Gap between sill and PVC window

Is this a horizontal gap?

When just filling (rather than bonding) I've used 'Decorators filler' because it can be wiped with a damp cloth.

Me too, unless running a bead the entire length etc.

Because uPVC moves all over the place then unless you are sticking two bits together permanently then you might be better off with something that maintains some flexibility?

Some in-laws had two bay windows fitted and log short, they made a pigs ear of it.

The inner sills were just stood on towers of packing pieces and siliconed in place. So remedial silicone was ever going to fix that so I ripped it all out, built inner and outer wall back up to the right height and reset the sill back on solidly.

The issue was first discovered when they tried to place a pot plant on there and it sunk 1/2"! ;-(

Cheers, T i m

decorators caulk.

Sort of very thick PVA glue.

Decorator's caulk. Sticks well to most materials. Remains slightly flexible so shouldn't crack. Note it shrinks, so you may need several applications to get it perfect.

screwfix Everbuild Window & Door Frame Sealant 300ml White code 26507

Weatherproof, durable and flexible acrylic sealant. Suitable for filling joints around aluminium, PVCu and wooden windows. Suits internal and external projects. Can be over painted with most emulsion and oil based paints. Virtually odour free and not corrosive on metal. Fully weatherproof when cured, this time is extended in cold conditions.

Yes lots of horror stories about cowboy contractors. A friend went on holiday leaving the neighbour to look after the workmen doing a bay window replacement. Looked fantastic for a month, then the little roof over the bay started to let water in and on inspection, yes the dreaded bodge job of if its not going to fit pack it, ie don't try to make sure the top is supported properly etc, Took a year to get it sorted out with insurance, warranties not worth the paper they were printed on and small claims etc. Nightmare. Brian

Caulk discolours over time IME. I'd use an acrylic sealant, which should deliver flexibility and a stay white finish. Then again, a high modulus silicone would seem to be the perfect solution

AKA 'decorators caulk'..

It's interior use only.

You weren't sure if it could be used ouside. But perhaps you don't actually understand what you write.

the fact is some 'decorators caulk' does not work well outside, the frame sealent i linked too does Nememis 'decorators caulk' from screwfix Hi teiboy, The manufacturer has advised the following: 'As this is a water based product we do not recommend it for external use.' Thanks for using Screwfix Q&A.

Since there is already a product available for outside use, why would anyone use one that says interior only?

Excepting those on here who never do any DIY, obviously.

JOOI, isn't this job an *inside* one though?

Cheers, T i m

So is external acrylic frame sealant a 'water based product'

Its just *more expensive*

which is why amateruts buy it while the pros use decorators caulk