Spray expanding foam over crushed cardboard boxes and 2 common household items and the neighbors will beg to know your secret.

Create captivating faux-concrete backyard boulders using just three simple materials, and watch your backyard transform into a tranquil and natural oasis. This DIY project is perfect for those who love the aesthetic of natural stone without the hassle and cost of heavy lifting and expensive materials. By using expanding foam, crushed cardboard boxes, and two common household items, you can craft stunning decorative pieces that will have your neighbors in awe.

These faux boulders work beautifully in garden settings, adding texture and visual interest. Pair them with lush greenery and trailing plants for a natural look. Use them as decorative accents around a pond or water feature, or place them strategically in flower beds to create a layered effect. Their neutral tones complement a variety of garden styles, from modern minimalist to rustic cottage gardens.

Expanding spray foam (2-3 cans)

Begin by crushing the cardboard boxes into irregular shapes to form the base of your boulders. This will give the boulders their bulk and natural shape.

Place the crushed cardboard on a concrete garage floor or any other flat, protected surface.

Hold the expanding spray foam can about eight inches above the cardboard and apply a generous layer over the boxes, ensuring all cardboard surfaces are covered.

Allow the foam to expand and cure according to the manufacturer's instructions, typically 1-2 hours.

Once the foam has fully expanded and hardened, use a utility knife to trim any excess foam and refine the shape of your boulders.

Apply a layer of spray adhesive over the foam to create a tacky surface that will help the paint adhere.

Finish by spraying a coat of gray paint over the entire surface of the foam to give it a realistic concrete appearance.

Allow the paint to dry completely before placing the boulders in your desired outdoor location.

For a more varied appearance, try experimenting with different shapes and sizes of crushed cardboard to create a range of boulder styles. Consider using different colors of spray paint to match your garden's color scheme or to simulate different types of stone. You can also add texture by sprinkling sand onto the wet paint or using a sponge to dab on additional layers of paint for a more weathered look. If you want to make the boulders more durable for outdoor use, apply a clear sealant to protect the paint from the elements.