We have all seen how shoddy grouting and poor quality joint finishes can spoil the appearance of even the most attractive pavers. A good standard of workmanship is essential to achieve a well-tooled, even, grout finish. The final visual effect is the key to assessing the quality of grouting, the uniformity of the paver joints, and the properties and composition of the grout.

Pavers are becoming more varied and complex, and require careful treatment. Non-porous pavers have a tendency to reject cement-based grouts. Very porous pavers can create conditions where the cement dehydrates too quickly at the interface with the paver and becomes soft and powdery, losing its bond strength.

Also paver growth and/or shrinkage become more significant the larger the paver, as the ratio of paver to grout increases, there is less grout to take up the paver movement.

Some materials exhibit long-term moisture movement. Perhaps the best-known example is the natural phenomenon of concrete shrinkage. One practical application of this knowledge was the traditional requirement that concrete products be permitted to dry for one month for every 25 mm of thickness. The rate of shrinkage will depend on the type of concrete, the exposed surface to volume ratio, and the prevailing climate (temperature, relative humidity, air flow, etc) conditions. Check the curing shrinkage rates with the relevant paver manufacturer.

If a thin cement based paver is laid on a wet mortar-bedding layer, its underside will absorb water. If the paver remains wet on its underside yet the top surface dries quickly, the paver will tend to bow and curl. When the size is over 400 mm x 400 mm, the tendency of concrete flag pavers to curl can be quite significant. Curling will persist at the perimeter and corners of the pavers until all the absorbed moisture diffuses through the paver, about 14 days, at which time the paver will tend to flatten out.

Cement grouts, even with additives, may not be temporarily or permanently elastic enough to stretch and retract sufficiently to contend with curing shrinkage (horizontal) and curling (vertical) stresses; grout cracking may occur.

The potential for deflection of the concrete sub-base needs to be considered. Some degree of deflection occurs in all floor structures subject to loads. So it is critical to confirm that deflection does not exceed prescribed limits when laying a rigid pavement with relatively thin pavers, otherwise grout cracking and de-bonding of the pavers may occur. Driveways, balconies, etc. need special attention.

So what can we do to reduce the incidence of grout cracking?

We could use an expensive epoxy grout, which is many times stronger than a cement-based grout, but then the grout will be stronger than the paver, and should movement stresses occur the paver would probably crack instead of the grout. So we can rule that out.

The adoption of the correct laying method will often play a part in the final appearance of the grouted joints. Voids in the bedding layer beneath the pavers lead to the grout slumping in the joints. Back-butter the pavers with a latex admixture such as Weldcrete. This not only gives improved adhesion, but also provides excellent resistance to water and water vapour, helping to reduce the curling problem by reducing the moisture variance between top and bottom of the paver.

Proper construction and location of movement joints is essential to reduce the effect of thermal and moisture expansion and contraction stresses. Ensure the sides of the paver are free of mould release oil, laitance or other contaminants that will reduce adhesion of the grout. Variations in the depth of paver joint will effect the curing time of the grout. An even curing rate will reduce the incidence of grout cracking, so clear bedding mortar and other debris from the joints prior to commencement of grouting.

One of the least expensive, yet most critically important materials in a rigid pavement construction is the grout. It only accounts for a small percentage of the total installed price, so use the best. They cost more but you generally get what you pay for. How much more is too much more? Only you can answer that question. Just remember consumers are becoming more demanding and more aware of their rights, and the grout represents a fair portion of what they see once you have completed the work.

Sand has a major influence on the properties of the grout. The size and grading of the sand particles have a direct influence on the workability of the grout and the bond strength of the masonry. Some sands are predominantly one particle size and produce a very harsh grout. Brickies sand has a higher proportion of very fine particles (usually clay). This makes the grout more plastic and easier to use, but will reduce bond strength and possibly create long term durability problems because of swelling and shrinkage of the clay particles with cycles of wetting and drying. Sand should meet AS2758:1 if possible.

While too little cement will produce a poor quality grout, grout with too high a cement content may not take up induced stresses very well. To improve workability and bond strength of grout, add a quality flexible grout fortifier such as Laticrete 1776, or use ASAs grout additive in place of water. Or use a methyl-cellulose water thickener, such a Dynex, which slows down the dehydration of the cement at the interface between grout and paver, improving the bond strength. Use a pre-bagged grout mix to ensure the correct type and grading of sand and ratio of sand to cement, and a colouring agent if required, in conjunction with a flexible grout additive.

If mixing your own grout, use a 3 sand: 1 cement mixture plus a flexible grout additive. Use only washed sand - as close to AS 2758:1 as possible, and free of silts and clays. Do not use fatty (brickies) sand. Bucket batch rather than shovel batch to ensure accurate and consistent mixes. Keep liquid content of grout mix as low as possible so that grout is just workable enough to go into the joints. The higher the fines (cement, silts in unwashed sand, colouring powders) and water content of the grout the greater the tendency for the grout itself to shrink, crack and pull away from the sides of the paver.
 

