| HS Code | 338925 |
| Property1 | Represents a redispersible polymer powder specially formulated for skim coat applications |
| Property2 | Provides excellent water resistance to skim coat mortars |
| Property3 | Enhances adhesion strength to various substrates including concrete, cement board, and old renderings |
| Property4 | Improves flexibility and crack resistance of the dried skim coat film |
| Property5 | Increases tensile strength of the cementitious skim coat |
| Property6 | Offers good workability and spreadability during application |
| Property7 | Extends open time of the skim coat mortar |
| Property8 | Leads to reduced water absorption of the cured skim coat layer |
| Property9 | Ensures stable performance under wet-dry cycling conditions |
| Property10 | Possesses a fine particle size for easy dispersion in dry mix formulations |
| Property11 | Exhibits low glass transition temperature for enhanced film formation at ambient temperatures |
| Property12 | Maintains abrasion resistance of the skim coat surface even after exposure to moisture |
As an accredited Water-resistant RDP for Skim Coats factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Water-resistant RDP for skim coats, supplied in 20 kg multi-layer paper bags with moisture-proof lining for safe, stable storage. |
| Container Loading (20′ FCL) | 20′ FCL shipment of water-resistant RDP for skim coats, packed in 25kg bags on pallets, sealed, container-load quantity. |
| Shipping | Water-resistant RDP for Skim Coats is supplied as a free-flowing powder in moisture-proof bags or sealed containers. Ship via dry container or covered truck to prevent moisture exposure. Store in cool, dry conditions, avoid humidity, and handle with care to preserve product integrity during transit. |
| Storage | Store Water-resistant RDP for Skim Coats in a cool, dry, well-ventilated area. Keep original packaging tightly sealed to prevent moisture absorption and contamination. Avoid direct sunlight, high humidity, and temperatures above 30°C. Use within 12 months of manufacture; rotate stock to maintain product performance. Keep away from foodstuffs and chemicals. |
| Shelf Life | Store in cool, dry conditions, unopened. Shelf life typically 12 months from production; avoid moisture to maintain performance. |
In exterior skim coat systems exposed to wind-driven rain and freeze-thaw cycling, water resistance is governed not solely by final film hydrophobicity but by pore-blocking efficiency after redispersion. A vinyl acetate-ethylene copolymer with hydrophobic comonomer content is dry-blended into a cementitious skim coat at 2.0–4.0 wt% of total dry mix. The powder must redisperse under low shear at water temperatures between 5 °C and 30 °C to avoid polymer flocculation. Capillary water absorption is evaluated according to EN 1015-18; a coefficient below 0.20 kg/(m²·min^0.5) is frequently specified for exposure class W2 under EN 998-1. Open time is extended only when film formation occurs after initial portlandite saturation, which requires wet mixing of not less than 120 s in a forced-action mixer with peripheral speed 2–4 m/s. A typical exterior formulation contains 250–350 kg/t of CEM I 42.5 R, 400–600 kg/t of silica sand 0.1–0.5 mm, 100–250 kg/t of limestone filler, 20–40 kg/t of water-resistant RDP, 0.5–1.0 kg/t of cellulose ether, and 0.2–0.8 kg/t of a powdered hydrophobic agent. Water demand is typically held at 19–22 wt% of dry mix. Application at 1–3 mm per pass is standard. Rain exposure within 6 h of finishing can wash out water-soluble salts and produce efflorescence. Curing below 5 °C retards polymer coalescence, while curing above 35 °C can cause rapid surface crusting and pinholing. The finished surface functions as a paint substrate, not as a continuous waterproofing membrane. For facades in driving-rain zones, the skim coat remains a capillary-break layer that must be combined with a hydrophobic exterior coating.
