Sash Window Mastic

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mac72
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Sash Window Mastic

Post by mac72 » Sat Apr 20, 2019 2:52 pm

Hi,

I recently got a company to overhaul my sash and case windows (strip off paintwork and replace rotten parts).

Unfortunately the sand mastic between the sash case and the outer stonework has cracked (see attached pic)

I am not a joiner (unfortunately!) but do do DIY. I am going to try to redo the mastic.

Can someone advise the best way to re-point the mastic so it does not crack again.

Many thanks
Mac
Cracked Mastic.JPG

thatsnotafestool
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Re: Sash Window Mastic

Post by thatsnotafestool » Sun Apr 21, 2019 8:04 am

Hi Mac

Are you sure that that is mastic ? It looks more like cement (or similar) to me. Is your property a period one ? Take a look at using burnt sand mastic..that's the traditional approach.

http://knowledge.masonsmortar.co.uk/kno ... and-mastic
The advantage of a bad memory is that one enjoys several times the same good things for the first time.
Friedrich Nietzsche

mac72
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Re: Sash Window Mastic

Post by mac72 » Sun Apr 21, 2019 1:21 pm

Thanks for the reply.

It is definitely sand mastic (I can scoop it out with a trowell). But the photo looks like cement so I see why you say that.

Not sure if it is burnt sand mastic. The joiners filled the gap between with window and stone with expanding foam them sealed with sand mastic.

Is there a technique to use to stop it cracking?

Thanks
Mac

mac72
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Re: Sash Window Mastic

Post by mac72 » Sun Apr 21, 2019 1:22 pm

My property is Grade A listed building within World Heritage Zone (built in 1800 and in Edinburgh 'New' Town).

thatsnotafestool
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Re: Sash Window Mastic

Post by thatsnotafestool » Sun Apr 21, 2019 3:38 pm

mac72 wrote:....The joiners filled the gap between with window and stone with expanding foam...
Thanks
Mac

That's probably why...bloody Philistines. They should have bedded in with lime mortar set back 5mm or so, let it dry and then dded the burnt sand mastic. You do need the proper sand IME...they probably got some in from Jewson's if they used foam ! I can't get up there easily but I know that the BSM I put in two years ago on a South facing side has not cracked.

Bad luck being listed ! We're about 70 miles due South of you, house originally built in 1750, Sir Walter Scott stayed there as did Rabbie but the listing people missed us :D So we can do what the hell we like !
The advantage of a bad memory is that one enjoys several times the same good things for the first time.
Friedrich Nietzsche

Meccarroll
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Re: Sash Window Mastic

Post by Meccarroll » Sun Apr 21, 2019 5:35 pm

thatsnotafestool wrote: but the listing people missed us :D So we can do what the hell we like !
Until now that is :lol:

mac72
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Re: Sash Window Mastic

Post by mac72 » Mon Apr 22, 2019 1:25 pm

Thanks again. Very useful advice.

Sounds like your home has quite a history....Rabbie and Walter Scott!!!

Cheers
Mac

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