Combine text from multiple cells based on criteria from other cells

I have a large Bill of Quantities (more than 3000 rows).
The person who made it separated the description in column "C" into different rows which makes it impossible to sort by description which I need to do.
The only criteria that I can use is column "E".
For example I want to combine C4 to C6 into F6 and than delete rows 4 and 5 using weather E4 to E6 is empty or not.

Please help.