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Can You Put Hardie Board Over Plywood? (Explained)

Hardie board is an alternative to traditional wood siding that is made with cement fibers for durability and aesthetic appeal. 

The combination of sand, water, cellulose wood fibers, and cement results in the production of a material that is fantastic for protecting the exteriors of residential buildings.

The fiber cement exterior siding has a positive position in the market due to the fact that it has low maintenance requirements, a long lifespan, and most importantly, an attractive appearance. These factors contributed to its positive reputation.

On the other hand, we have plywood, which is another important tool you need to meet your needs. Plywood is a kind of wood that is made by gluing together several layers of wood. 

Now let’s look at some interesting facts about these two products and see if they can be used together.

Putting hardie board over plywood

The Hardie board can be installed over plywood. Its installation on top of the plywood is a relatively common practice. Depending on the variety of available Hardie boards, you can choose whether or not to install plywood behind the board. However, you can utilize them for improved support.

Now, let’s see some of the reasons why you can put Hardie boards over plywood. 

Better support:

Shelving, workstations, and even walls are frequently built out of plywood these days. It is more affordable than most types of wood, but it cannot be utilized for structural applications. 

When there is plywood placed underneath the hardie board, the structure will have a reliable support system. Because of this, it will be easier to maintain in the long run.


If the existing siding on your house is in good enough condition to be used as the substrate, installing plywood is an option that will save you a significant amount of time when compared to using the existing siding.

The process of removing plywood would take a lot of time. First, you may need to remove old plywood then you will put in the new one. So it would take a few days or a week. Which is why you can put plywood under the hardie board.

Cost Savings:

When compared to the cost of removing the old siding and replacing it with a new base material. 

The amount of money you will save by using the old siding as the base for the new Hardie board siding can be anywhere from several hundred to several thousand dollars.

When compared to wood siding, Hardie board does not require nearly as much maintenance as wood siding does, which could end up saving you money in the long run.

In addition to this, there is a possibility that it possesses a higher level of resistance to the insects. It is able to tolerate the high temperatures. You will receive a warranty that is valid for a considerable amount of time with this purchase.

Will hardie board damage plywood? 

Yes, hardie board might damage plywood if it absorbs water or gets wet. There is no universal solution to this problem because it is contingent on the intended application of the Hardie board. 

In this case, installation of the Hardie board plays an important role. Based on the installation of your boards it can absorb water and get wet, which can damage the plywood. 

Hardie is an excellent siding product that is water resistant and resists moisture. However, if water is able to penetrate the surface layer and enter the siding, you will run into significant issues in the not too distant future.

Water enters siding through cracks, splits, and uncapped nail holes. Nail holes are others. Incorrect flashing or areas where water pools can soak siding. All of these issues may be due to improper Hardie siding installation.

The way Hardie siding is made and the fact that it contains cellulose, which is basically just sawdust and wood pulp, is one of its biggest problems. 

It’s a great product for siding, but make sure to keep it up and take care of it right, and keep an eye on any spots where water gathers. Which could damage your plywood in the long run.

Can you glue Hardie board to plywood? 

Yes, you can glue Hardie board to plywood. Over a plywood floor surface, a flooring option known as Hardie Plank could be installed using thinset as the adhesive to keep it firmly in place. Another option for this type of flooring is concrete tile.

The first thing you need to do is clean the plywood subfloors of dirt, dust, and other debris. Sweep or vacuum surface debris. You can use mineral spirits to get wax or grease off the floor. Let everything dry before moving on.

Then, follow the directions to mix thinset and water. The amount of water needed can vary from product to product. Mix thinset until it gets the consistency of cement.

With a trowel, spread thinset evenly over a subfloor that can be covered in 25 to 30 minutes. If you don’t, the thinset will dry and the planks won’t stick to it. Wait 10 minutes until the thinset gets sticky. 

Put the Hardie Plank boards on top of the thinset and twist each one to cover the back.

Install Hardie Plank flooring everywhere. Wet a sponge and use it to remove any extra thinset from between the boards. Put all the boards in place. These are how you can glue Hardie board to plywood.

What do you put under Hardibacker over plywood? 

You can put thinset under Hardibacker over plywood. Over a plywood subfloor, Hardie Plank flooring can be installed with thinset as the glue.

Follow the manufacturer’s instructions for mixing your thinset product with water in a bucket. Water requirements could be different for each product. Put the thinset through a cement-like consistency by vigorously stirring it.

If you don’t want the thinset to dry too much and the planks to peel up, spread it evenly with a trowel over an area of the subfloor that you can cover with Hardie Plank within 25 to 30 minutes. After about 10 minutes, the thinset will become tacky and ready to be used.

These are the steps that need to be followed in order to properly apply thinset under Hardibacker on plywood. It will help to stick the plywood and Hardie board 

How to install hardie board over plywood? 

Hardie board is installed over water-resistant drywall on the framing of vertical surfaces and over plywood on floors, countertops, and any other horizontal surface. 

Ceilings can also be made with Hardie board. When the Hardie board is put up correctly, a basic process must be followed. This makes sure that the surface is safe and stable enough for tiling.


Before you begin installing the Hardie board, you should first inspect the subfloor or any other foundational material. Be certain that the tops of all of the nails and screws are even with the top of the work surface.


Start by laying down the first piece of Hardie board. Take accurate measurements of the area where the Hardie board will be installed so that precise cuts can be made. 

In addition, when installing along a wall’s length, the sheet should be trimmed and, if necessary, fall directly on the stud’s vertical centerline.

Mix mortar:

If needed, prepare thin-set mortar according to the manufacturer’s instructions. If the walls don’t require mortar, skip the surface-measure.

Score the cut line:

To split the Hardie board, score along the lines drawn by surface-measuring. Use a wallboard block or other steel straightedge with a blade aligned with the cut line, and then score the line with a carbide knife. 

Break the Hardie board along the scored line by applying pressure on one side and lifting up on another.

Spread mortar and place the Hardie board:

Spread thin mortar over the level surface with a notched tile trowel, if needed. 

Attach the Hardie board using backer-board screws after positioning it on thin-set mortar or flush against the wall. Each screw head should be 6-8 inches across and 2 to 3 inches from the edges.

Complete the set up:

To finish the installation of a Hardie board panel, you will need to repeat the score, cut the line and place the Hardie Board through depending on the situation.

Apply tape:

In order to finish preparing the substrate, extend fiberglass tape to all of the seams that occur in which Hardie board frames come together. Apply the tape in an even layer across each seam.  Hardie board has now become prepared for the installation of tile.

Final Thoughts 

Plywood can be used as a base for installing Hardie boards. Over plywood, the Hardie board is frequently used as an interior overlay. Depending on the type of Hardie board you buy, you can decide whether or not to put plywood behind it. However, they can be employed to provide bolstered support.