Introduction To Exposed Aggregate Concrete
An exposed aggregate concrete surface is an decorative form of concrete appropriate for applications not only as aggregate driveways, but as sidewalks and patios as well. The attraction is in the completion which reveals the smooth textured little pebbles and small stones which are a component of the concrete. Quite different to the dull and plain concrete finish, in which the visible surface is mostly made up of what they call ‘fines’ on the exposed concrete surface. Exposed aggregate concrete creates a lot of visual interest by making Many Different Aggregate Patterns & Colours. Only a small amount of the exposed top layer is the usual plain gray colour of those ‘fines’ in the concrete.
Originally, an exposed aggregate concrete formation such as an aggregate driveway is not usually performed by oneself without a professional. Some believe that this may be because there is not enough information focused on people who like to do everything for themselves. Also, there aren’t that many DIY people to require the information needed. Despite this, if you search the web, libraries, home improvement shops and all the other resources one can discover, we can come up with a set of procedures for doing exposed aggregate concrete by ourselves or with the help of contractors.
If you’re project is large patio for example, let’s say about a thousand square feet, with an adjoining foot path, maybe eighteen feet in length. Most people may have done some good concrete labor, perhaps starting off with bedding for some fence posts in concrete, little sections of sidewalks, and even starting with a little water collection box is good practice as well as part of any water drainage system for a private home. Most people are not always convinced that exposed aggregate is a good choice even for DIY people. So some people do a test by applying it on small areas of your property. From here one can try 4 individual sections of concrete, every single one done uniquely to see the differences.
One can try out 2 of the four sections to be finished in an exposed aggregate concrete form, though utilizing different techniques to finish them. Upon checking the 4 different areas, one can choose to do your patio project with this technique of an exposed aggregate concrete finish to be written about in this article. All the experience you can get from doing some tests can be very valuable, being the reason why it’s a good idea for people who have little concrete experience to try something similar. One can also need to remove the test beds and discard it or cover it. The experience gained will help you decide later on.
As we utilize the phrase, exposed aggregate concrete, this means that the surface finish typifies the general composition of the concrete. Actually, this is the real case at some time during the evolution of the method. Although nowadays, the aggregate which is exposed on the revealed surface is properly seeded there for it’s good appearance usage. Placing the aggregates in the right way on the top layer of the still wet, soft concrete will be the main concentration for this literary piece.
Likewise, this piece is not about blending concrete, setting the right forms, or similar elements not directly connected to the exposed aggregate method. Such details are already seen from many other sources of information. Certain elements of what is discussed here is a mix of info from literature and a very few bits of info which is readily available on the internet. In most ways, one can gain more from personal experience with trial and error. Other techniques do exist, most professionals will espouse one over the other depending on how well or how ineffectively they can help, or if other methods are easier or actually harder. Some techniques are better for some projects than others, and here we will discuss one of those which can work for you and your home.
The First Phase: Planning
Exposed aggregate concrete prices vary subject to so many variables. Never assume that you can finish in a certain amount of time and effort to perform the job of completing an exposed aggregate concrete project. Most people require a double the amount of time to fully complete the basic finish, this does not even come with the acid washing or the clear-coating needed. Try to avoid doing too much in a short time, or not get enough people to work the project.
Most people need at least 2 helpers for a total of 3 working people, and each one needs to work pretty hard all day, its possible to approximately 125 square feet during the summer and that would be the maximum. Variables such as these will caused exposed aggregate concrete prices to fluctuate greatly. If its a cooler or cloudier time, the crew can do about 175 square feet. During extremely hot days, any concrete will dry almost as quickly as it is mixed and poured on the concrete, it can be very tiring to do 80 to 100 square feet per working day. Not having at least 3 people working will significantly lessen the quantity of surface which can be mixed and completed per 8 hour work shift.
Always ensure that all equipment and materials are at the job site before you start. Certify that all forms are fully set, and that you will not be plagued by constant interruptions like last-minute details such as cutting and installing re-bar or re-mesh on the concrete. Make the ramps and planking ready for moving men and materials already set up. Remove all unneeded obstacles and hazards from the job site even before you start.
Should you be getting water from a deep well, calculate if it will be enough to provide for the huge amounts of water the project needs for mixing and washing the finished top layer and please think about the advantage of having more and not less water. You will also require more water for cleaning tools, and after working so hard all day, to wash your body as well.
When your exposed aggregate concrete driveway means you need to pour part by part, think about which part need to be poured first, and make sure to protect the completed top layers from spills and other workplace incidents. Think about where the wash-water will be draining to never ever wash over an already finished top layer.
