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Can You Put Plaster Over Backer Board/Cement Board? (How To)  

It’s feasible to plaster over backer board or cement board. But for it to hold, careful planning and the use of additional products are necessary. It’s a task that is best left to experts to complete.

However, if you have never plastered before, it’s advisable that you plaster over blue board attached to the cement board.

When plastering backer board or cement board, prime the surface so that the plaster will stick to the surface. You don’t require a moisture barrier as cement board is moisture resistant. Apply two layers of plaster to the cement board and then finish with a thin final layer that you smooth properly.

Man putting plaster

You will usually require two coats of primer that is specially formulated to provide a strong grip on the plaster. Failing to apply a primer will result in your plaster falling off the cement board very soon after it is dry.

Cement board is used for applying tiles and damp applications like bathrooms and showers, so no waterproofing is required. The cement board does not rot, so any moisture will not cause any structural problems.

If your surface is not smooth enough for your liking, you can use a damp sponge to smooth the plaster if it is still damp.

If the paster has dried, then you can use sandpaper to smooth the surface until it reaches the required texture. Use the coarse grades of sandpaper, 60 or 80 grit first, and then use finer sandpaper such as 120 or 180 grit to get a silky-smooth finish.

You will be able to easily knock down any high spots and remove rough areas of plaster in preparation for painting.

Should You Put Plaster Over Backer Board/Cement Board?

Man putting plaster

It is quite possible to plaster over cement or backer board so long as you prepare the surface properly before applying the plaster.

Plastering cement board is the most challenging because it often won’t stick. The plaster will often begin to peel off before it has dried. You will require a good primer to ensure that the cement board is properly prepared and usually two coats are necessary for a good bond.

Plaster-Weld is a good option, but ask your hardware store for a suitable alternative if they don’t have it.

The plaster will have a good base to attach to, thanks to the chemical and mechanical bonding properties of the primer. Just make sure that you apply at least two coats for the best results.

If you add a small amount of sand and plaster mixed together and applied to the primer while it is not yet dry, it will help with the surface mechanical bonding properties.

If you’ve applied two coats and allowed it to dry properly, the plaster has the best chance of sticking to the cement board.

It will usually take two days for any peeling to occur, so if nothing happens, then you can assume that the plaster bond to the cement board is good.

What Tools Do You Need To Put Plaster Over Backer Board/Cement Board?

Tools used for floor

The correct plastering equipment can help you finish the work more quickly, more effectively, and with higher quality.

You’ll need a hawk and a finishing trowel to apply the plaster. Use a paint roller to apply bonding primer to the surface of the backer board or cement board. The use of a plastering trowel is necessary to smooth the plaster onto the wall after you’ve put the plaster on your hawk with a bucket trowel.

For mixing the plaster and applying it to your hawk, you’ll need a sizable pail and a bucket trowel.

A plasterer’s float, which is often made of wood but can also be made of metal, is used to smooth the plaster after it has been applied to the wall.

You might need to use a jointing knife or jointer after the plaster has been applied to the wall and smoothed.

These are specific to the edges of your wall and how you intend to complete the project. You can find them in various sizes and forms.

If you need to smooth out a somewhat rough region while the plaster is still wet, a sizable sponge will come in handy.

What Preparations Do You Need To Put Plaster Over Backer Board/Cement Board?

Man putting plaster

Plastering a wall is a job best left to the pros, since it may be difficult to get a good finish if you’ve never done it before.

When plastering cement boards, use an appropriate primer to help the plaster to adhere to the boards. Cover the floor with a drop sheet and when the primer is dry, apply two to three layers of plaster to the wall. Smooth it with a damp sponge or wait for it to dry and then sand any rough spots.

To mix your plaster, you’ll need a large bucket and, preferably, a drop sheet to protect the floor from the plaster, which may make a huge mess. This is especially true if your floor is carpeted.

Once the cement boards have been primed, apply two to three layers of plaster to the boards, making sure that the plaster is not completely dry between applications.

Make sure you have the equipment you need to mix and distribute the plaster on the wall, as well as sponges and sandpaper to ensure a flawlessly smooth surface when you’re through.

How To Put Plaster Over Backer Board/Cement Board

confused man standing

Plastering is a dying skill that takes years to perfect.

However, if you are a beginner DIY enthusiast and are willing to spend a significant amount of time sanding the surface once the plaster has dried, you can accomplish it.

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On applying plaster to cement board, coat it with an appropriate primer before applying plaster to the surface. Wait for it to dry after applying 2 to 3 layers, then sand the surface to knock down any high places or rough areas.

While the plaster is still wet, smooth the surface and sand down any irregularities after it has dried.

Make sure the plaster is spread thickly enough to form a strong connection with the primed surface. Otherwise, you risk the plaster splitting and crumbling after a few weeks or months.

The thickness of your first two layers of plaster should range from 3/8th of an inch to slightly more than 12 inches (10mm to 15 mm).

The final coat should preferably be no more than 3/8th of an inch (10 mm) thick, and you should avoid applying more than 3/8th of an inch (15 mm) thick in a single application.

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Allowing the plaster to cure completely between applications will cause it to fail to bond fully to the next layer. Make sure that you apply the plaster while the last layer is still slightly tacky.

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ReadyToDIY is the owner of this article. This post was published on December 8, 2022.

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