Characterization of earth-based mortars for rammed earth repair

M.I. Gomes, T.D. Gonçalves, Paulina Faria

Research output: Chapter in Book/Report/Conference proceedingChapterpeer-review


All over the world, many earth buildings are deteriorating
due to lack of maintenance and repair. Repairs
on rammed earth walls are mainly done with mortars,
by rendering application; however, often the repair is
inadequate, resorting to the use of incompatible materials,
including cement-based mortars. It has been
that such interventions, in walls that until that
day only had presented natural ageing issues, created
new problems, much more dangerous for the building
than the previous ones, causing serious deficiencies in
this type of construction. One of the problems is that
the detachment of the new cement-based mortar rendering
only occurs after some time but, until that occurrence,
degradations develop in the wall itself. When the
render detaches, instead of needing only a new render,
the surface has to be repaired in depth, with a repair
mortar. Consequently, it has been established that the
renders, and particularly repair mortars, should have
physical, mechanical and chemical properties similar to
those of the rammed earth walls.
This article intends to contribute to a better knowledge
of earth-based mortars used to repair the surface
of rammed earth walls. The studied mortars are based
on four types of earth: three of them were collected from
non-deteriorated parts of walls of unstabilized rammed
earth buildings located in Alentejo region, south of
Portugal; the fourth is a commercial earth, consisting
mainly of clay. Other components were also used, particularly:
sand to control shrinkage; binders stabilizers
such as dry hydrated air-lime, natural hydraulic lime,
Portland cement and natural cement; as well as natural
vegetal fibers (hemp fibers).
The experimental analysis of the mortars in the fresh
state consisted in determining the consistency by flow
table and the bulk density. In the hardened state, the
tests made it possible to evaluate the following properties:
linear and volumetric shrinkage; capillary water
absorption; drying capacity; dynamic modulus of
flexural and compressive strength.
Original languageEnglish
Title of host publicationEarth Construction and Tradition
EditorsHubert Feiglstorfer
Place of PublicationViena
PublisherInstitute of History of Art, Building Archaeology and Restoration at the Vienna University of Technology and IVA–ICRA (Institute for Comparative Research in Architecture
Number of pages17
ISBN (Print)978-3-900265-34-2
Publication statusPublished - 2016


  • Earth mortar
  • Earth stabilization
  • Physical characterization


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