I want to install engineered flooring over a concrete slab, and understand the need to install foam underlayment before the flooring. The instructional pictures I have seen show using spacers between the first course of flooring and the existing wall to achieve the required offset spacing.
I have two issues that need to be answered: In older homes, with walls that may not be perfectly straight, how do I ensure that the first course of flooring is straight? Should I strike a chalk line? Secondly, for floating floors, how do I ensure that the first course does not move as I add additional courses? Does the underlayment prevent excessive movement between it and the flooring?
Thanks for any help!