Tools You Will Need From Your Sydney Concrete Contractor
1. The right mixing tools, if you’re not ordering ‘ready-mix’ concrete from a supplier.
2. Durable shovels, rakes, hoes used for placing wet concrete into the forms you placed.
3. A standard wheelbarrow, make it 2.
4. Wood floats to even out the poured concrete.
5. Good sized steel trowels for working the poured concrete.
6. Lumber that’s at least 2 x 4 inches, long enough to reach across the forms, but less than 8-12 inches, this will be the screed.
7. Plastic brushes with medium long handles. These are the relatively soft bristled brush with a handle that keeps fingers out of the concrete effectively. Those used for removing snow from cars will be great. They’re like giant tooth brushes, you can find them in stores easily. Try to buy at least 3-4 so everyone has one to use.
8. Require a lawn roller. Most contractors make ones out of concrete using a 24 inch long section of 10 inch diameter tubing used for forms for the footings, plus some sections of steel to create an axle and handle for easy working.
9. At least 3-4 plastic pails, the 2-gallon sized ones.
10. Standard protective clothing, appropriate for dealing with wet concrete like gloves and rubber boots and coveralls if the weather is cold.
11. One piece of plywood approximately 2 feet square, when you need to kneel or stand on still moist concrete.
12. Wood blocks which are 2-by-4, 12 inch – 24 inch long
13. One 2 lb. Mason’s hammer for breaking up needed material.
1. Of course, you need concrete, you can have it mixed on site with a portable mixer, or coming from a ‘ready-mix’ supplier of your contractor.
2. Bullet or Pea-gravel which is 3/8″ in size and drain rock, approximately 1 gallon for every 3-5 square feet of surface that you need to cover.
3. Continuous supply of water coming with a garden hose and a durable spray nozzle.
4. Good quality cement and sand, sufficient for approximately 1 gallon of mortar during the finishing.
5. Enough workers. When mixing concrete in batches, it’s always best to have 3 persons at the least. Having 4 is better. Your day will go very fast though you can get fatigued every single day. Start as early as possible, particularly when you want to do an area exceeding 100 square feet per day.
Second Phase: Preparing The Aggregates
Choosing the right gravel and aggregates can have a big influence on the completed look of your exposed aggregate driveway. Make sure to consider selecting the aggregates which is best suited to the house and surroundings. Choosing can be based on any mix of shape, exposed aggregate colours, texture or smoothness, fractured, shiny, plain and also the size of the aggregates. Many landscape supply stores should have a range of aggregate selections, while others are able to get material which can meet your needs and desires.
When the project requires attempting to match an already installed exposed aggregate area, the following suggestion is very crucial. Completely wash the aggregates, approximately 6-8 gallons at a time in a wheelbarrow, wash them until your water is all clear as blended with the gravel. Store the cleaned gravel close to you, and then fill your plastic pails with these cleaned aggregates. You need to do this 24 hours prior to application.
Third Phase: Pouring the base
Start pouring concrete into your ready forms and begin tamping, spreading and everything needed for an ordinary poured surface. As the concrete is being blended there per batch, allow about 1 inch from your forms unfilled for now. As your forms are entirely filled to before 1 inch from the top, complete filling the forms to approximately ¼ of an inch from the very top layer. Get that 2-by-4 screed to even out the top surface, and also make it smooth with your wooden floats and the steel trowels in each hand.
A flat and even top layer that is thick with soft concrete is what you need here. Spread the concrete just sufficiently to create a good layer of soft cement, and do not overwork it at all. This requires good use judgment to make sure it is all flat as it should be since your screed will not be able to pass by the top edge of the forms which is usually performed when not doing an exposed aggregate project.
We know by now that leaving the top surface below the top of the forms is needed for enough space in the final layer of gravel aggregates. The upper layer should be applied in as few batches as can be done, so you get proper degree of moisture and amounts on the whole top surface. That helps a lot in the following phases. Enabling the concrete to cure until all the water is gone from the top layer.
This requires the surface to be adequately firm to support some weight, such as a pail of rocks on your 2-by-2 foot piece of plywood cover, though also adequately soft to press your aggregates into the cement but not make it hard. Since the water comes up, pay attention to any low portions which tend to collect water, use the trowels to make it as uniformly level as you can.
Fourth Phase – Seeding the aggregate top layer
As your concrete begins to cure, the time to seed the aggregate into the top surface has come. Get one plastic pail filled with the clean pea gravel, then make a soft sweeping motion and spread a layer of pea gravel onto the wet concrete. This gravel must not sink from it’s weight alone, it should stay on the surface for now. Get the brush to spread out the gravel on level, make sure the concrete underneath is nearly completely hidden.
