Background of the invention There are many applications in which it is required to mix two powders or to prepare a mix of a powder and a liquid. In particular in the building trade, one may need to mix flowable solids such as sand, cement and ballast and to add water to form wet concrete.

Hitherto, the conventional method used for mixing powders with one another and with liquids has been to churn the ingredients. Cement mixers used for preparing plaster, mortar, cement and concrete use a drum that constantly rotates in the same direction and has an internal screw for turning the constituents over or churning them until they are thoroughly mixed.

There are several disadvantages to mixing ingredients in this manner. The first is that the process is somewhat messy and the ingredients are often spilled. Second, the container used for the mixing is difficult to clean. When preparing building materials, contamination between batches can cause some materials, such as plaster, to become unworkable very quickly. Furthermore, cement mixers require power and cannot be used in locations where electricity is not readily available.

In US 5,743,636 single it is proposed to mix bag quantities of blended cement and aggregate with water to form concrete using a flexible mat that is arranged with a

shallow central basin bounded by a flat skirt. A plurality of handles, suitably four, are provided in the skirt near the mat edge. A sufficient amount of water to mix with a single bag or batch of pre-blended cement and aggregate is placed in the basin, and the batch amount of cement and aggregate is then poured onto the mat atop the water. Two persons grasp the mat by way of adjacent handles and mix the water with the cement and aggregate by alternately raising and lowering diagonally opposite mat handles.

Though this proposal avoids the need for power, it is still very messy, especially when used with fine powders such as plaster, because the powder is not contained during the mixing process nor while it is being poured from a bag into the basin of the mixing mat.

Object of the invention The present invention seeks therefore to provide a method of mixing flowable materials which can easily be carried out manually under clean conditions.

Summary of the invention According to a first aspect of the present invention, there is provided a method of mixing flowable materials, which comprises placing the materials to be mixed in an elongate flexible resealable bag having handles at its opposite ends and alternately raising and lowering the handles relative to one another to cause the materials to tumble alternately in opposite directions within the bag, the bag being closed during mixing to prevent powder from escaping.

Preferably, the resealable bag used for mixing is a disposable bag that serves also for packaging the constituents of the mixture.

According to a second aspect of the invention, there is provided a bag for enabling a flowable solid to be mixed with a liquid, the bag being elongate and having walls formed entirely of a flexible liquid impermeable material, the bag further having a handle at each end and a resealable mouth for enabling the ingredients to be mixed to be introduced into the bag.

In accordance with a further aspect of, the invention, there is provided a package comprising one or more flowable solids contained within an elongate flexible liquid- impermeable bag having a handle at each end for enabling the bag to be gripped manually and a resealable mouth for allowing a liquid to be added to the contents of the bag.

The seal used to close the bag need only be sufficient to prevent powder ingredients from escaping and may be formed in the same way as the extruded seals on some polythene bags which comprise a cylindrical bead on one side received in a cylindrical socket on the opposite side.

It is desirable for the bags used for mixing to be disposable bags so that they may also serve for packaging the constituents of the mixture. In this case, there is no need to clean the bags after use and there is no risk of cross contamination between batches of the mixture.

Brief description of the drawings The invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a mixing bag, Figure 2 is a plan view of the mixing bag shown in Figure 1 when empty, and Figure 3 is a view similar to that of Figure 2 showing a mixing bag with an alternative form of handle.

Detailed description of the preferred embodiments Figure 1 shows a banana-shaped mixing bag 10 with handles 12 at its opposite ends and a fastener 14 extending along its length. The bag 10 is made of a plastics material, such as polyethylene, which is liquid-impermeable and strong enough to support the weight of the mix which is to prepared within it. The fastener 14 is preferably of the extruded type used in resealable bags, having a part cylindrical bead along one side and an elongate part cylindrical socket for receiving the bead along the opposite side. It is alternatively possible to form the fastener as a zip fastener. The mouth of the bag may take other forms so long as it may be resealed after it has been opened. The "seal"in this context need not necessary be an airtight seal, so long as it is able to prevent the powder from escaping from the bag during mixing.

The bag of Figure 1 is shown in Figure 2 in its flat state, before being filled with the constituents of the mix.

The bag 10 can be formed by welding two sheets of plastics material along a generally elliptical path. The handles 12 are formed separately and attached to the plastics material of the bag. In the alternative construction shown in Figure 3, the handles 12'are formed by cut-outs with welded edges.

In use, of the bags in Figures 1,2 and 3 the constituents of the mix that is to be prepared are placed in the bag and the appropriate volume of liquid is added to the mix. For example, if preparing mortar, sand and cement would be placed in the bag and water would be added. The seal 14 is then closed to retain the powder within the bag and mixing is carried out by alternately raising the two handles 12 to cause the contents of the bag to roll and tumble alternately in opposite directions. Because all the mixture is contained in the bag, mixing can be carried out with

little or no mess and the tumbling action mixes the constituents almost as quickly and as thoroughly as a powered mixer.

The mix can be carried to the site where it is to be used by means of the same bag. If both handles 12 or 12' are held together, the bag 10 can be carried without the risk of spillage of the mix. Once the mix has been used, the bag can be re-used. If the mix is still wet, it can be washed out readily. If the mix is allowed to harden, on the other hand, because the material of the bag is flexible it can be peeled away from the hardened residue.

Even though the bag can readily be re-used, it is more convenient for it to be disposable and to this end it is possible to use the bag as the packaging for the constituents. Thus, when buying a bag of plaster, the powder would be packaged in a bag of the invention and the user would have only to open the bag and add water. The package may in this case additionally include a measuring vessel, such as a plastics ball or a graduated bucket, to ensure that the correct quantity of water is added to the mix.

Though the invention has been described by reference to building material, it may be used in other applications. For example, when baking, one may need to mix together powder ingredients such as flour, sugar and cocoa powder and then to add liquids such as water, milk and egg yokes to form a mix.