AU2016101410A4 - Wall Construction for Framed Building - Google Patents

Abstract

The invention describe a framed wall construction system and method where sheets of metal rib mesh are fastened to structural frames in an efficient manner, and on which fibre reinforced mortar is then sprayed or troweled onto to form layers of steel reinforced concrete 5 cladding on both sides of the fames. Various material can be optionally added within the cavity of the frames to deliver other desirable properties of the wall such as thermal and sound isolation. The method delivers constructed walls that has a solid feel and touch, straight and flat and crack resistant. Figure I Figure 2

Description

DESCRIPTION

BACKGROUND OF INVENTION

In framed house construction, timber is traditionally used in the construction of the structural frames. Once the frames are erected on site, cladding are fastened to both sides of the frames to form the final constructed walls. The cladding are normally boards or panels and can be of different materials. Some commonly used materials are compressed fibre cement, gypsum, concrete and clay.

Increasingly, light gauge galvanized steel strips, rolled into structurally robust cross sectional profile such as a “C” sectional profile, are used in the construction of the frames. There are advantages in using rolled light gauge steel over timber. Among them, steel is lighter on a comparative basis, water resistant and termite resistant. However there are also difficulties working with steel. One of them is the high thermal expansion coefficient of steel compared to timber. This creates difficulties when common cladding materials are used.

One frequently encountered issue is cracks in the cladding. When sheets of cladding such as compressed fibre cement boards are attached to the frames, using many screws and/or glue to form solid walls, the joints between consecutive boards are joined together using some strong jointing compounds and then flushed to hide the joints. However as a result of the difference in thermal expansion rate, in particular under the Australian climate where the difference in temperature between summer highs and winter lows may be more than 40 degree Celsius, the stress within the materials is great. In many instances this internal stress leads to cracks at the weakest points in the material, in particular on external walls where the temperature difference is greatest. The weakest points in the entire wall system are normally the joints of the board cladding. While there may not be structural consequences, the visual imperfection is not acceptable to building owners. Over the years, various flushing methods were developed to overcome this. However these methods are expensive to implement, resulting in low adoption especially in the competitive residential housing sector.

Other solutions are avoidance solutions. One such solution is the creation of expansion joints, which is a gap, in some less noticeable locations of the walls. In another solution, referred to as “expressed joints”, a gap is created between all consecutive boards. Yet another solution avoided the issue with “weather boards”, which are strips of boards, installed and overlapped each other horizontally, totally avoiding the need to flush.

While the above methods avoided the issue, not every building owner desire a house with those external appearances. In the residential housing market place, a desirable quality house to many people is still one that has flat, plain walls without joining lines everywhere. In addition the wall should not sound hollow and should feel robust. These two desirable properties are not achievable with board type cladding. Beyond the touch and feel of the walls, other desirable properties would be good noise and thermal isolation.

This invention provides a practical method of constructing the solid walls on structurally framed house in which the resulting walls are flat and plain and have no need for expansion joints. The resultant walls feel solid and robust and can easily achieve any thermal and acoustic specifications. The most important virtue is the ease of installation and the relative cheap cost of the described installation method.

THE INVENTION

This invention provides a method for constructing the solid walls for structurally framed houses. The frames may be constructed using timber or light gauge steel. An illustration of the installed structural frames using light gauge steel frames is shown in Figure 1. A rib mesh is an elongated metal sheet fabricated in such a way as to have ribs at regular intervals. Between the ribs, on the metal sheet, hundreds of small partially closed shapes are punched and the cut area pushed upward so as to form “hooks” in between the ribs. The type of shapes is not important and may be part of a circle, square, oval or any regular or irregular shapes. An example is shown in Figure 2

The rib mesh is fastened to both sides of the frames in a horizontal manner by means of screws or nails at the intersection of the ribs and the frames. The rib mesh is joined to each other by overlapping horizontally. Horizontal overlap is an essential element of the method although the amount of overlaps is not important. By allowing varying amount of overlap, there is no need to cut the sheets to precise lengths to accommodate the length of the walls.

See Figure 3 for an illustration of the installation. In one practical implementation, sheets of 2m length are procured. On site, bundles of the 2m length sheets are stacked together and bulk cut using a metal grinder into half to give sheets of lm length. A few other bundles of the 2m sheets are stacked together and bulk cut in one go into sheets with lengths of 0.6 m and 1.4 m. The two cuts give rise to bundles of the rib mesh that are 2m, 1.4m, lm, and 0.6m in length. With these bundles, any wall that is more than 0.6m in length can be exactly and fully covered without any further cuts. For example any wall between the lengths of 5m and 5.4m may be clad exactly end to end with 2 pieces of 2m length rib mesh and a piece of 1.4m length rib mesh with varying overlaps at the joint areas. The rib mesh may or may not be overlapped vertically.

Once the rib meshes are installed over all the walls, fibre reinforced mortar consisting of sand, cement, short polypropylene fibres and water is placed on top of the rib mesh. Other plastic based fibre or even natural fibre such as horse hairs may be used to substitute the polypropylene fibres. The fibre reinforced mortar can be trowelled on or sprayed onto the mesh by means of a mortar spraying machine. See Figure 4 for an illustration. As the mortar is placed onto the rib mesh, some of the mortar will be pushed through the gaps around the “hooks” to the back of the sheet of rib mesh. This tightly secured the mortar onto the rib mesh sheets. See Figure 5 for an illustration.

Once the mortar has cured, further industry standard plastering processes may be applied to deliver standard high quality finishes both internally and externally.

