I bought a concrete fountain in which the basin (water container) is comprises of 5 semi circular blocks that has to be mortar together on a concrete slab. The instruction says to use "PLASTIC CEMENT MORTAR MIX" to piece together the semi circular blocks. The problem is that I have found only plastic cement OR mortar in the home improvement store. Am I suppose to mix the 2 together? The plastic cements I found state that they are used for stucco base code only... Any guide will be appreciated. Thanks.