type of sealant used for exterior of uPVC windows

13 Dec 2006
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United Kingdom
Can anyone help me in the selection of the right sealant to reseal my uPVC windows ?
The wind has caused movment and there is a crack between the frame and the concrete cill and surrounds around the frame

Looking on line at the main suppliers there is a wide range of types of silicone available and selecting the right one is difficult.
Do I need to use a silicone remover to remove the old silicone ? -- if so how do you clean this off before applying the new sealant ?

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If silicone was originally used, it won’t (can’t) crack! It’s probably mastic sealer which has age hardened as this was more commonly used in the past. I doubt if the wind has caused the sealer to crack; either you either live in an extremely exposed location or the window frame is loose!

Remove/cut/rake out as much of the old sealer as you can - a white spirit cleaner will work on mastic but not silicone. Clean the UPVC frame with UPVC cleaner (don’t use oil based white spirit) before applying a new bead of trade, low modulus silicone frame sealer.
Thanks for that reply.

I think that it must have been mastic that has cracked and it will have been not helped by the wind as the gales here in the Outer hebrides are quite something!!

I will check-when this current gale abates-- for the window being loose as when the wind is over 80mph in a certain direction the windows flex slightly and I think that this (and the combination of the old mastick --20 years ) may be the problem !!

As to the uPVC cleaner can I use acetone ? or will it deplasticise the uPVC?
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thevancanman said:
and it will have been not helped by the wind as the gales here in the Outer hebrides are quite something!!
OK, I guess that would qualify as an extremely exposed area!

Acetone should be OK to clean the UPVC try it on a small bit first; it's only to remove any traces of grease so the silicone will key properly.

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