functions.php

/*
* replace read more buttons for out of stock items
**/
if (!function_exists('woocommerce_template_loop_add_to_cart')) {
function woocommerce_template_loop_add_to_cart() {
global $product;
if (!$product->is_in_stock()) {
	echo '<a href="'.get_permalink().'" rel="nofollow" class="outstock_button">Out of Stock</a>';
} 
else 
{ 
	woocommerce_get_template('loop/add-to-cart.php');
}
}
}