CELVOLIT 1320 VAE Emulsion for High-Performance Waterproofing

Aqueous vinyl acetate-ethylene (VAE) copolymer dispersion CELVOLIT 1320 is manufactured with a controlled elevated ethylene content to delimit the glass transition temperature of the film-forming polymer to a region below 0 °C without requiring external plasticizer. The product is supplied as an anionic-stabilised, APEO-free colloidal latex with 54–56 % non-volatile matter, a Brookfield RVT viscosity (spindle 4, 20 rpm, 23 °C) between 800 mPa·s and 2000 mPa·s, and a pH in the range 4.5–5.5. The minimum film-forming temperature (MFFT) determined per ISO 2115 is typically 0 °C, which permits coalescence on damp substrates at low ambient temperatures without the migration issues associated with ester- or phthalate-based coalescents commonly found in acrylic dispersions of equivalent softness.

What Distinguishes CELVOLIT 1320 from Conventional VAE Dispersions in Waterproofing Mortars?

The high molar proportion of ethylene units incorporated into the copolymer backbone shifts the polymer’s elastic domain well below the vitrification region that standard VAE grades (typical ethylene content 10–14 %) exhibit at service temperatures around −10 °C. In a conventional VAE with an MFFT near 5 °C, the binder contribution to crack-bridging capacity under EN 14891:2018 dynamic loading drops sharply once the substrate temperature approaches 0 °C; the material transitions into a semi-brittle regime where elongation-at-break values measured on free films per ISO 527-3 (Type 5 specimens, 200 mm/min crosshead speed) fall below 100 %. CELVOLIT 1320 retains a film elongation in excess of 400 % at −10 °C when tested under the same protocol, enabling it to fulfil the Class CM02P crack-bridging criterion (≥0.5 mm at −20 °C) without fibre reinforcement. The modified ethylene sequence distribution also depresses the water absorption of the pure polymer film to less than 10 % after 24 h immersion (ISO 62, 23 °C), compared with 20–30 % for older-generation VAE copolymer grades. This reduction of hydrophilic domains limits the hydrolytic chain scission that has historically shortened the wet-bond durability of polymer-modified cementitious (PCC) waterproofing layers exposed to permanent moisture. Mixing of polymer-modified cementitious waterproofing slurries containing CELVOLIT 1320 requires a specific energy input that disperses the latex into the cement-powder interstices without destabilising the protective colloid layer. In production-scale batching with a forced-action paddle mixer (planetary type, L/D ratio ≈1.8, rotational speed 280–320 rpm), the emulsion is first pre-diluted with 60 % of the total gauging water at 20 ± 3 °C. The dry-mortar premix—typically CEM I 42.5 R, graded silica sand 0.1–0.6 mm, and a polycarboxylate ether superplasticizer—is added and mixed for 180 s, rested for 120 s to allow wetting of fines, and then re-mixed for 90 s. A polymer dosage of 12–14 % by mass of hydraulic binder, corresponding to a polymer-cement ratio (p/c) of approximately 0.12–0.14 on dry solids, produces a film-forming network that co-continuously coats hydration products. Below p/c 0.10 the pore-coating action becomes discontinuous and water impermeability measured by the EN 12390-8 penetration test can exceed 10 mm under 5 bar pressure; above p/c 0.16 the open time extends beyond 45 min at 23 °C and 50 % RH, but compressive strength development per EN 196-1 at 28 d drops by approximately 25 % compared with the unmodified reference. The latter limitation mandates careful rheological adjustment when the material is applied by airless spray equipment requiring a nozzle pressure of 40–60 bar.

Film Formation Mechanics at Ambient Cure Without Plasticizer

During drying of the dispersed phase, water removal from the interstitial capillary pores forces the latex particles into close-packed arrays. Because the ethylene-rich copolymer segments retain segmental mobility even at 5 °C, irreversible coalescence into a homogeneous binder film commences without the evaporation-controlled diffusion restriction that high-Tg acrylic dispersions (> 25 °C MFFT) encounter. Differential scanning calorimetry of oven-dried films at 40 °C for 7 d shows a single glass transition midpoint at −2 °C with a half-width of less than 10 K, confirming complete coalescence and absence of residual particle boundaries that would otherwise nucleate water-wicking channels. However, cure rates below 70 % relative humidity are retarded: the high ethylene content lowers the hydrophilic character of the polymer, reducing the capillary pressure that drives compaction. In practice, applicators observe that trowelled coatings require a minimum 72 h curing at 20 °C and 80 % RH before exposure to standing water, whereas the identical formulation based on a conventional VAE with a higher vinyl acetate fraction develops impermeability within 48 h. This transient water sensitivity has been documented in field reports for exposed roof slabs where early rain ingress led to surface softening and blistering in the first 72 h after installation. Pre-wetting the substrate to a saturated-surface-dry condition and covering with polyethylene sheeting for the initial 48 h mitigates the risk.

