A gypsum tile backer sat under 24 inches of water for 48 hours and stayed dry behind

Host Jordan Smith ran the test with the panel set on spacers so air reached its back, the way it would sit over a stud cavity. After two days, according to the video, water had gone less than a millimeter into the face and had not wicked sideways past the edge of the column. The crew said plainly that this was a jobsite check and not a test run to the ANSI standard.

USG sells AquaSmart as a fiber-reinforced gypsum panel that is waterproof through its full thickness. The company says it meets Section 4.5 of ANSI A118.10, the waterproofness test in the standard for bonded waterproof membranes under tile, showing no visible water coming through after 48 hours under hydrostatic pressure. The panel is 0.42 inch thick and carries a 20-year limited warranty, according to USG's launch announcement published by TileLetter in June 2025.

Leaving the face bare does not mean skipping waterproofing altogether. USG says one coat of treatment over every seam and fastener gives waterproof performance under A118.10, against two full coats over the whole surface for backers that are not waterproof on their own. The Build Show soak checked the field of one board. It did not test taped seams, screw heads or the corner of a niche.

An earlier Build Show episode in which Smith introduced the same board named USG as its sponsor.