“There’s something not right about these pavers, can you come round and take a look?”
It’s the phone call every contractor, designer and supplier dreads; your client has given you their trust and investment to go ahead with the new pavement and it’s suddenly not performing the way it should.
Unfortunately, the symptoms that “something isn’t right” may not appear for several months – or even years – after the fact. Popping, cracking, drumminess, staining and discolouration are the most common complaints we hear about in relation to engineered paving stones. More than likely, the cause of each of these issues actually began at or before the time of installation.
Poorly installed paving reflects badly on everyone involved in the project and can be extremely costly to rectify, let alone the damage it can cause to reputations and valuable working relationships.
In this article, we’ll highlight some of the most common mistakes we frequently observe in relation to engineered paving stone that every contractor should avoid during installation.
Whether you are a contractor, designer or client, we highly recommend you read this article carefully before installing our products.
Think long term.
The first step in avoiding paving installation mistakes is to think long term. All paving looks fantastic during the first few weeks or even months. Properly installed and maintained paving continues to perform brilliantly and look fantastic for decades.
Over time, your project will be inundated with acidic rain and alkaline tap water, scorched and dried by the sun, encroached by tree roots and affected by subsurface pressures of the earth. These events occur naturally over vast areas far beyond the boundaries of your project site.
Within the site itself, every paver at some time or another is likely to be exposed to soil, compost and leaf litter, fertilisers, cleaning chemicals, food, grease, animal excrement and everything in between.
To maximise the value of the investment in a new engineered stone pavement, you must consider how it will respond to these conditions over the long term, educate those involved in your project, and take action accordingly.
PAVING INSTALLATION MISTAKE #1: FAILING TO PLAN FOR MOVEMENT
The earth’s surface is in a constant state of flux, continually expanding and contracting with the seasons and in response to changes in temperature, humidity and moisture. Tree roots, ever in search of water, can create enormous pressure on anything standing in their way.
Paving (concrete or natural or composite), while offering excellent rigidity and strength as a floor covering, is in itself also subject to expansion, contraction and warping due to changes in moisture, temperature and ground movement.
Every pavement therefore needs to be carefully planned to accommodate movement, especially in the case of large format pavers.
This means that the location of construction joints, contraction joints and expansion joints needs to be determined before construction begins.
Make a Plan. Check the Plan. Construct the Plan.
These three steps to avoid failure are so simple they are frequently overlooked.
Make a plan. It doesn’t take long to create a simple plan drawing of the site showing the extents of the proposed pavement and structural profile of its foundation. The plan should then be marked with the proposed alignment of all three joint types at the appropriate intervals.
Check the Plan. Show the plan to an experienced construction professional familiar with best practices in pavement construction for a second opinion before proceeding with the works.
Construct the Plan. Once the pavement has been set out and construction is underway, execute the joint placement as planned and checked. If this sounds obvious, it will come as no surprise for you to learn there have been many who, for reasons aplenty (it was already 4.30pm, we ran out of flex, had to feed my dog etc), changed course mid-way through installation, and later paid the price.
Architects and designers: we are aware that some of you would prefer not to break the beautiful flow of a paving pattern with expansion joints. Be aware, however, that you do run a high risk of cracked pavers if you choose not to include flexible joints in an expanse of pavement.
There are flexible materials available that can be selected to match in with the grout colour as much as possible. Furthermore, there is always the option of caulking every joint (which is advisable when specifying pavers of 1000x500mm or above) to help avoid both drumminess and grout cracking (although flexible joints alone won’t stop a paver from cracking: appropriately located expansion joints must also be considered on the project to prevent this).
Not adhering to these simple steps is both unprofessional and a risky oversight that can unexpectedly cripple a business through rectification costs, long after the pavement was installed. If in doubt, consult a structural engineer; the cost of their service is minimal in comparison the potential cost of rectification works.
Run joints both ways.
A common error we’ve observed is the failure to place joints both transversely and longitudinally. Joints must be placed in both directions at the correct minimum intervals. To minimise cuts and improve aesthetics, the unit size of the pavers and the proposed paving pattern can be used to adjust the exact joint placement whilst still meeting minimum structural requirements.
There is a significant amount of information available on the placement of joints in pavements from the Australian Building Commission, local government building departments, concrete suppliers. If in doubt, consult a certified structural engineer.
PAVING INSTALLATION MISTAKE #2: AVOIDANCE OR INCORRECT USE OF MORTAR ADDITIVES
This installation tip is most relevant for large format paving sizes: 600x600mm and above. As landscape design trends have adapted to include very large format pavers (far larger, longer and heavier than the standard 300x300mm paving units of the past decades), installation methods must also adapt to cope.
Mortar additives have been developed and introduced to the market for important reasons; they dramatically improve elasticity, workability and above all adhesion. Contractors can deliver a higher quality finish and avoid the risk of pavers coming unstuck from their foundation (de-bonding) when the correct adhesives are used within the installation process.
Mortar additives are particularly effective in giving both engineered and natural pavers the best possible chance of being installed neatly and adhering to a concrete foundation over the long term. Using a standard mortar mix consisting only of sand and cement is not sufficient for engineered stone applications.
Large format is not the same
The recent surge in popularity of large format pavers (600x600mm and above) has left many contractors (who were not aware these larger sizes require a completely new method of installation) in a compromising position.
Large format pavers are different to small format pavers; they’re heavier, hold (and lose) more moisture, span greater distances, and behave differently once in position. They’re more likely to ‘pop’ off their mortar base, become drummy and can be difficult to handle and install precisely. Large format pavers are typically more expensive to install and to replace.
Therefore, large format pavers cannot be installed using the same method as small format pavers. Using adhesive additives is one of the crucial components of installing large format pavers.
