GB2124610A

GB2124610A - Plastering material

Info

Publication number: GB2124610A
Application number: GB08320404A
Authority: GB
Inventors: Rentaro Naniwa; Hideho Tokuda
Original assignee: Nippon Kokan Ltd
Current assignee: JFE Engineering Corp
Priority date: 1982-07-28
Filing date: 1983-07-28
Publication date: 1984-02-22
Also published as: CA1218679A; ZA835458B; DE3327167A1; GB2124610B; KR840005419A; FR2531065B1; JPS5921564A; GB8320404D0; JPS6214515B2; KR900002297B1; FR2531065A1

Abstract

An improved thick set plastering material is prepared by adding to a conventional plastering material a synthetic high molecular (organic) admixture and a mixed aggregate wherein the ratio of inorganic binder to the mixed aggregate is 1:1 to 1:4 by volume and wherein the mixed aggregate includes slag and an organic or inorganic lightweight spheroidal substance. Such a plastering material can be laid on with a coat thickness of 5 mm to 20 mm in a single trowelling as well as being possibly applied in successive coats or layers as fresh mortar.

Description

SPECIFICATION Plastering material The present invention generally relates to cementing materials, such as plastering materials for interior and exterior works on structures, materials employed for repair and improvement works in building site, and troweliing materials for-forming bonding layers for tiles.

A typical known plastering material is a mixture prepared by mixing an inorganic binding material with a fine aggregate such as sand and the like in the ratio of one to three. A standard coating thickness obtained by of such a plastering material per single trowelling is about 1 mm to 5 mm depending on the kind of the plastering material. Therefore, in order to obtain a finishing or setting coat of 5 mm to 20 mm thickness, usually, trowelling must be conducted in about two or five stages. In addition, since it is difficult to successively overlay one coat on another in the state of fresh mortar by trowelling on account of the characteristics of the plastering material, it is obliged to perform trowelling such that after the first coat is left as it is for a sufficient curing period to harden, the second and third coats are overiaid on the hardened coat.Therefore, as the number of times of trowelling is larger, the term of works becomes longer. Moreover, since the causes of defects are complicated, such considerations must be taken that the inorganic binding material should be rich for the first coat in order to prevent dissociation but lean for the finishing coat in order to prevent cracking. The above-mentioned problems are encountered not only when a plastering work is initially conducted but also when a partially or totally dissociated portion of a plaster ground or finished layer is repaired, since, also in such a case, it is necessary to partially apply the plaster material by troweiling in two or three stages.In consequence, it disadvantageously takes a long term and large cost of works, and it is inconveniently difficult to obtain an excellent matching between the repaired portion and other healthy portions not requiring repair. Thus, if it is intended to obtain a coat of 5 mm to 20 mm thickness from a conventionally known plastering material in a single trowelling, it is practically impossible to obtain a coat thickness exceeding a standard coat thickness, within a range from 1 mm to 5 mm, in a single trowelling, owing to such factors as an insufficient adhesion with respect to the plaster ground surface, the slumping of the plaster material from the support and the difficuity in trowelling work.

Accordingly, it is a primary object of the invention to improve the thick set performance of plastering material by trowelling by adding a synthetic high molecular admixture and a mixed aggregate into the conventional plastering material.

To this end, according to the invention, there is provided a thick set plastering material consisting essentially of an inorganic binding material, a mixed aggregate and a synthetic high molecular admixture, the ratio of the inorganic binding material to the mixed aggregate being 1:1.0 to 4.0 (volume ratio), the mixed aggregate including slag and a lightweight spheroidal substance.

Fundamentally speaking, the workability of plastering materials can be represented by F value (corresponding to the press force of trowel), P value (corresponding to the resistance to slide of trowel) and M value (corresponding to the resistance of moment at the grip of trowel) which are shown in Fig.

1. As the results of various researches on aggregates added to plastering materials, a thick set plastering material has been obtained which has desired workability when applied in a thick layer.

