Expanding foam is a product that most DIYers find indispensable. While manufacturers label it as an insulating and sealant product, contractors and homeowners have come up with many other uses for it.
People often wonder if spray foam can be used to block water leaks. What follows is a closer look at how expanding foam and water react with each other, as well as steps that you can take to stop water leaks using it.
Related: Locations Around The House Where Expanding Foam Should NOT Be Used
Understanding Expanding Foam
Before discussing how to use expanding foam to stop water leaks, we need to take a closer look at what it is and how it handles contact with various levels of water.
What is expanding foam?
Spray foam is a liquid form of two organic compounds (Isocyanate and Polyol Resin) that expand when mixed. The foam contained in most canisters that you buy will expand up to 30 to 60 times after leaving the can.
It is a closed-cell foam, which is dense enough to prevent humidity from penetrating it or for mold to grow from it. Almost all spray foams that you buy will have at least this characteristic.
Are expanding foams water-resistant or waterproof?
- Water-resistant: Yes
- Waterproof: No
Before answering that question, we need to be clear about what each of those terms means.
Water-resistant indicates that something can withstand some penetration of water. The amount of resistance depends upon the density of the material.
Waterproof indicates an impervious material when it comes to water penetration.
Expanding foam is closed-cell, making it dense enough to have some form of water-resistance. Spray foam is not waterproof since it can break down over time if submerged underwater.
You can get a general idea of the resistance by reading the product’s label. Spray foams that are intended for indoor use only, or suggest that you avoid contact with water, will have low water-resistance. Products like Great Stuff Pond & Stone have a much higher resistance level (can be used as a water-resistant layer in pond conditions).
What happens when expanding foam gets wet?
In small quantities, water can help you when using spray foam. You can mist the surfaces the foam will cling to, as well as the foam surface after spraying is complete. That low level of water helps to activate the foam as it expands and speeds up the hardening.
Smaller quantities of water can delay the foam from adhering to a surface. The foam can overtake small droplets or trickles as it expands, allowing it to seal small punctures of cracks.
Larger quantities of water will cause the foam to harden in clumps as the water mixes with portions of the expanding compounds. That could prevent the expanding foam from forming a seal in the area you have sprayed.
Attempting to use a can of expanding foam under sitting water will not work, as the water will prevent the foam from attaching to any surfaces, and the foam will clump and rise to the surface.
Once spray foam is dry, the closed-cell material can repel water. If submerged, the foam will eventually begin to break down as water penetrates the foam between the cells.
Can you make expanding foam waterproof?
Another thing you might wonder about is if spray foam can be made waterproof. The short answer is no.
Canned spray foam is a medium-density closed-cell material. To become impervious to water penetration, you would have to alter the composition of the foam to make it a high-density closed-cell compound.
Where Can Expanding Foam Be Used To Stop Water Leaks?
- Foundations/Basement walls
- Exterior to interior wall penetrations
For most DIYers (and some professionals), spray foam is an option when stopping water leaks from entering the home through cracked foundations or basement walls. It will be more than sufficient if you locate and remove the source of water on the other side of the barrier. If that source remains, you will run the risk of the spray foam eventually breaking down (or forcing the water into other areas that will leak).
This product is less-than-ideal for use on plumbing unless you are sealing off a penetration point that is leaking. It does create an adequate moisture barrier that can prevent pipe moisture, mold, or metal rust from entering through a pipe penetration point.
Using Expanding Foam To Stop Water Leaks On Walls
- Locate leak on wall
- Determine source of leak
- Prepare crack or hole
- Spray as directed
- Verify leak has stopped
- Clean crack or hole
- Eliminate water source
Locating the crack or hole on an unfinished surface is easy. It becomes tricky if you are trying to find one sitting behind a finished wall. In that case, you might have to locate the entry point on the exterior of the wall or contact a professional.
Once you find the leak, you need to determine if spray foam will stop the leak. Heavy-duty damage from a collapsing wall, for example, will not be fixed by a can of expanding foam.
Next, you need to figure out what is causing the leak. Is it a broken water pipe? Water that is sitting between the wall and the ground?
Finding the source will allow you to eliminate it. Removing the water (if possible) will allow you to work without continuous leaking. You might have to shut off a sprinkler system or remove a portion of dirt near the wall to remove standing water.
From here, you need to prepare the crack or hole to accept the expanding foam. Remove loose debris and clean off surfaces when possible. A damp surface is ideal, but a wet surface can make it more difficult for the sealant to hold.
Before spraying, read the instructions carefully and use the spray foam as the manufacturer instructs you to do. For most products, this will involve filling gaps halfway, giving plenty of room for the foam to expand. Once you place the foam, give it time to work into the surface.
Allow the product to set before adding more. You will not want to give a complete hour, as water may prevent the foam from firming in the recommended amount of time. Apply extra only if you can work it into the crack water is leaking out.
Once the leak stops and the foam hardens, you can trim extra materials that are sticking out of the wall. Use caution as you trim down flush with the foundation or basement surface.
Finally, eliminate the water source. The best-placed expanding foam will break down over time if the water sits on its surface continuously. Fix broken pipes, shore up the ground around foundations or basements, or remove the water sources.
Using Expanding Foam To Stop Water Leaks On Wall Penetrations
For the most part, you can follow the same steps as described above. Keep in mind that most penetration points contain conduits, pipes, or metal sheeting. The foam needs to be able to adhere to all materials to help prevent water leaks.
The item penetrating the wall needs to be in good condition as well. If the object is damaged, it may continue to leak even if the penetration point is made waterproof. A leaking water pipe needs to replacing, not patched with expanding foam.
Stay Safe And Keep Clean
Avoid working in areas where there is a chance of electric shock. You also should avoid using foam on walls with severe damage. Be smart and call a professional.
Wear safety equipment, including eye protection and gloves. Most canned sealants are also flammable, so follow safety instructions around sources of flame and always have proper ventilation.
Expanding foam is messy and can be hard to clean up. Most manufacturers provide cleaning instructions, so follow them to keep your clothing, tools, and property safe from damage.
Related: How to Easily Remove Cured Expanding Foam From Carpet