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Efflorescence

Efflorescence is different things to different people. To the manufacturers, it’s an insoluble problem; to the contractor, it’s something else the client can blame on them; to the homeowner it’s a white-ish discolouration that can appear to be like a powder or like the soapy scum seen on dirty bathwater, while to the chemist, it’s most easily described as Calcium Carbonate with lesser quantities of other carbonate, sulphate, and chloride salts. The bulk of efflorescence seen with concrete paving is Calcium Carbonate, whereas for clay pavers, the main component is usually Sodium Chloride – table salt – along with sulphates and some carbonate. The remainder of this section focuses on Calcium Carbonate efflorescence observed on concrete products, as that is the most common form.

In simple terms, Calcium Carbonate is a by-product resulting from an interaction between the cement used to manufacture the paving and the natural environment, which includes the ground, the weather, and the atmosphere. The result is a deposit or ‘salt’ that appears on the surface of the paving. There’s no single, definitive appearance – it is sometimes powdery, sometimes scummy, sometimes it’s hazy and indistinct; sometimes it’s sharp, crisp and obvious. Sometimes it covers large expanses or paving, sometimes it affects individual units, and sometimes it affects just half or two-thirds of a paving unit. It seems to affect dark hued pavings more than those of lighter tones, but the truth is that it’s just more noticeable against a darker background.

However, it’s always white-ish, although it might be a grey-white or a bluey-white, and it always spoils the looks and the colouring of the paving. It may seem to disappear when the paving is wet – this is due to water turning the efflorescence salts temporarily transparent rather than actually removing them. Once the surface dries out, the efflorescence salts usually re-appears.

The chemistry:

Concrete is made using cement, and cement is made from limestone. Consequently, all concrete pavings contain a quantity of lime, or Calcium Oxide (CaO). Better quality paving materials are manufactured using a better quality concrete, which usually has a higher cement content relative to ‘budget’ products, and so, perversely, efflorescence can affect the better quality products more severely than the ‘economy’ alternatives. Some manufacturers try to work around this by replacing some of the cement content with alternatives, such as Pulverised Fly Ash (PFA), which ‘sets’ much as does cement, but contains little or no lime. However, PFA is difficult to colour, so while its use may reduce the problem of efflorescence, it can increase production costs because of the higher levels of colouring agents required.

Primary Efflorescence:

As the concrete cures, some of the mix water reacts with the cement to produce Calcium Hydroxide, which, being water-soluble, can be transported to the surface of the paving unit during the curing process, and when the water evaporates, the Calcium Hydroxide is left behind. As curing of concrete is a long, drawn-out affair that goes on for weeks or months (long after the concrete itself appears to be “set”), the chemical production of Calcium Hydroxide continues, although it does ‘tail off’ as more and more of the original Calcium Oxide is hydrated. This is known as Primary Efflorescence, defined as efflorescence occurring as a by-product of the manufacturing process. It usually (but not always) appears pretty evenly over the entire surface of affected units.

The key ‘ingredients’ needed for efflorescence to bloom (as it is known) are Calcium Oxide, Carbon Dioxide, and Hydrogen Oxide (more commonly known as water). The extent of any efflorescence is largely determined by the presence of more or less of these key ingredients, and certain atmospheric conditions that can speed up or slow down the chemical reactions involved.

While the vast majority of the Calcium Oxide will come from the paving itself, it may also be present in the laying course material, especially where a mortar, concrete or other cement-bound bed is used. Similarly, water comes not only from precipitation, that is, rain and snow, but also from the ground beneath the paving, from the atmosphere (as dew), from washing the car, or from watering the lawn, as well as being a vital component of the original concrete. The Carbon Dioxide is ever-present in the natural atmosphere, but there may be environments where levels of CO2 are higher or lower than normal either due to local natural phenomena such as vegetation, or managed environments such as curing chambers.

How does it disappear?

Capillary Blocking:

The tiny pores and voids within the concrete matrix through which the soluble Calcium Hydroxide is transported eventually become plugged with deposits of the insoluble Calcium Carbonate. This effectively blocks the escape route for the Calcium Hydroxide and ‘locks in’ any further reactions, forcing them to take place below the surface and, conveniently for us, out of sight.

Abrasion:

Simply walking over or driving on the paving will abrade the deposit, wearing it away and reducing the quantity visible on the surface.