More specifically, a plastering material suitable for thick coating has been obtained by employing as aggregate a mixed aggregate prepared by adding slag and a lightweight spheroidal substance into silica sand and sand equivalent thereto, which are conventionally known aggregates, in a predetermined proportion. The plastering material overcomes the above-mentioned problems of the conventional plastering materials and allows an appropriate pressure to be easily applied to the plaster ground surface with trowel. In addition, the plastering material is excellent in the adhesion to the ground, so that there is no possibility of slumping of the plastering material from the ground during or after the application of the former to the latter.Moreover, the plastering material is inevitably prevented from being applied in a thin layer, since if the material is unintentionally applied in a thin layer, the F value increases considerably.

As the aggregate for the plastering material in accordance with the invention, a mixed aggregate of silica sand, slag and a lightweight spheroidal substance is preferable, and the particle diameter of each of the components is desirably not larger than 3 mm, although it varys according to the thickness of the coat after the application of the plastering material and the use thereof. As the slag, blast furnace slag sand and/or sludge sand is employed, and as the lightweight spheroidal substance, glass hollow microsphere, synthetic high molecular spheroidal substance, pozzolanic spheroidal substance and so forth are employed, although these aggregates used must have qualities closely resembling those of the above-mentioned materials in such physical properties as particle diameter, shape and specific gravity.

The characteristics required of a plastering material suitable for thick coating are as follows: (1) possible to be trowelled within two to three times to obtain at least a total coat thickness of 20 mm, exceeding a standard coat thickness in the case of finish work, or possible to be overlaid on the previous coat not well dried within about three to five times in a short time until a total thickness of 50 mm is obtained in the case of repair work; (2) has no possibiliy of slumping or deformation thereof by its own weight during and after the application thereof, which means that the plastering material can properly solidify in a stage as early as possible after the completion of the trowelling work or has a large thixotropy.

(3) has deformability to absorb as much as possible any contraction deformation due to the constraint by the ground or support; (4) has a properly large trowel press force represented by the F value, becomes well attached to the ground or support, has an excellent adhesion, and is firmly solidified by compaction; (5) has a properly small resistance of moment at the grip of the trowel, represented by the M value, and hardly dissociates from the ground or support; (6) permit a smooth slide of the trowel (a small adhesion to the trowel, i.e., hardly sticks to the trowel surface and allows the trowel to be slid easily, which means that the (p value (the resistance to slide of the trowel) is small; and (7) makes it difficult to be laid in a thin layer, which means that it is easier for the operator to trowel the plastering material in a thick layer than in a thin layer, since the F value is extremely large when the operator trowels the plastering material in a thin layer.

The above-mentioned characteristics (1) to (7) are contrary to each other. For example, even if there is no possibility of any slumping or deformation of the plastering material, it may not be well pressed by the trowel, and the adhesion may be poor, or even if the plastering material is well attached to the ground or support with a moderate press force of the trowel, the plastering material may prevent the trowel from being slid easily.

It is considered that the plastering material in accordance with the invention can have all the above-mentioned characteristics, which are contrary to each other, owing to the fact that a synthetic high molecular admixture is added into an inorganic binding material, and as aggregate, slag and lightweight spheroidal substances are mixed into the material, in addition to silica sand, in properly determined proportions. According to the results of experiments, the composition ratio of the mixed aggregate allowing the plastering material to have the above-mentioned characteristics (1) to (7) is not larger than 70% wt. silica sand, 25% wt. to 75% wt. slag and 5% wt. to 50% wt. lightweight spheroidal substance, the sum of the silica sand and the slag being 95% wt. to 50% wt.

It has, however, been proved that, in case of employing only a substance of especially low specific gravity in lightweight spheroidal substances, the plastering material is still fit for use even if the proportion of the lightweight spheroidal substance in the mixed aggregate is on the order of 2 wt%.

