I have inherited a very old 5l tin of Evode rubberised bituminous waterproofer that's the consistency of very thick treacle. It must be at least 25 years old, I should think. If I can add a little somethingto it to thin it down to a workable consistency, it would save me having to ditch it and buy new. But what should I add? It says 'clean brushes with water', suggesting an emulsion, but I thought these things were bitumen solutions in an organic solvent. So should I use water or something like white spirit or petrol to thin it down?