Sealant or mastic?

[Bert Coules]

The various online guides to installing uPVC windows all recommend sealing the interior edges with silicone sealant and the exterior with frame mastic. But is there any reason why I can't use a weatherproof silicone for the outside? I don't in the least mind getting mastic if it's essential, but is it? I have to confess that I don't know the essential differences between mastic and sealant.

I've installed a uPVC window into a wooden frame set into the side of my sectional concrete garage. The exterior seal will be between the uPVC and the timber, with a second bead between the timber and the concrete.

Many thanks.

Bert

[Dave Plowman (News)]

I *think* the main difference is a sealant sets, a mastic not.

I've used exterior silicone round my windows successfully. I'm not sure a non setting stuff would be ideal if you could rub up against it. ;-)

[Bert Coules]

I was looking at a tube of Evo-Stik Frame Mastic in Wickes today: there's nothing on the label about a setting or curing time, but it does say "forms a tough, flexible, weatherproof seal". So maybe it hardens, maybe not...

That's handy to know. Thanks.

Bert