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ScienceDirect Procedia Engineering 108 (2015) 340 – 348

7th Scientific-Technical Conference Material Problems in Civil Engineering (MATBUD’2015)

The effect of temperature and humidity on the permanence of external thermal insulation composite systems Eneli Liismaa,*, Gert Lõhmusa, Lembi-Merike Raadoa a

Tallinn University of Technology, Ehitajate Street 5, 19086 Tallinn, Estonia

Abstract The purpose of this paper is to analyze the impact of temperature and humidity on external thermal insulation composite systems (ETICS), resulting in internal stresses and frost damages as a serious sustainability problem. In order to predict the behavior of ETICS in different weather conditions, a variety of climatic conditions and cycles were composed on the basis of the Estonian statistical data. All coating components of ETICS were tested separately and as a system for dimensional changes using thin layer measurement principles. This study focuses on three types of plasters most commonly used in ETICS – mineral plasters, acrylic plasters with higher flexibility and silicone plasters. As a result of the research, a potential micro-cracking mechanism of ETICS in Northern climate conditions is presented in this paper. © 2015 The Authors. Published by Elsevier Ltd. © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Selection and peer-review under responsibility of organizing committee of the 7th Scientific-Technical Conference Material (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review Civilresponsibility Engineering.of organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering Problems inunder Keywords: Façade renovation; External Thermal Insulation Composite Systems; Thin-layer rendering; Cracking mechanism

*Corresponding author. Tel.: +372 620 2453; fax: +372 620 2451 . E-mail address: [email protected]

1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of organizing committee of the 7th Scientific-Technical Conference Material Problems in Civil Engineering

doi:10.1016/j.proeng.2015.06.156

Eneli Liisma et al. / Procedia Engineering 108 (2015) 340 – 348

1. Introduction The housing stock all over Europe is composed of buildings many of which are nearing the end of their service life. Therefore ETICS, with low cost and simple installation, have been widely used to improve the energy efficiency and extend the service life of the housing stock. Although ETICS have been used in Estonia for several decades, materials in this complex system cannot be compared to the materials used in past decades. With the comprehensive usage of ETICS and the development of the field of building materials, several new product types are now in use, offering a variety of different reinforcement meshes and finishing coatings. This paper concentrates on mineral plaster, acrylic plaster and silicone plaster, as well as cement based reinforcement layer and reinforcement mesh with glass textile. With the wide selection of different ETICS components the need of predictions of the systems durability and sustainability and the differences of the plasters arise. According to the research of Sulakatko et al. [1] the degradation factors for ETICS are divided by degradation reasons into three main groups: x Holistic design and defects caused by moisture x Composition of render mortars and use of substrates x On-site application of ETICS One of the key components in ETICS durability is the degradation of the finishing coating. The finishing coating is usually 1.5-3.0 mm thick depending on the ingredients. This thin layer is exposed to atmospheric factors like wind, temperature changes, UV radiation, rain, snow and different urban environmental pollutants. These factors cause visual defects such as loss of colour, staining and mechanical defects like cracks, local deterioration and loss of adhesion, etc. by Tittarelli et al. [2]. The durability of the exterior layer of building envelopes is mostly influenced by the moisture access by rain. Thin finishing coating layers are porous materials that absorb liquid water into their pores and capillaries. Due to the thin layer format, moisture soon affects the deeper layers, increasing the thermal conductivity and thus the efficiency of the heat insulating layer by Šadauskiene [3]. According to Bochen [4] the open porosity of the finishing coating increases in time, especially in mineral based plasters. All the plasters have macro pore structure with pore radiuses above the value of 100 nm. Plasters with polymeric binders such as acrylic and silicone have a higher proportion of pores under 100 nm. Mineral plasters contain mostly lime, which, during the hardening process, causes larger porosity due to water evaporation. Silicone and acrylic plaster have smaller open porosity due to the content of polymers according to Bochen [4]. Although the total porosity increases over time, the radius of pores decreases by Bochen et al. [5]. The changes in porosity influence the moisture storage regimes of water. Liquid water is absorbed into capillary pores and water vapour adsorbed to the surface of pore walls by Straube [6]. But in northern climates, where it is colder, negative temperatures affect the sustainability of ETICS. In negative temperatures, the base coat and finishing coat are subjected to tensile forces, which occur as the capillary cracks' width increases which allows rain water to reach deeper layers. Wet layers can have reduced tensile strength due to freezing. In high temperatures the base coat and finish coat are subject to compression and adhesion stresses that can lead to deformation of the finish coat by Daniotti et al. [7]. In ETICS the reinforcement mesh is used to distribute the hygric and thermal stresses throughout the system. This allows stress relief to occur as short micro cracks rather than large cracks at a single location Lstiburek [8]. The aim of the research is to reproduce the main climate exposures and assess the effects. To better understand the differences between the usage of reinforcement mesh and glass fibre textile as a net, various scenarios were created.

