Nhibernate show_sql=false not working

This is how I create Session Factory using Fluent Nhibernate

    public static ISessionFactory CreateSessionFactory()
        {
            FluentNHibernate.Cfg.FluentConfiguration fconfig;


            fconfig = FluentNHibernate.Cfg.Fluently.Configure()
                        .Cache(c=>c.UseQueryCache())
                        .Database(FluentNHibernate.Cfg.Db.MsSqlConfiguration.MsSql2008 
                                        .ConnectionString(c => c.FromConnectionStringWithKey("Database"))
                        .ProxyFactoryFactory<NHibernate.ByteCode.LinFu.ProxyFactoryFactory>()
                        .Mappings(
                                  m =>  m.FluentMappings
                                        .AddFromAssemblyOf<NHibernateRepositoryRegistry>()
                                        .Conventions.Add<Conventions.PrimaryKeyConvention>()
                                        .Conventions.Add<Conventions.IdForeignKeyConvention>()
                                        .Conventions.Add<Conventions.ReferenceForeignKeyConstraintNameConvention>()
                            )
                   //  i have tried this but it did not work
                   //.ExposeConfiguration(config=>{config.SetProperty("show_sql", "false");});
           return fconfig.BuildSessionFactory();
        }

This is my log4net config inside Web.config

    <appender name="RollingFile" type="log4net.Appender.RollingFileAppender">
        <file value="nhibernate.log" />
        <appendToFile value="true" />
        <maximumFileSize value="100KB" />
        <maxSizeRollBackups value="2" />

        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%level %thread %logger - %message%newline" />
        </layout>
    </appender>
    <appender name="RollingFile2" type="log4net.Appender.RollingFileAppender">
        <file value="nhibernatesql.log" />
        <appendToFile value="true" />
        <maximumFileSize value="100KB" />
        <maxSizeRollBackups value="2" />

        <layout type="log4net.Layout.PatternLayout">
            <conversionPattern value="%level %thread %logger - %message%newline" />
        </layout>
    </appender>
    <logger name="NHibernate">
        <level value="INFO" />
        <appender-ref ref="RollingFile" />
    </logger>


    <logger name="NHibernate.SQL">
        <level value="ALL" />
        <appender-ref ref="RollingFile2" />
    </logger>
    <root>
        <level value="DEBUG" />
        <appender-ref ref="RollingFile" />
    </root>

</log4net>  

I had ShowSql() setup perviously

and I was trying to set it via web.config appsettings so i can turn on or off based on configuration

so I removed ShowSql() and tried following ( right now i am just passing "false" value )

.ExposeConfiguration(config=>{config.SetProperty("show_sql", "false");});

also tried

.ExposeConfiguration(config=>{config.SetProperty("hibernate.show_sql", "false");});

but I am still getting sql generated in nhibernatesql.log file

I am using NHibernate v3.1.0.4000 and FluentNHibernate v1.2.0.712 and ASP.NET MVC3

does anyone know why sql is still generating?

does show_sql or ShowSql() is only meant for Console.output purpose and sql is sent to log4net regardless ?

my main concern is slow performance if ShowSQL is set to true

not sure whether I am setting ShowSql somewhere else