NASCLA Accredited Commercial General ContractorFinishesHard
A commercial project requires the installation of large format porcelain tiles (24"x48") on a suspended concrete slab. To prevent lippage and ensure a durable installation, what is the maximum allowable variation in the substrate flatness over a 10-foot span, according to industry standards for this type of tile?
- A1/16 inch
- B1/4 inch
- C1/8 inch
- D3/32 inch
Show answer & explanationAnswer & explanation
Correct answer: A. 1/16 inch
For large format tiles (LFT), industry standards typically require a substrate flatness of no more than 1/16 inch variation in 10 feet to prevent lippage and ensure proper adhesive coverage. This is a stricter requirement than for smaller tiles.
Why the other options are wrong
- B. 1/4 inch is too large a variation and would almost certainly lead to lippage and bond failure with large format tiles.
- C. 1/8 inch is generally acceptable for smaller tiles (less than 15 inches on any side) but insufficient for large format tiles.
- D. 3/32 inch is still too much variation for large format tiles; the stricter 1/16 inch is necessary.
Large Format Tile Substrate Flatness
The precise maximum allowable deviation in a substrate's surface, typically 1/16 inch over a 10-foot span, required for successful installation of tiles with at least one edge 15 inches or longer.
- Crucial for preventing lippage
- Ensures proper adhesive coverage
- Stricter than for smaller tiles
Memory trick: Big tiles need a 'flat' path, like a 1/16 inch smooth road for a long journey.