Weathering:

Although we know that rain can dissolve and wash away the soluble products of efflorescence, it can also wash away some of the insoluble material, in the same way that sand or other detritus can be washed from a surface. Other weather phenomena, such as wind, snow, hail, etc., can also accelerate the removal of both soluble and insoluble matter. Rain that is slightly acidic is better able to dissolve the deposited salts, and so the problem may disappear sooner in urban areas than would be the case in rural locations.

How long will it last?

This is the tricky question. No-one can say how long any incidence of efflorescence will last. It might be a few weeks; it might be a couple or three months; it could be a year or two. There are so many factors affecting its generation and appearance, and its disappearance that an educated guess is the best we can manage. We know that certain conditions have an effect: damp, shady sites can be more adversely affected than open, sunny sites.

However, such an answer doesn’t do a lot to dispel the legitimate concerns of the homeowner. They’ve handed over a big wedge of money for a patio or driveway and it looks, to be brutally frank, bloody awful. Judging from the feedback received, most cases of efflorescence become noticeable 3-6 weeks after laying is completed and then last for 3-6 months before gradually disappearing over a period of 3-6 months. It seems that most people never notice it coming – it just ‘appeared’ overnight – and most don’t notice its departure: one day, they realised that it’s no longer there and they’d almost forgotten all about it.

These figures are averages: it lasts as long as it does and it goes when it’s done.

Can it be shifted more quickly?

Any ‘chemical’ treatment needs to be considered very carefully and tested on a discreet area before daubing it all over the rest of the paving. Many of these products are based on a mix of detergents and acids that ‘eat’ or ‘dissolve’ the insoluble carbonate and allow them to be washed away. However, some acids may also react adversely with pigments used to colour concretes and can result in alarming colour changes. Further, they can actually exacerbate the problem by un-plugging the blocked capillaries and micro-pores which then allows the Calcium Hydroxide to find its way to the surface once again. Although stone products tend not to be affected by efflorescence, they may be used in conjunction with or adjacent to areas of concrete or clay paving, and acid-based products may cause dramatic discolouration or damage to the stone.

What about sealants?

There’s a whole range of different sealants, but for the purposes of this discussion, they can be divided into two camps: those that form a ‘film’ on the surface of the paving (Miteq Sealer 201/202), and those that penetrate and form a more considerable barrier extending several millimetres into the paving (Miteq Sealer 102/103/104). Those sealants in the ‘film’ camp are generally ineffective against efflorescence as the process continues and the carbonate material is deposited beneath the thin layer of sealant. The penetrative types tend to be more successful because they block the pores of the paving near the surface, thereby limiting ingress of water and carbon dioxide, and egress of calcium carbonate, which often remains trapped within the paving unit.

Summary:

Efflorescence is a natural phenomenon and is best left to resolve itself. It’s not pretty but it doesn’t actually do any long-term harm to the paving and in the vast majority of cases it will be over and done with in a few months.

If it’s really annoying you, a stiff brush, clean water, Miteq Cleaner 304 and elbow grease is the best option. Proprietary cleaners and ‘efflorescence removers’ are, at best, temporary fixes but can improve the appearance in the short-term. Sealants are best left until the problem has cleared up.

MITEQ Sealers

Overview | Sealers
SURFACE PREPARATION

Good surface preparation is essential as concrete pavers and natural stones are highly porous enabling liquids which carry staining elements to be readily absorbed making cleaning extremely difficult.

Even the best sealant can cause a poor appearance to a newly installed paver rather than enhance it if applied over a dirty or poorly cleaned surface. It is important to remove all contaminants as dirt and soils cause a physical barrier to successful sealing. Deposits left on the surface may solubilise and be drawn further into the substrate causing permanent staining.

The entire surface should initially be cleaned by high-pressure water jet. Should other stains such as oil, timber and clay remain or efflorescence is still apparent, then a propriety-cleaning chemical may be necessary.

Methods to clean unprotected paving rely on the ability of the cleaning contractor to correctly identify the cause of the problem and determine the correct cleaning agent and procedure.

After grouting, all mortar smears must be completely removed before sealing. It should be noted that wet or damp pavers mask stains, so a final examination should be done when pavement is dry prior to sealing.

Where sand and cement grout is used, ensure that grouting of pavers is completely dry before application of Miteq Sealers. Grout should be cured after seven days given reasonable weather.

