Alternative to putty for metal windows

30 Aug 2012
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United Kingdom
I am in the process of refurbishing the first of many metal windows in my house. I'm using this first one as a kind of experiment to find the best way of going about it. So far I've:
  • Removed the casement/opener.
  • Had it dipped to remove the paint.
  • Primed it with Rustoleum 1085 Hard Hat Galva Zinc Cold Galvanising paint.
  • Read that the top coat should be a "non-saponifiable coating". Ignored that, because apparently nobody knows what non-saponifiable means, and plan to overcoat it with a bog-standard external satin white for wood & metal (I've painted one of the edges, and it doesn't go on very nicely, but I'm hoping a couple of coats will do the job).
I need to replace some of the putty, and wondered if using a 2-part wood filler would do the job? I assume it'd be stronger than putty, and I wouldn't have to wait a week+ for it to cure before painting. Is that a crazy idea? Or should I just get some proper putty for metal windows like this: and be more patient before painting? That putty claims to last for 10 years, which doesn't seem very long. I assume a 2-part filler (eg. that Ronseal stuff) would last longer?

I was tempted to use some Owatrol oil ( and keep the unpainted rusty steampunk look, but it wouldn't be in keeping with the style of the house. I'm keeping the brassy bit unpainted though - I think it's gorgeous!

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the top coat should be a "non-saponifiable coating". Ignored that, because apparently nobody knows what non-saponifiable means

A-level chemistry taught me that saponification is the formation of soaps by reacting oils/fats (strictly, fatty acids) with alkalis.

The wikipedia page for saponification ( ) describes a problem with oil paintings where the oil saponifies. I’ve not heard of this in connection with non-artistic paints.

Based again on my recollection of 30-year-old chemistry lessons plus a bit of wikipedia, an oil paint that is a solution of an unreactive pigment in a mineral oil (i.e. a white spirit like solvent) will be unsaponifiable. A paint made from a vegetable oil (linseed oil, for example) will be sapnifiable, to some extent. A water-based paint will not be saponifiable.

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