In addition, the plastering material in accordance with the invention can employ as the synthetic high molecular admixture a polymer dispersion of styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, acrylic ester copolymer, vinyl chloride copolymer or vinyl acetate copolymer, and/or watersoluble cellulose ether or other high molecular substance. The polymer-inorganic binding material ratio should be from more than 0 to not larger than 45% wt. on the basis of solid content. Moreover, the ratio of the inorganic binding material to the mixed aggregate is 1:1.0 to 4.0 by volume.

The invention employs as the inorganic binding material (referred to as "cement" hereinafter) ordinary Portland cement, high early strength Portland cement, alumina cement, mixed cement, gypsum, lime and so on. It is also possible to add an inorganic and/or organic fibrous material in order to further improve the reinforcing effect. The plastering material in accordance with the invention is used to cover ordinary structures internally and externally. The plastering material is, moreover, employed as a bonding material for pottery tiles and other stone or finishing materials used in internal and external works and as materials for forming insulating and sound absorbing layers. Further, the trowelled surface of the plastering material is suitable for the embossed finish by a roller or the like as it is. In addition, the plastering material is suitable for use as a material for repairing buildings and other structures and a material for filling the gap between members.

Each of the raw materials employed in the plastering material of the invention has such effects on the thick set plastering material as shown in Table 1.

TABLE 1

Has a ball bearing effect: the trowelling workability is improved owing to the spheroidal shape.

Permits the plaster to be more lightweight.

Possible to relax any stress generated Lightweight by the thermal and moisture movements spheroidal in the building frame and the finished substance layer and provides deformability.

Has moisture in an amount sufficient for the plastering material to hydrate even after gelling and hardening, so that workability is improved and the hydration is promoted. Increase in thixotropy. Suitable for the thick set plastering material.

Has a proper water absorption property, so that the plastering material starts the initial absorption of moisture during the application to begin to Slag solidify and hence hardly slumps or is not easily deformed.

Has a large angle of internal friction since it is pulverulent and grannular and has rough surface, so that an arch effect can be expected to be obtained, and the plastering material is well heid by the trowel.

Improves mechanical properties over a long period through alkaline hardening. Increase in thixotropy.

Suitable for the thick set plastering material.

Has a large angle of internal friction since it is pulverulent and granular as well as angular, so that an arch effect can be expected to be obtained, Silica sand and the plastering material hardly slumps and is not easily deformed.

Reduction in drying shrinkage amount.

Suitable for the thick set plastering material Improves water retention and workability during the work and adhesion to the ground or support and waterproofness Synthetic of the plastering material after it is high molecular hardened. Reduction in drying shrinkage admixture amount. Improvement in flexing resisrance and dehormabmty.

Suitable for the thick set plastering material.

With respect to the above-mentioned mixing proportions, if the proportion of the lightweight spheroidal substance is less than 2% wt., the plastering material will undesirably become adhesive to the trowel, deteriorating workability and making the plastering material impractical. On the other hand, if the mixing proportion of the lightweight spheroidal substance exceeds 50% wt., the plastering material cannot be well pressed by the trowel, and it becomes impossible to apply a necessary pressure to the ground surface. Therefore, the plastering material loses adhesion required and is impractical. In addition, a slag content less than 25% wt. makes it possible to lay on the plastering material in a thin layer, hindering the operator from daring to lay on the plastering material in a thick layer.Accordingly, a plastering material having a slag content less than 25% wt. is unsuitable for use as the thick set plastering material. On the other hand, a slag content exceeding 75% wt. renders contraction cracks to be easily caused. Moreover, it is possible to add an inorganic and/or organic fibrous material in order to further improve the reinforcing effect and prevent the generation of contraction cracks. The invention will be described hereinunder through experimental examples with reference to the accompanying drawings.