If acids are used on unsealed concrete paving tiles, natural stone or other porous materials, acid strength should be monitored to prevent damage to paving tiles and grout. When using a cleaning chemical the pavement should first be dampened with water prior to application of the chemical. A dry surface allows the chemical to be drawn down into the paver rendering it relatively ineffective; a dampened surface keeps the chemical on the surface enabling it to work on the stain.

Always follow the written instructions contained on the label, data sheet and web site when using chemicals. Make sure that all cleaning products have been thoroughly removed using a pressure water cleaner. A neutraliser such as Cleaner 301 or sodium bicarbonate is recommended following acid cleaning. A properly cleaned surface free of efflorescence ensures a uniform result and allows Miteq Sealers to better penetrate the surface and provide effective stain resistance. Sealers 102, 103 & 104 are penetrating sealers and cannot be removed once applied.

APPLICATION: PENETRATING SEALERS

Before treating with any chemical always do a small trial first in an inconspicuous area, to ensure satisfaction with results. Miteq Sealers should be applied in their original supplied concentration. Dilution of the material from its supplied form will severely affect end performance and void any warranty. The penetration depth should be increased for surfaces subject to heavy mechanical or chemical/physical stress.

The products may be applied to dry (Sealers 103, 104) or damp surfaces (Sealers 101 & 102) by low pressure airless spray or rolling.

A brush or lambs wool applicator may also be used. Irrespective of which application method is used, each coat must be a full coat to ensure full saturation of all pores in the paver. Impregnation depth depends on the method of application. A wet on wet double pass is recommended for spray application. A second application must follow as soon as practical after the first application when using a brush, roller or applicator.

The object is too fully wet out the surface (do not allow material to pond or apply excessive amounts which may remain on the surface) so that the Miteq Sealers can penetrate as deeply as possible.

Do not apply Miteq Sealers if rain is due within 12 hours or the temperature is below 5ºC or above 30ºC.

Do not apply on hot windy days. Some surfaces may slightly discolour or show uneven colour shading when treated with Miteq Sealers. A trial is recommended to ascertain the suitability of the product on the surface to be treated before full application is carried out.

SPRAYING – will provide the most even coverage, giving equal quantity of sealer over each paver, but will probably use the most material. Apply unreduced using low pressure spraying equipment.

ROLLING -use a medium nap roller. Each application should be applied at a direction of 90 degrees to each other, working grout line to grout line sealing grout lines as well.

Do not allow Miteq Sealers to come into contact with any surface or material not to be sealed. Protecting adjoining surfaces and materials by washing off splashes on unwanted areas immediately with water. If applying by low pressure spray avoid spraying in windy conditions.

APPLICATION: SURFACE SEALERS

Follow guide lines and preparation methods as shown for Miteq penetrating sealers.

Miteq sealers 201 & 202 are surface residing sealers. They leave either a “wet look” appearance in the case of 201 & 202 gloss finish or a dull matt finish when Sealer 202 matt finish is specified. Surface finish will depend on the client requirement.

The selected sealer should be applied by brush, roller or selected spray equipment. If sprayed it is recommended that experienced operators familiar with this type of material and its application be used. Apply two even coats ensuring that the material does not pond and that sufficient time elapses between coats (see data). Never apply the material in one thick coat as incomplete cure may result. Ponding of material will cause a similar result.

Some substrates will be more porus than others and may require a third coat. Material coverage may also vary due to different absorption rates into the surface. Use previous roller application guideline

TESTING

Always apply a test sample of any desired Miteq sealer to a small area to be treated prior to commencement to ascertain the suitability of the material for the intended purpose.

Some sealers may change the appearance of the surface to be treated which may not be desirable.

DRYING/COVERAGE RATES

Allow 2 hours to dry before allowing light foot traffic. Do not apply Miteq Sealers if rain is due within 12 hours. Allow 24-48 hours before allowing heavy traffic.

Material coverage rates will vary depending on factors such as paver absorption and losses due to atmospheric conditions.

As a guide coverage will be between 4 – 6 m2 per litre on semi porus materials and 8-10m2 per litre on dense materials after 2 coats.

A trial should be carried out to ascertain the required application rate. A second application may be required on some very porous surfaces.

LIFE EXPECTANCY

Long performance life (10 years+).Surfaces need to erode to reduce the effectiveness of Miteq Sealers.

