Whether a sealant is required depends on the base, if it is very smooth around the perimeter and to the footprint it is not generally necessary.
If the base is slightly rougher then with the DPC and wooden foundation beams it tend to compress and form a good seal naturally.
The composite beams have less give and do not compress, therefore is the base is bumpy a sealant may well be an idea, for extreme cases then a fillet of concrete can be used to prevent water getting underneath.
If the base is to the footprint this is unlikely to happen.
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