External and internal window frame caulks - cheap but durable?

For internal, caulk is cheaper and paintable

for external, a low modulus/neutral cure silicone is good

I only use silicone these day for serious underwater all the time seals.

Acrylic is better in every way except ultimate water resistance

Thanks. I wondered about that, but then I thought: Is there any point in paying extra to have a seal that's more waterproof than the surrounding masonry...

I do find it much nicer to work with - mainly because it's water soluble (until it cures, that is).

Al

Thanks. Would that include the stuff commonly called "flexible decorators' filler" sold for use in caulk guns - that can be got in 99p stores?

Al

yes

exterior grade is better though for outside. I think it has other stuff in it.

paying extra to have a seal that's more waterproof than the surrounding mas onry...

That might apply if you have paper masonry units.

Silicone's only £2 a tube.

NT

available in the UK.

but there are cheaper exterior frame caulks available these days. What I already have here is some tubes of Everbuild External Frame Sealant, an acrylic-based sealant, which I hope is suitable for the exterior (like the name suggests)- and some '151' Flexible Filler which I hope will be okay for the internal caulking. Can anyone recommend (or condemn) these products, before I commit? I'd like to avoid having to redo the job (in the near future at least).

You need Low Modulus Neutral cure.

It costs twice as much as the stuff that stinks of vinegar but being low modulus it will accomodate a high degree of movement without failing. UPVC, especially gutters and long trim sections expand and contract as much as metal does. It also seems to stick better than the cheaper stuff.

Unless your gunning technique is spot on, use masking tape and a tool to smooth and shape it (not fingers).

Use Oil based mastic for timber frames.

You won't get Low Modulus Neutral cure for that price, unless you are a trade buyer, buying quantity.

More like £3 to £4 in most places.