Fig. 1 shows the principles of an apparatus for testing the characteristics of the plastering material in accordance with the invention; Fig. 2 is a graph showing the relationship between the F value and the coat thickness of the plastering material in accordance with the invention; Fig. 3 is a graph showing the relationship between the M value and the coat thickness of the plastering material in accordance with the invention; Fig. 4 is a graph showing the relationship between the v value and the coat thickness of the plastering material in accordance with the invention; Fig. 5 is a graph showing the relationship between the F value and the P value of the plastering material in accordance with the invention; and Fig. 6 is a graph showing the relationship between the F value and the M value of the plastering material in accordance with the invention.

EXPERIMENTAL EXAMPLE 1 First of all, the aggregates employed have such qualities as shown in Table-2.

TABLE 2

Oven dry Bulk Solid volume Kind of specific density of aggregate aggregate gravity (Kg/l) (%) No. 5 No. 5 silica sand 2.60 1.33 51.4 Slag , 2.32 1.28 58.5 Glass hollow microsphere 0.70 0.38 54.3 The composition ratio of the mixed aggregate employed in the experiments is such as shown in Table-3.

TABLE 3

Composition ratio (wt) Mixed aggregate No. 5 silica sand Slag Glass hollow microsphere A 50 50 0 B 50 30 20 C 30 50 20 Cement mortar was formed by adding ordinary Portland cement, a polymer dispersion of styrenebutadiene rubber and water to each of the above-mentioned three kinds of mixed aggregates A, B, C, and was tested by an apparatus shown in Fig. 1 to measure the F value, P value and M value, and the results shown in Figs. 2 to 6 were obtained. In this case, the polymer-cement ratio was 7% wt. on the basis of solid content; the ratio of cement to mixed aggregate was 1:2 by volume; and the watercement ratio was 48% wt. In addition, the room temperature was 20 + 20C; the humidity was 60 + 5% RH; and the used water temperature was 1 80C.

The thick set characteristics of the above-mentioned three kinds of mortar by trowelling five minutes after kneading will be considered hereinunder according to the results of the experiments.

Referring first to Figs. 2 to 4, when laid on in a thick layer (20 mm) the mortar employing the mixed aggregate A has an extraordinarily small F value and an unusually large ç value, so that the mortar is difficult to apply. On the other hand, when laid on in a thin layer (5 mm) the mortar employing the mixed aggregate A has a small y value and properly large F and M values. Accordingly, it is suitable for use as a thin set mortar but unsuitable for a thick set mortar. The reason for this is assumed that the mixed aggregate includes no glass hollow microsphere.

The mortar employing the mixed aggregate B, on the other hand, does not have much large differences in the F, M and (p values between the cases where it is laid on in a thick layer and in a thin layer and hence can be laid on in a thin layer. Consequently, there is a possibility that even if instructed to lay on the mortar in a thick layer, the operator inevitably lays on the same in a thin layer. Therefore, although the mortar employing the mixed aggregate B can be used as a thick set mortar, it is not optimum.

The mortar employing the mixed aggregate C has properly large F and M values even when laid on in a thick layer (20 mm) and can be properly pressed against the ground or support by the trowel as well as has a small P value to allow the trowel to slide smoothly, so that the mortar is laid on in a thick layer. Moreover, if the mortar is laid on in a thin layer, the F and M values extremely increase, so that the operator unintentionally lays on the mortar thick in one stroke of trowelling at a building site. The reason for this is assumed that a larger amount of slag is mixed into the mixed aggregate and in addition, the glass hollow microsphere is mixed thereinto.

Figs. 5 and 6 show proper characteristic regions (shadowed regions) presumed in consideration of balance of the facilitation of the thick coating work and the improvement in the characteristics of the hardened finished layer due to the property of the mortar to be well pressed against the ground or support.

In the apparatus (referred to as "oblique charge-rheometer" see Fig. 1) employed in the abovementioned experiments, the length I (in the direction of advance) of a blade 1 (corresponding to the trowel surface) was 200 mm; the width thereof was 90 mm; the shortest distance h between the trowel surface and the grip center was 35 mm; the angle 0 made by the blade and the sample was 1.4 degrees; the velocity v of the blade was 25 cm/sec. and the coat thicknesses T were 5 mm, 10 mm, 1 5 mm and 20 mm. In Figs. 5 and 6, a symbol A denotes a coat thickness of 5 mm, while symbols 0, O and 5 designate coat thickness of 10 mum, 15 mm and 20 mm, respectively.

