The failure modes, ranked by frequency of grief
Slope and drain failures lead: floors flat under the tile store water in the assembly; drains poorly married to membranes leak quietly below everything, announcing themselves as stains on faraway ceilings. Both are day-one construction details, pre-slopes present, integrations per the method's engineering, and both are exactly what flood tests exist to catch.
Penetrations and corners follow: every valve, head, niche, bench, and fastener that passes through the membrane is a hole the system must seal by design, and corners concentrate both water and workmanship pressure. The accessory details, the niche membraned as part of the wall, the bench built inside the system rather than perched on it, the curb wrapped rather than capped, separate durable showers from scheduled failures.
Product mismatch and aftermath close the list: mixing components across systems, one brand's membrane with another's seam treatment, a setting material the membrane maker excludes, voids both engineering and warranties; and damage after installation, a fastener through the pan during glass mounting, a trade's screw into the wet wall, undoes perfect work invisibly. The cures are one named system executed whole, and a rule that nothing penetrates wet zones after membrane day without the installer's sign-off.
