Problem in number summation with Javascript

Question

I have 3 fields that I must add the value and present them in the total field, but when performing the sum Javascript is only concatenating the values

Sum function:

function calculateTotal(){
    var totalAmount = 0; 
    $("[id^='painting_']").each(function() {
        var id = $(this).attr('id');
        id = id.replace("painting_",'');
        var painting = $('#painting_'+id).val();
        var spares  = $('#spares_'+id).val();
        if(!spares) {
            spares = 0;
        }
        var labour  = $('#labour_'+id).val();
        if(!labour) {
            labour = 0;
        }
        var total=0;
        total = parseFloat(spares+labour+painting);
        $('#total_'+id).val(parseFloat(total));
        totalAmount += total;       
    }); 
    $('#subTotal').val(parseFloat(totalAmount));    
    var taxRate = $("#taxRate").val();
    var subTotal = $('#subTotal').val();    
    if(subTotal) {
        var taxAmount = subTotal*taxRate/100;
        $('#taxAmount').val(taxAmount);
        subTotal = parseFloat(subTotal)+parseFloat(taxAmount);
        $('#totalAftertax').val(parseFloat(subTotal));      
        var totalAftertax = $("#totalAftertax").val();
        $('#amountDue').val(totalAftertax);
    }
}