advice on exterior plaster in 4 layers

josephbeag · Post by **josephbeag** » Fri Sep 25, 2009 4:02 am -1100

Hi,
The Fraunhofer IBP materials database lists four layers for an exterior (lime cement) plaster. Exterior plaster is not installed in four layers in Ireland. I presume the four layers relate to the degree to which the materials calcify (closer to the outside air) and the amount of moisture it has to take. Is this right?

I want to model a modern exterior portland cement plaster and also a traditional exterior lime-based plaster, in four layers if this is the most accurate way. I don't know the characteristics of the Franuhofer IBP lime cement exterior plaster (how much portland cement how much lime etc). Can you clarify it's makeup and give guidance on the two versions I need to create? Are there other products within the database that you regard as acceptable alternatives?

For your information external cement plaster is judged to have a density of 1300 Kg/m3 and a conductivity of 0.57 W/mK in Ireland.
ISO 12524 lists plaster made of lime and sand as: density 1600, conductivity 0.80, specific heat as 1000, and dry mu-value as 10 and wet mu-value as 6. It also lists plaster made of cement and sand as 1800, 1.0, 1000, 10 and 6.

Many thanks.
Regards,
Joseph

Michael Hurd · Post by **Michael Hurd** » Fri Sep 25, 2009 4:35 am -1100

I have the same issue here in the United States. In one of the WUFI classes I attended years ago, we were instructed to use all 4 layers of the plaster to do plaster simulations, however, when I go read the data from the NRC-CNRC from the MEWS tasks I get the impression that the Regular Lime Stucco in the North American database is perhaps more representative of our plaster here. When I found the descriptions of the differing systems tested in the Canadian tests, I found them lacking in enough description to really decide which plaster system to use in simulations. Any help in this regard would be appreciated.

josephbeag · Post by **josephbeag** » Fri Sep 25, 2009 5:39 am -1100

Michael Hurd wrote:I have the same issue here in the United States... I get the impression that the Regular Lime Stucco in the North American database is perhaps more representative of our plaster here.

Hi Michael,
Thanks for that. I get confused by the reference to 'stucco': In Ireland this typically refers to historic decorative plaster used internally. Is the Regular Lime Stucco used in conservation or environmnetal projects in the US and is without portland cement?

Cheers,
Joseph

Michael Hurd · Post by **Michael Hurd** » Fri Sep 25, 2009 5:51 am -1100

Here in the states the terms Stucco and Plaster typically mean the same system. Occasionally you will see gypsum plaster used for interior applications, but the regular portland cement plaster gets used inside too. Most of what we use here in my firm is Portland cement plaster that has cement, lime, sand and water and possibly some acrylic admixture for workability.

josephbeag · Post by **josephbeag** » Wed Sep 30, 2009 8:09 am -1100

Hi,
Could someone at the Fraunhofer respond to my original email on this subject?

Many thanks.

Josephbeag

Manfred Kehrer · Wed Sep 30, 2009 7:06 pm -1100

Dear Joseph,

the mentioned layer system of the IBP Material Database is really a 4 layer system where IBP has done measurements on each layer. If a 4 layer plaster system is unusual in Ireland, you should not use it.

Whether you really need a 4 layer plaster depends on your specific project.
If you need exact values of your portland cement plaster you should contact the manufacturing company or do measurements by your own.

josephbeag · Post by **josephbeag** » Sun Oct 04, 2009 6:02 am -1100

Hi Manfred,
Can you identify a traditional lime render/plaster from the catalogues of material for external use? I say this because some may be for internal use and some lime plasters have cement in them.

Regards,
Josephbeag

Manfred Kehrer · Sun Oct 04, 2009 7:30 pm -1100

josephbeag wrote:Hi Manfred,
Can you identify a traditional lime render/plaster from the catalogues of material for external use?

The "Lime Plaster" or the "Cement Lime Plaster" should be the one. All plasters except of the "Interior Plaster" are for exterior use.

Daniel · Post by **Daniel** » Mon Oct 05, 2009 8:39 pm -1100

1. The four layers in the data base describe one specific two layer plaster system.

2. The two additional "resistance" layers represent a resistance interface between finish coat and base coat and between base coat and substrate where the pores are nearly blocked liqduid transport (Application of the plaster: absorbtion to the pores and hardening within the pore structure - crystallization).

3. The problem is, that the resistance layers can occur or not and differ very much - all depending on the plaster and subtrate properties.

4. The most important information to choose a plaster from the data base is to know (or assess) the diffusion resistance an A-value of the real material. These both values show the strongest influence on the hygrothermal behaviour of the whole wall.

Daniel

WUFI