Javier Del Ser, the Chief Executive Officer (CEO) of AIM-listed construction materials producer Steppe Cement, topped up his stake in the firm on Tuesday with the purchase of 650,000 ordinary shares at a price of 25p per share.Following the £162,500 transaction, Del Ser holds 12,867,660 ordinary shares in the company, equal to 7.19% of the total issued share capital.Steppe is a leading cement producer in Kazakhstan. Its cement production facilities consist of four wet kilns and one energy efficient dry kiln.Del Ser is the Chairman of Steppe's operating subsidiaries, Central Asia Cement and Karcement. He has other business interests in Kazakhstan, including being a director and large shareholder in the Chagala Group.The company said last week that third-quarter revenue was 28% higher than the year before at KZT 7,233m. Sales volumes of 518,433 tonnes were up 16% during the three months to September 30th.Top Director BuysSteppe Cement Ltd (STCM) Director name: Mr Javier del Ser PerezAmount purchased: 650,000 @ 25.00p Value: £162,500Smiths Group (SMIN) Director name: Mr Peter TurnerAmount purchased: 8,996 @ 1,048.15p Value: £94,292Deltex Medical Group (DEMG) Director name: Mr Nigel J KeenAmount purchased: 138,888 @ 24.00p Value: £33,333Deltex Medical Group (DEMG) Director name: Mr Edwin SnapeAmount purchased: 100,000 @ 24.00p Value: £24,000Deltex Medical Group (DEMG) Director name: Mr Charles Julian CazaletAmount purchased: 90,000 @ 24.00p Value: £21,600Deltex Medical Group (DEMG) Director name: Sir Duncan K NicholAmount purchased: 75,000 @ 24.00p Value: £18,000