The invention relates to flexible, flat substrates having an abrasive surface, characterised in that they can be obtained by applying an aqueous solution or dispersion of at least one pre-condensate of a thermocurable resin on the upper and/or lower side of a flexible, flat substrate, in an amount of at least 5 to 90% in weight in relation to the non-coated, dry substrate, the pre-condensate is cross-linked and the treated substrate is dried.