A water-base resin has both excellent storage stability and excellent curability at
room temperature, the water base resin being obtained by mixing a composite resin (C) and a polysiloxane (D), bringing about a
condensation reaction partially between them if necessary, and thereafter dispersing or dissolving the resulting mixture or partially condensed product into a water-base medium, wherein the composite resin (C) comprises a polysiloxane segment (A) and a
polymer segment (B), the polysiloxane segment (A) having at least one
silicon atom selected from the group consisting of a
silicon atom bearing at least one
organic group having a total
carbon number of at least 3 together with at least one hydrolyzable group and / or at least one hydroxyl group, a
silicon atom bearing one hydrolyzable group or one hydroxyl group together with two groups selected from the group consisting of methyl groups and ethyl groups, and a silicon atom bearing at least one triorganosiloxy group together with at least one hydrolyzable group and / or at least one hydroxyl group, and the
polymer segment (B) having at least one type of hydrophilic group selected from the group consisting of an anionic group, a cationic group, and a non-ionic group, and wherein the polysiloxane (D) has a hydrolyzable group bonded to a silicon atom and / or a hydroxyl group bonded to a silicon atom, the polysiloxane (D) having a structure represented by the following
structural formula (S-I) as an essential
structural unit:(wherein R1 in the formula denotes a
methyl group or an
ethyl group). A water-base curable resin composition comprising the water-base resin as an essential component produces a cured material which possesses excellent resistance
stain during outdoor
exposure as well as excellent durability such as
acid rain resistance and gloss retention during outdoor
exposure.