Published on 4/4/2021
Published by firstname.lastname@example.org
What is concrete dusting?
What causes concrete dusting, and what can we do about fixing it
Cover photo courtesy of Eco Ratio - The Release Agent Company
Recent wet weather on the East Coast of Australia has led to an incresed amount of Concrete Dusting.
What causes concrete dusting
Concrete dusting is often caused by the excessive use of water during finishing. Spraying the surface with water during finishing to facilitate either the movement of the trowelling machine from one area to another, or to wet a surface that has not been adequately protected against hot or drying conditions and allowed to dry out, may have the same effect as premature finishing. But it can also be caused by rainwater. Rainwater falling onto the surface before the concrete has achieved final set may also have the same effect as premature finishing.
Other major causes of CONCRETE DUSTING are:
Inappropriate concrete specification for the required strength and abrasion resistance.
The addition of water in excess of that required by the mix design. This generally increases
bleeding which results in more water and fines at the surface of the slab and ultimately in a weak, permeable surface layer with low wear resistance.
Premature finishing. If finishing operations are performed while bleed water is on the surface, the water will be worked back into the surface layer of the concrete producing a very high water-cement ratio and, therefore, a low- strength surface layer.
Inadequate curing. Failure to adequately cure (or not cure) concrete and allowing rapid drying of the surface (especially in hot, dry and windy weather) often results in a weaker surface layer which may dust even under foot traffic. Proper curing is an essential requirement for good quality concrete and a durable surface.
Inadequate compaction. If the surface is not adequately compacted or finished, reduced abrasion resistance will result.
Tips to avoid concrete dusting
Stop concrete dusting: solutions
Ecoratio wants to assist you in stopping concrete dusting problems with the following tips that reduce the chance of dusting concrete. Here you find some tips that can be the solution for concrete dusting:
Use the best available materials to cast your concrete. The aggregates that you are going to use need to be clean and of uniform shape to create the concrete mix design;
Bleed water on top of the surface will weaken the quality of your concrete.
A correctly design concrete mix with the lowest possible water cement ratio to achieve the desired workability will result in less bleed water and less dusting;
The most obvious solution to prevent dusting concrete is to let your concrete cure properly. When the concrete is properly cured, the structural integrity of the concrete will be at its best.
- Do not let your concrete dry out too fast!
- Do cover your newly cast concrete with polythene or damp hessian
- If covering with polythene make sure the ends of the formwork are also covered to avoid a ‘wind tunnel’, wind can rapidly dry out the concrete surface which will lead to dusting
- Do use an aliphatic alcohol
- Do use a concrete curing agent on the fresh concrete to seal the surface to stop moisture leaving the concrete too fast
- Once demoulded keep the concrete element out of direct sunlight and wind for as long as possible
- Once (and only) when the initial setting and hardening of the concrete has taken place then spray a fine water mist to keep the surface moist
Avoid using additional water when finishing your fresh concrete.
The surface may finish easier and it may look like you have achieved a good quality surface finish, but this normally only leads to severe dusting and concrete surface strength problems and should be avoided at all costs.
Do not use too much release agent on the moulds. In addition to dusting, it causes other problem such as surface voids and discoloration. Use one of Ecoratio’s release agents or custom-built spray systems for the best results.
How do we fix concrete dusting?
Concrete dusting occurs when the surface of your concrete is weak. Therefore we need to harden the surface up, and protect it from further deterioration. Repair of dusting floors is difficult; it is best to avoid or minimise the risk by adopting the techniques outlined above. Recommended repair methods include:
1. Application of a chemical surface hardener or dust inhibitor.
In the majority of cases, dusting can be rectified by the use of a surface hardener such as sodium or fluoro silicate. These products react with the calcium hydroxide in the concrete to produce additional cementitious compounds. They should be applied only to concrete that is at least 28 days old. Some surface hardeners may restrict future application of finishes. Surface hardeners should be applied in accordance with the manufacturer’s recommendations. note that they will not improve the appearance of the surface if it has been affected by the loss of the surface layer through wear.
2. Grinding the surface.
In more severe cases, the complete removal of the weak surface layer with a concrete grinder may be required. This will alter the appearance by leaving a smooth ‘polished’ concrete surface having the aggregate visible. note that the depth of the weak surface layer does not increase with time, so grinding back to sound concrete of adequate strength can be an effective solution.
3. Applying a topping.
The weak surface layer could be removed by scabbling and replaced
by a topping. If levels need to be maintained, a number of proprietary topping products that bond to the existing concrete can be placed at thicknesses of about 10 mm. If levels are flexible, a 70- to 80-mm-thick unbonded topping (overlay) on the existing floor can be used.
In some domestic applications, installation of a floor covering such as carpet or tiles may be a cost effective solution. The concrete surface should be checked for adequate strength if the floor covering is to be bonded to it.
Tony Partridge and Son Pty Ltd is a family owned and operated business. Tony has had over 30 years experience in the trade from small domestic works to large commercial projects. We are committed to prompt service and customer satisfaction. We specialise in exposed aggregate and stencil. Our professional experienced team takes pride in offering high quality work for all your concrete requirements.
Tough Floors is a Redlands based business that service all of South East Queensland including greater Brisbane, Gold Coast, Sunshine Coast, Logan, Ipswich, Toowoomba and Pine Rivers. We also cross the border into Northern NSW to work on various projects. Our specialist products include epoxy and polyurea/polyaspartic and polyurethane flooring that can be applied commonly to garage floors, patios, outdoor areas and in showrooms, retail outlets and a limitless range of commercial and industrial areas.
Towing and Roadside Assistance Services The old days of having an unreliable vehicle that doesn?t live past a certain dashboard miles number are over. Sometimes though our modern marvel of engineering cars, pickup trucks and SUV?s break down. And it?s never in a convenient location. Luckily we are the towing company in Queens that you can rely on to come to the rescue in these situations. As the local tow truck service in Queens we offer many other services.
For all your concrete apparel
There?s more to being a concreter than just screeding crete..
Principal at Hunter and Coast Concrete Pumping
Concreting the Hunter Valley and Newcastle for over 30 years
Thinking of sealing or resealing your concrete? Find out what you need to know here.
Join Australia's fastest growing business community - Qoin World
Boom and line pumps in Sydney at great prices..Call Now
Tags: concrete curing concrete densifiers concrete dust concrete dusting concrete finishing concrete hardener concrete sealer Eco Ratio release agents weak concrete
This article was written by email@example.com all rights reserved. The views and opinions expressed in this article are those of the author(s) and do not necessarily reflect those of concretebroker.com