Based on the previous information we can now select the particular grout to be used and specify it either by name or by a generic performance based set of properties. Next comes the important stage of installation of the machine or item and the placement of the grout to give us the link between the two. The best grout in the world will not perform its task if the guidelines provided by the manufacturer are not followed. If any doubt exists on site regarding the product or process being used it is important to consult with all parties involved and then proceed with an agreed plan.
Preparation of the foundation
The concrete foundation or plinth on to which we are grouting our machine or similar item will generally have been cast weeks before the grouting is to take place. This allows the concrete to do most of its shrinkage and to stabilise as well as gain the strength required to support the machine. A minimum 28 days (4 weeks) should be allowed unless special concrete mixes are being used. The next step is to remove the laitance layer from the surface of the cured concrete. This is a weak layer which could affect the bond strength to the foundation – particularly important when dynamic loads are expected and epoxy grouts are being used.
There are several ways the laitance layer can be removed on site – some are acceptable; some are not. It is critical that the laitance layer is removed without damaging the concrete below. The end result should be a surface showing around 50% clean aggregate with no dust or loose material evident.
Chemical retarders / acid wash – these are definitely NOT acceptable methods of preparation. Whilst they may remove the laitance layer they may also still leave a relatively weak surface thereby compromising any ability for the grout to bond to the foundation.
Jackhammers – again using these is NOT an acceptable method of preparation. The aggressive impact of these tools will loosen aggregate and leave fine cracks in the concrete surface which could be detrimental to the grouting result.
Scabblers and Chipping guns – these are very effective methods of preparation. When used properly with the correct multi-point heads, these machines should produce a sufficiently low impact force which will easily remove the cement matrix without disrupting the aggregate in the concrete. Small hand units are available and larger units can be used for larger areas.
Captive Blast machines – these can be a very effective method of preparing large areas. Tiny steel “shot” are flung onto the concrete surface and the impact breaks away the weaker cement matrix leaving exposed aggregate. These machines are adjustable to meet most concrete strength and depth of removal required.
Typical captive blast machine
Machine / Baseplate Installation
More than 50% of grouting applications will involve grouting a baseplate or soleplate to a concrete foundation of some kind and for most of these the baseplate will first be positioned and levelled to the required height leaving a gap to be grouted. How the baseplate is levelled is one of those contentious issues of grouting. Following are several methods each with “pros and cons”
Threaded bolt with 2 nuts – this is a common way to level small baseplates in non-critical applications. The lower nut under the baseplate can be adjusted up or down to suit and the top nut is tightened to “sandwich” the baseplate into position.
Pro – easy to do; allows for infinite adjustment
Con – even after grouting, the weight of the machine is still resting mostly on the lower nut and the threaded bolt; post-tensioning is impossible (tightening the top nut just squashes the baseplate without tensioning it down)
Metal shim plates – a common process used to level large equipment. The machine is lifted and thin metal shims are placed under the baseplate on to the concrete foundation and the machine lowered on to the shims.
Pro – easy to do; allows for nearly infinite adjustment; greater weight distribution than “bolt and 2 nuts”.
Con – unless the shims are removed after grouting, they will (like the bolt and 2 nuts) bear most of the weight; post tensioning is not possible unless the shims are removed (often not done!).
Plastic shim plates – same process as metal shims, however due to their “plastic” nature, plastic shims need not be removed as they will deform over time allowing all the weight to be taken by the grout.
Elastomeric blocks – not a system often used. Dense rubber blocks are put under the baseplate close to the holding down bolts and the machine is lowered on to them. They compress and take the weight, then final adjustment is made by tightening down the holding down bolts to compress the rubber further.
Pro – infinite adjustment, providing the correct density and size rubber block is used; the blocks can stay in place after grouting allowing post-tensioning
Con – care must be taken to ensure the rubber blocks don’t cause deformation of the baseplate during tightening down against the rubber blocks
Levelling Screws (Bolts) – generally the best method. Threaded holes are made through the baseplate. Bolts are then threaded into these holes from the top and the tip of the bolt rests on metal pads positioned on the foundation. The bolts are turned up or down to achieve the correct level of the machine. The grout is then installed and when hard enough, the bolts can be backed out of the threaded holes leaving only the grout to support the weight of the machine. One of the steps necessary to make this process a success is to isolate the thread of the bolts from adhering to the grout (especially resin grouts) – this can be achieved putting petrolatum tape or wax paste around the bolt before the grout is placed.
Pro – infinite adjustment; the bolts are removed after grouting; post-tensioning is possible
Con – extra cost of tapping holes in the baseplate
Typical levelling screw arrangement
It is common practice for anchor bolt or holding down bolts to be grouted into preformed pockets as part of the grouting process. Epoxy resin based grouts or specialist anchoring products are best for this application, as they have greater bond strength and tensile strength than typical cement based grouts. It is important that the filling of the anchor pockets is done as a separate process prior to the general grout application to ensure the anchor pockets are filled without entrapping air.
