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    • 17 September 2011 at 6:43 am #31552
      Tim Barrett

        I would like advice on the best type of plaster to use to give the best thermal conductivity. The walls are highly insulated with 100mm solid concrete blocks internally to give thermal mass so I don't want the plaster to insulate it in any way.

      • 17 September 2011 at 11:13 am #38086
        Anonymous

          I would like advice on the best type of plaster to use to give the best thermal conductivity. The walls are highly insulated with 100mm solid concrete blocks internally to give thermal mass so I don't want the plaster to insulate it in any way.

          Interesting question! I hope somebody knows the correct answer but in case they don't, here's some speculation:
          (1) keep the layer of plaster as thin as practicable

          (2) according to http://www.jupiterunderfloorheating.com/uploads/knowledgeBase/W1.PDF “Cement plaster e.g. Marmorit Rotkalk” has better conductivity than clay or gypsum plaster.

          (3) you could try mixing in some components with higher thermal conductivity, such as carbon fibres.

          But I think the first thing to do would be to model the effect of the layer of plaster to see what it effect it has and how much effort or money its worth spending on optimising it.

        • 17 September 2011 at 2:17 pm #38087
          A-tec Design
          Participant

            Why not render the walls and finish with a skim of plaster. This will give a thickness of 12mm and max 5mm.

          • 23 September 2011 at 9:10 pm #38088
            Mark Siddall
            Participant

              Dense blockwork has a conductivity in the range 1.1 to 1.2 W/(mK).
              13mm Dense gypsum (1300 kg/m3) has a conductivity of 0.57 W/(mk).
              13mm Densure gypsum (1000 kg/m3) has a conductivity of 0.4 W/(mk).
              Render, cement/sand, has a conductivity of about 1.0W/(mK).
              Render, gypsum/sand, has a conductivity of about 0.8W/(mK).

              Consider render with thin, 3mm, gypsum finish?? (a bit experimental as may crack due to differential propoerties.)

              Though if you think about the wall as a whole the insulation is likely have a conductivity of 10x greater than that of insulation.

              M

            • 29 September 2011 at 2:29 pm #38089
              Tim Barrett

                Thank you for that Mark and I'm sure you're right, it's hardly going to make any difference any way. I quite fancy using lime render and set for it's other properties, any thoughts?

                Tim

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