Noob question about updating label.

I'm having a label in a page which I need to be updatet multiple times when a method in the codebehind file fires, like this:
protected void updateLbl()
{
lbl1.Text = "test1";
Tread.Sleep(1000);
lbl1.Text += "test2";
}
but the label first updates when the method finishes. How can I solve this? Do I need AJAX?
Thanx in advance.
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