Method of applying washcoat to monolithic substrate

A method of coating a substrate monolith comprising a first end face and a second end face and a plurality of substantially parallel channels extending from the first end face to the second end face with a washcoat composition, wherein the method comprises the steps of:

• (a) locating a containment means on top of the first end face of the substrate monolith;
• (b) dosing a predetermined quantity of a rheologically pseudoplastic washcoat composition comprising a liquid phase, at least one polysaccharide rheology modifier and either one or both of (i) and (ii), wherein (i) is a suspension of metal oxide particles into the containment means;
• and (ii) is at least one metal salt solute in the liquid phase, and wherein the order of steps (a) and (b) is (a) then (b) or (b) then (a);
• (c) applying pressure to the washcoat composition thereby to generate a shear stress in the washcoat composition and to transfer an entirety of the washcoat composition into the channels of the substrate monolith by plug flow, wherein the predetermined quantity of the washcoat composition is such that no more than 1 wt % of the predetermined quantity of the washcoat composition is drawn though the substrate monolith and expelled;
• and
• (d) rotating a part-coated substrate monolith resulting from step (c) so that the second end face is located at the top;
• and
• (e) repeating steps (a) to (c) inclusive without drying the part-coated substrate monolith.