The F+ option refers to the characteristics of ceramic tiles for floating installation on supports. F+ can be classified as F+ for floating installation on supports unglazed B1a or unglazed decorated B1a ceramic tiles, classifiable as U3, U3s or U4 with a perforation resistance equal to or greater than P3.
Tiles classified F+ must meet more stringent criteria with regard to the following aspects.
Dimensional criteria
Tiles with the following dimensional characteristics can be classified F+ for laying on supports:
- Maximum elongation less than or equal to 3
- Maximum length:
- 1,200 mm for rectangular tiles
- 900 mm for squared tiles
- Minimum width of 300 mm
- Surface area between 1,600 and 1,800 cm2
- Minimum thickness of 18 mm
- Compliance with the other general dimensional criteria for UPEC classification.
Additional specifications for U classification: flexural strength
The required breaking strength varies according to the required U classification:
| U Class | Breaking strength (kN) | Modulus (N/mm²) |
| U3 | 7 | 35 |
| U3S | 7 | 35 |
| U4 | 11 | 40 |
The test is performed according to the method described in Annexe 12 of the cahier CSTB 3778_V3 of October 2018.
Additional specifications for classification P: Repeated shock test
To obtain the F+ classification, the tiles must withstand a repeated shock test.
The tiles are laid on supports adjustable in height. A steel ball with a mass of 320 g is dropped within a 5 cm from the centre of the tile, from a height of 80 cm. The test is carried out on 5 whole tiles. The ball drop test is repeated three times for each tile. No breakage is permitted.
The method of execution is specified in detail in Annexe 11 of the cahier CSTB 3778_V3 of October 2018.