Efflorescence requires the movement of moisture. Without moisture movement there would be no efflorescence on the surface to create the problem. Unfortunately, too many contractors routinely introduce large amounts of unnecessary “water of convenience” to the mix in order to facilitate concrete placement in hot weather. Primary efflorescence is caused by the excess water (bleed water) in the concrete containing lime from the slab reacting with carbon dioxide in the air to form calcium carbonate, leaving behind the soluble salts on the concrete surface. The fact that these salts are actually more soluble in acidic water coupled with increased bleed water in increases the likelihood of efflorescence showing up after concrete placement. Contributing further to efflorescence in hot weather pours are the coastal conditions which has high salinity in the air and dissociated chloride settles on the concrete and drains out this pore lime. High slump (watered down) concrete and the additional costal conditions are major contributors to efflorescence.
Secondary efflorescence is often described as water coming from underneath the slab or water that is introduced from the surface. Likely sources of secondary efflorescence would be a saturated base material, an improperly drained site or excessive amounts of water used by the contractor during his placement of concrete. When extra mix water and extra soluble salts like sodium chloride from the saline condition are added to concrete placed in hot weather followed by more acidic water from the concrete curing process, some degree of efflorescing is bound to occur.
Effects of Efflorescence:
This continuous drain of vital pore lime from the concrete or even plaster surface which could be due to acidic or saline conditions or due to the movement of water through the concrete or the masonry structure causes efflorescence in the plastered surface or concrete. Usually in internal plasters the formation is because of the raising dampness from any water source close by like a kitchen or a bathroom or even due to a porous sub base and a close water table where the base acts as a sponge to seep up water. External plaster efflorescence is due to internal water movement or due to external condensation of water on its surface which causes powdering of the plaster once all the lime and salts are drained out. Plaster efflorescence though ugly does not affect the structural strength but is causes a number of other problems like breathing difficulty, moss formation due to the wet floss which is conducive for such growth.
Concrete efflorescence reduces structural strength over time and forms tracks for further corrosion which increases exponentially once the pore lime and salts are drained out. Concrete is the most critical part to protect from such kind of chlorine or corrosive environment attack
Determine ahead of time if efflorescence is a likely problem waiting to happen:
- Look for signs of efflorescence
- Check the draining of the property
- Surface water’s proximity to the foundation
- Check the date and year of pour of the concrete
- Check if the concrete was placed on a saturated sub grade
- Check if a vapour retarder was used before concreting
- Check if granular material was placed over the vapour retarder
- Check vapour retarder and plumbing around the retarder
- Check if the concrete had any kind of pozzolans as additive
- Check for waterproofing admixture used
- Check for “water of convenience” added to the concrete
- Check for curing compound or liquid densifier applied
Testing for Vapour Transmission:
Determine the current vapour transmission rate (VTR). Use test method, Plastic Sheet Test (ASTM-D-4263), taping down a clear 18″ X 18″ sheet of poly and check 16 hours later for condensation or for a darkened concrete surface. Both are indications of vapour transmission. Another surface moisture test is The Calcium Chloride Test which quantifies the rate of vapour transmission. This is covered dish that is weighed before and after a twenty four hour period. Both are cost effective measures in determining whether vapour is active.
A note of caution when using these testing methods the plastic sheet and chloride tests will track moisture movement near the top only. When the atmospheric conditions are similar to the slab conditions the tests might not indicate significant vapour transmission because movement happens when the ambient conditions differ from the slab conditions. Moisture migrates and moves toward cool temperatures. Vapour emissions migrate and move toward heat. Hence when the HVAC is turned on it causes vapour in the slab to move towards the warmth or the lower humidity of the conditioned space bringing the whitish minerals with it. If the sealer is acrylic the vapour will pass through leaving the efflorescence. If urethanes or epoxies are on the floor, hydrostatic pressure may build and possibly cause delamination. Efflorescence can occur months or even years after the contractor has left the job due to circumstances similar to those just described or from seasonal ground water seeping under the slab or even from the condensation of sea water on the concrete surface draining the pore lime out. Testing the surface may not be enough to guarantee an efflorescence free project. It is important to determine the source and the rate of vapour transmission before prescribing a remedy.
