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What are Concrete Molds?

Wet concrete being poured.
In large project, concrete molds are called forms.
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  • Written By: Lou Paun
  • Edited By: Jay Garcia
  • Last Modified Date: 08 November 2014
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Finished concrete is a hard, durable substance with a variety of uses. Before the concrete mixture dries and hardens, it can be formed into many shapes. Concrete molds are used to create the shape the finished concrete will have.

In large scale projects, molds are called forms. Forms are built from wood to define the shape of concrete slabs, walls, sidewalks, and so on. They are kept in place while laying concrete and removed when the concrete shapes have dried and cured.

Molds for small projects can be designed in two different ways. Some ornamental molds have design details in the bottom and sides of the mold. After the concrete has dried, the mold is removed and the details, in reverse, are revealed in the concrete shape. It is necessary to oil these molds before using them, so that the concrete won’t stick to the mold as it dries. Otherwise, the details are likely to be damaged when the concrete mold is removed.

Other concrete molds are plain on the bottom and sides. After the mold is filled and the surface is leveled, details are added to the surface of the wet concrete. Mosaic and carved concrete shapes are often created this way.

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For smaller projects, concrete molds can be custom built in a particular shape. Melamine-coated particleboard is a good choice for building these molds to create many concrete shapes. Wet concrete doesn’t stick to this plastic surface, which makes it easy to remove the concrete mold from the dry concrete.

Readymade plastic molds can be purchased in a variety of forms. Many of them produce highly detailed pieces. All sorts of everyday objects can be used as concrete molds. A basket lined with plastic can be a mold for a concrete basket, for instance.

Crafters can build their own concrete molds with liquid urethane rubber or latex. The rubber is painted, poured, or sprayed onto a prepared surface and allowed to thicken. The rubber mold, which is a mirror image of the original object, is peeled off. It can then be filled with wet concrete to create an accurate copy of the original. Faux bois concrete shapes are usually made with this method.

Some projects require more than one mold. Concrete sinks, for example, are made with two concrete molds, one inside the other. The sink is created when wet concrete is poured into the space between the molds.

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anon928623
Post 3

Before the concrete mixture dries and hardens -- the word is "cures."

umbra21
Post 2

If you are hoping to make some garden features, like pots and things, with concrete you might want to consider using hypertufa instead.

It's basically cement, which has been mixed with peat moss or something like that.

People will add other things, like fiberglass, but if you are making it at home, you can just use some proportions of those two ingredients.

It comes out lighter than concrete and even lighter than terracotta, which can come in handy when you are planning to move things around the garden.

You can just use it with the same kind of concrete garden molds you would use with straight concrete or cement.

croydon
Post 1

I always thought that concrete was a modern invention as the process of making it seems to be quite involved.

But I suppose I shouldn't underestimate the abilities of people from early in our history, because the famous Roman pantheon is made from concrete. I am planning a trip to Rome and I was looking up the pantheon because I'm hoping to go and have a look at it. I don't know what I thought it was made out of though, because the structures of it must have been made in concrete casting molds.

It's even more incredible now that I know the amount of skill and artistry that went into making it. I'm really looking forward to seeing it in person.

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