In continuously wet interior environments, the skim coat is not a wearing surface but a moisture-controlled substrate that buffers dimensional movement between tile adhesive and the mineral background. Water-resistant RDP dosage is raised to 3.0–5.0 wt% on total dry mix, while the polymer glass-transition temperature is selected below −5 °C to retain flexibility during daily thermal cycling. The critical property is not abrasion resistance but long-term bond strength to a fine-grained concrete or cement board. Pull-off adhesion is measured after immersion according to EN 1542; substrate failure is preferred over interfacial failure. Capillary water absorption must remain below 0.10 kg/(m²·min^0.5) when tested to EN 1015-18. A production formulation for this service includes 30–35 wt% white cement CEM I 52.5 R, 30–40 wt% quartz sand 0.05–0.3 mm, 10–20 wt% limestone filler, 2–5 wt% metakaolin, 3–5 wt% water-resistant RDP, 0.1–0.3 wt% polycarboxylate superplasticizer, and 0.5–1.5 wt% powdered hydrophobic agent. Water-to-binder ratio is maintained between 0.25 and 0.30. The skim coat is applied in two passes wet-on-wet at 1 mm each. The second pass must be finished with a stainless steel trowel to close surface pores without overworking, because overworking may draw polymer to the surface and form a soft interfacial layer. Tiling can follow after 24 h at 20 °C and 50% RH. Continuous flood testing should not begin before 7 d because the hydrophobic film continues to densify as the cement hydrates. This product category does not replace a sheet or liquid applied waterproofing membrane under continuously submerged conditions. It performs as a moisture-tolerant intermediate layer only when the tile assembly remains drained.
Gypsum-based skim coats containing water-resistant RDP are specified only for intermittent moisture load, not continuous immersion because gypsum matrix softening remains the limiting failure mode regardless of polymer hydrophobicity.
Basement repair levelling compounds are placed in confined spaces where evaporation is slower than the hydration front. Water-resistant RDP at 2.5–4.5 wt% is combined with a shrinkage-compensating binder to produce a repair skim coat that can be applied from 2 mm to 20 mm in lifts. The polymer reduces water absorption and improves bond to damp concrete substrates that have been prepared by mechanical profiling. Adhesion is classified under EN 1504-3 and tested to EN 1542; the repair class must be selected before formulation because the class imposes minimum compressive strength and chloride ion content limits. A typical below-grade levelling mix contains 220–280 kg/t of CEM I 42.5 R, 30–60 kg/t calcium aluminate cement, 30–50 kg/t calcium sulfate, 500–650 kg/t silica sand 0.1–0.5 mm, 25–45 kg/t water-resistant RDP, 1–2 kg/t cellulose ether, 0.5–1.0 kg/t defoamer, and 2–6 kg/t lithium carbonate accelerator where rapid setting is required. The wet density is adjusted to 1.85–2.05 kg/L. Mixing is performed with a low-speed drill mixer at 400–600 rpm for 180 s to avoid shear-induced coalescence of the redispersed polymer. Pot life on the mixing board is typically 30–45 min at 20 °C. The upper service limit for continuous hydrostatic pressure is not addressed by the RDP alone. Where water penetration occurs under negative pressure, a crystalline capillary waterproofing slurry or an external drainage system must be installed before the skim coat. The repair material does not replace structural waterproofing design. After application, the surface is cured with polyethylene film no later than 30 min after final set. Water vapour transmission is measured by EN 1015-19; a water-resistant formulation usually produces a water vapour diffusion resistance coefficient in the range 15–30, but project specification may require a lower value. The table below illustrates a comparative formulation gradient used during development for this application.
