1/2 Vs. 1/4 Cement Board: What Are The Major Differences?

Cement board, sold under the trade names WonderBoard, Durock, and Hardiebacker, to name a few, is considered the standard underlayment for stone, porcelain, and ceramic tile installations. It is used as the substrate underneath virtually all tile flooring. It is the go-to backer board for wall-tile applications in moist environments, such as tub surrounds and shower enclosures.

1/4-inch board is easier to cut and screw or nail to substrate. However, it’s easier to crack since it is thinner. The 1/4-inch board is ideal for both countertop and floor installations. The 1/2-inch board can be tough to cut but is excellent for installing tile in your tub surround and is great at compensating for any difference in thickness.

With that said, let’s take a deeper look at the different sizes and thicknesses of cement board to understand better which is best for your project – ½ vs. ¼ cement board.

Cement board is most often found in sheets that are 3 feet by 5 feet. Although larger, 4 by 8 feet sheets are available, they are substantially heavier, making them difficult for DIYers to handle. If you were installing tile around a tub, for instance, consider how the large majority of tubs are about 5 feet long and less than 3 feet wide.

For this project, tile needs to be installed from the top of the tub to at least three inches above the showerhead, if not up to the ceiling. The tile also has to be extended a couple of inches past the tub on either side to shield your walls from moisture.

For tile installation with a tub of this size, you can see how it makes sense to purchase cement boards that measure 5 feet by 3 feet. All you need is one board to be installed vertically on each side of the tub and two sheets positioned horizontally along the back.

Cement board comes in two main thicknesses – ¼ inch and ½ inch. Though, you may find some boards as thick as 5/8 inch. A 3 by 5 panel that is ¼ inch thick weighs approximately 30 pounds, while a ½ inch panel ranges from 36 to 44 pounds.

According to industry standards, ½ inch cement board should be used on wall tile installations. In comparison, ¼ inch cement board is most suitable for floor and countertop installations. With this in mind, choose a cement board thickness based on the application:

Although it’s most recommended to use ½ inch or 5/8 inch cement boards for wall installations, like tub surrounds, you may be able to use ¼ cement board if you plan to install a plywood surround first. In this case, the ¼ inch board will make up for the difference in thickness.

However, this should only be done when it is permitted by local code and recommended by the product manufacturer. It’s also important to keep in mind that, if you choose to go this route, a waterproofing membrane must be installed between the plywood and cement board to protect the wood from swelling due to moisture exposure.

One of the most essential features that your backer board must have is the ability to resist any flexing when fastened horizontally every 16 inches. An underlayment that is flexible or fragile will crack the tiles and grout as the board warps, shifts, or breaks.

If a ¼ cement board panel is only secured at 16-inch intervals, it’s going to crack under the weight of someone accidentally crashing into it with all of their weight between the studs, resulting in cracking of both the tile and grout.

For this reason, USG (the manufacturer of Durock cement board) advocates that one should only use ½ inch thick cement boards for wall construction with the standard 16 inches spaced framing.

This indicates that a board of any less thickness is not suitable for underlaying tile. Instead, USG recommends that ¼ inch cement boards be reserved as underlayment for tile floor and countertop installations.

When it comes to the tub surround tile installations, if one of the walls extends into your bathroom, you can choose to either tile this “dry” section or leave it alone and paint it. If you plan on painting the wall, it makes sense to use drywall here. However, it would help if you did not use drywall as the underlayment in the tub/shower area.

In this situation, the backer board you use for the tub surround has to transition evenly to the drywall section. To do this, you need to use ½ inch thick cement board or build up a thinner board using plywood (as previously explained) to pair with the drywall.

Opt for mold-resistant drywall for your bathroom space, which commonly comes in panels that are either ½ inch or 5/8 inch thick.

Fiber cement board is another common form of the cementitious backer board. Also made of concrete, fiber cement board is reinforced by fiber throughout the product. It is suitable for dry and wet areas and is water durable enough for tub surrounds and shower enclosures.

However, fiber cement board is most often used on walls where the tile isn’t covering the entire wall since these boards can be finished with paint. For example, if your intention is to tile a tub surround, along with your bathroom walls up to wainscot height, a fiber cement board is recommended – which comes standard as ¼ inch thick.

Related Questions

Is cement board stronger than plywood?

When compared to plywood, a cement board has a greater load capacity. This means that when you use cement board as an underlayment, you can install tile virtually anywhere and still have great results. Whereas, with vertical tile applications, heavy tiles like slate are typically too heavy to stick to plywood.

Do I need to waterproof the cement board?

Although cement board is considered water-resistant, it is not waterproof. Therefore, you must place a water vapor membrane underneath the cement board or, ideally, apply a sealant on top.