Which Filling Product to use for Filling Top of Skirting? Fillers, sealants and adhesives for all types of DIY work. Help, advice and information on all aspects of this subject

[Bronk]

After some new pipework being fitted in bathroom the boxed in area behind skirting has had to be extended. It's not a very neat job! Resulting in where the vertical boarding of the boxing in sits a few mm higher than the horizontal batons (hard to explain!) So this area needs some sort of filling before it's painted. The area is approx 2m long and 8cm wide and approx 3mm deep. Any advice as to what the best filler/product would be for such an area? Thanks

[alfie_j]

I was going to suggest decorators caulk but at 8cm wide it might need to be replastered.
A photograph would be helpful though.