GB2179990A - Improvements in cavity walls having corroded wall ties - Google Patents

Abstract

A cavity wall is made sound or more sound by locating corroded ties (14), using a metal detector and inserting tie bolts (22) at locations remote from the corroded ties. Thereafter, mortar is removed to expose the outer ends of the corroded ties, a pouch (36) filled with grease is placed in the joint so as to overlie the tie end and the joint is re-pointed. To insert the tie bolt (22), holes (18, 20) are drilled in the outer and inner skins (10, 12) the bolt (with the bush (29) removed) is turned to expand the rubber bush (28) into engagement with the bore (20) and the nut (31) is then turned to expand the bush (29) into engagement with the bore (18). <IMAGE>

Description

SPECIFICATION Improvements in Building Structures The present invention relates to building structures and more particularly to cavity wall structures.

The usual cavity wall structure comprises outer and inner skins secured to one another by metal ties which bridge the cavity between the skins. The outer skin will usually be of brick construction and the inner skin may be of brick or lightweight blocks such as breeze blocks.

The ties are conventionally made of metal, such as mild steel usually galvanized. In time, the ties rust and thereby expand so causing the skins to bulge.

The outer ends of the ties embedded in the outer skin are particularly subject to corrosion, the outer skin being exposed to the weather.

It is known to render a cavity wall structure sound or more sound by locating the positions of the corroded ties using a metal detector, removing bricks from the outer skin at the located poSitions, extracting the corroded ties thereby exposed, grouting in replacement ties and replacing the removed bricks. Such a method is expensive and time consuming.

The present invention resides in a method of making a cavity wall structure sound or more sound, the cavity wall structure having outer and inner skins secured to one another by metal ties which bridge the cavity between the skins and which have become corroded, in which method the positions of the corroded ties are located, replacement ties are fitted between the skins at places remote from the corroded ties, mortar is removed from the joint between the bricks at least at the located positions of the corroded ties in order to expose the outer ends of the corroded ties, a packing element is placed in the joint so as to overlie the outer end portions of the corroded ties and the outer skin is re-pointed, at least at the located positions of the corroded ties, whereby the packing element isolates the corroded ties from the brickwork and the new mortar.

Preferably, the mortar of the outer skin is completely removed from around the corroded ties and advantageously, the packing element is a pouch which is slipped over the corroded tie so that the latter can no longer come into contact with the outer skin or the new mortar.

Preferably, the pouch is filled with an anticorrosion paste, such as grease. The grease may contain a rust inhibitor.

In carrying out the present invention it has been found to be unnecessary to remove the corroded ties since the corroded ties are protected from further substantial corrosion and any further corrosion which does take place, does not damage the outer skin.

The replacement ties are preferably tie bolts which are inserted through holes drilled through the skins and then tightened up.

The replacement tie preferably comprises a double-ended expansion bolt having at each end a rubber or plastics bush confined between a collar adjoining the shank ofthe bolt and a nut on the respective end of the bolt, such that tightening the nut expands the bush into firm engagement with the wall of a bore in which the tie is fitted.

The expansion bolt is preferably made of corrosion resistant material such as stainless steel as are the nuts.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a fragmentary somewhat diagrammatic vertical section through a cavity wall structure, and Fig. 2 is a perspective view of a pouch.

The cavity wall structure shown in the drawing comprises a brick outer skin 10 and a brick inner skin 12 but the invention is equally applicable to a cavity wall whose inner skin is made of breeze blocks or the like lightweight blocks. The inner and outer skins are secured to one another by metal ties 14 which are embedded in the mortar of the inner and outer skins and which bridge the cavity 16 between the skins.

During the course of time, the ties 14, which may be of a variety of types and materials, become corroded and thereby expand, causing the skins or at least the outer skin to tend to bulge, crack or become detached from the inner skin.

In accordance with a preferred embodiment of the present invention the positions of the corroded ties are located using a metal detector and these positions are marked on the outer skin 10 by suitable marking means. Holes 18 and 20 are then drilled through the outer skin 10 and into the inner skin 12 at points remote from the locations of the corroded ties. The ties are conventionally disposed in a grid pattern and thus the holes 18 and 20 are drilled in a similar but offset grid pattern. Although the holes 18 and 20 and corroded tie 14 are shown in the drawing in the same vertical plane, generally this will not be the case and the drawing is therefore purely diagrammatic. Replacement ties 22 are then inserted in the holes 18 and 20 from the outside.

Each replacement tie 22 comprises a double ended bolt 24 onto whose screw-threaded ends nuts 26, 27 are screwed to form abutment collars for rubber bushes 28, 29 with the interposition of washers 25. Nuts 30,31 are screwed on to the free ends of the tie bolt and are provided with screwdriver slots to enable these nuts to be tightened. Tightening of the nuts 30,31 expands the bushes 28, 29 into firm engagement with the holes 18 and 20. The bushes 28,29 are made of a rubber or plastics material which is specifically designed to withstand attack from acids invariably present in bricks and mortar. The tie bolt 24 and the nuts 30,31 are preferably made of stainless steel to resist corrosion.