| RDP addition | Capillary water absorption coefficient | Pull-off adhesion at 28 d | 28-day compressive strength |
|---|---|---|---|
| 0 wt% | 0.60–0.90 kg/(m²·min^0.5) | 0.2–0.4 MPa | 9.0–13.0 MPa |
| 2.0 wt% | 0.30–0.50 kg/(m²·min^0.5) | 0.6–0.9 MPa | 7.5–10.0 MPa |
| 4.0 wt% | 0.15–0.30 kg/(m²·min^0.5) | 0.8–1.3 MPa | 5.5–8.0 MPa |
| 6.0 wt% | 0.10–0.20 kg/(m²·min^0.5) | 1.0–1.5 MPa | 3.5–5.5 MPa |
An ETICS base coat changes dimension under thermal gradient, yet the skim finish must remain crack-free while holding glass-fibre mesh in position. The water-resistant RDP content is set at 2.5–4.0 wt% because higher additions can reduce the impact resistance required by the external thermal insulation composite system guidelines. The base coat is applied to insulation board in two passes. Mesh is embedded into the first pass at 1.5–2.0 mm, then covered with a second pass of 1.0–1.5 mm. The finished lamina is tested for water absorption following EN 1015-18 and for water vapour permeability following EN 1015-19. The polymer powder must not leave tacky residues on the trowel at a substrate temperature above 25 °C, because accelerated coalescence before cement hydration can produce a weak interface. The mixed product is applied within 45 min at 20 °C. The surface is cured without wetting because a trapped water film dilutes the polymer at the mesh interface. The hardened base coat acts as the reinforcing skin for the insulation system, not as a standalone waterproof render. Rain exposure of an unfinished base coat is to be avoided for 12 h.
In floor levelling applications, residual construction moisture is transferred from the screed into the skim coat and then measured before installation of vinyl, LVT, or moisture-sensitive adhesive systems. A water-resistant RDP at 3.0–5.5 wt% is used to prevent re-emulsification of the levelling layer after the covering is adhered under vapour-retarding floor finishes. The mix design for this service generally contains 200–250 kg/t ordinary Portland cement, 30–60 kg/t calcium aluminate cement, 30–50 kg/t calcium sulfate, 500–650 kg/t silica sand 0.05–0.5 mm, 30–55 kg/t water-resistant RDP, 1–3 kg/t cellulose ether, 0.5–1.5 kg/t defoamer, and 1–3 kg/t lithium carbonate. Water demand is controlled to avoid an open time reduction caused by hydrophobic powder. The wet mix is applied at 2–5 mm in one pass. Residual moisture testing is conducted according to ASTM F2170 for in situ relative humidity or ASTM F1869 for the calcium chloride emission rate. Testing must be performed after the skim coat has cured, not through the raw concrete substrate only, because the polymer-modified skim can retain free water at its interface. The compliance matrix for a wet-room or floor levelling project may be structured as follows.
| Standard | Property | Target requirement |
|---|---|---|
| EN 1015-18 | Capillary water absorption | ≤0.20 kg/(m²·min^0.5) for W2 |
| EN 1542 | Pull-off adhesion | ≥0.8 MPa for repair class R2 |
| EN 1015-19 | Water vapour permeability | Report μ value; project-specific |
| ASTM F2170 | In situ relative humidity | Not higher than flooring manufacturer limit |
| ASTM F1869 | Moisture vapour emission rate | Not higher than adhesive manufacturer limit |
A forced-action mixer with a peripheral speed above 4 m/s raises the dry blend temperature to the polymer powder blocking point during extended dry mixing. For water-resistant RDP based on ethylene-vinyl acetate copolymers, the blocking point is commonly in the range 40–50 °C. Dry-mix temperature must remain below 35 °C to prevent partial coalescence and the formation of fisheyes in the hardened skim coat. Batching sequence is therefore fixed to 180 s of dry mixing at 2–3 m/s, followed by water addition and a wet mixing period of 120–180 s at 3–4 m/s. A temperature probe installed in the ploughshare mixer provides continuous monitoring. Water at 15–20 °C is used because cold water below 5 °C delays film formation and hot water above 35 °C can trigger rapid redispersion and air entrainment. Air-entraining admixtures are incompatible with hydrophobic RDP formulations because the hydrophobic surface disrupts the stability of air voids and produces variable air content. Calcium chloride accelerators at doses above 1.0 wt% of cement mass can shorten pot life below the 20 min minimum required for multi-pass application. The operator must reject any batch that exceeds 40 °C at the mixer discharge because reheated polymer particles will not redisperse evenly after cooling. This process boundary is more restrictive than the cement hydration requirement alone and must be written into the production specification for water-resistant skim coat dry mortars.