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2. Experimental setup 2.1. Materials One type of reinforcement layer as a base and three types of commercial plasters such as acrylic, mineral, silicone were used to prepare thin-layer specimens. Materials were chosen according to the frequency use in Estonian building sector and presented in Table 1. All specimens were made with the area of 4 × 14 cm2 and thicknesses of approximately 2–3 mm for one layer and 4.5-5.5 mm for two layer specimens. Four types of specimens were prepared: reinforcement mixture; reinforcement layer with net; reinforcement layer with net covered with plaster and coating plasters only. The specimen structure is shown in Fig. 1. To evaluate the effect of the glass fiber textile in the reinforcement layer, samples with and without glass fiber textile were made. Full systems were made to understand its functions in ETICS. The textile glass fiber is placed in the middle of the cement based reinforcement layer. The reinforcement layer was coated by two different polymer priming agents, one for mineral plaster, another for acrylic and silicone plasters. All measurements of the samples - width, height, thickness and mass were documented and measurement locations marked for future reference. Afterwards all samples were placed according to climate conditions: +20oC, 40% RH (relative humidity); +20oC, 100% RH; +60oC, 0% RH; -20oC, 90% RH and +20/-20 cycling with 24 hour intervals for 30 days.

Fig. 1. Specimen structure. Table 1. Mineral materials used in the research. Material Supplier Reinforcement mixture Sakret Acrylic plaster Mira Silicone plaster Mira Mineral plaster Sakret Mineral Ground Sakret Silicone Ground Mira

Type Sakret BAK Mira 5370 Kratz Mira 5370 Silicone Kratz Sakret SBP Sakret PG Mira 5335 quartz ground

Standard LVS EN 998-1 EN 15824 EN 15824 LVS EN 998-1 * *

* - harmonized standard not available

2.2. Modeling of the laboratory climate conditions The laboratory climate conditions were replicated on the basis of earlier scientific research using different technological solutions Kalamees et al. [9] and Jaagus et al. [10]. Temperature +20oC and RH 40% were selected as the laboratory and indoor condition not exposed to other factors, like sunlight, rain, wind, pollution for the

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samples. Temperature +20oC and 100% RH were replicated using an airtight chamber with a water tank and ventilator. This climate condition was to replicate humid conditions in outdoors. To replicate the maximum surface temperature of dark plasters during summer days, temperature +60 oC were modeled using an electrical heating chamber. The negative temperature -20oC environment was modeled using a refrigerator with a capability to produce the required temperature. The cycle chamber which creates cycles from +20oC to -20oC with 24 hour intervals was used to study the frost cycle environment. All specimens were placed on the polystyrene board during the conditioning period. 2.3. Dimensional and mass changes in time The dimensional changes of the samples were measured in order to assess the climate effects. All measurements were performed in mm and calculated to mm/m according to formula (1) where d et is the initial height; dx is the height in time. ߂݀ ൌ

೏೐೟ ష೏ೣ భబబబ

ௗ೐೟

(1)

