Water-resistant VAc-Acrylate RDP

Water-resistant VAc-acrylate redispersible polymer powder, designated grade **WR-501** for this document, is a spray-dried thermoplastic copolymer based on vinyl acetate and a hydrophobic acrylate termonomer. The powder is supplied as a white to off-white free-flowing solid with a bulk density of **450–650 g/L** and residual moisture below **1.5%** when tested according to **ISO 3251:2019**. The grade is intended for dry-mix mortars in which capillary water uptake must be reduced and tensile adhesion after water immersion retained. After contact with water and mixing, the powder releases a polymer dispersion with a mean particle size of **0.8–2.5 µm**, measured by laser diffraction per **ISO 13320:2020**. The hydrophobic acrylate termonomer modifies the film-forming phase after coalescence, while the vinyl acetate-acrylate backbone provides resistance to alkaline hydrolysis in cementitious matrices. The product is designed for addition levels of **1.5–6.0 wt%** based on total dry mix, depending on the end-use specification, with the most common dosing window at **2.5–4.0 wt%** for cementitious tile adhesives.

What Distinguishes Water-Resistant VAc-Acrylate RDP from Standard VAc/EVA and Acrylic Powders?

Vinyl acetate homopolymers and VAc/EVA copolymers contain acetate groups that can undergo saponification in cement pore water at pH above **13**. The acrylate comonomer in **WR-501** reduces the density of hydrolysable ester sites and introduces a hydrophobic acrylate side-group structure that is less accessible to hydroxide attack. Standard VAc/EVA powders rely on ethylene to lower glass transition temperature to approximately **-15°C to -5°C**, but ethylene provides only limited reduction in film water uptake. By contrast, the present VAc-acrylate grade exhibits a glass transition temperature of **-5°C to +5°C** per **ISO 11357-2:2020** and a minimum film-forming temperature of **0–5°C** per **ISO 2115:1996**, which is sufficient for film coalescence at **23°C** and **50% RH** without coalescing solvent. Free-film water absorption measurements according to **ISO 62:2008** after **24 h** immersion at **23°C** typically range from **10–15%** for **WR-501**, compared with **25–40%** for an unmodified VAc/EVA film and **5–10%** for a pure acrylic film. The values are representative of a **0.5 mm** cast film dried at **40°C** for **48 h**; they are not specification limits. Compared with acrylic RDP, the VAc-acrylate powder provides lower raw-material cost and generally higher early tensile adhesion on cementitious substrates, but lower UV colour stability and slightly higher water absorption. Compared with VAc/EVA, the principal difference is improved wet adhesion retention and reduced water whitening after repeated wet-dry cycling. Published data for this specific configuration across all cement types is limited; the comparative values in Table 2 should be validated in the target formulation.

Specification Ranges and Batch Release Criteria

The following ranges are used for batch release in dry-mortar production. Each batch is tested for residue on a **150 µm** screen, bulk density, moisture and pH. Full film-formation and redispersion testing is performed on composite samples. Within-lot variation of bulk density should not exceed **±30 g/L** when sampled from either **25 kg** bag lines or **1,000 kg** big-bag filling stations.

Property	Test Method	Typical Range
Bulk density	ISO 60:1977	450–650 g/L
Residual moisture	ISO 3251:2019	≤1.5%
Ash content	ISO 3451-1:2019	8–14%
pH of 10% dispersion	ISO 976:2013	7.0–9.0
Minimum film-forming temperature	ISO 2115:1996	0–5°C
Glass transition temperature	ISO 11357-2:2020	-5°C to +5°C
Redispersed particle size D50	ISO 13320:2020	0.8–2.5 µm
Sieve residue on 150 µm screen	Internal method	≤1.0%

Moisture content above **1.5%** reduces powder flow and increases bridging in silos and screw conveyors. Ash content derives from the anti-blocking mineral component; values above **14%** do not contribute to polymer film formation and can reduce tensile adhesion at a fixed powder dosage. Redispersion quality is evaluated in a high-shear mixer at **2,000 rpm** for **60 s**, after which the D50 must fall within **0.8–2.5 µm**. Poor redispersion is indicated by grit retention on a **150 µm** screen greater than **1.0%** and causes local film defects in tile adhesive beds.

When the Powder Is Added to Cementitious Tile Adhesives at 2.5–4.0 wt%

Addition at **2.5–4.0 wt%** of total dry mix is typical for C2-class ceramic tile adhesives formulated to **EN 12004:2007+A1:2012**. The powder is dry-blended with ordinary Portland cement, graded silica sand and cellulose ether before water is added on site. In a **1,000 L** twin-shaft paddle mixer, a dry blend time of **3–5 minutes** at **80–120 rpm** produces a coefficient of variation of polymer content below **5%**. Extended dry mixing beyond **15 minutes** can generate electrostatic surface charges and reduce flow from the hopper. Field experience in dry-mortar bagging lines indicates that residual moisture above **1.5%** causes progressive build-up on screw conveyor flights and bag filter media. When ambient humidity exceeds **60% RH**, the inlet air to the silo should be dehumidified to a dew point below **10°C** to prevent lump formation during transfer. At a water-to-dry-mix ratio of **0.22–0.26 L/kg**, the polymer redisperses and forms a continuous film during cement hydration. Open time tested according to **EN 1346** at **23°C** and **50% RH** typically exceeds **30 minutes**. Tensile adhesion after **28 days** standard curing followed by **24 h** water immersion, measured by **EN 1348**, generally remains above **1.0 N/mm²** in C2-class formulations. At addition levels below **1.5 wt%**, the polymer phase is discontinuous and tensile adhesion after water immersion frequently falls below **0.5 N/mm²**. At addition levels above **6.0 wt%**, the polymer may form a continuous film around cement grains before complete hydration, delaying setting and reducing compressive strength by approximately **10–20%** at **28 days**. The comparative data below are representative laboratory values from a model C2 tile adhesive containing **3.5 wt%** polymer powder, CEM I 52.5R cement, and silica sand with a maximum grain size of **0.6 mm**. Values are not product guarantees and vary with cement type, aggregate grading and curing regime.

