We have a problem with loads of slugs and occasional rats coming in under our kitchen cupboards. Removed the kickboard to investigate and it's a bit of a mess with a large gap beneath the plaster and floor, so this must be where pests are coming in. Wondering how best to fill the gap. Was going to put boards across, but plaster is too lumpy so boards won't sit flat against the wall. Would expanding foam be suitable? Any advice appreciated. Many thanks