Whether it is polyfila or fire cement or any other form of cement it is important to keep the air out when storing it.
The problem I find is that the various manufacturers often supply a silly piece of plastic that is slightly smaller in diameter than the inside of the plastic tub and so the material around the outer edge goes dry and this gradually works it’s way into the core.
What I have found to work really well is a plastic food bag.
Just push the bag onto the top of the filler and as it is a bag you can work it into the edges.
You can then just fold the rest of the bag into the pot and put the lid on.
Just remember to lift an edge of the lid, push into the centre of the lid and then reseal the edge. This will remove some of the air from the tub and put the tub under a slight depression that will help keep the seal for longer.
When you want to use the material again it is a simple case of removing the lid and plastic bag – and whilst the bag is out you can turn it inside out and so stop the material stuck to it from drying out quite so quickly. Also, this stops the material stuck to the bag going everywhere.
This is a really simple idea, but must admit that the pollyfilla that has sat in the shed for 3 months between use has kept in a remarkably good condition and was as fresh as new when I opened it yesterday.
Obviously, you do need to stick to the manufacturers recommendations with regards to temperature and light conditions for storage.