The cavity in the structural frames may be left empty or be filled with materials that can achieve various desirable wall properties. To enhance thermal isolation between the exterior and the interior of the house, thermal insulation batts can be placed within the cavity during the installation of the rib mesh. To enhance acoustic isolation, acoustic batts may be placed within the cavity during the installation of the rib mesh. To enhance robust feel, light weight aerated concrete can be pumped into the cavity.

WORKING PRINCIPLES OF THE INVENTION

When two solid rigid pieces of material of different thermal expansion coefficient are fastened tightly together, changes in temperature will cause the materials to expand with different amount. This will cause great internal mechanical stress and tension. The stress in a solid piece of material is uniform throughout the material, in which case the location in the material where the bond is weakest will be the first to give way. Once a tiny crack occurred, the bond at that location become even weaker and further stress above the threshold will cause the crack to get bigger.

In this invention, the rib mesh is the interface with the frame. The rib mesh has hundreds of punch out “hooks”, which give the metal space to expand and contract all over the material.

As the amount of expansion is linearly related to the underlying length of the material, in this case, the size of the “hooks”, the actual amount of expansion at the “hook” is very small. Note that expansion is a naturally phenomenon and cannot be eradicated. By the innovative arrangement, the unavoidable movement due to temperature changes is engineered to be distributed throughout the material, reducing the stress in the cladding material.

In the same context, cracks also occur in the mortar. When there is mechanical stress in the mortar, the location that has the weakest bond will first crack. Once a particular area has cracks, the bonds are further weaker and any further stress will cause the cracks to become bigger and ugly. In the invention, hundreds of thousands of very thin micro fibre is mixed into the mortar. While the words fibre reinforced mortar are used, technically the micro fibre does not offer any additional structural strength to the mortar. Instead they created hundreds of thousands of “weak” points in the material. These “weak” points are the boundary between the mortar and the fibres. When mechanical stress occurs in the mortar, the boundaries of the fibre with the mortar the location are where the “cracks” would occur. However there are hundreds of thousands of these locations. Therefore the “cracks” would be microscopic in size and cannot be seen with the naked eye. To the building owners, what they do not see is “not there”.

ADVANTAGES OF THE INVENTION

The rib mesh can be installed onto the frames speedily for the following reasons. Firstly it is noted that the rib mesh will eventually be embedded within the mortar. As a result, there is no necessity to accurately position the rib mesh on the frame. This relaxation of the installation precision reduces installation time and the need for highly skill tradesmen in the installation task. In the event that certain points of the installed mesh are too high, most likely at the overlapped rib area, one just need to go around with a hammer during the general inspection, and give those points a few whacks to lower them. This treatment does not give rise to any performance degradation of the wall. Secondly, the invention specifies horizontal overlap of the rib mesh. As a result there is no need to accurately cut the length of the rib mesh to exactly fit the length of the walls. On site cutting for accurate placement is a very time consuming task, and takes the bulk of the time in board and panel installation, such as in the installation of compressed fibre cement boards.

The placement of the fibre reinforced mortar onto the rib mesh is quick especially in big jobs where a concrete spraying machine is used. Even in smaller jobs where the mortar is manually trowelled on, a single plasterer can do about 180 to 200 square metres of wall in a 8 hour day.

The mortar on each side of the wall for a nominal thickness of 20mm is about 43 kg/m2. Compared to a 10mm thick plasterboard which is about 10.5 kg/m2 and a 10mm thick compressed fibre cement board which is about 14kg/m2, the constructed walls of this invention deliver a deeper solid sound when knocked on, giving it a robust, massive feel. The feel is comparable to brick constructed walls.

The constructed walls of this invention has virtually no cracks and has no need for expansion joints. This is due to the innovative design of the rib mesh and fibre reinforced mortar.

As the wall is rendered, and if done in accordance to current industrial standards, it is straight and flat. It does not suffer from the wavy patterns commonly associated with board based installation. Of course the wall fitted with boards can also be rendered if there is a requirement for such a wall to be straight and flat. However the cost of doing so far outstrip the construction method of this invention.

Claims (4)

1. CLAIMS THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: Claim 1: A framed wall construction system comprising: a set of structural light gauge steel frames or timber frame, a collection of sheets of metal rib mesh with lengths LI, L2, to Ln where n is some integer and with L1<L2<... <Ln, and fibre reinforced mortar consisting of sand, cement, water and short polypropylene fibre, where a selected collection of the sheets of the meal rib mesh are laid out in a horizontal manner from top to bottom and screwed or nailed onto the structural steel or timber frames at the intersection of the rib and the studs of the frames. The selection of the collection is as follows: For a wall of length L, a collection of metal rib mesh sheets is selected from the available sheets with lengths LI, L2, to Ln such that the sum of the lengths of the collection is the smallest number greater than L. The selected collection of sheets is then fastened to the wall in a horizontal manner such that the two sheets at the two end of the wall are in line with the wall. The excess of the sum total of the lengths of the collection over the length of the wall are overlapped at the joints between consecutive sheets. And upon the installation of the metal rib mesh, fibre reinforced mortar are troweled or sprayed onto the rib mesh to cover the entire mesh to a depth up to or beyond the top of the rib.
2. Claim 2: A framed wall construction system as in Claim 1 where thermal insulation materials are placed within the cavity of the structural frames to enable the constructed wall to achieve good thermal isolation between the two sides of the wall.
3. Claim 3: A framed wall construction system as in Claim 1 where acoustic or sound barrier material are placed within the cavity of the structural frames to enable the constructed wall to achieve good sound isolation between the two sides of the wall.
4. Claim 4: A framed wall construction system as in Claim 1 where sand, mortar, mud, or aerated mortar are placed within the cavity of the structural frames to enable the constructed wall to achieve good impact sound isolation between the two sides of the wall.