no

As far as I've been able to gather, Polyfilla is mostly cellulose and has relatively poor water resistance. You could try protecting it with a polyurethane or acrylic varnish, but I can't make any promises about how well it would work.

Polymer clay is highly water-resistant after curing in an oven. Epoxy putty cures at room temperature and will withstand pretty much anything.

>>2909
I kept some dried polymer clay in water or possibly oil for a few years and it swelled up, went soft, fell apart.

There is an exterior grade of polyfilla that might be worth a try. Waterproof, think its based on cement, or cement+resin.

>>2910

Properly cured polymer clay is basically PVC, which has excellent water resistance but relatively poor resistance to oils. In the uncured or partially-cured state there'll be a lot of filler material and unbound plasticisers that aren't necessarily stable in water.

Thanks lads. I've double checked and my generic brand stuff is actually "plastic putty". It came with a hardening agent and the label claims it's water resistant. It's also hardened like rock, so I'm happy enough.

I'll let you all know if it melts in about two years time.

OP here an update: the plastic putty absolutely did not withstand exposure to regular warm water, and despite hardening like a rock, softened and came away in bits.

I've now been arsed to go to the shop and buy a proper waterproof glue and a caulking gun.

Lesson learned, don't be lazy when it comes to water and heat tolerance.