Is WonderBoard Fireproof: Cement Backer Fire Resistance

WonderBoard is a cement board commonly used as a backer board for tile installations in bathrooms and kitchens. It offers several advantages over traditional drywall, including superior moisture resistance and a more stable surface for tiles.

But is WonderBoard fireproof? Does it have a good fire rating?

This guide explains how resilient WonderBoard cement back is to fire and extreme heat.

Is wonderBoard fireproof?

Yes, WonderBoard is fireproof and has achieved a fire resistance rating for cementitious backer units per ANSI/UL 263 and CAN/ULC S101, Report No. 21766.

WonderBoard Cement Backer Fire Rating

WonderBoard cement backer has the following fire rating per the Material Safety Data Sheet (MSDS): Fire Resistance Ratings UL Rated Report No. 7L30 for floor protector and wall shield. One-hour rated — non-load-bearing WHI 6510381.01 7-10-91. Exceeds ANSI A118.9 specifications. CABO/NES Report NER #447.

Factors that Affect WonderBoard’s Fire Resistance

Several factors can influence WonderBoard’s fire resistance in assembly:

  • Composition: WonderBoard is primarily composed of Portland cement, silica, crystalline, quartz, calcium carbonate, and fiberglass mesh, which are non-combustible materials that contribute to WonderBoard’s fire resistance.
  • Thickness: The thickness plays a role in the fire-resistance level of the WonderBoards. Thicker boards tend to have a higher capacity to withstand heat. This is because it takes longer for heat to penetrate through a thicker material. WonderBoards range from 1/4 inch to 1/2 inch (6 mm to 13 mm).
  • Installation: Proper installation according to the manufacturer’s recommendations is crucial to ensure optimal fire performance for WonderBoard cement backers. This includes using the appropriate fasteners and avoiding gaps between boards.
  • Fire Exposure Conditions: The severity and duration of fire exposure will also impact WonderBoard’s performance. A minor fire may only cause the surface of the board to char, while a more intense fire could cause the board to crack or break.
Fireproof WonderBoard cement backer

Frequently Asked Questions

Does WonderBoard burn?

No, WonderBoard is not a combustible material and will not readily burn on its own. However, it can deteriorate and lose structural integrity when exposed to prolonged high temperatures.

Can WonderBoard be used in a fireplace?

WonderBoard is not recommended for direct use inside a fireplace. While it offers some fire resistance, it is not specifically designed to withstand the extreme heat and direct flames present in a fireplace. Special fire-resistant materials are required for fireplace applications such as HarideBacker or Durock.

WonderBoard is primarily used for wet tiling areas, such as bathrooms, for walls, ceilings, countertops, and vanities. It can also be used in decks, pools, and floors, as an interior or exterior substrate for ceramic tile, stone, slate, thin-brick veneers, stucco, and other similar surface systems.

Does WonderBoard require special installation methods to maintain its fire resistance?

WonderBoard should be installed following the manufacturer’s instructions to ensure optimal fire performance. This typically involves using galvanized roofing nails or approved screws and ensuring proper spacing between boards.

What about other types of cement boards? Are they fireproof?

Most cement boards offer similar fire resistance properties to WonderBoard. It’s always advisable to check the specific fire rating information for the particular cement board product you intend to use. To find out how resistant other popular brands of cement boards are, check out these related guides: Is Durock Fireproof? and Is HardieBacker Fireproof?


WonderBoard is a fireproof backer board that can offer fire resistance in the home. When used in a properly constructed wall, ceiling, or floor assembly, WonderBoard can help slow the spread of flames and improve overall fire resistance.

For optimal fire performance, follow the manufacturer’s installation recommendations and consult a professional for fire-rated assembly requirements.