GB2030059A - Water activatable cement webs - Google Patents

Abstract

A water-activatable cement web which comprises a substrate of fibrous material or foamed plastics material which is partially impregnated with a cementitious composition which is reactive with water to form a set mass, and a water impermeable membrane adhered to the membrane in the region which is substantially free from cement.

Description

SPECIFICATION water activatable cement webs In our prior patent specification 1,504,124, there is described a water activatable cement tape primarily intended for construction purposes comprising a fibrous or foamed plastics substrate impregnated with a cementitious composition. In use, such tapes are thoroughly wetted and pressed onto the surface to be coated or protected, such as a pipe or wall. While the tapes described in our above-mentioned prior patent have proved of value in many applications, they do suffer from the limitation that they are not impermeable to water in the dried, cured condition. While the permeability to water can be reduced by including additional amounts of elastomeric binder in the cementitious composition, such measures do not result in a fully waterimpermeable cured product.In our experiments to overcome this problem, attempts to marry the water activatable tapes described in our prior specification with a water impermeable membrane have met with the difficulty that adhesives do not bond readily to the cementitious surface of the dry uncured tape due to the powdery surface of the latter.

The present invention is based on the discovery that, if the substrate of the water activatable tape described in our above prior patent is coated from one side only so that the substrate is only partially impregnated and the cement does not significantly contaminate the other side of the tape, a waterproof membrane can be satisfactorily bonded to the side of the substrate which is substantially free from cement. The resulting tapes can be used in the same way as described in above prior specification for protecting pipework and building structures, or for effecting repairs of such structures and the resulting cured tape is capable of excluding water, both as liquid and vapour.

According to the present invention, there is provided a water-activatable cement web which comprises a substrate of fibrous material or foamed plastics material which is partially impregnated with a cementitious composition which is reactive with water to form a set mass, and a water-impermeable membrane adhered to the membrane in the region which is substantially free from cement.

The tapes in accordance with the present invention may be conveniently prepared using a slurry as described in our above prior British specification 1,504,124 and coating the slurry on one side only of a substrate such as woven hessian, polyester or viscose fabric or other suitable fabrics using a flat bed coater. When the cementitious coating has dried, the material which is to provide the water impermeable membrane is attached to the surface of the substrate, which is substantially free from cement. Any convenient method of forming the water impermeable membrane may be adopted, e.g. coating of extrusion as a hot melt or from organic solvent solution or dispersion. Emulsion coating is possible when the water content of the emulsion is sufficiently low and drying takes place rapidly after coating so that activation of the cement component is prevented.A further technique, which is useful in the case of thermoplastic sheets and foils, e.g. polyethylene, is by hot lamination.

An aternative method of producing a partially impregnated web involves fully impregnating a suitable substrate, e.g. by the dip coating method described in British Patent No. 1,504,124 and laminating the impregnated web with a second unimpregnated web so as to form a composite web in which one face is free from cement. If the two webs are brought together while the impregnated web is still wet, the two webs will stick together and remain bonded on drying without the need for additional adhesive.

A further alternative method of producing a partially impregnated web involves forming the web as a tube or sleeve (e.g. by knitting the web directly in tubular form or sewing the edges of an elongate web together) and impregnating the flattened tube by dip-coating or roller coating from both sides or by any other convenient method. If the thickness of the fabric is chosen so that the composition does not penetrate to the interior, the tube can be opened out again by slitting the edge to form a partially impregnated web having one surface uncontaminated with cement. In some circumstances it may be convenient to manufacture the web in tubular form and coat the inner surface of the tube with a water-impermeable material. This can be achieved using a suitably designed spraying or extrusion head.The resulting tubular products will have a reinforced curable cement outer surface and an inner surface having a coating or film of waterimpermeable material. Such products may be used for example in lining the interior of pipes, particularly water pipes and sewage pipes. Suitable methods of placement of such pipe linings are described in British Patents Nos. 1,340, 068 and 1,449,455, the tubular products of this invention normally being wetted just prior to insertion in the pipe. Alternatively tubular products for pipe lining purposes can be produced in accordance with the invention by forming the web into a tube, e.g. by sewing edges together, after application of the cement slurry and the waterimpermeable membrane.

The water impermeable membrane has the additional advantage in use that it restricts the evaporation of water from the wetted, activated tape and thereby ensures a more satisfactory cure of the cement than would otherwise occur. In accordance with the further feature of the invention, the waterproof membrane may be formulated so as to be permanently tacky. In this embodiment, the tacky membrane may be applied to the surface to be protected to form a temporary or permanent bond therewith. Alternatively, the cementitious layer may be wetted and used to adhere the tape to a surface and the tacky surface of the waterproof membrane used to bond a final decorative layer to the tape.

According to a further embodiment of the invention, a composite tape may be produced in which the membrane is positioned internally in the tape. This can be achieved by coating one side of the substrate with the cementitious composition and forming a sandwich by applying the water-proofing membrane between two layers of the resulting tape so that in the final product, the tape has both external surfaces coated with a cementitious composition and an internal water impermeable membrane.

