Decent Caulk for Windows

[LennyM1984]

The interior caulking on our windows keeps cracking and so I was after some recommendations for a decent flexible caulk.

The windows (UPVC) don't have any trims and so the caulking is going between the wooden window sill and the frame edge. I'm guessing that any change in humidity/temperature is causing enough movement for little cracks to occur

[Simpo Two]

Silicone is more flexible than caulk.

[OutInTheShed]

Silicone is stretchy.

Sealants like polyurethane are strong.

The general thing with sealants is they can only stretch so far, if there is 1mm of movement, a 2mm fillet of low modulus silicone might survive that, but you want a thicker fillet of e.g. polyurethane to to cope with the same amount of movement. Often the cure is to open out the gap then put a decent width of sealant in.
Or reduce the movement somehow.
Ideally the sealant should be under pressure not tension.
Wait till the weather opens the gap, then whack the sealant in?

Or reduce the movement!

[Lotobear]

Simpo Two said:

Silicone is more flexible than caulk.

True but the problem is that silicone cannot be overpainted

[LennyM1984]

Turns out that Siliconised Acrylic Caulk is what I needed. 12.5% stretch but still over-paintable. Will see how it performs.

[darreni]

Have a look at CT1, that can be overpainted.

https://www.ct1.com/products/ct1/

[dhutch]

LennyM1984 said:

Will see how it performs.

Let us know.

[119]

We had this issue on one of our old houses and gave up in the end and fitted some narrow trims around the window which were siliconed on and that seems to allow a bit more movement and never cracked again.

Not ideal but never had a problem after that!

[wolfracesonic]

Whatever you use, check what type of paint you can use on them, CT1 is water based only I think, not sure about the siliconised stuff.