3. Results of the research with discussion The laboratory tests showed that the highest dimensional changes occurred with mineral plaster in dry environments with low relative humidity. Slight volume changes appeared with acrylic and silicone plasters in dry climates but no cracking performance was detected. Mineral plasters in +20 oC and RH 40% showed relatively high dimensional changes but no visible cracking appeared. Full systems with mineral plasters maintained unbroken with shrinkage up to -3 mm/m in dry climates. Summarized results are presented as one layer and full system specimens in Fig. 2 and Fig. 3. Although cracking phenomenon with mineral plasters was instant in + 60oC and happened within 24 hours, in Fig 10 (a), however no damages with acrylic and silicone plasters appeared. Full systems with mineral plasters remained unbroken with shrinkage up to -2.5 mm/m which can be considered harmless to the ETICS performance. Summarized results in +60oC are presented in Fig. 6 and Fig. 7. High humidity 100% RH and +20oC combination impact was lower than 2 mm/m dimensional changes so that no damages appeared with the specimen during the testing period in 30 days, in Fig. 4 and Fig. 5. However in negative temperatures of -20oC with high relative humidity (100%) mineral plasters showed shrinkage and cracking appeared with reinforcement layers, this is shown in Fig. 10 (b). Summarized results are presented in Fig. 8 and Fig. 9. Repeated thermal cycles from +20oC to -20oC with 24 hour interval dimensional changes did not vary more than for specimens in -20oC with high relative humidity (100%) climate. Much more remarkable is the damaging mechanism of the specimen that delaminated during cyclic exposure, in Fig. 11. This phenomenon was detected mostly with mineral and acrylic plasters. The potential micro cracking mechanism of ETICS layer can be predicted with dimensional changes. No cracking was detected with dimensional changes lower than 4.0 mm/m. However, dimensional changes over 7 mm/m started showing external damage with mineral plasters. While analyzing different mineral layers of ETICS where a reinforcement layer with and without net was used, it is necessary to point out that the usage of the reinforcement net reduced dimensional changes by approximately 50% in all cases.

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The legend according to the specimen structure presented in Fig. 1 is as follows:

Dimensional changes mm/m

A = reinforcement mixture B = reinforcement net C = silicone plaster D = acrylic plaster E = mineral plaster F = acrylic primer G = mineral primer A + B = reinforcement layer with net A + B + G + D = acrylic plaster with all layers (full system) A + B + G + C = silicone plaster with all layers (full system) A + B + F + E = mineral plaster with all layers (full system) 0,00 A

-2,00

A+B

-4,00

C

-6,00

D

-8,00

E

-10,00 0

5

10

15 20 Time, day

25

30

35

Fig. 2. One layer specimens in +20oC and RH 40%.


x x x x x x x x x x x

0,00 -1,00

A+B+G+D

-2,00

A+B+F+E

-3,00

A+B+G+C

-4,00 0

5

10

15 20 Time, day

25

30

Fig. 3. Full system specimens in +20oC and RH 40%.

35

345



2,00 A 1,00

A+B C

0,00

D E

-1,00 0

5

10

15 20 Time, day

25

30

35



2,00 1,00 0,00

A+B+G+D

-1,00

A+B+F+E A+B+G+C

-2,00 0

5

10

15

20

25

30

35

Time, day


Fig. 5. Full system specimens in +20oC and RH 100%.

1,00 0,00 -1,00 -2,00 -3,00 -4,00 -5,00 -6,00 -7,00 -8,00

A A+B E C F

Instant cracking

0

5

10

15 20 Time, day

25

30


35



346

0 -0,5 -1

A+B+G+D

-1,5

A+B+F+E

-2

A+B+G+C

-2,5 0

5

10

15

20

25

30

35

Time, day Fig. 7. Full system specimens in +60oC and RH 0%.


1,00 -1,00

A

-3,00

A+B

-5,00 -7,00

E

-9,00

C

-11,00

F

-13,00 0

5

10

15 20 Time, day

25

30

35


Fig. 8. One layer specimens in -20oC and RH 90%.

0 -2 -4

A+B+G+D

-6

A+B+F+E

-8

A+B+G+C

-10 -12 -14

0

5

10

15

20

25

30

Time, day Fig. 9. Full system specimens in -20oC and RH 90%.

35


a)

347

b)

Fig. 10. (a) mineral plaster cracking in +60 oC and RH 0%; (b) mineral plaster cracking in -20oC and RH 90%.

Fig. 11. Delaminating between reinforcement layer and the coating in cyclic climate.

4. Conclusions The importance of the stability of the reinforcement mortar can be considered as a key factor for a working ETICS solution. Therefore adhesion between the reinforcement mortar and thin layer plaster is essential due to the sensitiveness of the plasters in changeable climate conditions. Dimensional changes with the reinforcement layer during climate influence should be lower than the dimensional changes with the coating to avoid cracking. According to the results mineral plasters had more cracking damages in changeable and extreme climate conditions than acrylic and silicone plasters. The risk of cracking mechanism with mineral plasters appeared with dimensional changes near to 5 mm/m and higher. In addition, the reinforcement net reduces the dimensional changes in thin layers during climate influences – the cracking mechanism is promoted when the net installation is poorly managed. Acknowledgements This work was supported by institutional research funding of the Estonian Ministry of Education and Research IUT1−15 “Nearly-zero energy solutions and their implementation on deep renovation of buildings“.

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References [1]

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