The invention will be illustrated with reference to the following Examples.

Example f Water Activatable Composite Tape with Pressure Sensitive Adhesive Layer A slurry of Portland cement in methyl ethyl acetate was prepared as described in Example 1 of our British patent No. 1,504,124. Methyl cellulose and nitrile rubber were added to the slurry as described in the specified Example of our British patent No. 1,504,124.

A web of hessian about 10 cms wide was coated on one surface only with the slurry using a flat bed coating machine set to a wet coating weight of 0.75-3.0 kg/m2. After drying it was observed that, while some penetration of the cementitious slurry into the hessian web occurred, the uncoated side was substantially free from cement.

A hot melt polymer composition was prepared from the following ingredients: Parts by Weight 1. Bitumen (450 Pen) 72 2. Asbestos fibres 5.5 3. Powdered calcium carbonate 1 6 4. Lutanol J.30 1 5. Polyethylene 5.5 Lutanol J.30 is a polyvinyl ether available from BASF and is present in this formulation as an adhesive promoter. The hot melt composition was prepared by mixing ingredients 2 to 4 into the molten bitumen.

The resulting hot melt composition was coated onto the side of the hessian remote from the cement coating at a temperature of 11 0,C. and a coating weight of 0.7 kg/m2 using a roller coating machine. On cooling, the bituminous adhesive coating exhibited a high degree of permanent tack and could be firmly bonded to concrete and other surfaces by finger pressure.

After activation of the cementitious coating and ailowing the cement to cure, a hard, water vapour impermeable layer was produced.

Example 2 Water Activated Composite Tape with Non-tacky Layer A web of hessian tape was coated on one side only with a cementitious slurry and then dried as described in the previous Example.

A hot melt adhesive composition was prepared from the following ingredients: Parts by Weight 1. Ethylene-vinyl acetate copolymer (vinyl acetate content = 28% melt index =6) 35 2. Esterified rosin 25 3. Barium sulphate 30 The EVA copolymer and the rosin were melted together and the barium sulphate dispersed in the melt. A coating of the resulting hot melt composition was applied at a coating weight of 0.7 kg/m2 to the cement-free side of the hessian tape as described in Example 1. On cooling, the EVA adhesive layer was firmly bonded to the hessian and had a tack-free surface.

The composite tape is preferably used by wetting the tape and pressing the cementitious surface into contact with a substrate such as a wall or roof structure. By virtue of the presence of the layer of EVA adhesive, the evaporation of water from the wetted tape is retarded and this increases the strength of the cured cement. In addition, the EVA adhesive layer provides a substantially waterproof membrane which protects the building structure against ingress of water. The rate of cure of the cement can be increased if desired by using an aqueous activating solution containing an accelerator such as calcium chloride or by applying hot water to the cement web. The latter technique can be used advantageously in lining the interior of pipes, which can be filled with hot water after placement of the web in contact with the interior of the pipe.

The above two Examples were repeated using the formulation described in Example 2 of Patent 1,503,124.

It will be appreciated by those skilled in the art that many variations and modifications may be made in the composite tapes as described in the Examples above.

For example, the coating weight of the water impermeable membrane can be varied according to the particular end purpose in view and the nature of the substrate and other variables.

However, at present we prefer to utilise a coating weight of between about 0.1 or 0.2 and 5 kg/m2, especially between 0.75 and 2 kg/m2.

The formulation of the water impermeable membrane can be varied widely in accordance with measures known in the art to achieve the degree of surface tack or water-impermeability or other properties required for a specific end use.

For example, the membrane may be a formulation based on bituminous material, nitrile rubber, polyurethane, polychloroprene, styrene-butadiene rubber, epichlorohydrin rubber, natural and reclaimed rubber and synthetic polyisoprene, chlorinated polyisoprene, polyisobutylene, polybutadiene, butyl and chlorosulphonated polyethylene elastomers, polyolefins, polyvinyl ethers, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyrate polyamides, polyacrylates, polymethacrylates, polystyrene, polyvinyl chloride, ABS, polyvinylidene chloride, chlorinated natural rubber, ethylene-vinyl acetate, polysulphide, silicones, polyesters, unsaturated polyesters, epoxide resins, drying oil based materials such as alkyd resins. Such polymers or copolymers may be used separately or in admixture with two or more polymers or additional modifying agents.

Examples of suitable modifying agents include natural and/or synthetic resins e.g. hydrocarbon resins, phenolic resins, wood resin derivatives, natural and/or synthetic waxes, e.g. paraffin wax, plasticisers, e.g. dicyclohexyl phthalate, mineral or synthetic fillers, which may be particulate or fibrous in nature e.g. clays, calcium carbonate and asbestos.

