Can You Plaster Over Expanding Foam? (Explained)

Though possible, plastering over expanding foam requires skill and experience. It’s not the easiest DIY task.

But with some tips and guidance, you should be able to plaster over expanding foam. This article will address everything you need to know about plastering over expanding foam.

can you plaster over expanding foam

Will Plaster Adhere to Expanding Foam?

Plaster will adhere to expanding foam depending on the following factors;

1. The Expanding Foam Used

If you look into expanding foams, you will realize that there are two main types. The first is the regular expanding foam found in most homes.

This type is the one that’s used for DIY purposes, such as filling small holes and holding together various components within a home.

The other type of expanding foam is the one used for home insulation. This type is sprayed from wall to wall, and quite often, this usually requires a professional touch.

With the latter type, it’s much easier to plaster because it has been designed to be used for large-scale purposes.

For the typical expanding foam, it may not be the best plaster-friendly surface, but we will show you the techniques needed to plaster over it.

Also, when plastering over expanding foam. You need to check for compatibility. Certain expanding foams mention that the foam can be plastered over on the packaging label.

2. The Application Process

For most DIYourselfers, getting plaster to adhere to expanding foam is usually a nightmare, mainly because of the structure of expanding foam.

Without prior knowledge and experience, you may find it hard for the plaster to stick to the expanding foam. Before engaging in such a project, ensure that you perform adequate research.

3. The Size of the Project

Another factor that most people often overlook is the size of a project. Plastering over expanding foam is more of a hack and not a recommendable construction procedure.

Being a hack, it’s only effective when done in a small area. However, if you are plastering over a large area that has been filled with expanding foam, the plaster will stick for a while.

But that area will be highly susceptible to damage. Therefore, before embarking on such a project, consider the size of the area that you want to work on.

How to Plaster Over Expanding Foam?

As mentioned earlier, plastering over expanding foam is tricky. But it’s not impossible. It’s a project one can pull off with the right tools and knowledge. Here is a quick guide on how to do that.

Step 1 – Gather Tools and Equipment

You will need a few things to plaster over expanding foam. First, you will need a cutting tool such as a hacksaw or sharp knife.

Feel free to choose a cutting tool of your choice depending on the area you are working on. Therefore, you can also use a sharp blade if you are cutting expanding foam on a small hole in the wall.

The other tools you will need are a quality wall filler, some screws, and then plaster. Once you gather these tools, you are ready to start the project.

Step 2 – Cut the Foam Slightly Beneath the Surface

The thing about expanding foam is that it inflates and most cases protrude further from the surface. Expanding foam can’t be plastered directly over in such a state because there will be no uniform finish.

To avoid any complications, you should cut the foam slightly deeper from the surface. The space created is where the plaster will sit.

Step 3 – Add Some Screws into the Space Left by the Expanding Foam

Why would you need screws for such a project? Expanding foam isn’t the best surface for the plaster to adhere to. Therefore, you will need something else for the plaster to stick to.

Screws do an excellent job of filling the space left by the foam. They are also ideal candidates for adhering to plastic.

Grab some screws and place them diagonally in the hole that has the expanding foam. Make sure that the screws are firmly held.

If you are interested in a durable plastering job, you can add a quality wall filler. The purpose of the wall filler will be to create a transitional layer from the expanding foam to the plaster.

It will firmly hold the screws and the expanding foam in place and ensure the project lasts for as long as possible. So if you can get your hands on some filler, do not hesitate to apply it.

Step 4 – Plaster the Surface

With filler and screws inside the hole with expanding foam, you can wrap up the project by applying some plaster.

As you plaster over the expanding foam, ensure that the surface is uniform. That will provide a more aesthetic and pleasant finish.

Will a Plastered Expanding Foam Patch Show?

If you follow the above guide, the patch won’t be visible when the plaster cures. However, if it does. You can always conceal the patch with some quality paint.

How Soon Can You Plaster Over Expanding Foam?

Most expanding foams take about twenty or thirty minutes to be tack-free. Please do not be tempted to plaster over expanding foam immediately after spraying it, even when it no longer looks tacky.

The best thing to do would be to wait for at least a day for the expanding foam to cure. The soonest you can plaster over expanding foam is within 12 hours. Rushing the project can always lead to unpleasant outcomes.

Can You Plaster an Entire Wall Covered with Expanding Foam?

You may find yourself interested in plastering an entire wall covered with expanding foam in certain situations.

In our guide above on how to plaster over expanding foam, we touched on small projects such as a small hole in a wall that you had to cover with expanding foam.

However, if you are dealing with an entire wall covered with expanding foam, you may need expert assistance.

In the above scenario, you may have to do a couple of things. First, you should contact the guys who insulated the wall with expanding foam. They will be better positioned to tell you whether it’s possible to plaster the wall.

Because you may not have been the one involved in the application of the expanding foam, you can at least try and figure out the name. It should be easier to research the possibility of plastering over expanding foam with the brand’s name.

The procedure will require some cutting back of the foam. That’s another thing you need to be aware of. Also, you may need to introduce new materials that will help hold the plaster in place.

For a wall that has been covered in expanding foam, plastering over it will be a tedious and complicated process.

You should call the experts for a professional finish and eliminate guesswork. Some construction companies can even advise you to remove the entire insulation and use plasterboard instead.

Is Replacing Expanding Foam with Plasterboard Better?

Suppose you continue to research plastering over expanding foam, especially if you intend to do this on a larger area. You may come across the above advice.

People who have been doing this for a while will prefer to replace the expanding foam with plasterboard since it’s more plaster-friendly, and you are assured of long-term results.

If plastering over expanding foam seems like a stretch, you should consider cutting all the foam on the wall and replacing it with a plasterboard before plastering over it.

However, you should be careful when cutting all the expanding foam on a wall. Expanding foam could have been used to hold pipes in the walls. Therefore, if you come in too aggressively, you may damage something on the inside.

Can You Use Plaster on the Void or Hole Instead of Expanding Foam?

If you hadn’t sprayed the expanding foam into the void that you want to plaster over, you might get the idea to fill the plaster into that hole and forego the need for expanding foam.

This may seem like a brilliant idea. However, there are drawbacks. First, if there are pipes in the wall, especially those made out of copper, layering them with cement isn’t the most advisable thing to do.

Secondly, if the hole is relatively big, you may need to use a lot of plaster which would have otherwise been filled by expanding foam.

Also, plaster without any backer may not last for very long. Such concerns need not be taken lightly. To be safe, you can use a plasterboard on that hole.

Why Would You Want to Plaster Over Expanding Foam?

As we wrap up our guide, we must finish up with one crucial question. Why should you plaster over expanding foam in the first place? Isn’t it more convenient to let the expanding foam in its original state?

To answer this question, you need to understand the uses of plaster. This building material is used as a coating for protecting and decorating internal walls.

Imagine a hole in your house filled with expanding foam and left naked. Wouldn’t it look hideous? In such scenarios, plaster does a great job of hiding these imperfections on your walls.

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