If you wish to cover a big surface, it may require you affix some kind of scaffolding for working on portions which are away from the edges. Make it a point to get a highly even spread of the gravel, and never leave any areas which have an excess of concrete exposed. All portions with exposed concrete bigger than the average dollar coin can be a gap. And avoid creating areas with excess gravel, since there will not be sufficient concrete to keep the aggregates attached to the substrate, and can lead to a hollow area that has unexposed aggregates.
From this point, you may notice some areas that may not have sufficient concrete cream at the top layer surface to set your aggregates into. Start mixing a batch of sand and cement, at a ratio of 3 is to 1 or 4 is to 1, somewhat wet, and gently spread it over the exposed aggregates as required to surround any loose gravel thoroughly.
Fifth Phase: Pressing the stones into the Exposed Concrete
Phase 5 should start as soon as an area is uniformly covered with the aggregates. Begin with the pressing the gravel into the surface with a wood float, or just a block of lumber, like a 12-18 inch section of 2 X 4 planking. Apply a pressing or gentle tapping motion to the process. During this phase you may start to see areas that require a some more aggregates, so place more pebbles in place as needed, and begin compressing into the concrete.
At this stage, your concrete must be getting relatively firm, so that you can lean on it with your hand without leaving any marks. It should possibly be necessary to apply some small patches of the mortar in a few places as you begin placing and pressing your aggregates. Ensure that there are no heaps of mortar that are above the general top layer. Make use of the brushes to slowly distribute the mortar over a wide surface. Use brushes of the correct firmness which will be used in a tapping action, where the ends of the bristles tap the aggregates into the cement. It is one of the most effective ways of bringing up a bit of water and concrete cream, along with working any applied mortar over any loose aggregates.
As the workers have compressed the aggregates into a big area and you are satisfied that there are no empty spaces or heaps of unneeded stones, start rolling the gravel into the concrete with your lawn roller apparatus. Should the temperature be high, work must be done fast at this point. Start rolling the gravel until it is entirely compressed into your beds, as the roller starts to draw up a small layer of concrete fines all over aggregates. Never worry that the stones are disappearing into the mixture. They must be pressed in so that the layer on top appears evenly covered with the fines of the concrete.
From that point we should be able to walk softly on the top layer to work the roller. Never twist your feet while doing this, and avoid digging in your heels or toes, this can create foot marks on the surface. When we start to roll the surface, do not steer the roller during the time it is on the concrete, since any twists can make the stones go up and out and leave holes or empty spaces.
When the concrete is excessively soft at this point it may be possible to see some ridges being created at the edge of the lawn roller. When and if it occurs, cease rolling and wait for a few minutes, unless the concrete has firmed up enough to completely stabilize the lawn roller. When the gravel becomes hard to roll on the surface, you can spray the concrete with some water to loosen it up just a bit to make it soft.
Avoid adding too much since it can substantially lessen the durability of the concrete and also lower the bonding strength of the cement to your aggregates. Each of the workers must be full busy at this point, pressing, rolling, and always looking over the area for any differences. Slowly, the aggregates can all be compressed into the beds, and the whole upper layer can be covered from the adequate layer of cream and aggregates mixed together. Avoid leaving just the stones being revealed.
There will be cases where, if the concrete gets excessively dry, that it will lead to the aggregates to get attached to the roller. When and if this occurs, ensure the aggregates are cleaned off from the top of the lawn roller prior to making a complete turn, these excess stones can lead to an indentation on the top layer. Applying a fine mist of water to the top layer can usually solve such situations.
By this time, the aggregates are all compressed into the concrete driveway, go down on your hands and knees to see across it, search for any ridges left over by the roller action. When and if you see some, and you probably will, roll them out, or simply use that 2 foot block of 2 X 4 planking and lay it flat across the high area. Use the mason’s hammer and pound up and down the board to even out the surface. Try to move the board all over do it again until the high spot is even. Always scan all over the surface and try to get it as even as you can.
Time for a break! On cool days, it can take as long as one hour to cure. But on hot days, it should only be 5 or 10 minutes before it cures.
Phase 6: Exposing the Aggregate Concrete
As the fines on the concrete’s top layer start to lose its shiny wet look, and may start to have a plain exposed aggregate colours. Start by slowly brushing the surface with a soft bristled brush or same sized broom with plastic bristles. Collect all the fine concrete within small heaps, as you start to show the shapes of the aggregates in the concrete layer.
Should any of the stones get removed out from the brushing, cease a bit and wait for a while longer. When you brush, take away just enough material so that the shape of each stone becomes very visible, though not so much which makes the pieces rise up above the concrete surrounding them. Its not about removing all of the concrete, simply remove sufficiently to see the shape of the stones per piece. The exposed aggregate colour will stay the same as the wet cement. In order to get access to the interior layers, get your piece of plywood for kneeling and standing on gently.
