Fast-drying screed and screed mixture for producing the screed

Abstract

The invention relates to screed mixtures, comprising an inorganic binder, processing additives and drying additives. Self-levelling floor screeds according to the invention can be produced from these screed mixtures, said self-levelling floor screeds drying much more quickly than self-levelling floor screeds with the same composition, but which contain no drying additives.

Claims

1. A screed mixture, comprising an inorganic binder, processing additives for improving processability of the screed, and drying additives, wherein the drying additives are selected from hydrophobing agents, or wherein the drying additives are selected from a mixture of hydrophobing agents and pore forming agents, or a mixture of hydrophobing agents and porous additives, or a mixture of hydrophobing agents, pore forming agents and porous additives, wherein the hydrophobing agent is contained in a quantity of 0.03 to 0.15 wt. % related to the total mass of the screed mixture, or wherein the drying additives are selected from a mixture of pore forming agents and porous additives, wherein the pore forming agent and the porous additive are each contained in a quantity of 0.001 to 10 wt. % related to the total mass of the screed mixture.

2. The screed mixture according to claim 1, wherein the inorganic binder is a calcium sulphate-containing binder or a cement-containing binder.

3. The screed mixture according to claim 1, wherein the screed mixture also contains fillers.

4. The screed mixture according to claim 1, wherein the hydrophobing agent is contained in a quantity of 0.03 to 0.08 wt. % related to the total mass of the screed mixture.

5. The screed mixture according to claim 1, wherein said processing additives are selected from the group consisting of liquefiers, alkaline initiators, retarders, crystalline initiators, stabilisers and defoamers.

6. A self-levelling floor screed, comprising an inorganic binder, fillers, processing additives for improving processability of the screed, and drying additives, wherein the drying additives are selected from hydrophobing agents, or wherein the drying additives are selected from a mixture of hydrophobing agents and pore forming agents, or a mixture of hydrophobing agents and porous additives, or a mixture of hydrophobing agents, pore forming agents and porous additives, wherein the hydrophobing agent is contained in a quantity of 0.03 to 0.15 wt. % related to the total mass of the screed mixture, and/or the drying additives are selected from a mixture of pore forming agents and porous additives, wherein the pore forming agent and the porous additive are each contained in a quantity of 0.001 to 10 wt. % related to the total mass of the screed mixture.

7. The self-levelling floor screed according to claim 6, wherein the binder is a calcium sulphate-containing or a cement-containing binder.

8. The self-levelling floor screed according to claim 6, wherein said processing additives are selected from the group consisting of liquefiers, alkaline initiators, retarders, crystalline initiators, stabilisers and defoamers.

9. A method including the use of a hydrophobing agent as a drying additive, the method including a step of adding the hydrophobing agent to a chemically setting binder composition in a quantity of 0.03 to 0.15 wt. % related to the total mass of the composition.

10. The method according to claim 9, wherein the chemically setting binder composition is a screed mixture, a screed compound, a screed premixed dry mortar or a self-levelling floor screed.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in greater detail below with the aid of examples of embodiment. In the figures:

(2) FIG. 1: shows a diagram in which the residual moisture is plotted against the drying time, wherein screed samples with different quantities of hydrophobing agent have been used.

(3) FIG. 2: shows a bar diagram in which, for constant residual moistures of 1 and 0.5%, the content of hydrophobing agent in individual screed samples is plotted against the drying time.

(4) FIG. 3: shows a bar diagram in which the compressive strength and bending tensile strength are plotted against the content of hydrophobing agent in the individual screed samples.

(5) FIG. 4: shows a diagram in which the drying profile for samples with hydrophobing agents, samples with pore forming agents and samples with a combination of a porous additive and pore forming agents are represented by way of comparison.

(6) FIG. 5: shows a diagram in which the drying profile for samples with a porous additive and the drying profile of the associated zero sample are represented.

(7) The determination of the moisture content and the drying profile of the self-levelling floor screed samples took place by means of the Darr method according to DIN 1048-5:1991-06. The Darr method is the most precise way of determining the moisture content of a sample. The material sample is taken by means of a hammer and chisel over the entire cross-section. The sample material thus obtained is immediately sealed in a vapour-tight container. The sample is size-reduced in the laboratory and weighed in a small dish. The sample in the small dish is then heated in a drying cabinet to 40° C., until the mass of the sample body diminishes by not more than 0.1% in 24 hours. The moisture content as a mass fraction in % results from the mass difference before and after the drying.

(8) $\frac{M_1-M_2}{M_2-M_0}\times 100=F_{\mathrm{Darr}}\left[\mathrm{wt}.\%\right]$
M.sub.0 vessel empty
M.sub.1 vessel+sample (moist)
M.sub.2 vessel+sample (dry)
F.sub.darr moisture content

(9) The moisture content can alternatively also be determined by the CM measurement according to DIN EN 18560-4:2012-06.

(10) The bending tensile strength and compressive strength of the self-levelling floor screed were tested according to DIN EN 13892-2:2002.

(11) The tests represented in FIGS. 1 to 5 were carried out with a calcium sulphate-based binder compound. The stated hydrophobing agent fractions relate to the binder compound.

(12) The binder compound was mixed in the laboratory with the provided quantity of 62 wt. % additive. Storage of the samples took place with a constant room climate with a temperature of 20±1° C. and 65±3% relative air humidity.

(13) The dependence of the drying time on the hydrophobing agent fraction is represented in FIGS. 1 and 2. A hydrophobing agent on a siliconate base was used. The sample composition was identical in all the screed samples, apart from the varied quantity of hydrophobing agent. The water/solid ratio (w/s) of the screed samples was 0.165.

