicker)
 

Adam W.

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Epoxy Resin is the go-to wood repair for Architects working on timber conservation projects . Basically its a posh version of car body filla .
I have used Epoxy Resin filler on external wood renovation for over 30 years its a superb solution. You can drill file sand paint repairs and it has a super-fine composition to fill the tiniest of scratches and surface imperfections. How & When To Use An Epoxy Wood Filler - Old House Journal Magazine
Oh God!..........Architects.

It's got to be the most overrated profession ever.
 

Jacob

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Oh God!..........Architects.

It's got to be the most overrated profession ever.
It is rather! I've met a few who have been sensible enough to take good advice but some not - their training is much too broad for many purposes and until they have specialised for enough years in one area they may not know their Rrs from their elbows.
 

Jacob

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ps that's not to poo poo the traditional approach favoured by Jacob et al. just to say this may be less...finicky.(and much quicker)
Really? Your process sounds much more more finicky and much slower! Not to mention more expensive!
 

johnnyb

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how long does a 20mm putty fill take to set before you can paint? how long does each coat of linseed paint take to set. how long does raw linseed primer coat take to set? how many coats? I've no idea tbh but I recall coley thought it was an intensive process and he didn't start using it despite initial interest.
 

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