The effects of accelerator CaCl2 with 1 percent, 2 percent, 3 percent, 4 percent, 5 percent comparing to cement weight in Acacia mangium wood particle - cement mixture to some main physical and mechanical properties of this composite board including density, water absorption, thickness swelling, bending strength and its modulus of elasticity, internal bond were investigated. The results show that the amount of CaCl2 dramatically affects these properties of cement composite board. When this CaCl2 amount increase from 1 percent to 5 percent, the water absorption decrease from 35.62 percent to 18.925 percent
thickness swelling decrease from 3.46 percent to 1.28 percent
density change slightly from 0.95 to 1.109 g/cm3. When the CaCl2 amount increase from 1 percent to 3 percent, bending strength increase from 2.42 MPa to 3.09 MPa, then decrease to 2.76 MPa when this amount increase to 45 percent. The internal bond of cement board increase from 0.1691 MPa to 0.452 MPa with the increase of CaCl2 amount from 1 percent to 5 percent. The suitable amount of CaCl2 for making cement composite board from Acacia mangium should be 3 percent.