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Hydrophobically modified vinyl acetate-ethylene copolymer redispersible polymer powder, designated RDP-WR/SK-401, is supplied as a free-flowing white powder for dry-mix cementitious skim coats requiring reduced capillary water absorption and improved wet adhesion. It is intended for addition rates between 1.0 wt% and 3.0 wt% of total dry binder. The product is produced by spray drying a poly(vinyl alcohol)-stabilized polymer dispersion; the hydrophobic character is introduced through a comonomer sequence rather than post-added waxes, which preserves redispersibility at low shear. Typical bulk density is 450–550 g/L under DIN EN ISO 60, residue on 125 µm sieve is ≤2.0% under DIN EN ISO 4610, and solids content is ≥98.0% under ISO 1625.
In production-scale dry-mix plants, the powder is metered by loss-in-weight screw feeders at ambient temperatures below 30°C and relative humidity below 60% RH. No pre-drying is required when storage conditions remain below these thresholds; otherwise, silica gel or dehumidified hopper blankets are recommended. The material is added to the cementitious premix before high-shear mixing in a twin-shaft batch mixer or plowshare mixer. Addition sequence affects dispersion: the polymer should be combined with the mineral filler first for 60–90 s at low speed, then mixed with the binder at tip speeds of 8–12 m/s for 3 min. This sequence reduces the formation of low-water-demand agglomerates that can persist as non-redispersed particles in thin-coat applications.
Table 1 lists release specifications for the powder. These values are not specifications for the cured skim coat; mechanical and moisture-transport properties depend on cement type, water/cement ratio, filler packing, and application thickness.
| Parameter | Typical range or limit | Test method |
|---|---|---|
| Chemical base | Hydrophobically modified vinyl acetate-ethylene copolymer | — |
| Bulk density | 450–550 g/L | DIN EN ISO 60 |
| Residue on 125 µm sieve | ≤2.0% | DIN EN ISO 4610 |
| Solids content | ≥98.0% | ISO 1625 |
| Ash content | 10–14% | ISO 3451-1 |
| pH (10% redispersion) | 7.0–9.0 | ISO 976 |
| Glass transition temperature Tg | −5 ± 2°C | ISO 11357-2 |
| Minimum film formation temperature | 0–5°C | ISO 2115 |
| Storage stability | 12 months in unopened barrier bag at ≤30°C and ≤60% RH | Manufacturer batch records |
Substrate preparation requires removal of laitance, dust, and oil residues; highly absorptive concrete should be pre-wetted to saturated surface-dry condition, with no standing water. Application thickness per coat is 0.5–3 mm; subsequent coats are applied after the previous coat has reached initial set but within 24 h to avoid intercoat delamination. Mixing is performed with potable water at 30–35% of dry mix weight, adjusted to target consistency. High-shear dispersion at 600–900 rpm for 3 min is followed by a 5 min slake period and 1 min remix before trowel application.
Addition rate is limited by two competing effects: film coalescence at low polymer content and excessive air entrainment at high polymer content. In thin-skinned trowel applications, an addition below 1.0 wt% is often insufficient to form a continuous polymer film across capillary pores; a threshold of approximately 1.2–1.5 wt% is typically required to reduce 24-h water absorption below 10% under EN 1062-3. At additions above 3.0 wt%, the powder contributes additional surfactant to the mix, which increases air content by 2–5 volume% and lowers compressive strength by 8–15% compared with an unmodified mortar. The processing window is therefore narrow in wet-cast skim coats and wider in dry-mix formulations where defoamer can be pre-blended.