To sum up, according to the invention, the above-mentioned mixed aggregate is employed as aggregate, and 25% wt. to 75% wt. slag and 5% wt. to 50% wt. lightweight spheroidal substance are mixed thereinto. Therefore, the plastering material in accordance with the invention has properly large F and M values and is small in P value, so that the material can advantageously satisfy the various characteristics required of a thick set plastering material.

Next, the adhesive strength under tension of the finished layer of the mortar employing the mixed aggregate C at the age of four weeks was measured, the mortar being laid on an RC frame wall in a single trowelling with a thickness of 1 5 mm, to obtain 10.5 to 13.7 Kgf/cm2 on five test specimens.

In the above-mentioned experiment, the hardened cement mortar showed a reliable adhesion, and no crack nor craze was caused even after three months elapsed.

Next, mortar specimens were prepared in accordance with JISR 5201 and cured to the age of four weeks in an environment of 20"C and 60% RH to obtain the flexural strength and the flexural modulus of elasticity. The results are shown in Table-4. It has been confirmed that the mortar employing the mixed aggregate C is smaller in both flexural strength and flexural modulus of elasticity than the mortar employing a mixed aggregate D as well as excellent in deformability and able to relax the stress generated by the thermal and moisture movements.

TABLE 4 The number of specimens: three

Flexural strength Flexural modulus of elasticity Mixed aggregate (Kgf/cm2) (Kgf/cm2 x 105) A 55.2 0.77 B 37.4 0.41 C 35.8 0.46 D 59.2 1.09 Note: D is composed of silica sand, slag and glass hollow microsphere in the ratio of 50:50:0 by weight, including no synthetic high molecular admixture, having a water-cement ratio of 48 wt.%.

Moreover, to perform a water absorption test, mortar specimens were prepared in accordance with JISA 6203 and cured to the age of four weeks in an environment of 200C and 60% RH to obtain the air-dry unit weight and the water absorption (after absorbing water for 48 hours). The results are shown in Table-S. The waterproofness has been proved to be satisfactory.

TABLE 5 The number of specimens: three

Air-dry unit Water adsorption Mixed aggregate weight (% vol.) A 1.60 15.5 B 1.18 14.1 C 1.14 15.8 D 1.99 . 15.3 15.3 Note: D is the same as Table-4.

EXPERIMENTAL EXAMPLE 2 The qualities of the employed aggregates are such as shown in Table-6.

TABLE 6

Oven dry Bulk solid volume Klnd of specific density of aggregate.

aggregate gravity (Kg/l) (%) Mixed silica sand 2.60 1.49 57.6 Slag 2.32 1.22 55.3 Glass hollow microsphere 0.70 0.38 54.3 Note: the mixed silica sand is composed of No. 3 silica sand and No. 6 silica sand in the ratio of 60:40 by weight.

The composition ratio of the mixed aggregates employed in the experiments are such as shown Table-7.

TABLE 7

Composition ratio. (wt) Mixed aggregate Mixed silica sand Slag Glass hollow microsphere E 35 60 5 F 50 45 5 Cement mortars were prepared by adding ordinary Portland Cement, a polymer dispersion of styrene-butadiene rubber and water to each of the above-mentioned two kinds of mixed aggregates E, F, and various characteristics thereof were measured to obtain the results shown in Table-8 and Table9.

In this case, the polymer-cement ratio was 4% wt. on the basis of solid content; the ratio of the cement to the mixed aggregate was 1:2.5 by volume; and the water-cement ratio was 56% wt. for the mixed aggregate E and 55% wt. for the mixed aggregate F. The room temperature was 25 + 30C; the humidity was 65 + 5% RH; and the used water temperature was 21 OC.

The testing method and conditions were the same as those in Experimental Example 1.

