Decay and erosion of masonry

The decay of stone and brickwork is a serious problem in many civic and commercial buildings as this leads to physical loss of the outer fabric, dampness and concerns about safety. The problem of stone decay is also very apparent in the deterioration of historic architecture and masonry.

Acid rain and pollution are the major causes of the decay. The erosion of our heritage and escalating costs of restoration and replacement has focused attention of arresting these problems. In most cases the use of preservatives and consolidation are the only available methods of retaining the history of our building facades and architecture.

Causes of Decay in Masonry

Loss or erosion of the cementing matrix in the substrate by acid attack
Disruption of the inter-granular bonds in the substrate by increased tensile stresses caused by salt crystallization

Defence Against Attack

Any preservative applied in conservation work must fulfill two important criteria by:-

Replacing the internal cementing matrix to strengthen the friable pore structure
Prevent the migration of soluble slats, without affecting water vapour permeability, to reduce the effects of salt crystallization

The Wacker OH100 Preservation System

The Wacker Stone Strengthener OH100 preservative products have been used in the UK for nearly 30 years and have been shown to meet the above criteria over and over again.

The Wacker Consolidation System is based on silicic acid ethyl esters and is a ready for use product. It is applied to the surface of prepared substrates where it is absorbed through capillary action in the masonry. The low molecular weight encourages optimum penetration into the substrate. The esters hydrolyze in the presence of atmospheric humidity and with the aid of catalysts form a silicic acid gel. This is then converted into silicon dioxide (SiO2), to replace chemically the natural binder, which has been lost (see simplified equation)
catalyst
Si(OR)₄ + 4H₂O ----------> Si(OH)₄ + ROH

Si(OH)_4- ---------> SiO₂ + 2H₂O

This demonstrates that a solid binder can be introduced into the substrate by the use of liquid silicic acid ethyl esters.

The remarkable consolidation achieved with the Wacker OH100 product does not seal the pores in the masonry and the treated substrate retains its water vapour permeability.

The Wacker OH100 product does not possess any real hydrophobic or water repellent qualities. The substrate must be impregnated with a recommended silicone water repellent, which, again, does not affect water vapour permeability.

The amount of Wacker OH100 needed for consolidation depends on the type and porosity of the substrate. It may range from 0.5 to 10 litres/sq.m. and the amount required is normally determined by carrying out a small test area.

To achieve the required depth of penetration, apply Wacker OH100 through a series of continuous applications ("wet on wet") until the substrate does not absorb any more of the product. This will provide the consumption volume of product litres/m2 of the area to be treated.

Technical assistance and a Code of Practice are available to provide information about the suitability of any substrate with regard to consolidation with Wacker OH100.

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