Troubleshooting Guide - Limewash staining coming through

Tŷ-Mawr ‌‌ posted this on 1 Apr 2016

Limewash staining coming through

  1. Soluble salts/creosotes/chimney tar – can be transported through the plaster/render by water and deposited on the surface when the water evaporates. Certain historic mortars and brickwork will naturally contain such compounds, especially in historic chimneys.   These salts can lead to a discolouration on the surface of the plaster/render; in general, they are more unsightly as opposed to seriously harmful to the plaster/render.
  2. Limewash applied too early to lime hemp plaster - Hemp plaster must be allowed to carbonate fully before the application of decorative finishes. 


Commonly a problem with the renovation of damp chimney places. If the walls are damp they should be allowed to dry out prior to the application of the new lime plaster, otherwise, it is likely that the water will carry the soluble salts through the new plasterwork to be deposited on the surface of the plasterwork. The use of Silane Primer in conjunction with Beeck’s mineral paints. The Silane Primer is especially good at reducing the capillary water transport in the zone close to the zone of salt-laden substrates whilst avoiding further water intake. Beeck’s Silane Primer is a solvent containing primer based on organosilicon ingredients of a particularly high penetration depth. For use outdoors on any alkaline mineral building material characterised by a high absorbency e.g. lime and cement plasters, lime sandstone and concrete.

In short, the salts are prevented from moving through this primer whilst the water vapour is still able to do so. 

Damp walls should be allowed to dry out sufficiently before the application of any plasters; this is especially the case with hemp plasters. If the hemp is going onto a particularly non-porous background then our dry premixed hydraulic lime may be more appropriate as it has a degree of the chemical set that can reduce drying times. Please contact the manufacturer if you think that you might benefit from this, or if you are unsure about your project prior to beginning it.

If you think that there is likely to be a problem with the leaching of salts or minerals from the wall, then it is suggested that you prime the wall first with Primal. This is a low-viscosity, water-based acrylic emulsion which offers excellent durability and flexibility as it ages. It is also vapour permeable. Please contact Ty-Mawr for details. 

Categories: Limewash