Do you sweep and clean your bare concrete garage floor only to have it feeling gritty and dusty the next day? Even after washing it down, can you can run your fingers over the concrete once dry and get a white, dusty film on your fingertips? If so, you may have a problem with concrete dusting of your garage floor. This problem is actually more common than some may suspect. In most cases, however, dusting of your garage floor can be stopped or significantly reduced.
What is concrete dusting and what causes it?
Dusting is the chalking and/or powdering of the concrete at the surface. It is primarily caused by the disintegration or breaking down of the very top layer of weakened concrete. Foot traffic, cars, and yes, even cleaning, can just add to the problem.
There are many reasons for this weakened layer of concrete. It can range from poor mixing of the concrete, excess clay or silt in the concrete mix, old age, or even insufficient curing at the surface. The most common reason, however, is excess bleed water at the surface during the finishing process.
If there is too much water in the concrete mix, this water will rise to the surface during the finishing process (troweling). This bleed water can carry the finer particles and cement to the surface, forming a layer of laitance at the upper most top of the slab. This same condition can be caused as well when water is added to the surface during the finishing process in a last ditch effort to create a smooth troweled surface.
This surface laitance is actually a porous layer of softer concrete that slowly breaks down and creates the white powdery surface. In some cases it can easily be scratched with a sharp screwdriver or nail. Sweeping of the concrete never seems to get it completely clean since the surface is in a constant state of disintegration.
If left untreated, this fine concrete dust can become extremely annoying as it finds its way onto the surface of cars, work benches, laundry machines, and anything else kept in the garage. It can also easily be tracked into the house on the bottom of your shoes.
How to stop a dusting garage floor
Fortunately, stopping concrete dusting of your garage floor is not a difficult process in most cases. Doing so not only fixes the dusting problem, it seals your concrete and protects it from further damage at the same time.
For light dusting, the simple solution is to apply a siliconate penetrating sealer. Siliconate sealers chemically react with the concrete and form a calcium silicate barrier at the surface. This barrier not only seals the concrete, it helps to strengthen the weakened layer of laitance at the surface.
Siliconate sealers do not change the appearance of the concrete, but it will bead water and protect the concrete from road salts, freeze thaw damage, and even help resist stains. Application is easy and the only prep necessary is to clean the garage floor. You can learn more about siliconate sealers here.
If the dusting is a bit more extreme, but the surface isn’t so soft that you can easily scratch or gouge it with a screw driver, then you may need to take a two-step approach to stop or severely reduce the concrete dusting. This method requires the application of a densifier first and a water repellant sealer second.
Densifiers are actually a concrete hardener. They are used primarily for polishing concrete but have other uses as well, including the reduction of concrete dusting. They work similar to a siliconate sealer, but they penetrate deeper and have a stronger chemical reaction with the concrete. They can actually increase the surface strength of concrete up to 40% depending on the condition of the concrete.
Unlike siliconate sealers, however, densifiers do not form a protective barrier at the sub surface since the molecular structure of the densifier is much smaller. Because they do such a good job of making good concrete more dense, they are sometimes mistaken for a sealer since water tends to bead after application.
The key is to use a straight densifier with no sealer added. Lithium based densifiers are the easiest to apply and usually the most effective. As with the siliconate sealer, all that is required is to clean the concrete before application. Densifiers will not change the look of the concrete and they are easy to apply as well.
You will need to wait a week after applying the densifier before cleaning the concrete again for application of the sealer. Densifiers take time to react and can push up dust and moisture in the concrete to the surface while it cures.
If the dusting has stopped after you clean the concrete, then application of a sealer will not be necessary. If some dusting remains, then you will need to follow through with the second step of applying a water repellant sealer.
You can use a siliconate sealer or something with even more protection like this product from GhostShield. If you are unsure about which water repelling sealer you want to apply, we suggest contacting the manufacturer or vendor to get their recommendation.
If the surface of your concrete is soft enough to scratch with a screwdriver or your dusting is severe, your best option is a floor coating such as epoxy. A properly applied coating will not only enhance the looks of your garage floor, it will last for years and provide excellent protection from the elements, including chemicals and automotive fluids.
Grinding of the garage floor in preparation for an epoxy coating is highly recommended when dusting is the issue. Acid etching will not effectively remove laitance. If epoxy is applied to dusting concrete that was prepped only with acid etching, the epoxy can peel up at a later date. The bottom of the epoxy will have a thin layer of concrete dust that separated from the surface.
Grinding of the surface will remove the laitance and upper layer of soft concrete in order to provide for the proper surface profile for the epoxy or coating to adhere permanently.
While concrete dusting can be a real nuisance in your garage, it doesn’t mean that you can’t tackle the issue with a little bit of DIY effort on your part. Unless the dusting is severe, proper cleaning of the floor and easy application of a penetrating sealer usually gets the job done. All that is required is some cleaning supplies and a pump up garden sprayer to apply the sealer.
If the dusting is severe enough that the concrete can be scratched easily, we recommend contacting a floor coating contractor if you do not feel comfortable with grinding the concrete or installing an epoxy coating yourself.
Finally, don’t forget to contact a quality vendor or manufacturer to ask questions if you are unsure. Home improvement centers generally are not well educated on such topics and may not carry the proper product to use. Vendors who specialize in concrete coating and sealing products, on the other hand, are extremely knowledgeable and can help you to successfully stop concrete dusting of your garage floor.