GB2238822A

GB2238822A - Building repair system

Info

Publication number: GB2238822A
Application number: GB9025350A
Authority: GB
Inventors: Brian Philip Hardy; Richard Binns
Original assignee: HYDRA REMEDIAL SYSTEMS Ltd
Current assignee: HYDRA REMEDIAL SYSTEMS Ltd
Priority date: 1989-12-06
Filing date: 1990-11-21
Publication date: 1991-06-12
Anticipated expiration: 2010-11-21
Also published as: GB9025350D0; GB2238822B

Abstract

A method for facilitating the replacement of the corner column of a Boswell house comprises removing each of the existing corner columns in stages to leave a cut-away in the walls of the house. Securing means (6) are then secured in the end walls (5) of the cut-away and a replacement corner column is provided by filling the cut-away with repair mortar which bonds with and is secured in position by the said securing means (6). <IMAGE>

Description

DESCRIPTION BUILDING REPAIR SYSTEM The present invention relates to a building repair system and, in particular, to a method of repairing Boswell houses.

Boswell houses comprise at each corner a precast reinforced concrete column with cast in-situ clinker concrete cavity walls. The walls are cast directly on the foundations, which are simple strip footings cast in similar materials to the walls, and a damp proof course (dpc) is provided approximately six inches above ground level. The ground floors are usually solid concrete slabs. Around the basic system design a variety of layouts have been used to provide two-storey semidetached and terraced blocks.

The present reinforced concrete corner columns are L-shaped in section with 12" legs and are two storeys high, except for the single storey high columns used as the corners of passageways within terraced blocks. The reinforcement within the concrete columns takes the form of a square cage of steel with three vertical bars embedded in the column and a fourth in the open internal angle to provide a link between each column and the walls. The columns are supported on the dpe without any fixing to the foundations and the column heads are tied together at the eaves by steel rods which are embedded in the last lift of the concrete walls; the steel rods or ties provide temporary support to the column heads during construction of the walls.

The walls comprise two leaves of cast in-situ clinker concrete which is cast in lifts or sections of approximately 1811, a complete ring of all external walls being cast at one time with the shuttering positioned by the corner columns. The two leaves are connected by concrete ribs or ties at approximately 2'6" centres using pieces of slate or timber to form the bottom shutter to the ties. These ties are staggered in alternate courses.

The walls are not reinforced.

Structural defects have been found in Boswell houses, to the extent that the future of such houses has become questionable and there is a requirement for a system of repairing Boswell houses which is economical and relatively simple to carry out in order to avoid having to demolish the houses and build new ones at many times the cost of repair.

The deterioration of Boswell houses can be split into two distinct elements: a) The corner columns suffer from carbonation of the concrete and subsequent corrosion of the reinforcing bars, causing spalling and disruption of the render, b) The clinker concrete walls are subject to dimensional instability due to hydration and dehydration of the carbon fraction of the aggregate.

The present invention is particularly concerned with providing a solution to the problem of deterioration of corner columns. This deterioration has been caused in the main by moisture penetrating the carbonated and!or cracked concrete of the corner columns causing corrosion of the steel reinforcement set inside each column.

Although the columns do not carry any direct loading, they tie the corners of the walls of the houses together. The disintegration of these columns therefore affects the robustness of the construction and reduces its ability to restrain movement within the walls. The cracking induced in the corner columns also provides additional paths for the ingress of moisture to the wall concrete.

It is an object of the present invention to provide a building repair system for Boswell houses and, more specifically, a building repair system which allows the corner columns to be replaced.

According to the present invention there is provided a repair system for facilitating the replacement of the corner column of a Boswell house, wherein each of the existing corner columns is removed In stages to leave a cut-away in the walls of the house adjacent thereto, securing means are secured in the end walls of the cutaway and a replacement corner column is provided by filling the cut-away with repair mortar which replacement corner column bonds with and is secured in position by the said securing means.

Preferably, the end face of each wall is drilled with holes, each of which receives a stainless steel thread dowel, one end of which extends beyond the end face of the wall. Conveniently, each dowel is secured in place by means of a resin adhesive.

Preferably, a reinforcing mesh is secured between the free ends of the dowels, and together with the dowels provides a secure bond with the repair mortar which fills the cut-away. This, of course, ensure that full bonding is achieved with the adjacent walls at the corner of the house.

As indicated hereinabove, the existing corner column is removed in stages. One way of doing this is to make a cut in each wall to the thickness of the corner column.

This cut is made adjacent to any cracks in the wall so that the cracked portion of the wall is removed with the corner column. Then the corner column is cut and broken out in stages. Once the corner column has been removed the inside faces of the cut-away are grit blasted to ensure a laitance-free, fine gripping texture.

The repair mortar is conveniently sprayed on to ensure quick and simple application, and is preferably left with an "as sprayed" rough finish. The mortar may comprise an accelerator to speed initial set and hence allow high build layers.

Simple restraint is provided at first floor level and at the eaves of the house by tying the floor and roof joists to the walls of the house. In this respect brackets are secured to the walls, adjacent to the joists, by fixing resin anchored dowels into the inner leaf of the external cavity walls. These brackets are conveniently spaced at 1.2. metre centres and are secured to the joists by nails, screws or the like.

Preferably, stainless steel cavity ties are fixed between the leaves of the cavity wall. Alternatively, cavity wall insulation foam, such as Tyofoam, can be introduced into the exterior wall cavity and this effectively ties the leaves of the cavity wall together.

