HardieBacker 12mm FAQs

JamesHardie Products

Questions & Answers

  • 12mm HardieBacker for walls
  • 6mm HardieBacker ideal for floors
  • Portland Cement & additives
  • Immune to water damage
  • Exclusive MoldBlock Technology
  • Ultimate in Durability
  • Exceptional Workability
  • Superior Tile Bond Strength
  • No Special Handling Required

Phone to order

01803 813 803

Lines open 7:30 - 17:00 Mon - Fri

Product Details

These questions and answers are largely the same as for the 6mm HardieBacker, but a few questions that are more specific to that product have been left out.

Q. Which should I use, HardieBacker EZ Grid™ 6mm cement backerboard or HardieBacker® 12mm cement backerboard?

A. Although both products can be used on floors, walls or worktops, HardieBacker EZ Grid™ 6mm is primarily used on floors, because the thinner board decreases the transition to the other floor surfaces. HardieBacker 12mm cement backerboard is primarily used on walls to match up to the 12.5 mm plasterboard and to provide improved impact resistance. It also has a high load carrying capacity so will support the weight of heavy natural stone products better.

Q. What kind of block or brick can HardieBacker be installed on to?

A. HardieBacker can be installed on any type of block, brick or masonry wall. Use a heavy duty wall anchor/plug, with a min embedment of 50mm into the structure, suitable for use with your substrate – check with the manufacturer of the fixing for your application

Q. What is HardieBacker cement backerboard made of?

A. It is made of Portland cement, ground sand, cellulose and selective additives. It contains no asbestos, formaldehyde, gypsum or glass fibre.

Q. Where can HardieBacker cement backerboard be installed?

A. It can be installed anywhere in your home where ceramic or natural stone tiles are to be applied over timber floors or on studwork walls. HardieBacker® cement board is suitable for use on interior floors, walls and worktops.

Q. Can HardieBacker cement backerboard be used in wet areas?

A. Yes. HardieBacker cement backerboard is water resistant and immune to water damage. It won’t rot, swell or warp.


Q. Why can’t I put HardieBacker cement backerboard directly onto concrete or other subfloors?

A. The primary function of HardieBacker cement backerboard is to provide a water resistant flat surface to tile on; it is not designed for use over concrete. The minimum sub-floor specified is 15.8 mm exterior grade plywood sub-flooring with a deflection not greater than 3mm for live and dead loads over joists that do not exceed a span of 400 mm centres.

Q. Can I use HardieBacker cement backerboard to build up the level of a concrete floor?

A. No. The primary function of HardieBacker cement board is to provide a water resistant flat surface to tile on; it is not designed for use over concrete.

Q. Which side goes up, smooth or rough?

A. Either is acceptable, but we recommend installing the grid side up on HardieBacker EZ Grid™ 6mm and the smooth face up for HardieBacker® 12mm cement backerboard.

Q. Why do you have to use a cementitious tile adhesive between the HardieBacker® cement backerboard and the sub-floor?

A. Cementitious tile adhesive is specified between the HardieBacker® cement backerboard and the sub-floor to eliminate any deviations between our product and the sub-floor. This decreases the probability of popping or cracking tiles due to deflection and air pockets.

Q. How do I cut HardieBacker cement backerboard?

A. HardieBacker® cement backerboard should be cut using HardieBacker® score and snap knife, available from your HardieBacker® cement backerboard stockist.

Q. Where can I get a HardieBacker score and snap knife?

A. Your local HardieBacker cement backerboard stockist can provide you with a HardieBacker score and snap Knife. Please check the Find your supplier tool on our website to find the supplier nearest to you.

Q. Why do I have to tape the joints? What is the purpose of the 50 mm wide alkaline resistant tape?

A. The tape will tie the sheets of HardieBacker cement backerboard together helping to disperse any movement of the substrate and therefore decreasing the probability of popping or cracking tiles along the seams.

Q. Where can I get the 50 mm wide alkaline resistant glass fibre mesh reinforcing tape?

A. See your local HardieBacker cement board stockist, or call UK Customer Service on 0800 0683103

Q. What is the correct fixing pattern for installing HardieBacker® 12mm cement backerboard?

A. Fix HardieBacker cement backerboard sheets with HardieBacker screws for wood or for metal (as the substrate dictates) every 200 mm around the perimeter and on all supporting studs. Keep fixings 15mm from sheet edges and 50 mm in from sheet corners.


Q. Why can’t I get the screws to sit flush with the HardieBacker® cement backerboard?

A. The screws that you are using do not have the power to rout out the material in order for the screw head to sit flush. Be sure to use HardieBacker® screws for wood or metal, as they are specifically designed for the job. If you continue to have difficulties, we recommend switching to galvanised clout nails.

Q. Can HardieBacker EZ Grid™ 6mm be used in a shower wall application?

A. We recommend HardieBacker 12mm cement backerboard as it is more suited to wall applications. If you need to fix HardieBacker EZ Grid™ 6mm cement board to a wall please contact our UK Customer Service on 0800 068 3103.

Q. Can HardieBacker® cement board be installed directly to masonry walls?

Yes. Place 3 vertical 10-12mm beads of high strength, single part, gap filling cartridge adhesive evenly down the back of the board and fasten HardieBacker® with 9 (6mm x 60mm) stainless steel screws into brown wall plugs. * For bumpy walls, in place of a cartridge adhesive, use a 6mm square notched trowel with a cement based tile adhesive to act as a gap filler, and follow with the same screws and brown wall plugs.

Q. Can I fix HardieBacker cement backerboard using a dot and dab technique?

A. No. HardieBacker cement board is not suited to this type of fixing application.

Q. Can I plaster over HardieBacker cement backerboard?

A. Yes. However, the hydraulic action (suction) of HardieBacker is far greater than that of Plasterboard so we suggest plastering a small test area first to check that the water is not being sucked from the plaster too quickly. If the plaster dries too quickly due to the suction of the board it will be difficult to work and in some cases the bond between the HardieBacker and the plaster coats will be weak causing the plaster to crack or craze.

If the test area shows the suction to be too great, with the plaster drying too quickly, then often this can be corrected by dampening the area to be plastered with a wet sponge or household plant spray. In extreme cases it may be necessary to coat the wall with dilute PVA to slow down the suction, but please check with our technical department before considering this option as over application of PVA will seal the HardieBacker permanently preventing the plaster from bonding at all.

Q. Can I use HardieBacker cement board to prevent ground water penetrating my cellar?

A. No. HardieBacker cement backerboard is not a waterproof board. You should seek professional advice regarding the waterproofing of cellar walls and floors.

Q. Can I use HardieBacker cement backerboard outside?

A. No. HardieBacker cement backerboard is not suitable for external use.

Q. Can I use HardieBacker cement backerboard in conjunction with under floor heating?

A. Yes, HardieBacker cement backerboard is suitable for under floor heating. It should always be placed between the structural timber floor and the heating element. Never place heating under HardieBacker® cement backerboard as there is a risk of damaging the system when fixing down the backerboard.

Q. Do I need to treat HardieBacker cement backerboard before I tile onto it?

A. No. HardieBacker cement backerboard is ready to tile once installed, just wipe it down with a damp cloth to remove any dust prior to tiling.

Q. Can I paint HardieBacker cement backerboard?

A. Yes, HardieBacker cement backerboard is suitable for a wide range of paint coatings. We do however recommend that you plaster the board first, to ensure the best possible finish.

Delivery details

Usually within 14 days

We offer next day delivery, when required, for our normal delivery days (Monday to Friday) and areas. Customers are requested to phone in before 12.00pm on the day prior to delivery with their complete product listing, delivery address and payment details.