(14) It can clearly be seen that the drying period is significantly shortened only in a narrow fraction range from 0.03 to 0.15 wt. % hydrophobing agent, see FIG. 2. The use of the hydrophobing agent is limited, moreover, by the falling strength values of the screed from a content of 0.1 wt. %, preferably even 0.08 wt. % hydrophobing agent, see FIG. 3. Calcium sulphate or cement screeds of the strength class of at least C20 F4 according to DIN EN 13813:2002 are normally used in house building.

(15) The sample containing a fraction of 0.1 wt. % hydrophobing agent dries quickest (FIG. 1). Screed samples containing more or less hydrophobing agent require longer to achieve the same residual moisture.

(16) A bar diagram is illustrated in FIG. 2 in which, for the residual moistures 1% and 0.5% of screed samples, the hydrophobing agent concentration is plotted against the drying time (days) that was required to achieve the corresponding residual moisture.

(17) It can clearly be seen that the drying period is significantly shortened only in a narrow fraction range from 0.03 to 0.15 wt. % hydrophobing agent. If lower or higher fractions of hydrophobing agents are used, the drying time is lengthened, in particular to achieve a residual moisture of 0.5%.

(18) The bar diagram in FIG. 3 shows the compressive strength and the bending tensile strength, determined according to DIN EN 13892-2:2002, of screed samples with different fractions of hydrophobing agent. From a content of approx. 0.05 wt. % hydrophobing agent, in particular the compressive strength of the screed samples consistently diminishes with an increasing content of hydrophobing agent. In the content range from 0.03 to 0.08 wt. % hydrophobing agent, the strengths lie within class C20 F4 according to DIN EN 13813:2002. This fraction range is therefore a particularly preferred range.

(19) With a variation of the formulation, for example of the binder fractions, higher strength classes can of course also be achieved.

(20) The bending tensile strength also diminishes with an increasing hydrophobing agent content. In the range from 0.03 to 0.08 wt. %, values up to 5 N/mm.sup.2 are however still achieved, which corresponds to a class F5 according to DIN EN 13813.

(21) The preferred range of the fraction of hydrophobing agent between 0.03 and 0.15 wt. % and the particularly preferred range between 0.03 and 0.08 wt. % can be deduced from these investigations. An optimum combination of short drying time and yet sufficient compressive and bending tensile strengths results in these ranges.

(22) The drying profile for screed samples with hydrophobing agent, screed samples with pore forming agents and for screed samples with a combination of porous additive and pore forming agents is represented in FIG. 4. In each case, a zero sample (reference) for the employed water/solid ratios is also shown. FIG. 5 shows a drying profile for a screed sample, which exclusively contains a porous additive as a drying additive, as well as the associated zero sample.

(23) The tests are based on a binder compound formulation stated by way of example below:

(24) TABLE-US-00001 binder: alpha-hemihydrate 97.2 wt. % binder: cement 2.46 wt. % processing additives melamine sulphonate, 0.15 wt. % fruit acid drying additive siliconate 0.19 wt. %

(25) In order to produce a screed, the binder compound is mixed with 59 wt. % quartz sand as an additive.

(26) If only one drying additive is added, a hydrophobing agent is preferably used, since the latter, when used alone, produces the best results with regard to the drying time up to reaching a residual moisture content of 1 and 0.5%, see also table 1. When use is made of 0.1 wt. % hydrophobing agent and a water/solid ratio of 0.165, a residual moisture content of 1% is achieved after 9.5 days and a residual moisture content of 0.5% after 13 days. Associated zero sample A reaches these values after 20 and 30.5 days, respectively. Accordingly, the invention also comprises the use of a hydrophobing agent as a drying additive in setting binder compositions, in particular in screed binder compounds, screed premixed dry mortars or self-levelling floor screeds.

(27) TABLE-US-00002 TABLE 1 Drying period [days] Residual moisture content 1% 0.5% 1% 0.5% Water/solid ratio 0.165 0.165 0.16 0.16 Zero sample A 20 30.5 18 30 Pore forming agent 14.5 22.5 Hydrophobing agent 9.5 13 Porous additive + pore forming agent 11 16 Zero sample B 21.5 33.5 Porous additive 19 29

(28) If only a pore forming agent with a water/solid ratio of 0.16 is added, a residual moisture content of the screed sample of 1% is reached after 14.5 days and of 0.5% after 22.5 days. Associated zero sample A reaches the residual moisture value of 1% after 18 days, the value of 0.5% only after 30 days.

(29) If only a porous additive is used as a drying additive, see FIG. 5, the screed sample reaches a residual moisture content of 1% after 19 days and a residual moisture content of 0.5% after 29 days. Zero sample B for a water/solid ratio of 0.16 reaches the corresponding values after 21.5 and respectively 33.5 days.

(30) The different drying periods of zero samples A and B result from the different binder fractions. Zero sample A contains a higher fraction of binder.

(31) As represented in FIG. 4, it emerges, completely surprisingly, that a combination of pore forming agents and porous additive in a screed sample leads to markedly shortened drying times. A residual moisture value of 1% was reached after 11 days, a residual moisture value of 0.5% even being reached after only 16 days. For comparison, the values of zero sample A: residual moisture content 1% after 20 days, residual moisture content of 0.5% after 30.5 days. This result was surprising, because with a single addition of pore forming agents or porous additive faster drying is achieved compared to the respective zero sample, but the time-saving is comparatively small. If, on the other hand, a combination of these two drying additives is added, the drying time is shortened significantly and to a much greater extent than with the addition of only one of these two drying additives.