An additive manufacturing apparatus for building a product according to a planned geometry by successive solidification of a radiation-curable fluid in a solidification layer extending in a vertical direction from a surface of the fluid to a surface of the product. The apparatus includes: a vat holding the fluid; a support holding the product; a mechanism to control feeding of fluid to the solidification layer; a curing radiation source to generate a 2D exposure pattern of curing radiation in the solidification layer. The exposure pattern is defined by a curing radiation pattern geometry and/or curing radiation intensity. A radiation sensor receives radiation from the solidification layer. The radiation sensor generates a sensor signal having information indicative of a solidification process status. A control system is connected to the feed control mechanism and the curing radiation source. The control system receives the sensor signal and responsive thereto adjusts parameters controlling the solidification in the solidification layer.