Straight Butt joints will only work if you have square edged worktops, if they come with a slight chamfer or roundover (such as Ikea) then you will have to use a shallow masons mitre. Basically the female part of the cut only needs to be deep enough to remove the edge moulding.
Also remember to use slotted brackets to hold the worktop down to the carcases to allow for movement across their width. And apply your chosen finish to the underside before fixing to avoid unbalanced moisture take-up or release.
And to be super safe you should use food safe silicon as the mould inhibitors in some of the silicons can be harmful, but you would need to eat a lot of it :wink:
Jason
