Two lanes will now be closed on the westbound carriageway between 5am on Saturday, 4 July and 10am Sunday 6 July.
Chris Pope, Highways Agency project sponsor, said:
The Second Severn Crossing is a vital transport link between England and Wales, and this work will help keep it operating safely for many years to come.
We have planned the work carefully to cause the least possible disruption to road users and will also be taking the opportunity during the closures to carry out other work such as gulley clearing, white lining and lighting maintenance to reduce the need for traffic management in the future.
The work is being carried out when traffic flows are lowest but road users are advised to plan ahead and allow longer for their journeys.
One lane will remain open during the work, but if delays occur signing will direct road users to use the M48 Severn Crossing.
Members of the public should contact the Highways Agency Information Line on 0300 123 5000
Journalists should contact the Highways Agency press office on 0844 693 1448 and use the menu to speak to the most appropriate press officer