{{ propApi.closeIcon }}
Our industry
Our industry $vuetify.icons.faArrowRight
Economic research and forecasting Economics Housing outlook Tailored market research Economic reports and data Inspiring Australia's building professionals HOUSING The only place to get your industry news Newsroom
Business support
Business support $vuetify.icons.faArrowRight
Become an apprentice host Hire an apprentice Why host an HIA apprentice? Apprentice partner program Builder and manufacturer program Industry insurance Construction legal expenses insurance Construction works insurance Home warranty insurance Tradies and tool insurance Paperwork gone digital Contracts Online HIA Tradepass HR Docs SafeScan - managing workplace safety Planning and safety services Building and planning services How can HIA Safety help you? Independent site inspections Trusted legal support Legal advice and guidance Professional services Industrial relations
Resources & advice
Resources & advice $vuetify.icons.faArrowRight
Building it right Building codes Australian standards Getting it right on site See all Building materials and products Concrete, bricks and walls Getting products approved Use the right products for the job See all Managing your business Dealing with contracts Handling disputes Managing your employees See all Managing your safety Falls from heights Safety rules Working with silica See all Building your business Growing your business Maintaining your business See all Other subjects COVID-19 Getting approval to build Sustainable homes
Careers & learning
Careers & learning $vuetify.icons.faArrowRight
A rewarding career Become an apprentice Apprenticeships on offer Hear what our apprentices say Advice for parents and guardians Study with us Find a course Get your builder's licence Qualifications Learn with HIA
HIA community
HIA community $vuetify.icons.faArrowRight
Join HIA Sign me up How do I become a member? What's in it for me? Get involved Become an award judge Join a committee Partner with us Get to know us Our members Our people Our partners Mates Rates What we do Mental health program Charitable Foundation GreenSmart
Awards & events
Awards & events $vuetify.icons.faArrowRight
Awards Australian Housing Awards Awards program National Conference Industry networking Events
HIA products
HIA products $vuetify.icons.faArrowRight
Shop @ HIA Products Digital Australian Standards Contracts Online Shipping and delivery Purchasing terms & conditions
About Contact Newsroom
$vuetify.icons.faTimes
$vuetify.icons.faMapMarker Set my location Use the field below to update your location
Address
Change location
{{propApi.title}}
{{propApi.text}} {{region}} Change location
{{propApi.title}}
{{propApi.successMessage}} {{region}} Change location

$vuetify.icons.faPhone1300 650 620

Efflorescence in masonry

What is efflorescence in masonry, how can it be prevented and what can be done to remove it when it occurs post-construction?

In this Article

  • What is efflorescence?
  • Why and how does efflorescence occur?
  • How to prevent efflorescence
  • Australian Standard AS/NZS 2311 Part 3.10.4 and 3.10.5

What is efflorescence?

‘Efflorescence’ is the term most commonly used to describe the deposit of crusty white mineral salts that appear on a masonry surface (concrete, render, brick or mortar) that have leached out from within the substrate when moisture migrates through it.

Any efflorescence on the surface must be removed prior to painting as it is regarded as a poor and friable base that prevents paints and coating systems from adhering effectively.

Paint systems adhering normally to the surface of the substrate can also be forced off (delaminated), when the pressure caused by the growth of salt crystals builds up beneath the paint film, resulting in its gradual but irreversible destruction. Since the mineral salt crystals are not fluid, the pressure is therefore not uniform, so the coating does not form smooth rounded blisters.

The paint film may stretch to form the outline of the growing crystals or the paint film may just rupture, crack, flake or peel.

Why and how does efflorescence occur?

Efflorescence in masonry appears as white alkaline salts on the surface and consists mainly of calcium carbonate. A reasonable amount of moisture is required for it to form.

The carbonation process occurs when alkaline salts such as Lime (calcium hydroxide) within the pores of the substrate react with atmospheric carbon dioxide to form calcium carbonate, which is transported to the surface by moisture. Concrete or mortar with high levels of Portland cement contains high concentrations of calcium that, in turn, can produce excess salts.