RE-COATING

Readily recoated. It is important to remove all contaminants and clean the pavement surface thoroughly by power washing before re-coating. (See surface preparation).

SHELF LIFE

Miteq Penetrating Sealers can be stored in sealed containers for 6 months without loss of performance. The product must be protected against frost and should not be stored at temperatures below 0ºC. Storage for a longer period of time at temperatures above 35ºC should also be avoided.

Solvent based sealers (103/4) should not be allowed to come into contact with water during storage or use.

CLEAN UP

Wash equipment thoroughly with clean water or the recommended solvent.

MAINTENANCE

Given time the elements will normally remove surface stains. Periodic washing with a power washer is all that is usually required. Should a stain remain, contact Miteq for direct advice.

HEALTH AND SAFETY

Always follow good industrial health and safety practices. If Miteq Sealers are splashed on skin wash off thoroughly with water before it can dry. Wear eye protection during application.

Read technical data sheet and consult MSDS in conjunction with the information contained in this document.

Operators should always refer to the MSDS for safety precautions.

Further information is available from our web site www.miteq.com.au

PACKAGING

Non-returnable plastic containers & metal cans.

MITEQ Cleaners

Overview | Cleaners
Cleaner 304 is an especially designed liquid acid cleaner based on phosphoric and nitric acids. It finds use in a number of cleaning applications where strong mineral acids are required to solubilise metal salts on concrete surfaces.

Cleaner 304 does not contain hydrochloric or sulphuric acids, which may contribute to efflorescence.

APPLICATIONS

Cleaner 304 is especially suited to the removal of efflorescence from concrete, clay and terracotta surfaces. Cleaner 304 will also remove dirt and attack vegetable oil and fat spots on these surfaces.

It is important to note that the paved area to be treated must be dampened with water before applying Cleaner 304. Always check in an inconspicuous area to ensure that no discolouration or patchiness occurs following application. Uniform application of Cleaner 304 is essential. In all cases it is recommended that a small area of the surface to be treated is tested before full-scale treatment.

On concrete pavers, Cleaner 304 should be applied as a diluted solution from between one part of Cleaner 304 to 15 parts of water. Dilution rate will depend on the difficulty encountered in removing spoils etc. Concentrated Cleaner 304 is corrosive and will cause pitting of concrete; however it is gentler on the surface of a concrete paver unlike hydrochloric acid. Contact time should be limited to no more than 3 minutes.

Apply Cleaner 304 in a diluted format (see data) from a bucket and broom or brush into the surface for approximately 20 seconds concentrating on the areas most affected. Once applied leave Cleaner 304 on the surface of the paver for between 30-60 seconds.

The amount of time you leave the product on the surface will be based on the level of efflorescence experienced. Obviously a higher level of efflorescence will require a stronger concentrate of Cleaner 304 and a longer application rate and VICE VERSA.

After this period has elapsed the pavers must be rinsed with a high pressure hose, or garden hose at a very high volume. A high pressure hose is more effective in removing Cleaner 304 from the paver surface and neutralising the area and is recommended.

Continue to follow this process in cleaning the entire paving area working from the highest point and working towards the lower point in your paving area. Remember to work with a dilution ratio and application timeframe that works best for your paving project.

Clay and Terracotta surfaces are more resistant to the effects of acid and longer contact times and stronger solutions may be used. The surfaces should be rinsed and neutralised after application.

Please Note: It is highly recommended that you clean your pavers once laid with CLEANER 304 prior to the application of an appropriate sealer. Miteq can advise of various sealers that would be most suitable providing long lasting protection for your paving area.

SAFETY NOTE

Cleaner 304 is a highly corrosive liquid containing a blend of Nitric and Phosphoric Acids. Wear goggles and rubber gloves.

Read technical data sheet and consult MSDS in conjunction with the information contained in this document.

Operators should always refer to the MSDS for safety precautions.

PACKAGING

5 Litre and 20 Litre containers.

All information given in this product overview sheet and by the company’s technical staff is complied from the best information currently available to the company. The company accepts no responsibility whatsoever for its accuracy or for any results which may be obtained by customers. Any customer who relies upon any advice or information given in this product overview sheet by the company or its technical staff does so entirely at its own risk and the company will not be liable for any loss or damage thereby suffered notwithstanding any duty of care on the part of the company or its staff in compiling or giving the advice or information.