Chemical Damp Proofing Solutions

Installing a liquid DPC

Replastering

Chemical solutions attempt to block rising damp by injecting water-repellent chemicals into the walls. This is a 2 step process:

1. Installation of a „liquid damp proof course“: holes are drilled alongside the base of the wall 10-15 cms apart then the chemicals are injected into the drilled holes with or without pressure. The chemicals should spread enough in the masonry to form a continuous water repellent layer to prevent future water infiltration.

2. Replastering:  rising damp will carry the dilluted ground salts up into the wall fabric. When water evaporates the salts will be deposited into the plaster. Because salts attract the moisture from the air, the plaster can become wet again. To prevent this the salty plaster will be replaced with fresh, non-salty plaster. Normally special water- and salt resistant plaster is used for this purpose.

Although the chemical procedures are often marketed as a simple, easy „plug-and-play“ operations with excellent and lasting results, this is far from the truth. There is a complex set of chemical reactions taking place inside the wall in which a multitude of factors can influence the final outcome.

Weak Points

The weak points of the technology that account for a 25-40% failure rate[1] are:

- Distribution of the chemicals in the masonry: the injected chemicals do not spread as evenly as some of the animated videos show, leaving spots untreated where water can still rise.

viscous fingering

The injected chemicals will leave untreated gaps in the brickwork

- The aging of chemicals: as water evaporates the chemicals in the capillaries will shrink. As a result a new, secondary capillary system will form and the moisture will rise again.

- Chemicals impacted by other factors: there are several other factors that impact the injected chemicals, such as wall’s temperature, salt content and pH value (acidic or basic nature). Low temperatures (typically under 5 oC) slow down the reaction of the chemical agents and their water repellent properties might not fully develop. Salts can inhibit the reactions altogether.

- Wall thickness limitations: water repellents develop their water-repellency after certain chemical reactions. Some chemicals  (e.g. silicates) need to react with atmospheric CO2 to become water repellent. Deep inside the thicker walls there is less CO2 present, which limits the maximum injectable depth of these chemicals to about 50 cm.

Mistakes In Application

Research has shown that the method of injection is just as important as the properties of the chemical agents. The failure rate can be worsened to over 60%[2] by the following common mistakes in application:

- No or incorrect selection of the chemical agent: each masonry type works best with a specific chemical agent. For example: building materials with smaller pores need chemicals with smaller molecules (e.g. silans). Some chemicals react best in high pH (basic) environments so they are suitable for sandstone and cement but not bricks. Precise knowledge of both the building materials and chemicals is needed to match the two for best results.[3]

Pre-drying of masonry with heating elements (thermo-injections)

Chemicals injected under pressure

Chemicals injected
under pressure

- No pre- or post-drying of the masonry with heating elements: research results have shown that drying out the walls before and after the injection in order to reduce its water content has significantly increased the long-term reliability of the chemical DPC. Yet this step is frequently omitted for financial reasons or lack of proper equipment.

- Too short injection times[4]: the injection times are often too short for the chemical to fully saturate the brickwork. E.g. pressure injections may need between 5-20 minutes per drill hole which is often reduced to under 1 minute. This will result in low penetration depth and insufficient spread.

- Injecting thick walls (over 50 cm thick): many of the damp buildings in Scotland are old stone buildings with 50-110 cm thick walls. Damp proofing companies will often inject these walls taking the risk of failure.

Replastering: there is a considerable debate in professional circles about how much replastering is needed after a chemical injection. Professionals acknowledge,  that replastering fulfills not one but two major functions: 1. the replacement of the old, salty plaster, and 2. the hiding of an unreliable chemical DPC[5].

Furthermore, damp proofers have an interest in carrying out more replastering than strictly necessary to finish the job quicker, without having to wait for the walls to dry out. Dense sand-cement renders used in replastering have poor thermal insulation resulting in an increased risk of condensation and mould.[6]

With correct procedure and expert application a success rate of 80-95% [7] is attainable short term.

Advantages

- Relatively cheap if only short wall sections have to be injected.

Disadvantages

- Not suitable for old historical buildings where interfering with the building structure is prohibited.

- Injecting stone walls can be problematic.

- Relatively high failure rate in the long run.

- Work intensive, requires messy building work.

- The replastering masks the potential failure of the DPC, giving building owners a false peace of mind that the dampness problem has been fixed when it hasn‘t.

- Not a permanent solution long term to the dampness problem.

- Does not offer a solution to the problem of existing dampness inside the walls. Walls can only dry out through the slow natural evaporation.

- Damp walls degrade the thermal insulation of the building resulting in increased heating costs.

- Invasive, non-reversible: the chemicals can‘t be removed from the walls once injected.

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[1]. Ing. C.A.M. (Kees) Snepvangers: „The  distribution  of  injection  fluids  against  rising  damp  in masonry: models and risk factors“, OTB Research Institute for  Housing,  Urban  and  Mobility  Studies,  The  Netherlands

[2]. Dipl. Eng. Dr. Balak, M: „Injection technology for post-construction  damp proofing of masonry – Latest findings“, Masonry Magazine 11 (2007), Ernst & Sohn Publications

[3]. Loek J.A.R van der Klugt & Jaap A.G. Koek: „The Effective Use of Water Repellents“, TNO Building and Construction Research, The Netherlands

[4]. I‘Anson, S J; Hoff (1990). „Chemical Injection Treatment for Rising Damp - II. Calculation of Injection Times“. Building and Environment 25 (1): 63–70

[5]. Burkinshaw, Ralf: „Remedying Damp“. RICS Books, page 81. ISBN 978-1-84219-305-1

[6]. http://en.wikipedia.org/wiki/Damp_%28structural%29

[7]. Michael Balak, Anton Pech: „Masonry Drainage: from Basics to Practical Applications“, page 159, 2.ed (2008), Springer Wien New York

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