A method and apparatus for preparing foundry moulds or cores wherein separate charges of sand and binder on the one hand and sand and catalyst on the other hand are supplied to a mixing chamber in which the separate charges are mechanically intermixed to produce a final sand/binder/catalyst mixture. The final mixture is then passed by gravity into a blowing chamber and the mixing chamber and the blowing chamber are moved apart to allow the final mixture to be blown from the blowing chamber into a mould or core box and further to allow the mixing chamber to be cleaned by suitable cleaning means.