Written using references from work by: Rod Lester, Mike Wheat, Tom Lynch, Richard Bowman, Peter Hartog, Richard P. Goldberg, and Australian Standards AS3958:1 and AS 2758:1

Generally speaking, the slower the cement dehydrates (dries out) the stronger it becomes. Cement, after reacting with water, takes about 28 days to attain 95% of its strength. Cement achieves 80% of its strength in one to three days, provided it has the necessary water to sustain hydration; this period of time is called the �initial curing time�. If the cement is starved of moisture before hydration is complete it will become soft and powdery and loose bond strength. Hot weather increases the possibility of cracking, as does low humidity and high winds � provide shade and wind breaks if necessary. The slower the grout cures, the stronger it will be and it is therefore less likely to crack; Also the slower coloured cement based grout cures, the darker it will be when it dries out completely.

Will all this stop grout problems? Maybe, maybe not. A lot depends on the quality of workmanship, proper joint preparation, grout quality, and the nature and degree of stresses encountered. But if you put into practice the items covered here, it will make a difference and you will know that you have done your best to give your client a quality finish.

Colour and concrete

AToday the palette of colours that can be achieved for building materials with oxide colouring pigment powders is almost unlimited. The powders are man-made, high purity, ultra-fine, solid, non-dissolving particles of inorganic mineral substances such as iron oxide, which often occur naturally in the earth and are called ochres. Colours include red, yellow and black iron oxides; titanium oxide � which provides white; chromium oxide � which gives green shades, and cobalt compounds - providing blues.

Many concrete product colours are enhanced to make them brighter by using off-white cement instead of grey cement. Off-white cement may be made whiter with white oxide. It is literally possible to produce concrete slabs, pavements, pre-cast units and concrete products in thousands of colours and shades.

Mineral oxides are UV resistant and colourfast. Because they are inorganic substances, they provide permanent and durable colouration for many types of materials and products. They are used in the building and construction industries to through-colour concrete, asphalt, brick and block masonry and mortar, grout, concrete and gypsum plaster-bound products and many other composite materials.

Getting the best result

Efficient and thorough mixing of all pigments provides for optimal dispersion (de-agglomeration) of their particles to achieve the strongest colouring shades from a given dose rate and uniformity of colour. So to get the best out of a pigment, make sure it�s thoroughly mixed into the mixture being coloured.

The particular colour shade of a given pigment in a manufacturer�s range of mineral oxides is unique and each varies slightly in its colouring strength � one to another, but for most uses pigment dose rates of 5% and 10% by weight of the cement or binder weight in a concrete mix are typically used. For most colours, the 10% dose rate is the approximate saturation dose rate level for cement bound materials.

The use of a higher dose can be wasteful. For a less intense colouring shade, you can use a lower weight percentage dose.

Mineral oxide pigments are regarded as being chemically inert, and therefore non-toxic and safe to use.

For maximum intensity of colour related to the dose rate used, ensure that the pigment powder is thoroughly mixed into the mixture of the concrete, mortar or grout components to ensure that the particles are properly dispersed.

Be careful not to use excess water in a cement-bound mix. With thorough mixing, the lower the quantity of water compared with that of the cement, the higher will be the colouring intensity, mechanical strengths and durability of the hardened material.

Colour pigment oxide will not fade away but the binders in concrete, asphalt or other composite material that bind the pigment particles may! Mineral oxide pigments are the most permanent and durable of all pigment types.

Ensure hard, durable, wear resistant materials that incorporate these pigments by adopting the recommended industry guides to achieve these properties. For instance, with concrete or mortar, keep the water content compared with the cement content as low as possible. Certain admixtures for concrete can help you to do this while maintaining as easily workable mix.

It also helps, to achieve durability of cement bound materials, to cure them for an adequate time. Curing in this sense is a procedure, adopted from several available, to prevent the evaporation of the water used to mix concrete or mortar while it is hardening after it sets. One way is to cover the concrete immediately after it sets with damp hessian cloth, bags, or wet towels, and keep them damp. Curing also assists in stopping the formation of unsightly white laitance or efflorescence.

Ability Building Chemicals Co, manufacturers of the �abilox� range of permanent colour pigment oxides with over 40 different colours in the range. Ability also produces various admixtures for concrete along with various surface coatings.

For further information call Peter Gray on 9457 6488 
 
 
 

  
 
Saving your paving, the right paving sealer

by John McNidder

Many people, including professionals, have unrealistic expectations of pavers whether natural stone or man made. All porous pavers will stain or be difficult to clean or maintain.