When Polymeric Interpenetration Limits Water Vapor Permeability to Below 18 g/m²·d

The continuous polymer phase created by CELVOLIT 1320 fills the capillary pores of the cement matrix at the micron scale, creating a tortuous diffusion path for water vapour. Measurements on 2 mm-thick cementitious coatings (p/c 0.13, cured 28 d at 23 °C and 50 % RH) according to ASTM E96 (wet-cup method, 23 °C, 50 % RH gradient) yield water vapour transmission rates of 16–20 g/m²·d. This places the system below the 25 g/m²·d threshold often specified for breathable facade coatings, yet the value remains significantly higher than that of pure polymer films because un-hydrated cement particles and residual calcium hydroxide maintain a discrete micro-porosity. The interpenetration of the polymeric network through the hydration-product scaffold improves adhesion after water immersion: pull-off strength tested per ASTM D7234 (dolly, 50 mm diameter, portable pull tester) on concrete substrates immersed in 23 °C water for 14 d remains above 1.2 MPa, with cohesive failure exclusively in the substrate. Formulations devoid of the polymer lose adhesion within 14 d of immersion, dropping below 0.4 MPa. Long-term submersion tests conducted at 23 °C in deionized water according to ISO 2812-2 reveal that the high-ethylene VAE exhibits slower hydrolytic degradation than polyvinyl acetate homopolymer but cannot match the chemical stability of carboxylated styrene-butadiene latexes under combined alkaline (pH 13.5) and elevated temperature (60 °C) conditions. After 90 d immersion in calcium-hydroxide-saturated water at 60 °C, films isolated from mortar show a reduction in tensile strength of approximately 30 % (from initial 4.5 MPa down to 3.1 MPa), attributable to acetate ester saponification. Consequently, CELVOLIT 1320 is not recommended for containment structures where the coating will operate continuously above 50 °C in strongly alkaline leachates.

Typical physical properties of CELVOLIT 1320 dispersion

Property	Value	Test Method
Solids content	55 ± 1 %	ISO 3251 (1 h, 105 °C)
Brookfield RVT viscosity	800–2000 mPa·s (sp. 4, 20 rpm, 23 °C)	ISO 2555
pH	4.5–5.5	ISO 976
MFFT	≈0 °C	ISO 2115
Particle size (D₅₀)	0.8–1.5 µm	Laser diffraction (ISO 13320)
Density at 20 °C	≈1.08 g/cm³	ISO 2811-1
Freeze–thaw stability	Non-stable—avoid storage below 5 °C	Internal method, 5 cycles -5 °C/+23 °C
Storage shelf life	12 months in original sealed containers at 5–30 °C	Per manufacturer’s QM system

The dispersion’s sensitivity to frost is a directly limiting operational boundary. Freeze-induced coagulation is irreversible; once the latex has been subjected to temperatures at or below −2 °C, the formation of grit and a rapid viscosity rise render the material unsuitable for subsequent use. In logistically demanding construction sites where overnight temperatures may fall, the emulsion must be stored in heated containers capable of maintaining internal temperature above +7 °C. Attempts to add anti-freeze agents such as ethylene glycol compromise film integrity as the glycol remains trapped in the dried polymer matrix and acts as a permanent plasticiser, lowering tensile modulus and increasing water uptake by 15–20 %. Comparative performance data for polymer-modified cementitious waterproofing slurries prepared with a constant p/c ratio of 0.13 on a CEM I 42.5 R base, silica sand 0.1–0.5 mm, and a comb-type PCE superplasticizer are summarised below. The standard VAE reference corresponds to a commercial grade with MFFT ≈4 °C and ethylene content ≈12 %; the styrene-acrylic (SA) reference is a carboxylated dispersion with MFFT ≈20 °C and requires 2 % plasticiser on polymer solids to achieve film formation at 5 °C.

Performance of mortars modified with different polymer dispersions

Parameter	CELVOLIT 1320-modified	Standard VAE-modified	Styrene-acrylic + plasticiser	Test protocol
Crack bridging at 23 °C	1.1–1.4 mm	0.6–0.8 mm	0.9–1.2 mm	EN 14891 Method A
Crack bridging at -10 °C	0.6–0.8 mm	≤0.2 mm	0.2–0.4 mm	EN 14891 Method B
Adhesion after water immersion (14 d)	1.2–1.5 MPa	0.8–1.0 MPa	1.3–1.6 MPa	ASTM D7234
Water impermeability (5 bar, 24 h)	3–5 mm penetration	8–12 mm penetration	2–4 mm penetration	EN 12390-8
Compressive strength 28 d	28–32 MPa	30–34 MPa	22–26 MPa	EN 196-1
Open time (trowel)	35–45 min	30–35 min	40–50 min	Internal scrape test

The data illustrate that while the styrene-acrylic system can deliver marginally superior impermeability and wet adhesion, it does so at the expense of compressive strength and freeze-flexibility unless substantial plasticiser is added; the plasticised SA coat can exhibit exudation of the coalescing agent in sustained damp conditions, causing staining and adhesion decay at the laminate interface with finishing plasters. The standard VAE, although offering the simplest handling without plasticiser, fails crack-bridging requirements at low temperatures. CELVOLIT 1320 occupies a technically robust middle ground for exposed waterproofing membranes subject to diurnal thermal cycles down to −15 °C, particularly where the specification mandates no fugitive plasticiser. The slower early water resistance described above must be factored into site scheduling; published data for this specific configuration of production under rapid-track formwork stripping is limited, but anecdotal reports from pre-fabricated bathroom pod manufacturers indicate that installation over green concrete (less than 7 d of curing) without surface priming leads to occasional blistering that resolves only after extended dry-out periods exceeding 14 d at 20 °C.