Can You Caulk Over Expanding Foam?

Expanding foam is useful for insulation and sealing various gaps and cracks. However, if you’ve never used this material before, you might wonder whether it’s acceptable to use caulk to cover it.

You can’t caulk over expanding foam. Doing so may cause the foam to react with the caulk and re-expand. To cover expanding foam, you should trim it and paint over it.

The rest of this article will discuss how to cover expanding foam properly. I’ll also include detailed instructions on how to paint over the material. Keep reading if you’re planning on using expanding foam in your home.

What Happens if You Caulk Over Expanding Foam?

You shouldn’t use caulk to cover expanding foam because the materials could react with each other and cause the caulk to re-expand.

Expanding foam, which comes in a can, provides polyurethane or isocyanate thermal insulation. Caulk contains polyurethane, making it an excellent material for sealing cracks and gaps.

Because both expanding foam and caulk contain polyurethane, if you try to cover the foam with caulk, it may start to expand again and ruin your original application.

Therefore, I don’t recommend caulking over expanding foam. You should only use one to seal any gaps or cracks.

How To Properly Cover Expanding Foam

Expanding foam can be difficult to cover up. Once applied, the foam rises as it expands and hardens. If you need to make the foam aesthetically pleasing, the best way to do so is to trim it down and paint over it.

cuts off excess foam

Caulk is a popular choice for filling any gaps or cracks in walls, but it isn’t always the best option. Unlike applying caulk, trimming and painting allow you to cover expanding foam without sacrificing insulation value or creating an unsightly mess.

To trim expanding foam, follow these steps:

  1. Allow the foam to cure completely. Most types of foam take under 24 hours to cure, and some foams take as little as 12 hours. I recommend looking at the packaging on your foam so you have a good idea of how long you’ll need to wait. The foam is completely cured when you can touch it without feeling sticky.
  1. Wear your protective equipment. Polyurethane can be toxic and dangerous for people with respiratory problems. I suggest putting on a mask and a pair of goggles.
  1. Cut the excess foam until it sits flush against the wall. You may have to make multiple slices, so keep going until the foam is flat. If a utility knife doesn’t work, I suggest using a metal scraper. 
  1. Sand the foam with sandpaper or a sanding block. Doing so will smooth and shape the material, making it easier to work with.
  1. Wipe the foam down with a damp cloth to remove any leftover dust. If the area is particularly dusty, I recommend blowing it with pressurized air to get rid of it.

My favorite scraper is the Tarvol Flexible Putty Knife (available on I like this scraper because the blade is strong, durable, and flexible, so it’ll be able to scrape away the foam effectively and quickly. I also like that the handle is rubberized and comfortable to hold, so you won’t hurt your hand while getting this job done. 

Once the foam is flat and smooth, follow these steps to paint over it:

  1. Choose your preferred painting method. If you’re covering a large area, I suggest using spray paint because it’ll be less time-consuming, and you’ll get an even application. Use a paint roller for a large area if you don’t want to use aerosol. 
  1. If you’re covering a small area, you can use a hand brush, especially if you need to apply the paint precisely. For more information, you can read my guide on paint rollers versus paint brushes.
  1. Apply the first coat lightly. Ensure that there’s no foam exposed. 
  1. Once the paint has dried, apply a new coat until you’re satisfied with how the color looks. Don’t be discouraged if it takes more coats than you were prepared for, as the foam will cause imperfections in the paint job that may still be visible after the initial coats.

If you’re impatient to get the job done, you can use a fan to speed up the drying process. Expanding foam is heat-resistant, so you can also try drying the area with a hair dryer. I like this Tornado Store High-Velocity Drum Fan (available on because it moves large air volumes, despite its small size. I also like that the fan is made from durable aluminum and has a rust-resistant grille, so it’ll last a long time.

Additionally, I suggest using acrylic paint for the best results. Acrylic works best with polyurethane. After three or four coats, you should be good to go.

Related Posts:

When To Use Expanding Foam

Expanding foam is an extremely versatile material that you can use in various ways. It’s great for sealing and filling gaps, creating insulation, and providing noise-proofing. What’s even better is that you can easily disguise it with acrylic paint to match almost any environment.

using expanding foam

You can use it for various purposes other than insulation, such as:

  • Protecting fragile items
  • Stabilizing fixtures
  • Plugging holes in the exterior of your house
  • Filling pipe holes
  • Stabilizing your plumbing pipes
  • Filling spaces underneath concrete or patios
  • Silencing a sink by applying foam to the bottom
  • Using it as an adhesive for stones, bird baths, or waterfalls

If you need to fill in cracks or gaps around windows or doors, you can apply expanding foam and then paint over it with colors that match the existing walls or trim. Even if you don’t have much experience with painting, the results will still look great when finished.


Expanding foam is a great way to fix various things in your home, especially cracks and gaps. However, you’ll want to cover it up after you’ve applied the material.

You shouldn’t use caulk to cover expanding foam because the polyurethane in the caulk could react with the polyurethane in the paint and re-expand. Instead, I suggest trimming the expanding foam and painting it with acrylic paint.