Damp behind kitchen cupboard

The best way to seal the gap between the wall and floor is by using a flexible sealer, such as a silicone sealant. This will help to prevent moisture from entering the area and help to stop the dampness issue. You will need to ensure that all the surfaces are clean and dry before applying the sealant and that the gap is completely filled. Once the sealant is applied, it should be left to cure before being exposed to water.

If only we could cure this issue , it’s everywhere. If you have a wooden suspended floor , fit a strip of wood over the gap , if it’s a concrete flood , leave it alone . The actual issue is there is a space behind the cupboards where air is trapped with no chance of exchange, if there is any way to ventilate it , do that but in most cases , there is almost nothing you can do . If you ever get a new kitchen , fit thick insulation in the gap to fill the air space ; that is a cure .

The damp may not be coming from the gap although you can fill it insulating foam. But I would put a damp meter on the wall to see if it's the dpc that needs replacing.

When completing damp proofing work there should be no plaster in contact with the floor as it can track the damp up from the floor especially if it’s a concrete floor the plaster should never be in contact, we use a breathable plaster called limelite or we tank the wall with a MEMBRAME and ensure there is at least a 2.5 inch gap to make sure this doesn’t happen on our jobs