Dynamic Count Blank For Worksheet Change

I'm trying to change my code below to count blank cells between a given point "c11" and the next non-blank cell to set a validation list in all the cells inbetween I think this is what I want to do because right now if I insert a row in the middle of the hardcoded range I get an error.

Private Sub Worksheet_Change(ByVal Target As Excel.Range)
Dim Add As String, Size As String, Sch As String
If Not rTarget Is Nothing Then
If Not Intersect(Target, rTarget) Is Nothing Then
Macro1
End If
End If
With Range("c11:c52").Validation
.Delete
.Add Type:=xlValidateList, AlertStyle:=xlValidAlertStop, Operator:= _
xlBetween, Formula1:="=MaterialList"
.IgnoreBlank = True................