It should be recognised that there must be water (moisture) present to dissolve and/or transport these salts so the source of the moisture needs to be either blocked (if it’s external to the substrate, such as groundwater) or exhausted (if moisture is emanating from within the substrate, such as rising damp).

As moisture enters and moves through the substrate it dissolves mineral salts (mainly calcium carbonate) that are present in the cement (or plaster). When the mineral salt solution finds its way to the surface of the substrate, the water evaporates, leaving behind a white deposit of crystalline salts.

Efflorescence may occur within the first year of a new construction project and may only be an aesthetic concern on an unpainted substrate.

Efflorescence due to residual moisture within the substrate will cease naturally as the masonry dries and cures. However, when the efflorescence continues unabated it is likely that moisture ingress from an external source is occurring, which can present significant ongoing problems.

How to prevent efflorescence

Without doubt, the best way to prevent efflorescence from occurring in the first instance is to put the following practices into effect at the design and construction phase:

  • Ensure that the substrate is fully cured (at least 28–30 days for concrete and cement render / 10 weeks for fibrous or set plaster, depending on ambient conditions) prior to painting.
  • Good drainage to prevent water ‘ponding or pooling’ on horizontal surfaces wherever possible
  • Keep masonry dry during construction by covering it with plastic sheeting
  • Installation of appropriate moisture barriers (waterproofing) to effectively prevent rising, falling or lateral damp or any water ingress from an external location (such as soil) as this can activate the alkaline salts within the masonry substrate allowing these salts to be transported to the surface by moisture
  • Avoid painting highly alkaline masonry surfaces that have a pH of 10 or over. (Note: A pH of 10 is actually 10 times more alkaline than a pH of 9 – Ref: AS/NZS 2311)
  • Avoid painting damp masonry surfaces that have a moisture reading above 10% (using a standard moisture meter) as the coating system can impede the desired loss of residual moisture from the substrate
  • Use proprietary factory mixed cement renders that are lime free or low in calcium and polymer reinforced
  • Specify and select masonry ingredients that have low calcium or low salt content (e.g. clean washed sand)
  • Protect bare and non-painted masonry from moisture ingress by applying water repellents such as silanes or silicone solutions.

Australian Standard AS/NZS 2311Part 3.10.4 and 3.10.5

Efflorescence 3.10.4

Salt, generally alkaline, may be transported to the surface of plaster by the movement of moisture to a surface from which it can evaporate. Efflorescence due to residual moisture will cease naturally as the plaster cures, whereas efflorescence caused by moisture ingress may continue indefinitely while there are salts present to be transported, unless the source of moisture ingress is detected and eliminated, whereupon the decline in moisture levels and cessation of efflorescence will proceed as for residual moisture.

The cessation of efflorescence may be ascertained by brushing or wiping an affected surface free of existing efflorescence, then waiting a reasonable period to ensure its continuing absence.

Part 3.10.5 states:

3.10.5 Moisture ingress

Moisture ingress generally becomes apparent in new plasterwork as a failure of moisture levels to decline as expected despite conditions being adequate for such moisture loss to occur – i.e., in terms of time, temperature, relative humidity and ventilation rate. The source of moisture should then be traced and rectified before moisture levels can decline to a normal equilibrium. Any side effects of the elevated moisture levels, such as disintegration of the plaster or mould growth, should also be rectified before proceeding to paint.

References

  • AS/NZS 2311 Guide to the painting of buildings
  • Dulux Protective Coatings Tech Note 1.3.6 Problems with Concrete – Efflorescence

To find out more, contact HIA’s Building Services team.

Email us

Share with your network:

More articles on:

{{ tag.label }} {{ tag.label }} $vuetify.icons.faTimes
Find guides, how-tos, resources and more

Business support


 

Supporting building professionals with custom built services and products.

  • Legal support
  • Contracts Online
  • Host an HIA apprentice
  • Insurance services
  • Managing safety

Explore Business support

Building it right topics


 

Can’t find what you need, check out other resources that might be closer to the mark.