The sealing of small porous rigid articles by impregnation with a liquid synthetic resin impregnant and sequent curing of resin in the pores and provides a liquid (meth)acrylic ester impregnant composition comprising a free radical catalyst, an inhibitor and a higher alkyl (meth)acrylic ester and/or polyfunctional (meth)acrylic ester which has been obtained by transesterification in the presence of an organotitanium catalyst and from which the catalyst residue has not been removed. The catalyst residue has been found to improve sealing and thermal stability of the cured impregnant.