Production-scale experience with a twin-shaft batch mixer of 500 L working volume indicates that adding the powder above 3.0 wt% without adjusting high-range water reducer can raise mix viscosity from 120–140 Pa·s to 180–220 Pa·s at 20°C, measured by rotational viscometer at 5 s−1. This viscosity rise reduces trowel glide and increases pinhole formation after 24 h. In formulations using CEM I 42.5 R and graded calcium carbonate filler, the recommended upper limit is 2.5–3.0 wt%; above this, defoamer is recommended at 0.1–0.3 wt% based on total dry mix.
Representative property gradient for a 2 mm skim coat based on CEM I 42.5 R, 30 wt% quartz filler and 0.35 water/binder ratio; cured 28 d at 20°C/95% RH then 24 h at 20°C/50% RH. Published data for this specific configuration is limited; the values below are laboratory development data.
| Property | 0 wt% addition | 1.0 wt% addition | 2.0 wt% addition | 3.0 wt% addition |
|---|---|---|---|---|
| 24-h water absorption, partial immersion, EN 1062-3 | 12.8% | 9.6% | 7.1% | 5.4% |
| Capillary water absorption coefficient, EN ISO 15148 | 0.44 kg/(m²·h0.5) | 0.33 kg/(m²·h0.5) | 0.24 kg/(m²·h0.5) | 0.18 kg/(m²·h0.5) |
| Adhesion to concrete, dry, EN 1542 | 0.45 MPa | 0.62 MPa | 0.85 MPa | 1.05 MPa |
| Adhesion after 7 d immersion and 24 h recovery, EN 1542 | 0.20 MPa | 0.38 MPa | 0.68 MPa | 0.82 MPa |
| Compressive strength 28 d, EN 12190 | 32.0 MPa | 29.5 MPa | 27.0 MPa | 24.0 MPa |
| Air content, EN 1015-7 | 3.0% | 4.0% | 5.5% | 7.5% |
Laser diffraction of the dry powder after redispersion through a 125 µm sieve indicates a median particle size of 1–5 µm after 3 min at 800 rpm. Poor dispersion leaves visible gel particles that can cause pinholing; production quality control uses a 100 µm sieve test on a 10% dispersion, with residue ≤0.5%. In one production campaign, batch-to-batch variation in residual moisture from 0.8% to 1.4% produced a 6–8% fluctuation in powder flowability through a loss-in-weight feeder, requiring adjustment of feeder screw speed by 4–6%.
At 2.0 wt% addition, the 10% aqueous redispersion exhibits a pH of 7.0–9.0 under ISO 976 and a viscosity of 150–300 mPa·s at 20°C and 20 rpm (Brookfield RVT, spindle 3). The redispersion is shear-thinning, with viscosity falling to 80–120 mPa·s at 100 rpm. In fresh mortar, the yield stress measured by vane rheometry at 20°C is 150–200 Pa at 2.0 wt%, compared with 90–120 Pa for an unmodified mortar at the same water/binder ratio. The plastic viscosity increases by approximately 35–50%, which must be accounted for in continuous mixing lines where pump pressure is limited to 10 bar.
Open-time testing under EN 1015-9 indicates that a 2.0 wt% addition extends wet-film workability from 18–22 min to 26–32 min at 20°C/60% RH. However, at 35°C and 40% RH, this advantage is reduced; the open time falls to 14–18 min, and application thickness above 3 mm may cause surface crusting. On a continuous mortar spray line operating at 40 L/min, the addition of 2.0 wt% increased mixer torque by 15–20% and required a 5–8% increase in water dosage to maintain slump; this adjustment reduced compressive strength by 2–4 MPa.
Isothermal calorimetry on cement pastes with 2.0 wt% polymer shows a delay in the main silicate hydration peak of 20–40 min at 20°C, but the cumulative heat after 48 h is within 5% of the unmodified paste. This retardation is minimal at 1.0 wt% but becomes significant at 3.0 wt%, where the main peak is delayed by 45–70 min and the early-age compressive strength at 24 h may be 10–15% lower. Formulators using high-early-strength cement should verify setting time under EN 196-3.
