10 Important Issues You MUST Be Aware of When Buying Pattern Imprinted Concrete and The Key Questions To Ask
When investing in your property, you should be confident you are getting the highest possible quality. In this report we highlight the 10 most common pitfalls, and arm you with the knowledge you need to ask the right questions before buying.
There are a number of key considerations when choosing a contractor to install pattern imprinted concrete paving. Below is a list of points that are essential for a good quality project, including aesthetics, long term durability and periodic maintenance.
It should be stressed that this is not a technical bulletin; the aim of the report is to be informative, easy to understand and not misleading in any way. To make these points technically would take many pages of difficult to understand, and possibly overcomplicated industry jargon.
Minimising the chance of cracking:
Issue #1: Inadequate concrete thickness.
The short version here is that the thicker the concrete, the less likely it is to crack.
Ensure that a MINIMUM of 100mm (4˝) of concrete is used in your installation for normal domestic driveways. Decorative Concrete Specialists will often use 150mm on heavily trafficked areas.
KEY QUESTION: Ask your contracting company how much concrete they will be using. They should be using a minimum of one cubic metre of concrete for every ten square metres of paving.
Issue #2: Incorrect Movement Joint spacings and locations.
Firstly, it is worth noting that the vast majority of the time, movement joints installed in concrete are called ‘contraction joints’ (crack control or crack inducing joints). They are NOT ‘expansion joints’, as they are often referred to by people not familiar with the construction industry.
Best practice guidelines when installing Control Joints:
- having a maximum individual slab size of 20m².
- Follow the maximum length to width rule of 2:1 – (e.g. a long thin area of concrete, like a path, will require more frequent joints than a rectangular driveway.)
- To incorporate joints into corners or high stress areas wherever possible.
KEY QUESTION: Ask your contracting company for a drawing detailing where they propose to install the movement joints.
Issue #3: Contraction joints are cut too late.
It is normal practice to use a diamond blade to insert joints into the concrete. These are cut between ⅓ and ½ of the thickness but NEVER through the full slab. It is good practice to cut within 24 hours of the concrete being laid. The sooner these joints are installed, the less the likelihood of the concrete cracking. This becomes more important in warmer weather.
In colder conditions, it may not be possible to cut the joints in within 24 hours; it may damage the surface of the concrete. However, the colder the weather, the less likely the concrete will crack prior to the joints being cut in.
In very hot summer conditions and in high stress areas, joints are sometimes cut in prior to, or during the printing process. This is not the normal method of installing contraction joints but can be sometimes imperative to a good installation. When joints are cut into the concrete before it has hardened, the joint need not be so deep and are cut in between ¼ and ⅓ of the slab depth.
KEY QUESTION: Ask your contracting company when they plan cutting the joints, or if they may cut some of the joints into the concrete while it is still soft.
Achieving a good quality print
Issue #4: Too large an area for the temperature and available man-power
The higher the temperature, the faster the concrete will set. Therefore, in warmer weather it is good practice to undertake smaller concrete pours than would be undertaken in cooler conditions. Too much concrete for too little manpower will result in poor quality.
Issue #5: Not enough imprinting mats in the set to provide two complete rows.
The number of imprinting mats available makes a big difference to the end product. Logically, the concrete can be printed more quickly with more mats. The quicker you get through the print, the less chance there is of the concrete curing too much, resulting in a shallow print.
The industry standard is 6 rigid imprinting mats in a set plus one super flexible imprinting mat for getting into the awkward areas. Often 6 imprinting mats is not the optimum number. At the very least, enough mats are required to span the width of the job. The ideal scenario is to have two complete rows of imprinting mats.
KEY QUESTION: Ask your contracting company how many imprinting mats they will be using on your job.
Achieving Long term durability
Issue #6: Insufficient Colour Surface Hardener (CSH) used.
Colour Surface Hardener (CSH) is used by almost every company in the industry. CSH is integral to the process. In fact, it can be argued that CSH is actually more important than the type and strength of the concrete.
The reason for this is two fold:
1/ CSH will make any concrete surface more durable in terms of abrasion and freeze/thaw resistance. The increase in surface durability is significant because the strength of the surface is almost twice the strength of the main concrete slab. Using a generous quantity of CSH will produce a better quality surface.
The industry standard is one 25kg bag per 10m² (or 2.5kgs per m²). Better surfaces are always achieved using more CSH. Quality contractors will be looking at using one bag per 10m² as the bare minimum and not the norm. Often, the concrete will use 1.5 bags per 10m² and therefore contractors should allow one bag for every 6.5m².
For example, a quality installation company will have 9 bags of CSH on site for a 60m² job and not only the bare minimum of 6 bags.
KEY QUESTION: Ask your contracting company how many bags of CSH they will have on site to use on your job.