Always make certain to prevent toes and feet from digging into the soft concrete, and removing any of the stones or creating marks on the top layer. Remove any heaps of sand and cement from this layer. Form here, the concrete should be becoming very firm; adequately firm to walk on, and any brushing should begin to need real work to reveal the shapes of the aggregates. Slowly, you will be able to take off all of the excess material, and the surface texture should be getting a pebbled look which is our goal, though it will still resemble wet exposed aggregate colours.
This is followed by the process of change. Slowly spray the surface with a garden hose and water. Spray at a low angle all over the surface to show the stones, and slowly brush using a soft broom to work the last remnants of sand and cement from the upper layer. The change from the plain gray exposed aggregate colours of the wet concrete to the flashy wet clean aggregates can be quite amazing. All that hard work will be well worth it from here alone.
When the remaining materials like cement, sand and aggregates are removed, look for any areas that are not adequately revealed. Get a brush to finish these areas and water it as needed. Never use a strong spray, since it can dislodge the aggregates and create small pits on the top layer. At this time, a person should be able to walk freely on this layer, yet they still need to use caution and not kick any stones from of the concrete. Should any do get possibly dislodged; it’s not possible put them back at that stage. Also, the effect of the roller on the stones can be seen more clearly. All aggregates should be aligned with themselves and a flat section of each stone is on the top layer, this same layer on the completed surface will be very smooth. Your exposed aggregate project should be comfortable to walk on with just the soles of feet with no footwear.
As the aggregate becomes really exposed, the stones may have a slightly opaque coat of gray cement on them. That should strip off when time passes, though one could etch it off with some muriatic acid. Those stones may have a dull grayish coat on them that can seem to ho away from water. The best suggestion is to keep the top layer moist for a several days, when needed, even after completion. It will enable the concrete to attain its optimum durability.
There are many clear-coat finishes sold at various home improvement shops, suppliers of plastic, and even paint shops. Finishes must be applied as per the company’s instructions these usually suggest that the surface must be well and dry for a long time prior to and after application. The majority can create a glazed look, the same effect of water on the exposed aggregates, this is what people like the most.
Some tips before you finish your project
An essential element with regards to washing the cement off of the surface; any wash water coming fro the project has very high pH levels and filled with suspended solid particles. Never permit this water to get into storm drains which go into the wild streams and rivers where animals live. All cement particles are harmful to fish and any eggs they have. Prior to starting your project, make a pit around the site sufficient to keep all of the water which runs off while cleaning and setting. This water will simply soak into the soil, and keep the solids from entering the water table.
The professional way that exposed aggregate concrete finishes get done
With professional contractors, they use 3 ways of attaining exposed aggregate concrete finishes: starting with a seeding the chosen aggregate on top of the concrete surface, a monolithic method in which particular aggregate, often gap-graded, can be blended with the batches of concrete, and lastly, exposing the gap-graded aggregates with a specific topping process.
A monolithic exposed aggregate concrete finish is produced like this:
1. Pour the concrete with your selected aggregate in a normal way where workers fill the wood or precast forms with the material and simply rod the surface with a straight board, usually a straight 2″ X 4″ board or plank of wood using a sawing motion or back and forth all over the forms from one side to the next, followed by closing the upper layer as done usually.
2. Next, the surface is sprayed with a retarder. One can buy this from any contractors supply store or shop. Chemical retarders usually have sugars though any formulations which are created for use with concrete are highly advisable for a more consistent working of the concrete. This retarding solution can slow the set traits of the unrevealed surface layer enabling the inside to harden whereas the outside surface stays soft to work with properly.
3. This last part is the hardest step. As the concrete becomes firm enough to hold body weight without dislodging any of the aggregates, the top layer is water washed using a hose and bristle brush to take away the upper layer of cement ‘cream’. We should be careful not to dislodge the aggregates and not to overexpose the aggregate too much since that can lead to the aggregate losing its bond and/or becoming dislodged.
Last suggestion about Exposed Concrete
Not working fast enough during this portion of the process will create high possibility of hard work in taking off the upper paste surface. Using a retarding solution allows us to slow the setting of the top surface though it will not stop it entirely. When the wanted surface texture has been attained the concrete must washed with muriatic acid stain and then sealed with a clear sealing agent plus a curing substance which is also available at any local contractor supply store or chain.
After reading this entire article you would by now have a good solid idea of the pros and cons of Exposed concrete, including all the possibilities not to mention the total cost of exposed aggregate concrete per square meter after all is complete. Exposed Aggregate Prices vary according to many different details which is why the above information is important. If you would like to know more about concrete work such as driveways, patios and pool decks etc, including exposed aggregate finish options then please read above.