HARDIBACKER SUBFLOOR INSTALLATION GUIDE
Posted on April 11, 2019
1 | Ensure subfloor is structurally sound on existing structures:• Ensure subfloor is not damaged. Replace any loose, warped, uneven or damaged sections of floor.• Make certain subfloor is a clean and flat surface.For all floors:• Use minimum 5/8 exterior grade plywood or 23/32 OSB with Exposure 1 classification or better, complying with local building codes and ANSI A108.11.• Joist spacing not to exceed 24” on center.• The floor must be engineered not to exceed the L/360 deflection criteria (L/720 for natural stone), including live and dead design loads, for the specific joist spacing used.
2 | Determine layout of HardieBacker® cement board• Stagger all HardieBacker® cement board joints. Do not align with subfloor joints.• Never allow all four corners of boards to meet at one point.• We recommend an 1/8” gap between board edges.• Keep sheet edges 1/8” back from walls and cabinet bases.• Score and snap boards to required sizes and make necessary cutouts.
3 | Attach HardieBacker cement board to subfloor• Apply a supporting bed of mortar or modified thinset to subfloor using a 1/4”square-notched trowel.• Embed HardieBacker cement board firmly and evenly in the wet mortar.• Use the fastener pattern as a guide. Fasten HardieBacker cement board with specified screws (as listed in “Materials Required”) every 8” over the entire surface. Keep fasteners between 3/8″ and 3/4″ from board edges and 2″ from board corners.• Set fastener heads flush with the surface without over-driving.
4 | Tape joints prior to tiling • Prior to setting the tile, fill all joints with the same mortar used to set the tiles.• Embed 2” wide high-strength alkali-resistant glass fiber tape in the mortar and level.