Similarly, the nature of the cementitious slurry can be varied widely as indicated in our above mentioned British patent. In addition, stearic acid or other saturated or unsaturated fatty acids or esters and synthetic waxes can be incorporated in the cementitious slurry to act as a waerproofing aid and thereby further enhance the waterproof properties of the final cured materials.

In many cases the tape or webs produced in accordance with the invention will be overlapped when applied to a building structure. It may therefore be advantageous, particularly in the case of composite tapes having a pressure sensitive layer, to coat the cement slurry in a band leaving an uncoated margin at each edge on the cement-coated side. This arrangement enables the individual lengths of tape to be overlapped and the tacky surface bonded to the cement-free margin of the adjacent length of tape.

The composite tapes of the present invention will find a number of uses in building construction, repair and related applications. These include: 1. Waterproofing coatings.

2. Construction of roofing, particularly flat roofing.

3. Roof flashings.

4. Protecting steelwork from corrosion and fire damage.

5. Pipe-wrapping.

6. Upgrading the fire resistance of polymeric coatings.

7. Damp-proof courses.

8. Waterproofing foundations, e.g. in basements.

9. Containment of water, e.g. in tanks and swimming pools and internal lining of water pipes.

10. Protecting insulation.

With regard to the last-mentioned use, the composite tapes may be used with advantage in the external insulating of buildings, as described in our copending patent application, No.

37004/78, filed coterminously with the present application.

In roofing applications of the cement impregnated webs, it is preferred to use a bituminous water-impermeable membrane bonded to the web. The bituminous composition can be used to bond the web to the roof and the web then activated to cause the cement to set. The end result is a water-impermeable membrane which is strengthened and possesses fire-resistance as a result of the reinforced cement layer.

Water-proofing of foundations of buildings is conveniently carried out as follows, using a bituminous coated cement web. The web is stuck to the inside of the concrete shuttering using the tacky, bituminous surface and the shuttering then filled with concrete in the usual way. The wet concrete will activate the cement in the web which will become securely attached to the exterior of the resulting concrete structure. The bituminous layer will part from the shuttering when this is removed leaving a concrete structure having a securely bonded waterproof bituminous covering. This procedure avoids the normal laborious and messy procedure of painting the exterior of cured concrete structures with a thick bituminous, waterproofing paint.

The cementitious compositions used to impregnate the web are preferably of the same general character as described in our British Patent No. 1,504,124. This prior patent describes water activatable tapes comprising a substrate of fibrous or foamed plastics material impregnated with a cement, an organic binder which binds the cement to the substrate while the cement is in its uncured state and a hydrophilic thickener. The purpose of the hydrophilic thickener is to assist the penetration of the water into the tape on activation. In some circumstances, the organic binder can be dispensed with, but preferably the organic binder is an elastomeric polymer such as a natural or synthetic rubber. When activating the cement in the web, an aqueous solution may be employed which contains substances which promote or retard the rate of cure of the cement.

Claims (14)

1. A water-activatable cement web which comprises a substrate of fibrous material or foamed plastics material which is partially impregnated with a cementitious composition which is reactive with water to form a set mass, and a water impermeable membrane adhered to the membrane in the region which is substantially free from cement.

2. A cement web according to Claim 1 wherein the substrate is coated from one side with the cementitious composition, the opposite side of the substrate being substantially free from cement.

3. A cement web according to Claim 1 wherein a substrate of fibrous material or foamed plastics material is fully impregnated with the cementitious composition and is laminated to a substrate which is substantially free from cement.

4. A cement web according to any one of the preceding Claims wherein the water impermeable membrane is a polymer composition.

5. A cement web according to any one of the preceding Claims wherein the water impermeable membrane is coated onto the cement-free surface of the substrate as a hot melt.

6. A cement web according to any one of the preceding Claims wherein the water impermeable membrane is thermoplastics foil or sheet which is attached to the cement free surface of the substrate by hot lamination or extrusion.

7. A cement web according to any one of the preceding Claims wherein the membrane is applied to the substrate at a coating weight of from 0.75 to 2 kg/m2.

8. A cement web according to any one of the preceding Claims wherein the water impermeable membrane has a permanently tacky surface.

9. Water activatable cement webs substantially as described with reference to the Examples.

1Q. A method of covering or protecting a structure which comprises applying to the structure a cement web as claimed in any one of claims 1 to 7 and 9, which has been wetted with water or an aqueous activating solution, the web being positioned so that the cement bearing surface is in contact with the structure.

11. A method according to Claim 10 wherein the web is heated to accelerate hardening of the cement.

12. A method of covering or protecting a structure which comprises adhering to the structure a cement web as claimed in Claim 8 by pressing the tacky surface of the membrane into contact with the structure, the cement web being wetted to activate the cement.

13. A method according to claim 10 wherein the structure is a pipe and the web is in the form of a tube which is inserted into the pipe with the cement impregnated surface facing outwardly.

14. A structure which has been covered with a cement web by the method claimed in any one of claims 10 to 13.