If cement based grouts are being used for anchoring then the anchor pocket must be presoaked with water for at least 2 hours (preferably 24 hours) and the water vacuumed out just prior to the grout being placed. The anchor holes must also be undercut (tapered) or rough sided to provide mechanical resistance against pulling out. This is also the case when using polyester resin based anchoring systems which have limited bond strength and are prone to shrinkage.
Depending on the particular application and engineering requirements, there may be a requirement for the anchor bolts to be isolated from the grout and even from part length of the anchor material to allow for free stretch in the bolt when tensioned at the end of the installation. This can be achieved using foam pipe insulation or petrolatum wrapping tape or similar. Refer to the relevant design requirement on site.
The method of installation (placement) will determine the extent and type of formwork required. Small baseplates which are being grouted using a “dry pack” method will only require basic formwork to be erected on the 2 back edges to provide a “stop” to pack the grout in against and then work forward. Trowel applied grouts will be similar to dry pack and both of these types of applications will typically be done using a suitable cement based grout.
Flowable and fluid applications require much more complex formwork to achieve the desired result. The grout should be flowed in a single pass from one side of the baseplate to the other – ideally across the smaller dimension. The most common arrangement is a header box on one side into which the grout will be poured. Lateral formwork is then placed against the baseplate to direct the flow and maintain the head of pressure. At the side opposite the header box will be an exit form constructed approximately 50mm away from the baseplate which allows the progress of the grout to be monitored. For large pours it may be necessary to construct a moveable header box which can be moved along the length of the pour or have several header boxes and simultaneously pour the grout in. NEVER attempt to pour grout from more than one side unless the pour has been well planned with air relief holes positioned in the baseplate as this is likely to trap air under the baseplate.
Formwork materials – it is important that once the installed grout has set, any formwork can be easily removed without damaging the grout. This is particularly the case with cement based grouts which will often be “stripped” before the grout has achieved significant strength. Good quality new form-ply can generally be used for cement based grouts without the need for form release agents. However, if the grout is found to be sticking to the formwork, a thin application of a quality form release should limit this. You must be careful not to allow form release agent to contaminate the prepared concrete foundation.
For epoxy based grouts is it often necessary to use a wax release to ensure bonding to the formwork doesn’t occur. Wax floor polish (solid type) is a good release agent which can be rubbed onto the forms during erection. Do not use liquids as these could run and contaminate the concrete foundation.
When it does come time to remove the formwork, use a gentle tapping action to protect the fresh grout which may still be relatively weak.
The following drawings are examples of formwork set ups when installing flowable / fluid grouts. There may be variations of these required on site depending on the actual configuration and shape of the installation but the basic principle remains to flow the grout via a header box on one side, under the baseplate in one flow to the opposite side.
Typical grout formwork set up
Typical lateral formwork arrangement
Pre-soak the substrate
One step in the process of installing cement based grouts which is often overlooked is pre-soaking the concrete foundation before applying cement based grout. This simple step can have a dramatic effect on the outcome. This only applies to cement based grouts; do NOT pre-soak when using resin based grouts.
Once the formwork is in place and any sealant applied had cured sufficiently, the formwork should be filled with clean potable water for a minimum of 2 hours, preferably 24 hours, before the grout is applied. This has three benefits:
Minimises moisture loss – the water added to the cement based grout occupies a volume when the grout is placed. If this water is lost into a dry concrete foundation during the initial setting of the grout then there is likely to be more shrinkage in the grout than expected and shrinkage cracks or voids may occur. Even with dry pack and trowel applications the concrete foundation should be dampened thoroughly before the application of any cement based grout.
Increased low properties – pouring a flowable or fluid cement based grout on to a dry concrete foundation will result in greatly reduced flow of the grout. The dry concrete will suck the mix water from the grout and cause it to false set at the interface greatly reducing the chance of the grout making it through to the exit side.
Increased bond – pre-soaking with water is critical to achieving the maximum bond strength to the concrete foundation.
During construction of the formwork, incorporate sealable outlets for the presoaking water to be drained out.
Correct mixing of the grout is critical to the success of the total job. Sufficient man power and suitable equipment are essential.
Temperature considerations – All grouts should be stored (pre-conditioned) at suitable temperatures – typically above 10°C and below 30°C; ideal conditions are at 23°C. This not only protects the shelf life of the product but also improves the mixing and placement properties of the products. On site it can be difficult to meet these temperatures, especially in hot regions. Chilled water is often added to cement based grouts to help lower mixing temperatures. Products should be kept in shaded areas to lower mix temperatures. In cold regions it helps to store epoxy based products in heated rooms to improve mixing ability and flow properties. Care needs to be taken in hot regions. If the epoxy based grout is too warm then it will have a much shorter working time and may also develop an unacceptable peak exothermic temperature during curing, resulting in cracks in the cured grout.