In a preferred method of carrying out the invention, direct access to the nut 30 at the inside is not required so that the hole 20 in the inner skin 12 can be drilled as a blind bore, thus not disturbing the plasterwork inside the building. To expand the bush 28, the tie bolt 24 is inserted with the outer bush 29 and the outer nut 31 removed. A box spanner can then be applied to the nut 27 to turn the tie bolt 24.

The bush 28 is prevented from turning by its engagement with the wall of the hole 20 and this prevents the inner nut 30 from turning. The tie bolt 24 is thereby screwed into the nut 30 to expand the bush 28. Alternatively, with the abutment nut 27 removed, a box spanner can be engaged with the abutment nut 26 to turn the latter. After the inner bush 28 has been expanded, the outer bush 29 and the nut 31 are placed on the tie bolt 24 and the nut 31 is tighted to expand the bush 29 into tight engagement with the wall of the hole 18 in the outer skin 10.

A rubber collar 23 is received on the shank 32 of the tie bolt 24 and is located between the inner and outer skins. This is to prevent any water running along the tie bolt from the outer skin 10 from reaching the inner skin 12. Such water drips off the collar 23.

Whilst a specific embodiment of tie bolt has been illustrated, various double-ended tie bolts may be used to tie together inner and outer skins as appropriate. Tie bolts are already available both of whose ends can be tightened by access from the outside only. Such known tie bolts are generally not so satisfactory when the inner skin is of breeze block or similar lightweight blocks which are apt to be damaged under pressure from conventional expansion bolts ofthe collet type.

After the replacement ties 22 have been inserted so that the shanks 32 of the ties bridge the cavity 16 to tie the inner and outer skins 10 and 12 together, the corroded ties 14 are exposed by removing the mortar from between the bricks at the located positions of the corroded ties. A pouch 36 (Fig. 2) is then inserted in the gap between the bricks so as to overlie the outer portions of the ties 14, and the pouch preferably extends into the cavity 16, as shown. Such pouch may be made of a plastics material, such as polypropylene.

The pouch 36 is advantageously filled with an anti-corrosion paste, such as grease, to inhibit further corrosion of the ties 14. The grease may contain an anti-corrosion agent and preferably contains a filler to help retain the grease in the pouch, particularly in hot conditions as might prevail when the outer skin 10 is exposed to the direct sun's rays.

After the pouch 36 has been put in place, the outer wall is re-pointed at least at the locations where the mortar has been removed to expose the ends of the corroded ties 14. Further expansion due to any further corrosion oftheties 14 which may nevertheless take place, does not affect the new mortar because the grease-filled pouch 36 isolates the new mortar from the corroded ties.

In general, corrosion of the ties takes place principally in the outer skin so that it is generally unnecessary to treat the inner skin but, if desired, the mortar can likewise be removed at the inner skin to expose the inner ends of the corroded ties and pouches can be inserted in the gap between the bricks or blocks over the inner end portions of the ties prior to re-pointing.

Claims (11)

1. A method of making a cavity wall structure sound or more sound, the cavity wall structure having outer and inner skins secured to one another by metal ties which bridge the cavity between the skins and which have become corroded, in which method the positions of the corroded ties are located, replacement ties are fitted between the skins at places remote from the corroded ties, mortar is removed from the joint between the bricks at least at the located positions of the corroded ties in order to expose the outer ends of the corroded ties, a packing element is placed in the joint so as to overlie the outer end portions of the corroded ties and the outer skin is re-pointed, at least at the located positions of the corroded ties, whereby the packing element isolates from the corroded ties from the brickwork and the new mortar.

2. A method as claimed in claim 1, in which the replacement ties are tie bolts which are inserted in holes drilled in the skins and then tightened up.

3. A method as claimed in claim 2, in which the hole drilled in the inner skin is a blind bore.

4. A method as claimed in claim 2 or 3, in which each tie bolt has adjacent each end a rubber or plastics bush which is expanded into engagement with the respective hole.

5. A method as claimed in claim 4, in which the tie bolt is turned to expand the bush adjacent the inner end thereof, the bush being prevented from turning by its engagement with the wall of the hole and thereby preventing a nut at the inner end of the tie bolt from turning.

6. A method as claimed in any of claims 2 to 5, in which a rubber collar is received on the shank of the tie bolt between the inner and outer skins.

7. A method as claimed in any preceding claim, in which a metal detector is used to locate the positions of the corroded ties.

8. A method as claimed in any preceding claim, in which the mortar of the outer skin is completely removed from around the corroded ties.

9. A method as claimed in any preceding claim, in which the packing element is a pouch which is slipped over the corroded tie.

10. A method as claimed in claim 9, in which the pouch is filled with an anti-corrosion paste.

11. A method of making a cavity wall structure sound or more sound, substantially as herein described with reference to the accompanying drawings.