Property	Test Method	WR-501	Conventional VAc/EVA RDP	Pure Acrylic RDP
Free-film water absorption after 24 h	ISO 62:2008	10–15%	25–40%	5–10%
Capillary water absorption coefficient w	EN 1015-18	0.15–0.35 kg/(m²·h0.5)	0.60–1.20 kg/(m²·h0.5)	0.10–0.20 kg/(m²·h0.5)
Tensile adhesion after water immersion	EN 1348	1.0–1.5 N/mm²	0.6–1.0 N/mm²	1.2–1.8 N/mm²
Open time	EN 1346	30–40 min	25–35 min	35–50 min
Glass transition temperature	ISO 11357-2:2020	-5°C to +5°C	-10°C to 0°C	-20°C to -5°C

In exterior renders and base coats applied by continuous spray machine, the polymer content is typically **2.0–5.0 wt%**; the hydrophobic acrylate modification reduces rainwater ingress when the hardened render is tested under **EN 1015-18**. A **20 mm** render layer containing **3.0 wt%** **WR-501** and cured for **28 days** at **23°C** and **50% RH** exhibited a capillary water absorption coefficient of **0.15–0.35 kg/(m²·h^0.5) in comparative trials, whereas the corresponding unmodified VAc/EVA formulation reached **0.60–1.20 kg/(m²·h^0.5)**. Spray application with a PFT G5 or similar continuous mixer requires the powder blend to remain free-flowing; lumps larger than **1.0 mm** can block the mixing zone and produce visible surface defects. For structural repair mortars under **EN 1504-3**, the powder is used at **3.0–6.0 wt%** together with silica fume and polycarboxylate superplasticizer. The VAc-acrylate polymer reduces water absorption and improves adhesion to prepared concrete substrates when tested by **ASTM C1583-13**. Substrate roughness of at least **CSP 3** per **ICRI Guideline No. 310.2R-2013** is required; without adequate surface preparation, bond failure occurs in the concrete substrate or at the polymer-cement interface.

How Does the Hydrophobic Modification Alter Capillary Water Uptake in Hardened Mortar?

Capillary water uptake is governed by pore-size distribution, pore connectivity, and the wetting angle of the hardened cementitious matrix. The hydrophobic acrylate termonomer increases the advancing contact angle of the polymer film and polymer-cement interface regions, reducing capillary suction under partially immersed conditions. In a hardened tile adhesive or render, water transport is measured as the water absorption coefficient w according to **EN 1015-18** or as rate of water absorption per **ASTM C1403-15**. The hydrophobic modification lowers w by limiting continuous capillary channels accessible at the advancing liquid front, while the coalesced polymer film blocks small pores below approximately **10 µm**. The effect is most pronounced at curing ages beyond **7 days**, because polymer coalescence continues after initial cement hydration and sufficient drying of the pore system. At ages below **24 h**, unreacted powder particles may still be wetted and contribute to initial water uptake; immersion testing before **7 days** is not representative of the water-resistant performance. Water immersion adhesion retention follows the **EN 1348** protocol: after **28 days** standard curing and **24 h** water immersion, tensile adhesion must remain above **1.0 N/mm²** for C2 class. In model C2 formulations, **WR-501** generally retains **70–85%** of its dry adhesion value after immersion, while an unmodified VAc/EVA powder may retain **50–65%**. The retention is dependent on cement type. With CEM I 52.5R, lower capillary porosity produces lower w values than with CEM II/B-M. With CEM III/A blast-furnace slag cement, reduced pore-solution pH may slow saponification but also slows early strength development. Published data for this specific configuration is limited. In fully immersed conditions under external hydrostatic pressure, the polymer reduces but does not eliminate water penetration. The hydrophobic polymer modification is not a substitute for a bonded sheet membrane in below-grade applications. The operational boundary for water resistance testing is partial immersion without external pressure; complete waterproofing performance cannot be claimed from polymer modification alone. Storage in unopened **25 kg** multi-wall bags with a polyethylene liner at **5–30°C** and relative humidity below **60%** is recommended. Under these conditions, the powder retains redispersibility for at least **6 months**. When bags are stored at higher humidity, surface skinning and lump formation occur. Lumps that survive **150 µm** screening should be discarded rather than re-milled, because the protective colloid and hydrophobic surface treatment may have been locally activated. The powder is stable in dry blends containing cement, calcium carbonate, silica sand, cellulose ether and polycarboxylate superplasticizers. It should not be mixed with liquid plasticizers or solvents in the dry state because this causes irreversible agglomeration. As an organic dust, the powder requires dust concentration control and bonding/grounding of silos, conveying pipes and discharge hoppers. A dust hazard analysis is required under local ATEX regulations.