PAVING INSTALLATION MISTAKE #3: STORING PAVERS ON SITE (OR DOING SO INCORRECTLY)
Although incredibly durable, engineered paving stone (like natural stone) is susceptible to irreversible staining when stored incorrectly prior to installation. If handled correctly, once installed, cleaned and sealed, engineered paving stone will age evenly and withstand the elements for decades.
The reason storage is so important is because engineered stone is selected for consistency in its appearance and not variation, as with natural stone. If not stored under stable conditions or exposed directly to the weather for prolonged periods, a freshly manufactured batch of pavers can quickly present discolouring and other undesirable markings.
To avoid disappointment, we strongly recommend you arrange delivery of engineered stone to your project site for a time just prior to installation, even if your order is ready ahead of time.
Anston are more than happy to store pavers safely in our warehouse until that time arrives.
If you have to store them on site:
Of course, there are circumstances where the opportunity to get the pavers into the project is limited to a small window of time, and on occasion much earlier than the intended time for installation.
If you must store engineered stone pavers on site, we urge you to abide by these three simple guidelines:
- Leave the shrink wrap intact. Do not open, cut, slice, damage or remove the protective plastic shrink wrap that was applied when the pavers left the factory. The ingress of moisture and dirt can cause the pavers to sweat and discolour.
- Keep the pavers dry. Ideally, the pavers should be stored undercover, in a protected space, such as a shed. If such a protected environment is not available, an alternative roof structure such as a carport should be used. If a carport is also not an option, a waterproof tarpaulin should be fitted securely and in such a way as to allow water to shed and prevent pooling.
- Do not stack. When the time is approaching to lay the pavers, do not unwrap and stack pavers in various locations across the project site. Remove and install small batches at a time, as appropriate to the area being paved. This will help greatly in avoiding stained edges.
PAVING INSTALLATION MISTAKE #4: INCORRECT MORTAR RATIOS AND MIXING METHOD
Under time pressure, the haste to get through a project as fast as possible can cause some elements of paving installation to be carried out with less care than is advisable. Don’t let incorrect mortar ratios or poorly mixed mortar be one of those careless mistakes; it’s an expensive and time consuming error to rectify.
Any experienced landscaper will tell you that when it comes down to it, mixing mortar is somewhere between art and science. In established paving crews, the task of mixing mortar is rarely given to the least experienced member without close supervision. Not only do the correct ratios need to be adhered to for each mix, but extreme temperatures can affect working times, calling for adjustments in water to achieve the right working consistency.
The following are common mortar mixing mistakes to be avoided:
- Incorrect sequence: adding water to the mix of sand and cement. Always add sand and cement to water. More water / additive can be introduced carefully once the mix is first blended to adjust the working consistency.
- Insufficiently cleaning the mixing vessel between mixes. This ensures consistent ratios for each batch rather than simply “topping-up” the previous batch. This can also result in poorly blended mortar because of the build-up hardening inside reducing the churn effect of the mixing fins.
- Incorrectly measured additive/plasticiser. Too much and the mix goes off too early, too little and adhesion suffers. Measuring rather than guessing also aids costing, because you’ll use the amounts you’ve calculated, rather than reaching the end of the tub with several mixes still to go and vice versa.
- Insufficient mixing time. The mortar must be evenly blended throughout, free from lumps or clumps of both sand and cement.
- Using grey cement. We always advise choosing white over grey cement, which can slump and cause issues with adhesion.
The general guide to mortar ratios approved by Anston is as follows:
Bonding slurry
6 parts washed sand : 1 part GP white cement
Water
Mortar bed
3 parts washed sand : 1 part GP white cement
1 part water and/or additive
Jointing/Grout
Equally as important as mortar though often overlooked. Select a premium grade dry packet formula with a fine texture that flows freely and shrinks to achieve a high compressive strength. Follow the manufacturer’s specifications for mixing.
We also recommend giving consideration to the colour of the grout being used. You can read more about selecting the right grout colour in our journal.
PAVING INSTALLATION #5: NOT ACID WASHING
Nothing says “slack” more than a mortar stained pavement. A dusty white/grey coating and pockmarks of dried cement are the last things anyone involved in the project wants to see for the big reveal.
And yet, this act of tardiness rears its head from time to time, which really is a shame – particularly on commercial projects where time and budget limits can cause the cleaning process to be neglected entirely.
A cement and grout film on your pavers is not the same as efflorescence, which is a natural chemical process that can be avoided by proper base preparation, adequate drainage and sealing. In this instance, we’re referring to a pavement that hasn’t been properly cleaned after installation.
One of the fantastic attributes of engineered paving stone is that it responds very well to acid washing and can be effectively cleaned back to its original condition time and time again.
Acid washing involves the use of a light acid formula to dissolve deposits of mortar and other stains that have occurred during construction so they can be easily washed away.
Incidentally, acid washing pavers soon after installation can also assist to dissolve and remove any calcium carbonate (efflorescence) present at the time as well.
Paving Installation Mistakes – The long and the short of it
There are multiple factors at play in any landscape project, all competing for attention. A new pavement typically represents one of the heftier investments by the client in any project and a disappointing outcome affects everyone involved.
The errors detailed in this article are the most common ones we encounter at Anston, and so to save everyone’s time, money and reputation, we choose to invest a lot of time in educating our customers. As you’ve probably realised, these errors are also not that difficult to avoid. By being aware of the potential consequences and understanding the reasons each pose a threat to your project, you can be more assured of a long-lasting outcome for your project and/or your client.
If you have any concerns, or would like more information, there are additional helpful articles on our website. Of course, any member of our team will be happy to give you the right advice too, all you have to do is ask!