The exterior of the house is protected against further moisture ingress by the application of an external insulation and stainless steel reinforced render.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figs. 1, 2 and 3 each show a sectional view of the corner of a Boswell house with a reinforced concrete corner column therein in progressive stages of removal; Fig. 4 shows a sectional view of the corner of a Boswell house after replacement of the reinforced concrete corner column; Fig. 5 shows a sectional view through the wall of a Boswell house after modification; Fig. 6 shows a plan view of the floor/roof ties with the joists running perpendicular to the external wall, and Fig. 7 shows a plan view of the floor/roof ties with the joints running parallel to the wall.

Referring to Figs. 1, 2 and 3 there is shown a sectional view through a corner of a Boswell house with the reinforced concrete corner column 1 in progressive stages of removal. In each of Figs. 1, 2 and 3 the portions of the corner column 1 to be removed are indicated by reference numberal 8 and are shown shaded.

Initially, a cut 2 is made in the surface of the concrete wall 3 adjacent to the corner column 1. This cut is made to the thickness of the corner column 1 and adjacent to any cracks 4 in the wall 3 so that the cracked portion of the wall 2 is removed with the corner column 1.

The corner column 1 is removed in sections 8 of approximately 80mm to 100mm square by dry cutting the corner column and breaking out.

As shown in Fig. 3 the remains of the reinforcing cage embedded within the walls of the house are also removed, though this is not absolutely essential.

Once the original corner column has been removed the inside faces of the cut-away are grit blasted to ensure a laitance-free, fine gripping texture. Holes are then drilled in the end face 5 of each wall 2 to receive stainless steel threaded dowels 6. Typically these are 3OOmm long and are embedded in the end face of the wall for half their length. Each dowel 6 is secured in its hole by a resin adhesive.

With the dowels 6 in position a stainless steel grid mesh 7 is secured between the dowels to maintain 45mm nominal cover on both sides of the corner. A repair mortar, such as Sakret SM4PS, is then dry sprayed into the cut-away to fill it level with the existing render.

As an alternative to spraying, the cut-away can be shuttered and repair concrete poured into the space until it is filled. Then the shuttering is removed. Sakret SM4PS is a pre-bagged mortar comprising graded cements, non-reactive graded aggregate and an accelerator to speed initial set and hence allow high build layers. The concrete bonds to the dowels 6 and to the mesh 7 and ensures full bonding between the walls 2 and the new corner column 9.

An external coating is then applied over the corner column and the walls of the building as shown in Fig. 5.

The existing render 10 on the exterior faces of the building is first made good where necessary. Then insulation boards 11 are secured to the exterior faces of the building by tile adhesive 12. If required, as an alternative to, or in addition to the tile adhesive, mechanical fixing means can be used. Typically, the mechanical fixing means comprises expansion dowels. Mesh reinforcement 13 is then secured to the wall to provide a key for a subsequently applied layer of render 14.

Finally, a decorative finish 15 is applied - for example dry dash.

As shown a cavity foam insulation 18, such as Tyofoam, is introduced into the cavity between the inner and outer leaves 19 and 20 of the external wall to improve the house insulation and provide an effective tie between the leaves. However, as an alternative to this, stainless steel ties can be used to tie the cavity wall leaves together.

In order to prevent movement of the walls simple restraint may be provided at first floor and eaves level.

Referring to Figs. 6 and 7 of the accompanying drawings the simple restraint takes the form of L-shaped brackets 30 which are secured to the inner leaf 31 of the external wall of the building and to a single joist 32, where this runs perpendicular to the wall, as shown in Fig. 6, or a plurality of joists 32, where these run parallel to the wall, as shown in Fig. 6. The brackets 30, which comprise a mild steel strap, are each secured at one end to the inner leaf of the wall by means of dowel 33 which is positively secured In a specially drilled hole in the inner leaf of the cavity wall by means of a resin adhesive which is introduced into a specially measured out space 34 in the cavity insulation 35 introduced between the two leaves of the wall. (Such a space need not be specially provided if the wall leaves are secured together with cavity wall ties). The other end of the mild steel strap is nailed or screwed to the joists 32.

Claims

1. A method for facilitating the replacement of the corner column of a Boswell house, wherein each of the existing corner columns is removed in stages to leave a cut-away in the walls of the house adjacent thereto, securing means are secured in the end walls of the cutaway and a replacement corner column is provided by filling the cut-away with repair mortar which replacement corner column bonds with and is secured in position by the said securing means.

2. A method according to claim 1, wherein the end face of each wall is drilled with holes, each of which receives a stainless steel thread dowel, one end of which extends beyond the end face of the wall.

3. A method according to claim 2, wherein a reinforcing mesh is secured between the free ends of the dowels, and together with the dowels provides a secure bond with the repair mortar which fills the cut-away.

4. A method according to any preceding claim, wherein the existing corner column is removed by first making a cut in each wall to the thickness of the corner column, each cut being made adjacent to any cracks in the wall so that the cracked portion of the wall is removed with the corner column, secondly the corner column is cut and broken out in stages and finally once the corner column has been removed the. inside faces of the cut-away are grit blasted to ensure a laitance-free, fine gripping texture.

5. A method according to any preceding claim, wherein repair mortar is conveniently sprayed on to ensure quick and simple application.

6. A method according to any preceding claim, wherein simple restraint is provided at first floor level and at the eaves of the house by tying the floor and roof joists to the walls of the house.

7. A method according to claim 6, wherein brackets are secured to the walls, adjacent to the joists, by fixing resin anchored dowels into the inner leaf of the external cavity walls.

8. A method for facilitating the replacement of the corner column of a Boswell house, substantially as hereinbefore described with reference to the accompanying drawings.