WPF grid fusionné

Bonjour, Dans ma fenetre j'ai un grid qui contient 3 colonnes ( celle du milieu 400 pixel )

Dans la colonne du milieu j'ai un autre grid de 8 x 8 ( taille de 50 x 50 pixels ) ( jeu d'échec )
Dans la première colonne de gauche j'ai un grid de 2 x 6 pour les pieces morte

Mon problème est que le grid des pieces morte et le grid de l’échiquier son coller

Voici images :

http://s10.postimg.org/oskntt4hl/grid1.png

Résulat :

http://s24.postimg.org/w6cte6rat/resultat.png

Code XML :

Code:

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<UserControl x:Class="JeuEchecs.fenetreEchiquier"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="700" d:DesignWidth="1000" 
             HorizontalAlignment="Center" VerticalAlignment="Center"
             BorderBrush="Black" BorderThickness="1.0">
    <!-- L'échiquier -->
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition Width="400"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Grid Grid.Column="0" Name="grilleMort" Width="100" Height="300" HorizontalAlignment="Center" VerticalAlignment="Center">
            <Grid.RowDefinitions>
                <RowDefinition Height="50" />
                <RowDefinition Height="50" />
                <RowDefinition Height="50" />
                <RowDefinition Height="50" />
                <RowDefinition Height="50" />
                <RowDefinition Height="50" />
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="50" />
                <ColumnDefinition Width="50" />
            </Grid.ColumnDefinitions>
        </Grid>
        <Grid Grid.Column="1" Name="grilleCases" MouseLeftButtonDown="grilleCases_MouseLeftButtonDown" Height="400" Width="400">
        <Grid.RowDefinitions>
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
            <RowDefinition Height="50" />
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
            <ColumnDefinition Width="50" />
        </Grid.ColumnDefinitions>
    </Grid>
    </Grid>
</UserControl>