WP 8.1 App Grid has padding on the top and bottom...

Question

I have a Grid as shown below.  When I have height/width set to auto on the row and column definitions.  As expected the buttons in each column are flush against each.  The height always has a padding at the top and bottom of the grid
cell.  
Why would it have padding a the top and bottom and how do I remove it since there is no padding attack property?
Thanks,
   Michael
Example below:
<Grid x:Name="ContentRoot"
Grid.Row="1"
Margin="19,9.833,53,0" HorizontalAlignment="Center" VerticalAlignment="Top">
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Button Content="1" />
<Button Grid.Column="1" Content="2" />
<Button Grid.Column="2" Content="3" />
<Button Grid.Row="1" Content="4" />
<Button Grid.Row="2"
Grid.Column="1"
Content="5" />
<Button Grid.Row="3"
Grid.Column="2"
Content="6" />
</Grid>

Answer 1

The margin in the grid is causing the gap.  I would remove it
<Grid x:Name="ContentRoot"
Grid.Row="1"
Margin="19,9.833,53,0" HorizontalAlignment="Center" VerticalAlignment="Top">