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How to make a rock out of concrete


You can make realistic-looking rocks in many shapes and sizes easily and with little money

Rocks made out of concrete can be in any shape or size. They are easy and inexpensive to make and are a realistic complement to traditional stones you will find at a landscaping or garden center. To reduce weight, manmade rocks can also be hollow on the inside.

Fake rocks made out of concrete can be smooth or rough and you can even encourage moss growth for added realism. Paint the rocks for a realistic look or add whimsical touches such as leaf patterns or pebbles.

The supply list includes:

-A dust mask
-A mixing tub for the concrete
-Measuring pitchers for the ingredients
-Trowel
-Hoe
-Rubber gloves (concrete mix will eat through latex gloves)
-Two cardboard boxes, one large and one small to create the hollow inside of the rock
-Plastic trash bag
-Wadded up newspapers or other types of sturdy fillers

The concrete recipe:

-2 parts cement
-2 parts sand (#20 Builder's sand is best, but playground sand can be used)
-1 part vermiculite or perlite
-2 handfuls of fibermesh (the best resource for this is an inexpensive air conditioner filter - remove all the cardboard and tear apart the fibers. Use gloves)
-Water as needed

Set up the work area in a shady spot and out of the way. The rock will need to remain in place for about a week.

The larger cardboard box will determine the size of the base of your rock. Remember, the bottom of this box will be the top of the rock. Use wadded up newspaper in each of the corners and built up along each of the sides. This will keep the rock rounded on top. Add stones and rocks underneath and around the newspaper wads for extra support and interesting indentations.

Cover the box interior with a trash bag or plastic liner. Smooth it out or leave the wrinkles in for added rock texture.

Now you are ready to mix the concrete.

Add all the dry ingredients and combine them with a hoe or by hand (be sure to wear gloves and the dust mask). Add a little water at a time and continue mixing. Be careful not to add too much water as this will destabilize the strength of the concrete. The final result should look like thick mud.

Use a trowel or other type of scoop to begin filling the bottom of the box. The thickness should be at least four inches deep before inserting the smaller box. Tamp the mixture down and stir it around to release air pockets.

Add the smaller box with a weight, such as stones or a brick inside to hold it in place as you continue filling the sides of the outer box with concrete. The smaller box creates the hollow space inside your rock. The opening will be on the bottom side when the rock is turned over. Smaller rocks may not need a hollow area inside.

To include leaf patterns, place fresh or dried leaves along the liner and press into place with the concrete mix.

When the box is full, add additional newspaper wads between the liner and the upper edges of the box. When you turn the piece over, the rock will now have a natural curve around its bottom side rather than sitting flattened on the ground.

Cover the form with plastic and leave it alone for a couple days. If it has hardened enough in that time, you can remove it carefully from the forms. Test the hardness by scraping it with a screwdriver. If any marks can be made in the concrete, it should sit for a few more hours, unless you are planning to add carvings to the rock.

After removing the form, smooth the rock's surface with a scraper. Mist the rock once a day for about a week. For final curing and added strength, leave the rock alone for at least three weeks.

The rock can be painted and sealed, if you wish, and is now ready for placement. If you want to encourage moss growth, make sure the design contains a flattened indentation somewhere on the top. Find a rock on which moss is already growing and remove part of the moss and its base. Use wet dirt to hold it in place on your new rock and keep it moist until it takes hold.

With or without moss, your fake rocks will fool just about anyone.

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