Try running the following macro. It makes all table borders a 0.25pt 20% gray line.
Code:
Sub DoTableBorders()
Application.ScreenUpdating = False
Dim SBar As Boolean, i As Long, j As Long, k As Long
With ActiveDocument
k = .Tables.Count
If k = 0 Then Exit Sub
For i = 1 To k
Application.StatusBar = "Processing Table " & i & " of " & k
For j = 1 To 6
With .Tables(i).Borders(j)
.LineStyle = wdLineStyleSingle
.LineWidth = wdLineWidth025pt
.Color = wdColorGray20
End With
Next
DoEvents
Next
End With
StatusBar = ""
Application.ScreenUpdating = True
End Sub
The macro reports its progress on the status bar.