TABLE 8 The number of specimens: three

Flexural strength Flexural modulus of Mixed aggregate (Kgf/cm2) elasticity (Kgf/cm2 x 105) E ~1 25.4 0.62 F 30.9 0.77 TABLE 9

Air-dry unit Water absorption Mixed aggregate weight (% vol.) E 1.83 18.7 F 1.93 18.0 Table-1 0 shows the results of testing the adhesive strength under tension of walls at the age of four weeks having concrete grounds coated with the above-mentioned polymer cement mortars to a thickness of 25 mm, respectively.

TABLE 10 The number of specimens: three

Mixed aggregate Adhesive strength by traction (Kgf/cm2) E 6.8 F 5.5 The walls finished with the respective polymer cement mortars were excellent in deformability, so that no crack nor craze was caused even after three months elapsed.

EXPERIMENTAL EXAMPLE 3 Cement mortars were prepared by adding ordinary Portland cement, water-soluble cellulose ether and water to each of the same mixed aggregates E, F as those two kinds of mixed aggregates employed in Experimental Example 2, and various characteristics thereof were measured to obtain the results shown in Table-1 1 and Table-1 2.

In this case, the polymer-cement ratio was 0.3% wt.; the ratio of the cement to the mixed aggregate was 1:2.5 by volume; and the water-cement ratio was 67% wt. for both the mixed aggregates E, F. The room temperature was 25 + 30C; the humidity was 65 + 5% RH; and the used water temperature was 21 OC.

The testing method and conditions were the same as those in Experimental Examples 1 and 2.

TABLE 11 The number of specimens: three

Flexural strength Flexural modulus of Mixed aggregate (Kgf/cm2) elasticity {Kgf/cm2 x 105) E 22.0 0.80 F 21.8 0.63 TABLE 12

Air-dry unit z Water absorption Mixed aggregate weight (% vol.) E 1.81 19.3 1.88 14.1 Table-1 3 shows the results of testing the adhesive strength by traction of walls at the age of four weeks having concrete grounds coated with the above-mentioned polymer cement mortars to a thickness of 22 mm, respectively.

TABLE 13 The number of specimens: three

Mixed aggregate | Adhesive strength by traction (Kgf/cm2) 0 E | 5.2 F | 5.6 The walls finished with the respective polymer cement mortars were excellent in deformability, so that only a small number of crazes were caused when three months had passed; no crack was caused.

The thick set plastering material in accordance with the invention will be described hereinunder through practical examples.

PRACTICAL EXAMPLE 1 Cement and a mixed aggregate perpared by mixing 50% wt. silica sand, 40% wt. blast-furnace slag sand shown in Table-2 and 10% wt. glass hollow microsphere were compounded with each other in the ratio of 1 to 2.5 by volume. Moreover, a polymer dispersion of styrene-butadiene rubber was added to the cement in a polymer-cement ratio of 10% wt. on the basis of solid content. The cement mortar kneaded with a water-cement ratio of 35% wt. was applied in one to two successive coats or layers in the state of fresh mortar on an RC external wall surface of about 5 m2 to a thickness of 1 5 mm to 25 mm for the purpose of repair. As a result, no abnormalities such as crack, craze and partial dissociation were found after six months elapsed.

PRACTICAL EXAMPLE 2 Cement and a mixed aggregate prepared by mixing 30% wt. silica sand, 50% wt. blast-furnace slag sand shown in Table-2 and 20% wt. glass hollow microsphere were compounded with each other in the ratio of 1 to 2 by volume. Moreover, ethylene-vinyl acetate copolymer emulsion was added to the cement in a polymer-cement ratio of 10% wt. on the basis of solid content. The cement mortar kneaded with a water-cement ratio of 45% wt. was applied in two to three successive coats or layers in the state of fresh mortar on a ceiling RC beam over an area of about 10 m2 to a thickness of 30 mm to 50 mm for the purpose of repairing a portion of the lower end part of the beam where the initially applied mortar had been dissociated from the horizontal reinforcing bar. As a result, no abnormality was found after six months passed.The adhesive strength by traction of the mortar at the same age was not less than 10 Kgf/cm2.

