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7 Places Where Not To Use Expanding Foam

Expanding foam is one of the best products available for providing insulation and sealing areas that allow air to move in or out of your home. The foam can penetrate spaces and fill voids as the liquid expands into foam before hardening.

Contractors and homeowners alike use spray foam in new construction, renovations, and repairs. There are times and places where expanding foam is less-than-ideal. The following list highlights situations where you should avoid using spray foam to prevent potential damage to you or your property.

where not to use expanding foam

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1. Avoid Closed-Cell Expanding Foam In Walls

Using expanding foam to insulate existing walls is a popular alternative to tearing down drywall and installing other insulating materials. If you plan on doing this yourself, avoid using closed-cell spray foam.

These products do not expand as much as open-celled foams. That means it will be harder to fill larger voids between wall studs. Using closed-cell foams will require more foam as well as more holes to fill your walls.

The foam will likely leave voids that will allow air and heat transfer, reducing the effectiveness of your insulation project. This type of expanding foam is more rigid, and it may cause movement of loose structures within the wall as it sets.

2. Do Not Use High Expansion Products Around Doors And Windows

Manufacturers often label expanding foam products as High Expansion or Low Expansion. As the name would suggest, high expansion products will fill large voids, and low expansion products are for smaller spaces.

Avoid using High Expansion foams between door or window frames. These are tight spaces, and the expanding foam could build up enough pressure to pop these frames from the wall.

Use a Low Expansion foam for these voids instead. They tend to expand only one-third of the volume that High Expansion products do. Low expansion foam will build far less pressure in these tight spaces.

3. Do Not Spray Foam As A Permanant Basement Leak Repair

Spray foam is a quick way to stop leaks through your basement or foundation walls. Expanding foam is not a permanent fix, and using it as one will cause problems.

The source of the leak continues to provide water along the exterior of the wall. That water will move into other areas and create new leaks. If the expanding foam did not completely stop a leak, water could damage other building components (like wooden studs).

Expanding foams are not waterproof. These products have varying levels of water-resistance, depending upon the formula. Standing water will eventually begin to break down the foam over time, making expanding foam a temporary solution at best.

4. Avoid Open Cell Spray Foam On The Roof

Open-cell foam is more flexible, and it is breathable. That will allow moisture penetration from one side of the foam to the other.

If moisture penetrates the foam, it can potentially gather between it and the wood on your roof. That can lead to eventual wood rot if the expanding foam stays in place.

You would need to remove the expanding foam to allow the wood to dry. If you plan to use open-cell spray foam beneath the shingles of your home, have a professional install it. The key is to form an airtight seal to prevent leaks.

5. Do Not Use Expanding Foam Near Electrical Boxes

Many homeowners want to use spray foam between an electrical box and an exterior wall. You should avoid doing this, as it will cause you more problems than it solves.

The foam can work into the box as it expands. It can cover wires and jam up components.

Safety is another consideration. Spray foam contains many flammable chemicals that present a hazard until the product cures (which is usually eight hours). Some foam formulas remain flammable even after it has cured completely.

6. Do Not Use Expanding Foam Around Ceiling Lights, Fans, Or Open Flames

Do not try to spray foam into the voids around recessed fixtures. Ceiling lights and fan motors can generate heat.

If these items overheat, they may stop working. The heat can also build around the fixtures, increasing the risk of fires.

Avoid using expanding foam near open flames, such as a pilot light. The foam can catch fire, even after it has cured or “gassed-off” completely.

7. Avoid Using Expanding Foam As A Waterproof Barrier

Open-cell spray foam allows air and moisture transfer, giving it low water-resistant qualities. Closed-cell foam lacks space in its structure, giving it a much higher level of water-resistance. These foams are not impervious to water penetration and will eventually break down if submerged or in contact with standing water.

That includes products designed for use in wet locations, such as Great Stuff Pond & Stone. It has a higher-level of water-resistance, but it is not waterproof.

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