The main function of a sealer is to protect porous pavers and cement-based grout from damage caused by water, salt and oil-based stains, they do not halt normal wear and tear due to abrasion. There are many sealers on the market, yet none of them claim to be stain-proof; treatment with sealers slows down the action of staining materials, the better the quality of the sealer the greater its stain resistance. In many instances stains will weather off over time, however if some stains stick, such as car tyre rubber, which can be abraded by the surface texture and become lodged in the fine pores of the paver, they can be removed from a sealed surface using the appropriate solvent and correct cleaning technique, whereas they often cannot be removed from an unsealed surface.

Sealers in the main are either water-based or solvent-based. The base functions as a carrier taking the sealer components in to the paver; once it has done this the water evaporates while the solvent flashes off quickly. Solvent molecules are smaller than water molecules and will penetrate dense materials more readily. Water will penetrate dense surfaces such as granite, but will not generally penetrate as deeply as a solvent molecule. In hot weather the solvent carrier may dissipate so quickly that the sealer will not penetrate very far at all. However it is not how deep the sealer penetrates the paver but how close the sealer is to the surface where it guard against stain penetration. Neither type of sealer is superior to the other, although there are suitable differences relating to application techniques and curing times.

Sealers fall in to two types:

1. Penetrating sealers are designed to be absorbed �in� (below) the paver surface, coating the walls of the pores with a thin film of sealer thus allowing the paver to breathe and leaving the paver with a completely natural appearance. Small amounts of contaminants may stain the paver, but these can be removed using the correct solvent and cleaning method.

2. Surface sealers on the other hand are designed to bond �on� to the surface causing a barrier to form and normally give a low to high sheen, but which prevents the paver from breathing.

Immediately after sealing, water will bead on the paver surface. This is a result of the surface tension. The first time the sealed surface is cleaned the surface tension is released, resulting in the water no longer holding a strong bead. Released surface tension does not necessarily relate to a reduction in stain resistance.

Regardles of whether water-based or solvent-based, penetrating type or coating types sealers are considered, there are certain important attributes that a sealer must exhibit to ensure performance and longevity:

Stain resistance: This is the primary reason for sealing. Choose a sealer that offers protection against contaminants that are likely to be encountered. For example, fat around barbeque areas.

Breathability: This is an often overlooked, but very important quality that a sealer must possess. Natural stone and many man-made pavers must be allowed to breathe (i.e. allow moisture remaining in the paver to pass through as a vapour) but to repel liquids. If they do not, the pavers are likely to deteriorate more quickly and discolouration or spalling of the sealer is likely to occur.

Chemical resistance: With the myriad of cleaners and various chemicals used on and around pavements today, a sealer must be highly resistant to chemicals ranging from acids to alkaline cleaners, otherwise life expectancy will be reduced and sealers require frequent re-application.

Health & environmental considerations: Certain job sites, especially commercial sites may require water-based sealers, to avoid the increased safety precautions, such as strong odours normally associated with solvent-based sealers, also most solvent-based sealers contain �volatile organic compounds� that are defined as being ozone-depleting or detrimental to our environment.

Slip resistance: A sealer, whether it be penetrating or coating type, should not adversely affect the pavers slip resistance. Sealed surfaces should be properly maintained to reduce chances of slip-fall accidents.

U.V resistance: Sealers should be resistant to ultra-violet light and not yellow or deteriorate due to U.V exposure.

Thermal expansion: A paver installation will expand and contract depending in the weather. The sealer used therefore must also be capable of expanding and contracting, coping with both freeze thaw and high temperature conditions or it will be adversely affected and quickly lose its sealing capabilities.

Easy reapplication: Choose a sealer that does not require stripping when reapplication is necessary (usually due to surface wear on surface-type sealers and loss of stain resistance on a penetrating type sealer), as removing an existing sealer is often difficult and arduous and as a consequence, expensive.

Waterproofing: Ideally sealers must allow moisture vapour transmission and are not designed to hold on hydrostatic head. If water proofing is required a water proof membrane or agent should be used.

Sealers range in price from very inexpensive to very expensive with the price usually having a direct correlation to performance and longevity. Sealers properly selected and used can be extremely beneficial in the protection, on going maintenance and longevity of a paver installation. Haphazard choice and application on the other hand, can result in poor performance, increased maintenance and frequent re-application. 
 
 John McNidder of Claytek can be contacted on 0414 645 796.

Ref: Stone Sealers, Bill Tran of Aquamix Inc. Discovering Stone, Volume 3 Issue No 5

Specifying Sealers & Characteristics of Sealers,

Luke Dawson, Dry Treat (Australia) Pty Ltd

"Article first appeared in Earthstyle magazine, the official publication of the Landscape Industries Association of Victoria"