Concrete is one of the most commonly used building materials in existence. It is especially used on floors but at times you want to put plywood over it.
It is perfectly fine to install plywood over an existing concrete floor, provided it is dry. It is important to check the moisture level and ensure that it is below 6% before you attach any type of subflooring, especially plywood. Otherwise, you may have to give it more time to cure.
The curing of the concrete is where many people tend to go wrong. Generally speaking, you will need to wait at least two months before you even start checking the moisture levels.
Although there may be some wiggle room as far as how low the moisture content should be, it should be down in the mid to low single digits.
There are also other reasons why you may want to think about options when it comes to putting plywood over concrete. When you make the right decision, you can have a solid subfloor but if you make the wrong decision, you will end up regretting it.
Can You Put Plywood Over Concrete Flooring?
There are two general questions that you need to ask when you are thinking about putting plywood over concrete. Can you put plywood over concrete and should you?
As far as actually putting the plywood over concrete, that isn’t a problem. As we discussed, as long as the concrete has cured and has a low moisture content, plywood will work perfectly fine as a subfloor over it.
Generally speaking, a plywood subfloor should be at least 3/4 inch thick. That is true, regardless of whether you are putting it over concrete or if you are installing it over floor joists.
You also need to think about the type of plywood you use. Some people will think about using pressure-treated plywood, but that is not generally a good idea. Why?
Pressure-treated plywood has some issues that regular plywood does not have. It may split and have other difficulties, but regular plywood can do the same.
For the most part, people consider using pressure-treated plywood because they are in an area that is prone to flood. If you are in a flood zone or are thinking about using plywood over concrete in a basement that floods regularly, think about using something else.
Concrete may stand up to flooding, as can other types of floor, such as tile. If you put plywood down and any type of flooding occurs, however, you are going to have difficulties.
Not only can it ruin the plywood and any type of flooring you have on top of it, you might also end up with mold problems. At times, the mold can even grow under the floor on the plywood and be a hidden issue that might not be discovered for many years.
There are also other reasons why you need to think carefully before using plywood over concrete. The condition of the concrete is an important factor, especially if it is an old concrete slab.
Putting plywood over a smooth, flat concrete slab is not going to be a difficulty in most cases. Older slabs tend to have problems, including cracks, bumps, lumps, and high or low spots.
Any of those difficulties can cause issues, and if there is an issue with the concrete, it will eventually show up in the subfloor. That gets even worse when you put a floor over top of the plywood because it will cause issues with the finished floor as well.
There isn’t a problem with putting plywood over an old concrete slab but you need to ensure it is in good shape. Filling cracks, grinding down any high levels and floating the floor to raise any low levels is important.
You will also need to clean the floor thoroughly. This isn’t only to remove dust and dirt, it is to get rid of any grease and oil that may be on the concrete slab.
Something else to consider is the way that the plywood is attached to the concrete floor. There are a number of different options that may be beneficial, depending upon the condition of the floor and the individual circumstances.
Floating Floor – This may be an option in some cases but it is not typically selected for plywood over concrete. If you are going to select a floating option, you should use some type of plastic sheeting.
Glue down – this is an option in some cases but it is not always going to be preferable. One of the reasons why you should not use glue down is because any type of moisture barrier, such as plastic, will not work well with the adhesive.
Nail down – This is perhaps one of the best options. It may still be necessary to use some plastic sheeting or you may use roofing felt to provide a moisture barrier. You will have to use a special tool, such as a Ramset gun to attach the plywood to the concrete.
Be very careful about the condition of the floor. You can check for high or low spots by either using water or marbles.
As a water test, you can pour water from a bucket on the floor. It will run off of the high spots and collect in the low spots. If the concrete is not sealed, the water may soak in before you can tell where some of the high and low spots exist.
Run a scraper over the floor to check for any lumps or bumps that could be a problem. You may not notice these when you put down the plywood but it can cause lumps or bumps in the plywood and ultimately, the finished floor.
Any type of cracks or seams in the concrete will eventually show up in the floor. Three-quarter inch plywood can cover some very small cracks but it could eventually settle and you will see the seam in the finished floor.
You can grind down any high spots with a surfaced or floor grinder and fill cracks with a quick-drying compound. You might also want to use a self-leveling compound over a clean floor for a flawless finish.
Should You Put Plywood Over Concrete Flooring? Reasons Why Not And Why Yes
As is the case with any type of building material, there are going to be both good and bad associated with putting plywood over concrete. Here are some things to consider.
The main benefit of putting plywood over concrete is how affordable it is. Plywood is also very versatile and easy to work with. When you compare it to other types of floors, including hardwood and tile, it is not going to be as strong but it can make a very suitable subfloor for all other flooring materials.
Here are a few of the pros and cons of using plywood over concrete.
Pros of using plywood over concrete:
Affordability – Plywood is not cheap by any means but it is typically a lot less expensive than other options, including tile and hardwood floor. It is a great way to prepare a subfloor for all other types of flooring.
Flexible – If you have any problem with the plywood, it is not difficult to pull it out and put another piece down. You can even stain or paint plywood if you want to use it as a finished floor.
Installation – The installation of a plywood floor is very simple. You will find that it goes down easily in a matter of hours.
Cons of using plywood over concrete:
Durability – Although plywood is a very good choice for subfloors, it is easier to damage than other types of finished floor.
Knots – If you are using plywood as a finished floor, there are likely to be knots that can come loose and make it necessary to repair the floor.
Curb Appeal – There is a definite lack of curb appeal when it comes to plywood as a finished floor. As a subfloor, however, it’s a great idea.
How To Put Plywood Over Concrete Flooring
Putting plywood over a concrete floor is a relatively straightforward process. Here are some things to consider.
The most important consideration for putting plywood over concrete is preparing the floor. You will need to check for any damage, as well as high or low spots and repair them so that you are dealing with a flat, smooth surface. After you have fixed the concrete, you can put the plywood down and attach it quickly.
There are a few things to watch for when it comes to preparing the concrete for plywood. This is more important for older concrete slabs but it can happen with any slab.
High/low spots – if there are any high or low spots, they will need to be ground down or floated with a leveling compound.
Cracks – When cracks appear in the concrete floor, they will likely also eventually appear in the subfloor and finished floor. You can repair cracks by filling them with a quick-drying compound.
Seams – Like cracks, seams may also be a problem and they can be filled with a quick-drying compound.
After you have the concrete prepared, you can then begin attaching the plywood floor. This is best done by putting down some type of vapor barrier and then attaching the plywood.
The easiest way to attach the plywood is to use some type of gas-actuated tool. You can also use Tapcons, although that will take some time for a larger floor surface.
Try to run the plywood in the opposite direction of the floor. It isn’t going to make a difference with tile but if you are using hardwood or vinyl strips, it can make a difference.
Once the plywood is installed, you can either stain or paint it if desired. You can also simply use it as a subfloor for all other types of flooring.
What Tools And Preparation Are Needed?
As is the case with any job, much of the work is in the preparation for putting plywood over concrete.
Generally speaking, the only preparation you will need to do with the concrete is to clean it and make sure it is flat and level. Grinding down high spots or filling in low spots is an important part of preparing the subfloor. You might also find it beneficial to float the floor with a self-leveling compound.
The following are some of the tools you will need to put plywood over concrete:
- Tape Measure
- Floor Grinder
- Long Level
- Drill With Concrete Bits
- Utility Knife
- Safety Glasses
Putting plywood over an existing concrete floor is an excellent way to upgrade the floor or prepare for any other finished floor. As long as the concrete is free of defects, level, and dry, it makes an excellent subsurface for plywood.