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Can You Put Plaster over OSB Board? (How To)

Oriented strand board (OSB) has a very rough finish, unlike drywall, and plywood. Therefore, one option is to apply something over the OSB board to make it perfectly smooth. In this article, I will explain whether it’s possible to apply plaster over OSB board.

Generally, you can put plaster over OSB board. It typically takes a minimum of 3 coats of plaster to create a smooth and flat surface. Unlike drywall which only requires 2 coats. OSB board can be plastered in the exact same way as other surfaces that are commonly plastered.

Set of OSB Board

There are a few steps you should do to prepare OSB board before applying plaster to it. Below, I will explain what these are. As well as, whether it’s a good idea to put plaster over OSB board, and the tools you will need to apply plaster over OSB board.

Can You Put Plaster over OSB Board? (How To)

OSB board has a rougher surface than other types of materials that are used for floors and walls. It also typically finished with a final layer of somewhat shiny adhesive or resin. Therefore, this is a summary of if it’s possible to put plaster over OSB board.

In general, plaster can be applied over OSB board. However, typically 3 coats of plaster are required to get a perfectly flat surface. If only, one or two coats of plaster will make the rough surface that OSB has less visible, but it won’t be perfectly smooth like drywall.

A coat of plaster should be left for about 20 minutes before another coat is applied. But, if it’s a rainy day or you are in a humid climate then give it slightly longer. Therefore, it’s possible to completely plaster over OSB in a single day.

Should You Put Plaster over OSB Board?

Man preparing plaster

OSB board is not a common material used for walls, and floors. But, plastering over interior surfaces in a home is a very old technique. So, here’s a rundown of how well plaster adheres to OSB board, how it looks, and if it’s a good idea to use it on OSB board.

In general, it’s perfectly fine to apply plaster over OSB board. The main difference is that around 2 or more coats are required, and typically 3 coats to get a perfectly smooth surface that is similar to drywall. Therefore, it takes a bit longer, and more work to plaster over OSB board.

The uneven surface that drywall has means that one layer of plaster, won’t make the surface of an OSB board smooth. And the uneven surface of the OSB board will easily show through. Unlike drywall that is virtually perfectly smooth to start with.

What Tools Do You Need to Put Plaster over OSB Board?

Man preparing plaster

Plastering a wall or surface requires a few special tools that most people don’t have. It’s also important to know that you have everything before starting to plaster OSB board so you can do it all in one go. So, this is what tools you need to put plaster over OSB board.

Overall, you need a bucket, trowel, bucket trowel, hawk (also called a hand board), a mixer, water brush, and hand brush. A hawk is used for holding the plaster in your hand, while you apply it using a trowel. A good sized trowel for beginners is a 14 inch plastering trowel.

Here’s what each of the tools are used for and why you need them:

  • Bucket – used for mixing and holding the plaster
  • Trowel – used for applying the plaster to the wall
  • Hawk (also called a hand board) – used in one hand to hold the plaster, that you scoop up using a trowel
  • Mixer – used to mix up the plaster
  • Water brush – used for finishing the wall – similar to a large paint brush
  • Hand brush – for sweeping the floor after you’re finished.

A mixer is optional. A mixer is a handheld tool that cuts down the time it takes to mix the plaster.

Nowadays a mixer is always used, and can be purchased for around $100. Plaster can be mixed by hand but takes much more time and effort.

What Preparations Do You Need to Put Plaster over OSB Board

Fixing OSB Board

Before applying plaster over OSB there are a few essential things you need to do. Luckily, they are very easy to do, and don’t take a lot of time. Here’s what you should do to OSB board before applying plaster to it.

In general, roughen the surface using coarse sandpaper (24 to 36 grit), remove any oil or grease on the surface if present, and fill in any holes or cracks that are larger than 1 inch (2.5 cm) in diameter first using the plaster or caulk. Also, pull out or hammer in and screws or nails.

OSB board typically has a varnish type finish that is shiny. Roughing up the surface by quickly sanding it, helps the plaster to adhere to the OSB board. In some cases grease or oil can accidentally get on OSB board.

If this happens, it should be removed. Mineral spirits work well to break down grease. However, typically this won’t be an issue.

Lastly if there are any large holes they should be filled in and left to dry before applying the layer of plaster. The reason is some can require a unique method to fill them in.

Interestingly, the ways to fill in holes in drywall are the same methods that can be used on OSB board.

How to Put Plaster over OSB Board

confused man standing

It’s important to use the proper techniques when applying plaster. OSB board is no different, here are instructions for how to apply plaster over OSB board, and any special considerations you need to be aware of.

Overall, first rough up the surface using sandpaper. Next, mix up the plaster, and apply it to the wall. Typically, 3 or more coats are required. After each coat wait at least 20 minutes before applying the next coat of plaster. Below, are step by step instructions.

Plastering is a very simple skill. Below, is a video that shows the whole process from start to finish. OSB board can be treated exactly the same as drywall – which is far more common to use as the walls of home.

Copyright article owner is for this article. This post was first published on 2022-11-25.

As a general rule, you can put plaster over OSB board. However, a few coats of plaster are required. One coat of plaster won’t be smooth, even if you apply a layer of paint afterwards. Apply enough coats of plaster until it’s smooth. Typically requires 3 to 4 coats.

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ReadyToDIY is the owner of this article. This post was published on 2022-11-25.

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