PRACTICAL EXAMPLE 3 Cement and a mixed aggregate prepared by mixing 40% wt. silica sand, 55% wt. blast-furnace slag sand shown in Table-6 and 5% wt. glass hollow microsphere were compounded with each other in the ratio of 1 to 1.5 by volume. Moreover, a polymer dispersion of styrene-butadene rubber was added to the cement in a polymer-cement ratio of 7% wt. on the basis of solid content. The cement mortar kneaded with a water-cement ratio of 38% wt. was employed as a mortar for bonding tiles.The ground or support, which was a waterproof wood chip-cement board of 1 2 mm thickness, was rendered with a cement-rich, polymer-rich mortar having a polymer-cement ratio of 12% (on the basis of the weight of the solid content of a polymer dispersion of styrene-butadiene rubber), the ratio of cement to mixed aggregate of 1:0.7 by volume and a water-cement ratio of 30% wt. Thereafter, exterior tiles of 108 by 60 mm having a thickness of 1 6 mm were contact-bonded to the first coat by means of the abovementioned mortar with a bonding layer thickness of 8 to 12 mm. As a result, no abnormalities such as partial dissociation and crack were found after six months elapsed. The adhesive strength by traction of the mortar at the same age was 5 to 7 Kgf/cm2.

PRACTICAL EXAMPLE 4 Cement and a mixed aggregate prepared by mixing 34% wt. silica sand, 63% wt. blast-furnace slag sand shown in Table-6,2.5% wt. glass hollow microsphere and 0.5% wt. foamed polystyrene particle having a maximum size of about 3 mm which is mixed with flake and sphere-like form were compounded with each other in the ratio of 1 to 2.5 by volume. Moreover, a polymer dispersion of styrene-butadiene rubber was added to the cement in a polymer-cement ratio of 5% wt. on the basis of solid content. The cement mortar kneaded with a water-cement ratio of 52% wt. was applied in two or three successive coats or layers in the state of fresh mortar on an exterior wall over an area of about 3 m2 to a thickness of 20 mm to 30 mm for the support of finishing. As a result, no abnormalities such as partial dissociation and crack were found after two months passed. The adhesive strength by traction of the mortal at the age of eight weeks was about 4 to 6 Kgf/cm2.

Claims

1. A plastering material consisting essentially of an inorganic binding material, a mixed aggregate and a synthetic high molecular admixture, wherein the ratio of the inorganic binding material to the mixed aggregate is 1:1.0 to 1:4.0 by volume, and wherein the mixed aggregate includes slag and a lightweight spheroidal substance.

2. A plastering material as claimed in claim 1, wherein the synthetic high molecular admixture is a water-soluble or dispersion-like polymer and/or a blend of a plurality of such polymers, and wherein the polymer-inorganic binding material ratio is selected to be between more than 0 and not more than 45% wt. on the basis of solid content.

3. A plastering material as claimed in claim 1 or 2, wherein the said slag is blast furnace slag sand and/or sludge sand, and wherein the sieve nominal dimension thereof is not larger than 5 mm.

4. A plastering material as claimed in any of claims 1 to 3, wherein the said lightweight spheroidal substance is an organic and/or inorganic hollow microsphere and/or spheroidal substance and has a specific gravity of not larger than 1.70 and a coefficient of water absorption of not larger than 10%, and the sieve nominal dimension thereof is not larger than 3 mm.

5. A plastering material as claimed in any of claims 1 to 4, wherein the slag content in the said mixture aggregate is 25% wt. to 75% wt. with respect to the mixed aggregate, and wherein the lightweight spheroidal substance content in the mixed aggregate is 5% wt. to 50% wt. with respect to the mixed aggregate.

6. A plastering material according to claim 1, substantially as herein described in any of the foregoing examples.