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Can You Put Plaster Over Caulk/Sealant? (How To)

There are a few main materials used when finishing the interior of a home, these are plaster, caulk, and paint. All of these materials are easy to work with, but it’s important to do things in the right order, and using a proper method to ensure it lasts a very long time. So, in this article I will explain if it’s possible and recommended to plaster over caulk.

As a general rule, you can plaster over caulk/sealant. But, best practice is to use caulk or sealant after a wall has been plastered. But, plaster adheres well to caulk. To allow better adhesion rough up the surface of the caulk using coarse grit sandpaper before applying plaster.

Man putting plaster on the corner of the walls

The main purpose of caulk is to keep a watertight seal that is flexible. If corners and edges are plastered they will crack due to the expansion and contraction of the wall, and is the main reason a flexible material like caulk is used for these areas. There are a few things to be aware of when applying plaster over caulk/sealant, below I will cover everything you need to be aware of, as well as, the exact method to apply plaster over caulk.

Can You Put Plaster Over Caulk/Sealant? (How To)

Caulk has a few different uses, however, typically is applied after any surfaces have been plastered. But, it’s important to know what all the potential options are when working with plaster or caulk so here is whether you can put plaster over caulk/sealant.

Overall, it’s possible to plaster over caulk/sealant. But, only do so for small amounts of caulk. Plaster adheres best to a surface that is rougher. Whereas, plaster does not last as long on very smooth surfaces like a painted wall, or caulk. So, rough up the caulk using sandpaper first.

The main thing to be aware of is that caulk is ideally suited to areas that have movement. Such as between a wall and ceiling. Whereas, plaster is very rigid and doesn’t flex nearly as much as caulk.

However, caulk is also commonly used to fill in holes and cracks. And it works very well for this purpose. Therefore, there are two cases where plastering over caulk may be feasible:

  1. Over a crack or hole filled with caulk
  2. Where caulk has been used between along a join such as a wall and the floor

It does not make sense to use plaster along a join. Joins between two surfaces such as a wall, and the ceiling have a lot of movement. If plaster is applied to these areas it will crack.

Should You Put Plaster Over Caulk/Sealant?

Man putting plaster on the side of the kitchen faucet

While it’s possible to apply plaster over caulk, it’s important to know what to watch out for, and if there are any downsides to doing so. So, this is if it’s a good idea to put plaster over caulk.

In general, avoid plastering over caulk/sealant. Caulk should ideally be applied after plaster. But, plaster will adhere to caulk as it’s perfectly fine to plaster over caulk. But, do not plaster over caulk joins between two walls. Plastering over holes or cracks filled with caulk is perfectly fine.

Caulk in bathrooms, and other areas that are very humid can develop mold. Never plaster over caulk that has mold. Instead, remove the caulk first and apply a new layer of caulk.

This is only possible where caulk has been used along a straight edge, such as where the shower pan meets the floor. You should rough up the caulk surface and make it as even as possible. Doing so will mean you need to use fewer coats of plaster.

After applying a coat of plaster you should wait 20 minutes, before applying another coat. If the underlying caulk is very uneven, you will need to apply more layers of plaster to get a perfectly flat finish.

What Tools Do You Need To Put Plaster Over Caulk/Sealant

Tools used for plaster

There are a few minimum tools you need to apply plaster. However, there are a few additional things you need to apply plaster over caulk depending on the state of the caulk. Here is a list of everything you need to apply plaster over caulk/sealant.

Overall, a trowel, bucket, hand board (also called a hawk), a mixer, water brush, and coarse grit sandpaper. Denatured alcohol is optional and is necessary if the caulk is very uneven. Denatured alcohol will reliquify caulk so you can smooth it out.

Below is a table that explains what each tool is used for, and why you need it:


What it’s used for


Mixing up the plaster


Applying the plaster to the caulk

Hand board (hawk)

For holding the plaster after you’ve taken some out of the bucket. Used in one hand, while you trowel it on to the caulk using the other hand.


Optional but highly recommended. For mixing the plaster. They cost on average $100 but save a lot of time, and can be reused for other plastering jobs

Water brush

For brushing the finished plaster surface to smooth it out and make the wet plaster very smooth

Coarse sandpaper

For roughing up the surface of the caulk. Allows far better adhesion of the plaster to the caulk. Which makes the plaster stronger and more resistant to cracking.

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Denatured alcohol

Optional – Only required if the caulk is rough and uneven. Ideally, the caulk should be smooth and flat. Using sandpaper can take too long for very uneven caulk. Or, not be possible.

All of these items/tools are required for plastering any surface. The only additional thing you will need for caulk is denatured alcohol. But, this is also optional depending on whether the caulk is uneven.

It’s a good idea to use it if there are bumps and grooves in the caulk that stick out by more than about 3 mm. If you use sandpaper it will take too long. Especially for larger areas of caulk.

What Preparations Do You Need To Put Plaster Over Caulk/Sealant?

Man putting plaster

Before putting caulk over plaster there are a few preparatory steps that you should do. Doing so will ensure the plaster lasts a very long time, and reduces the number of coats of plaster you need to apply to the caulk/sealant. Here are the preparatory steps you should do when applying plaster over caulk.

Copyright article owner is for this article. This post was first published on December 12, 2022.

In general, always sand the caulk using coarse grit sandpaper. Doing so roughs up the caulk, and allows the plaster to adhere much better to the caulk. After that brush off the area thoroughly to remove any dust and debris. Then, you can apply a first coat of plaster over the caulk.

The good thing about plaster is that it’s very forgiving of the underlying surface. For example, it’s possible to plaster over fairly rough surfaces and achieve a smooth flat finish. However, the more even the underlying caulk is, the fewer coats of plaster need to be applied. Therefore, you should smooth off the caulk using the sandpaper as much as you can.

Another very good option is denatured alcohol. Denatured alcohol will re-liquify caulk, and you can then smooth it off far easier than sanding it. Also, caulk can be removed from joins, such as, between the wall and a ceiling, using a scraper. A screwdriver, and chisel can also be used but aren’t as effective as a scraper.

Essentially you scrape the caulking out of the join. However, it’s common to use caulk to fill in cracks, and small holes. If this is done, then you can plaster directly over the caulk.

Before doing so, rough up the caulk using coarse grit sandpaper to get better adhesion between the plaster and the caulk. When this is done plaster will last a lot longer.

Many people also use fiberglass sheets to strengthen plaster. This is recommended but optional.

How To Put Plaster Over Caulk/Sealant

confused man standing

Applying plaster over caulk is very easy to do. Here are step by step instructions for how to apply plaster over caulk/sealant.

In general, rough up the surface of the caulk using coarse grit sandpaper. After that, mix up the plaster in a bucket and apply it using a trowel. The packaging on your plaster will state how thick each coat should be, and is typically, ½ an inch (1.25 cm) thick.

Typically, it will state you need to wait about 20 minutes after applying a layer of plaster, before applying another one.

The steps to plaster over caulk are the same as the steps to plaster a regular wall. It’s very simple and easy to do:

Overall, plaster can be applied over caulk. But, ideally caulk should be used after a wall or surface has been plastered. To allow better adhesion rough up the caulk using a coarse grit sandpaper. After that plaster can be applied using the regular method of plastering a surface.

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ReadyToDIY is the owner of this article. This post was published on December 12, 2022.

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