Well drained site, vapour retarder, densifiers and specialized pozzolanic admixtures are the best deterrents to efflorescence. This can be achieved by placing the concrete directly on the vapour retarder or over granular material on top of the vapour retarder. Elevated slabs are quite common in commercial construction and they are placed on well compacted soil and proper foundation. The most important factor is minimizing water in all the important areas mainly the sub grade, the concrete and the procedures performed by the contractor. These all require huge amounts of water, but keeping water to a minimum helps ensure that efflorescence is controllable.
Efflorescence reducing measures are: site surface drainage; a well graded concrete mix with a water reducer to minimize paste; concrete not exceeding a 4″ slump; that the concrete be well consolidated (one man vibratory screeds do a great job); placed directly on a vapor retarder and cured in some fashion. All these factors contribute to a concrete that has a minimum amount of bleed water with a lesser pore and capillary network that will resist rather than facilitate absorption and movement of moisture…in other words, a dense and relatively impermeable concrete slab.
Now for more specifics…an option to the vapor retarder is a waterproofing admixture like INCAP ADMIX o pore blocking chemicals like TECHNOBUILD DRI BLOCK to help prevent efflorescence. This can be added to the concrete at the plant batching stage.
Helpful mix design factors include ordering a well graded a mix from the ready mix producer. The advantage gained from a well graded mix design is the reduction of the weakest part of concrete, the cement paste (cement and water), making for a denser concrete than with a standard mix. Another important mix design consideration is the replacement of 15% to 20% of the Portland cement with fly ash which contributes significantly to lessening efflorescence. Fly ash brings three important benefits to reducing efflorescence. Fly ash reduces the amount of Portland cement and free lime as well as chemically binding up a portion of the free lime and salts that cause efflorescence. In addition, fly ash requires less water again resulting in a denser paste which aids in keeping moisture from traveling up from the bottom and from the top down. Water reducers of course, are also helpful at minimizing the amount of water and a reduction of cement (paste).
The closer a mix design gets to the desired water cement ratio of 0.40 Kg of water to 1 Kg of cement, the fewer efflorescence issues arise, especially with a mix including fly ash. Keeping multiple pours consistent with the mix design, sub grade conditions and finishing practices will produce consistent results. Warm concrete and hot ambient temperatures encourage efflorescence because the salts are actually more soluble in warmer temperatures plus concrete tends to bleed the excess water used for convenience further encouraging the upward transportation of moisture and soluble salts along with it.
Curing becomes important as we recognize that moisture moves much more slowly through denser concrete from either direction. When concrete is kept moist for a longer period, especially the first few days, more capillaries and pores fill partially or completely to form a denser and more impermeable matrix that discourages the migration of moisture and soluble salts. Conversely concrete that is placed at a high slump and not cured acts as a sponge, full of miniature raceways allowing easy movement of moisture from the bottom up and top down. Cure and seal membrane also help better curing of concrete.
Application Process for Efflorescence:
Plaster Efflorescence Process and Treatment:
Block water seepage from all sources, main points would be the base of the masonry wall, grout using products like PROTEX or EPIKOTE LV or UREKOTE LV to fill out the base of the wall and block water passage.
Apply PROTEX LS to saturation for coverage and application refer to the TDS, this process will fill out all possible porous tracts and avoid water seepage if any.
Apply polymer modified two component coating based on TECKCRYL 300 and TECKCRYL 333 for high adhesion and elasticity
In case of heavy efflorescence use two component plaster based on TECKCRYL 3030 and TECKCRYL 333.
Concrete Efflorescence Process and Treatment:
Block water seepage from all sources, main points would be the base concrete or from the sides exposed to the elements, use products like PROTEX LS, INCAP GP or for heavy efflorescence use INCAP CONC.
Use EPIKOTE 210 or UREKOTE 210 for exposed concrete from the elements
For corroded rebars apply TECHNOBUILD PCI 220 which will penetrate the concrete to the corroded steel and convert rust apply all protective membrane after this treatment.
For new structures use INCAP ADMIX as the primary additive for protection and densification of concrete, this will bind the pore lime and form crystals with the structure and give additional strength and corrosion protection to the concrete.
For plastering light efflorescence use TECKCRYL 300 and TECKCRYL 333 as bond coat apply 2 coats for better results.
For plastering heavy efflorescence use TECKCRYL 3030 and TECKCRYL 333 as plaster this will give maximum protection of the concrete from any kind of chlorine ion or chemical attack.
For Further Details
B-26 Goodwill Sanskruthi, Bhairavnagar,
Dhanori Road, Pune – 411015, Maharashtra
Ph: +91 20-27171412