Is Expanding Foam Waterproof? Not Really

Are you thinking about patching up a gap with expanding foam and wondering, “Hey, will this stuff stand up to water?” You’re not alone!

Let’s dive into this common question and see if expanding foam really is the waterproof wonder we hope it is.

How Waterproof Is Expanding Foam?

Generally, expanding foam is water-resistant and can handle occasional exposure to water and moisture.

Open-cell expanding foam is like a sponge, it’s made of tiny bubbles that are not closed off from each other. Water can seep into these spaces, making this type of expanding foam less water-resistant.

Closed-cell expanding foam has tiny bubbles that are completely closed off from each other. This makes it denser and more resistant to water penetration.

While both types of expanding foam offer some level of water resistance, closed-cell expanding foam is the more waterproof of the two.

Neither should be considered a complete waterproof solution for areas with constant exposure to water or moisture.

What About Expanding Foam Labeled as Waterproof?

Expanding foam products labeled as ‘waterproof’ indicates these products offer a higher degree of water resistance compared to others and can withstand more prolonged exposure to moisture.

In most cases, ‘waterproof’ expanding foam products are closed-cell foams. They’re denser and less permeable, which makes them more effective at preventing water penetration.

However, even these products have their limits.

While they’re more resistant to water, they may still not be the best choice for areas constantly exposed to water or very high humidity.

As always, when choosing a product for a specific project, check the manufacturer’s information. If in doubt, consult with a professional to ensure it’s suitable for your needs.

Don’t Use Expanding Foam to Stop Leaks

Don’t ever use expanding foam to stop leaks in a pipe or water line.

The foam might seal the leak initially, but over time, the pressure from the water flow will cause the seal to fail.

Expanding foam is more accurately described as water-resistant rather than fully waterproof.

While it can handle some moisture, it’s not designed for constant contact with water or high-pressure systems.

Is Expanding Foam Waterproof When Cut?

Expanding foam is not waterproof when cut. If you cut into open-cell expanding foam or closed-cell expanding foam, the exposed interior could potentially absorb some moisture.

If the foam is in a place where it could be exposed to water, seal the cut area with a waterproofing sealant to ensure water can’t penetrate.

Is Polycell Expanding Foam Waterproof?

Polycell expanding foam is designed to be water-resistant. It’s great for sealing gaps, stopping drafts, and preventing leaks.

While it can handle a fair amount of moisture, Polycell expanding foam isn’t designed to be a fully waterproof solution. After a while, it will start to absorb moisture.

If your project involves an area exposed to water, you might want to look for an alternative solution.

Is Expanding Foam Waterproof for the Bathroom?

If you’re looking to waterproof areas in the bathroom that are frequently exposed to water, don’t use expanding foam.

Expanding foam, especially when cut or damaged, will not hold up indefinitely in high-moisture conditions.

Use a more specialized waterproofing product instead.

What Happens if Expanding Foam Gets Wet?

When expanding foam is still wet or uncured, water can interfere with its ability to properly expand and harden.

This could potentially lead to a weaker seal that might not be as durable or efficient at insulating.

Once the expanding foam has cured and hardened, it becomes water-resistant. That means it can handle some water without any significant changes to its structure or performance.

However, expanding foam is not completely waterproof, especially if it’s open-cell foam or if it’s been cut.

In these cases, water can seep in, and if it gets trapped, it could lead to problems like mold or mildew over time.

In a nutshell, it’s best to let expanding foam cure in a dry environment and limit its exposure to constant moisture, even after it’s fully cured.

Can You Use Expanding Foam in the Rain?

Using expanding foam in the rain isn’t the best idea. Applying expanding foam in wet conditions, such as rain, can interfere with its ability to properly expand, adhere to surfaces, and harden.

Rain or moisture can weaken its structure and reduce its effectiveness as an insulator and sealant.

Does Expanding Foam Work Underwater?

Expanding foam isn’t designed to hold up under continuous water exposure, like being submerged underwater.

If you’re looking for a solution to seal or insulate something underwater, use a specialized underwater adhesive or sealant.

Where to Buy Waterproof Expanding Foam

You can buy water-resistant or waterproof expanding foam from home improvement stores like Home Depot or Lowe’s, online marketplaces such as Amazon or eBay, specialist retailers focusing on DIY or construction supplies, or directly from the manufacturers through their websites.

What Is the Best Waterproof Expanding Foam?

The best waterproof expanding foam can vary depending on the specific application and requirements of your project.

Here are a few popular products you may want to consider using.

Great Stuff Pond & Stone

This is a polyurethane-based foam sealant designed to secure stones in place in ponds and waterfall constructions. It’s been designed to be safe for fish.

You can get it from Amazon.

Loctite TITE FOAM Window and Door

This closed-cell polyurethane foam is water-resistant and is often used around windows and doors to create an airtight and waterproof seal.

It’s designed to be flexible to accommodate the natural movement of building materials.

You can get it from Loctite.

Touch ‘n Foam Landscape Exterior Filler Adhesive

This foam sealant is designed for outdoor use, including around ponds, and is noted for its strong adhesion and water resistance.

You can get it from Amazon.