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Gap between exterior sill and window

Discussion in 'Windows and Doors' started by ColinHardie, 2 Jul 2009.

  1. ColinHardie


    5 Feb 2009
    Thanks Received:
    West Lothian
    United Kingdom
    I am about to embark on fitting some exterior sills to my newly built, as yet unfinished extension. The UPVC windows have been fitted but the gap left at the bottom for the sill to be place is about a brick high. This sills that I have bought are quite low profile (in keeping with the existing house).

    My question is that when I mortar these into position there will still be an inch or so gap between the sill and the underside of the window. My thoughts in order to minimize this gap was to build up the mortar a little upon which the sill sits, fill in the aforementioned gap with expanding foam (to provide something for the sealant to adhere to) and the seal it using some exterior mastic.

    Can anyone see a problem with this and if so provide an alternative solution? Someone I spoke to mentioned filling the gap with sand mastic but I was not sure.

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