The Australian Hemp Masonry Company

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Retrofitting

Many of Australia’s existing buildings are neither thermally effective, nor cheap to run. Moulds are also an issue in much of our built infrastructure.

Hemp masonry, or hempcrete is much more flexible than cement.  It is a robust building material with very little shrinkage. It adheres to steel, brick, concrete, wood and old plaster or render and it can also be cast against brick, old stone or cob (earth) walls either on the inside or the outside.

Used in conservation work in Europe and the UK, the material is demonstrating that it has major potential as an insulating plaster in renovation of buildings where the damp in old walls is an issue, providing a more effective solution than dry-walling.

The hemp wicks the moisture from the damp substrate. Where dry walling is used in this kind of situation on the other hand, condensation  accumulates behind the dry-walling, concealing the problem rather than managing it.

Hempcrete can be used as infill for very small sections of buildings, or to replace or insulate walls externally or internally.

Retrofitting can be done in a number of different ways:

  • existing  uninsulated internal walls can be replaced, using the frame to form up a standard 150mm Hemp masonry internal wall instead. This will improve both thermal insulation and acoustic isolation.
  • gyprock walls can be removed on one side of a wall.  Retaining the gyprock on the other side, install a breather membrane to ensure that moisture from the mix doesn’t affect the gyprock, then attach formwork to the studs to create the desired thickness of wall cavity. The thicker the walls the higher the R value.
  • internal gyprock can be removed from weatherboard clad external walls, or from brick veneer and with appropriate detailing hemp can be retrofitted internally.
  • brick homes are  retrofitted externally in the UK by attaching temporary studs to the existing surface and fixing the formwork to these, to create a 150mm – 200m thermal envelope around the existing build. Depending on the thickness of the walls, if needed, once the wall section has been completed, the studs can be removed and the gaps filled with hemp lime material. When the wall is cured it can be finished with AHMC’s Hemp-lime render, or other lime or clay renders.

While several of these situations require home owners to sacrifice a small amount of internal space to enable their internal walls to be retrofitted, retrofitting will improve indoor air quality in all of the above situations. Hemp manages the moisture in buildings very well.

There will also be significant energy-efficiency gains and improved thermal and acoustic comfort.