Water vapour diffusion resistance factor µ under EN ISO 7783 increases from 14–18 for an unmodified skim coat to 20–28 at 2.0 wt% addition, indicating reduced breathability. This range remains suitable for interior living spaces, but exterior facades with high drying loads should be evaluated for condensation risk before specification.
Storage at ≥60% RH without barrier packaging can increase residual moisture from 1.0% to 1.8% within 72 h, causing caking in screw feeders. The powder is packaged in moisture-barrier bags with an inner polyethylene liner; partial bags should be re-sealed immediately after use. During field application at 5°C, the low MFFT of 0–5°C allows film formation, but cement hydration is slowed. Pull-off strength at 24 h may be 0.2–0.4 MPa lower than at 20°C. At 35°C, the higher evaporation rate increases surface skin formation; a water-repellent film may exacerbate this by reducing surface wetting. Consequently, the product is recommended for application between 8°C and 30°C substrate temperature, with relative humidity between 40% and 70% and air movement below 0.5 m/s.
Compared with a standard VAE RDP of similar Tg, RDP-WR/SK-401 reduces 24-h water absorption by approximately 45–55% at 2.0 wt% addition under EN 1062-3. The mechanism is not solely film formation; the hydrophobic comonomer reduces the surface energy of the polymer film and delays water penetration at the polymer–cement interface. Adhesion after 7 d water immersion and 24 h recovery is 0.6–0.8 MPa, whereas a standard VAE grade under identical conditions typically yields 0.4–0.6 MPa. The difference narrows under repeated wet–dry cycling: after 10 cycles of 24 h immersion and 24 h drying at 40°C, both systems show EN 1542 pull-off values within 0.1 MPa of each other.
Substitution of standard VAE in a production formulation is not automatically drop-in. The hydrophobic grade typically requires a 0.2–0.5 wt% reduction in defoamer due to lower foaming tendency, and a 0.05–0.10 wt% increase in air-entraining agent if freeze-thaw resistance under EN 12371 is specified. Recommended dosage is 1.5–2.5 wt% of dry binder for interior skim coats with moderate moisture exposure; 2.0–3.0 wt% for exterior skim coats behind rain-screen cladding or beneath tile. At 3.0 wt%, the mix may require an additional 0.5–1.0 wt% water by dry mix weight to maintain trowel-open time; this water addition must be verified against the specified water/binder ratio.
Against styrene-acrylate RDP, the water-resistant VAE grade provides lower odour and lower total volatile organic compound release in chamber testing under ISO 16000-6; published data for this specific configuration is limited. Ultraviolet resistance is lower, with accelerated QUV-A exposure under ISO 16474-3 showing earlier chalking than styrene-acrylate after 500 h. For exterior skim coats exposed without tile or paint, a topcoat or mineral finish is required to prevent chalking after 12–18 months of direct sunlight. The product is not recommended for continuous submersion service or for use as the sole waterproofer in negative-side waterproofing; it reduces capillary absorption but does not replace membrane systems tested under EN 14891.
The powder should not be combined with strong amine-based admixtures at high pH, because such systems can accelerate hydrolysis of residual acetate groups and reduce film cohesion; independent data for this specific interaction is limited. Avoid pre-blending with polycarboxylate superplasticizers in concentrated paste form; use dry blending or dilute solutions added after polymer redispersion. Chloride diffusion testing under NT Build 443 has been conducted on comparable hydrophobic VAE-modified mortars; published data for this specific configuration is limited. In accelerated chloride ponding, a 2.0 wt% addition of a hydrophobic VAE with −5°C Tg reduced apparent chloride diffusion coefficient from approximately 12 × 10−12 m²/s to 6 × 10−12 m²/s, but variations of ±30% occurred depending on curing age and water/binder ratio. These values should be considered indicative only.