Achieving Colour Consistency Across the Whole Surface Area
Insufficient Colour Surface Hardener (CSH) used. (Again!)
Using insufficient CSH also contributes to a patchy or untrue colour. It is often possible to use the bare minimum of CSH on a job requiring only one delivery of concrete . This means the colour achieved is not a true representation of the colour chosen, making it very difficult, without a comparison for the customer to realise.
On a job requiring more than one delivery of concrete, it is highly likely that the second load may end up being a significantly different shade to the first, should insufficient CSH be used. For many reasons, the concrete companies are unable to produce two or more identical mixes. However, using the correct ratios of CSH will negate this problem entirely.
KEY QUESTION: Ask your contracting company how many bags of CSH they will have on site to use on your job.
Issue #7: Integral colour is used instead of CSH.
Certain Pattern Imprinted Concrete paving companies will promote the use of an integrally coloured concrete (coloured throughout the whole concrete slab) for two reasons:
1/ At point of sale it sounds better to the layperson that the whole of the concrete slab is coloured rather than ‘just the surface’ using CSH.
2/ It makes the job easier to do. The concrete is delivered to site coloured so the surface does not need to have CSH applied, reducing labour significantly.
The downside of using an integrally coloured concrete is that:
1/ The surface will not be as durable as one which has been colour hardened.
2/ Colour inconsistencies are much more likely if CSH is not used.
Interestingly, organisations such as Disney use integral colour for nearly all their concrete paving requirements, however will specify that CSH must be used for all the pattern imprinted, stamped or textured concrete surfaces.
KEY QUESTION: Ensure your contracting company are going to be using CSH.
Issue #8: Excessive Secondary Colour left on the surface of the paving.
A powder, often called Antique Release Agent, is applied to the surface of the soft, coloured concrete, prior to imprinting the pattern. This powder serves two purposes:
- It prevents the imprinting mats sticking to the surface of the soft concrete.
- It provides a secondary colour to the paving once excess is removed.
When the surface is washed off, most of the powder is removed. This exposes the true chosen colour but with ‘antiqued’ and highlighted textures giving a more authentic and natural look.
It is essential that the area is washed thoroughly before sealing the surface. If not enough release agent is removed, then it t will act as a contaminant between the sealer and the paving causing the seal (in extreme circumstances) to peel away.
If this does happen it is a time consuming and expensive process to remedy, therefore to ensure sufficient release agent is removed it is highly recommended to use a Release Agent Wash and a light acid solution to complete the process.
KEY QUESTION: Check with your contracting company that they will be using a release agent wash and an acid wash, to ensure adequate removal of the release agent from the wearing surface of the paving.
Issue #9: Water based sealant is used.
Some companies will use a water based sealant as opposed to a solvent based acrylic sealant; this is generally due to the mistaken belief that, it can be applied to a damp surface.
Contrary to what may seem logical, a water-based sealer is just as likely to fail as a solvent based sealant when applied to a damp surface. If failure does occur, rectifying a problem with a solvent based sealant is easy. Problems experienced when using a water based alternatives are far more difficult to resolve. I the area is clean, solvent based sealants can, be painted over the existing surface. Water based sealants may need to be removed and rubbed down completely before re-applying.
Any application of sealant may require some simple remedial work to correct minor imperfections. Conditions need to be perfect when sealing and unfortunately, weather is beyond our control! Any remedial work is a straightforward and successful process when using solvent based sealants.
Generally an area of pattern imprinted concrete will benefit from a reseal every 3-5 years. This is a simple process if a solvent based sealer has been used.
Often D.I.Y stores or builder’s merchants promote aqueous sealants. Sealing pattern imprinted concrete with a water-based sealer, will create problems that are not at all easy to resolve. If you need advice, call us.
KEY QUESTION: Check with your contracting company that they will be using a solvent based sealer.
Issue #10: Joints not filled with a silicone joint filler.
Pattern imprinted concrete requires very minimal maintenance and is truly a weed free product. Weeds will not grow through concrete. If the control joints are left unfilled, dirt may build up and weeds may grow.
To minimise the chance of weed growth in the movement joints, we apply bead of silicone filler into the joint. This is not designed to make the joint water proof; it is to reduce dirt build up in the joints. No dirt means no, weed growth, and IF a weed does grow in a movement joint it is easy to remove. as the roots are not in soil.
KEY QUESTION: Check with your contracting company that they will be applying silicone joint filler to all movement joints that are cut with a diamond blade.
We hope you’ve found this report useful. It is not intended to cover every single aspect of pattern imprinted concrete but as long as these disciplines are adhered to your installation will be successful and give you many years of pleasure, whoever you choose to do the job.
If you have any questions or wish to raise any other points not covered, please call us on 01793 322098 and we’ll be happy to talk to you in more detail.
Download our PDF – Click Here