Monday, January 10, 2011

Clay plaster in passive house

We are doing clay plaster in the middle of winter... here some video from the passive house under construction in Bratislava.

The load bearing walls and ceilings are made from massive wooden elements (Lignotrend). Before we put on the clay plaster, reed mats are fixed to the walls. Some partition walls are laid with clay bricks and will also be rendered later. All in all there will be over 15t of clay material in the building.

This will not only give the building some additional mass, but the clay will function as a humidity buffer. If there is too much humidity it will be absorbed, if there is little (below 50%RH), it will give off a humidity. This is very helpful in winter time, when ventilation causes a drop of relative humidity levels inside (due to temperature differences outside/inside).

The house is insulated with blown in cellulose (30cm), the windows are not built in yet and are just covered with the outer soft wood fibre boards (52mm) wrapping the whole building. We are heating inside and at the same time using a ventilator with 5000m3/h to keep the air exchange high. Very good drying potential.

Will come back to this building to show how things work out later...

Friday, January 7, 2011

Preliminary Blower Door Test on a Limestone building without inside plaster

Although the building did not have a final plaster layer inside (the airtight layer), I wanted to check how well this type of construction does with just the Polystyrene insulation glued to the outside. I expected a value around 1 for the Blower Door Test (BDT), but the first measurement was even better: n50 = 0,79!

Here is a short video I made with my iPhone and edited directly on the phone…

First, it is important to notice that the Polystyrene blocks (500x1000x300mm) were glued to the full surface. The plaster glue was troweled on the polystyrene blocks and then evenly distributed with a 10mm “comb” trowel. The Polystyrene was then pressed into that surface – a 5-6mm adjustment of the surface was possible. This was sufficient, because the walls from Limestone can be built very precise.

Of course the wall is still leaky – there are areas where we could not measure any leaks, but on other places some leakages were to expect. I presume there are areas where the Polystyrene connects to the glue and where there is still some air gaps in-between the troweled glue. Wall corners and some holes that were drilled to attach some connection elements from Dosteba were leaking. This will all easily be eliminated later by the inside plaster.

The electrical installation was without problem. Before mounting the electric boxes, the drilled holes were filled with gypsum, and then the plastic box pressed inside. The superfluous gypsum fills all gaps and does not crack.

Looking forward to the next BDT, I am confident we will get a result below n50 = 0,3.