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How to Remove Expanding Foam From Brickwork and Masonry

removing spray foam from brick

When a gap needs filling or a draft needs sealing, we’ve all reached for a can of expanding foam to do the job. Chances are, we’ve all gone a little overboard at least once. After all, expanding foam expands, and sometimes it expands a bit more than we expected it to—all over your nice brickwork and masonry. As frustrating as that can be, it’s not a lost cause. Here’s how you get rid of stuck-on expanding foam without having to tear your whole wall down and start over. 

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Catch Expanding Foam Before It Dries

Expanding foam is much easier to remove from brick and masonry (and from anything else, for that matter) if you’re able to get to it before it sets. Once it’s hardened, spray foam is incredibly durable. It’ll most likely outlive your grandchildren if it’s not exposed to direct sunlight. So do yourself a favor and try to remove it while it’s still in a semi-liquid state. 

Use Protection

Right off the bat, it’s important to keep in mind that expanding foam in its liquid state isn’t something you want to get on your skin if you can avoid it. The stuff that’s used to remove it—acetone (more on that a little later)—is even worse. So take some precautions to protect yourself. Gloves are a must, and you should also wear eye protection in case of spatter, and a face mask to protect your lungs from fumes. 

Remove With a Rag

As quickly as you can, use a dry rag or paper towel to wipe away as much of the still-wet expanding foam as possible. And wipe it away gently. Think of it as gathering the loose foam up with the towel and removing it from the wall with a pulling motion. Avoid pushing the foam deeper into the grain of the brickwork or masonry. You should be able to get most of it off this way.  

Blot With Acetone

Dip the corner of a clean rag in acetone and blot away the remaining foam. Acetone is one of the few things that will dissolve expanding foam, and dabbing with a rag should break it down enough to easily wipe it away. Acetone is the active ingredient in nail polish remover (if you’re able to swipe some from the missus, it will do the job nicely) but it’s also the main ingredient in PVC cleaners like Oatey All-Purpose Pipe Cleaner, which is great for removing expanding foam. Use a natural cotton cloth for this purpose; acetone breaks down many man-made fibers along with the spray foam. 

Rinse

Once you’ve removed all visible traces of the expanding foam, use a different rag with clean water to rinse away as much of the acetone as possible. Acetone will seep into the crevices of brick and mortar, so get in there with water quickly to rinse most of it away. 

A Word on Safety

Acetone is nasty stuff, and you really shouldn’t get it on your skin. It can cause redness and irritation, and with prolonged exposure can cause your skin to becomr dry and cracked. Sure, your wife basically dips her whole hand in it to take her nail polish off, but that’s a diluted version of it and, honestly, even then it’s really not a great idea. Wear a pair of high quality rubber gloves like butyl rubber gloves, which are designed to be chemical resistant. Acetone will eat through latex gloves in 10 minutes, and nitrile gloves in 4 minutes. 

Removing Dried-On Expanding Foam

Unfortunately, it’s not always possible to remove excess foam before it dries. Maybe you walked away after filling a gap in the wall, and the expanding foam overspilled the cavity before you had a chance to check on it. Or maybe you’re renovating an older home only to discover that some over-eager DIYer before you got a little wild with a can of Great Stuff, and just left it on the brickwork. In any case, removing foam once it has cured is an uphill battle, but one you can still win. 

Cut Off What You Can

Start out by using a utility knife to cut off the biggest chunks of expanding foam. Get down as close to the brickwork or masonry as you can, cutting at an angle nearly parallel with the surface. You may also be able to use a paint scraper to get down even closer. At this point, there will still be foam deep in the texture of the brick, but the surface should be close to clean.  

Scrape, Scrub and Scour

Getting the foam out of every nook and cranny in the brick or masonry texture is going to be the tricky part, but you can scrub a lot of it our with the right tools. The trick is to find brushes that are strong enough to dislodge the foam, but not so abrasive that they damage the brickwork. Avoid metal bristles, as they can really do some damage. Stiff nylon brushes are better, and should be able to get most of the foam out if you work in a firm, circular motion. The ultra-stiff industrial stripping brushes made by Drilbrush are great, as that attach to any power drill, which does a lot of the work for you. Again, you should be wearing goggles and masks to keep small particles of foam out of your eyes and lungs. 

Your Old Pal Acetone

After scrubbing and scouring your brick with a stiff nylon brush, there may still be a small amount of foam residue left on the surface. It’s time to turn to acetone once again. Unfortunately, acetone doesn’t dissolve it anywhere near as effectively once the foam has cured. Its effectibveness depends on what kind of foam you’re dealing with, but it will still loosen its bond with the brick or masonry surface. Dab some acetone on the surface with a rag, and then give the surface another scrub to dislodge the last remaining traces of form. Once you’re done, rinse the surface with water. 

Pressure Washer

Another option is to use a pressure washer, at least if the wall you’re trying to remove expanding foam from happens to be outside. That said, you should avoid the high-pressure settings so you don’t damage the brick. The effectiveness of a pressure washer on expanding foam varies, but if the foam has been outdoors and exposed to the sun’s UV rays for a few years, it’s likely to have weakened enough that a pressure washer on a lower setting (up to 1500 psi) can do the trick. 

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