Cement based grouts – the water to cement ratio in cement based grout is critical to the strength achieved and to the consistency required for the application. Water must be of drinkable quality (potable) and must be accurately measured in line with the manufacturer’s guidelines. Never exceed the manufacturer’s recommended maximum water addition. The water should always be poured into the mixing vessel first then the grout powder added while mixing progresses. Mixing time should be monitored with a stopwatch or clock to ensure sufficient time for the additives to begin working to produce the required final product – generally in the range of 3 to 5 minutes once all the powder has been added.
Epoxy resin based grouts – one critical aspect of mixing epoxy based materials is the mix ratio. Unlike cement based grouts where there is a range of water additions available to vary the consistency, epoxy based materials must only be mixed at the ratio supplied and as full kits – all of the base resin must be mixed with all of the hardener (as well as the filler component if using a 3 part mix). The other important aspect of mixing epoxies is to ensure a uniform mix is achieved throughout the mix volume. Poor mixing will leave a sticky resin at the surface and in the body of the grout, reducing the grout strength and other properties.
Monitoring mixing time will help to ensure a good mix.
Mixing equipment – Various types of mixing equipment are available for cement based grouts, from simple 20 litre buckets and hand held mixers to complex high volume mixing machines with built in pumps for large projects. The important thing is that the mixer can shear the grout powder and water to produce a thoroughly mixed product. Free-fall type “concrete mixers” are generally not suitable and should not be used. BEWARE: some “grout pumps” are only suitable for cement slurry grouts containing no aggregate – these machines will generally not be suitable for many of the types of grout being discussed in this document due to the aggregate in the grouts. Mixing by hand is also not acceptable except for cement based “dry-pack” consistency applications. Grout manufacturers will be able to either supply suitable equipment or direct users to the appropriate suppliers taking into account the product being used and the volumes being installed. Most equipment suitable for cement based grouts will also be suitable for mixing epoxy based grouts.
Typical grout mixing equipment
The most simple way to place cement based grout in small volumes is to mix the product to a trowellable consistency, push the product into place under a baseplate and finish the edges, generally at a 45° slope from the bottom of the baseplates out onto the foundation as shown in the image below.
The grout should not extend up past the bottom of the baseplate in case the steel baseplate expands with heat, in which case the grout at the sides may crack away. Finishing at a 45° angle will help shed water away from the baseplate as well as improve the appearance of the finished installation and reduce sharp edges which may be prone to damage.
The same situation could be done using a “dry-pack” cement based grout. In this case the grout is mixed at a very low water ratio; just enough water for the grout to hold shape. The product is then rammed into place under the baseplate simply using a piece of wood and a hammer to build the grout out from formwork on the opposite sides. Generally formwork is required on 2 sides to build the grout out from.
Once the size of the baseplate increases (say more than 450mm square) it becomes viable to form up the area and pour or pump a grout into place. The extra work in erecting the formwork is offset by the speed in application of the pourable grout as well as the practicality of this method over trowel or dry-packing large areas of grout. As mentioned earlier, when flowing a grout under a baseplate it should be done in one continuous pour action, from one side only, until the grout emerges from under the baseplate on the opposite side. This helps ensure any air or residual presoak water is expelled and there is complete contact of the grout and the entire underside of the baseplate. During this process it is acceptable to gently “rod” the grout or use flexible strapping to help the flow, however with cement based grouts this activity should be kept to a minimum as excessive vibration of the mix could result in water segregating from the grout which will then accumulate under the baseplate and severely affect the effective bearing area. Vibrators should NEVER be used.
Pumping grouts through injection ports in a baseplate is possible providing it is well planned to ensure air pockets are not created. Pumping grout under baseplates horizontally is also acceptable; the hose should be inserted to the farthest point under the baseplate and slowly withdrawn as the grout is pumped in. This can also be a useful procedure to complete a failed grout pour where the initial grout pour has failed to reach the opposite side for some reason.
Curing and protection
When installing grouts in open areas, especially in the warmer months, consideration should be given to erecting temporary shades / tenting over the baseplate site to limit direct sunlight which can significantly increase the temperature of the baseplate and foundation.
Cement based grouts – as with any cementitious product it is important to protect the freshly installed grout from excessive loss of moisture which could lead to shrinkage and loss of strength. Maintaining the moisture content is particularly important for the first 7 days while the cementitious grout cures. This is best achieved with the application of a good quality curing compound or by keeping the surface damp with wet hessian on exposed surfaces after the grout has achieved its initial set then on the remainder of the grout once the forms are stripped. The baseplate along with the grout should also be protected as much as possible from extremes in weather – both hot and cold. Large volume pours of cement based grouts can generate significant heat from hydration; insulation from sudden cold temperature should be considered.
Epoxy based grouts – as with cement based grouts, epoxy grout installations should be protected from weather extremes during the first few days after application particularly when large volumes are involved and there is likelihood of exothermic heat evolving from the epoxy reaction. In hot regions, consideration should be given to carrying out large epoxy pours after sunset to take advantage of the cooler part of the day. Exposure to sudden cold night temperatures for example could cause the grout to crack during its curing phase. Insulation blanketing may need to be considered.
Source: parchem – FOSROC constructive solutions