You can't use concrete for adhesive because it has aggregate in it. Aggregate will hold the work you're trying to bond apart. Mortar is a better adhesive for masonry products.
Yes, you can use concrete as an adhesive to hold bricks together, but it is not the best option and not recommended by professionals; instead, use a thinset to keep the bricks in place.
mortar. which is essentially concrete without gravel. or more precisely finer "gravel" sand. the chemical reaction that occurs during the drying process bonds the mortar to the bricks, and brick to mortar.
