Pavers Over Concrete
Don't Set These Pavers In Sand Over Concrete
So your concrete needs a little love. Perhaps the painted deck has faded. Maybe you’re just ready for a new look.
There isn’t anything structurally wrong with the deck so it would seem your options are open. You’ve been thinking of installing pavers over concrete.
CAUTION – Some pavers, if set in sand over concrete, could develop problems. This article will look at all the installation methods for exterior tiles and pavers. We will discuss the pros and cons of each method. And we will show you which materials absolutely cannot be set in sand over concrete and tell you why. Plus we will tell you which materials may have issues if they are set using this method.
Basically, there are three methods of installation when looking at a concrete surface:
- Stick a tile to the concrete with thinset
- Stick a thin marble or pavers to the concrete with the mudset method
- Installing pavers over concrete in sand
Sticking tile to concrete with thinset
This method of installation is similar to setting any interior floor tile. An adhesive mortar (made of cement and fine sand) is used to attach the tile to the concrete.
The difference is the tile itself. Click here to see photos of exterior porcelain tile.
While an interior tile may be smooth, manufacturers have made exterior porcelain tiles with texture.
This texture (which may or may not be visible to the eye) causes something called slip-resistance. There are even tests to measure the amount of slip resistance a tile has. Plus there are industry standards that specify how much slip resistance a tile should have in order to be used in certain applications. Click here to read what the Tile Council Of North America has to say slip resistance.
Generally, marble and pavers are not installed using thinset.
Sticking Marble or Pavers to Concrete with Mud
A mudset installation process is similar to a thinset method, in that the tile is stuck to the surface with an adhesive. The major difference is the setting material itself – which is nicknamed mud. This mud – as the name implies – is a thicker mortar.
This thicker bed of setting materials allows installers to raise and lower individual pieces to avoid lippage.
You may ask why the installer can’t just pile up more thinset and achieve the same results. Well, the mud is stiff. Think of making a mud pie. You can mold it and shape it and it keeps it’s shape. You don’t even need a pie pan to contain the mixture.
In keeping with the pie analogy – thinset is more like pumpkin puree. A dollup of this mixture may stay put, but once the installer places a tile on the thinset, the adhesive will squish out the sides. This does not allow much ability of move the tile up or down.
Most installers will want to use the mudset method to install marble or pavers in order to avoid lippage. Lippage is where one tile juts up above another.
Generally, it takes longer to install tile using the mudset method than the thinset method. That extra time, coupled with using more setting materials, is why a mudset installation costs more than a thinset installation.
Set Paver On A Concrete Slab With Sand
In this method, instead of glueing the paver to the concrete with mud, the paver is laid on top of a layer of sand.
Many pavers can be set using this method with no problems. But some natural stones could develop issues if set using this installation method.
Pavers were designed to be set in sand. So why could some develop issues if set in sand over concrete?
Let’s compare the moisture flow with sand set vs sand set over concrete.
When pavers are set directly in sand – liquid falls on the pavers. This water seeps through the cracks and it keeps on going. Sand is permeable. Look at the beach. The wave washes over the sand. When the wave retreats all the liquid seems to disappear.
But if the paver is set onto sand which has been laid over a concrete surface, any moisture that seeps in has no place to go. It’s trapped between the paver and the concrete.
This can lead to Efflorescence. Click here to read more about efflorescence.
Some pavers may experience cosmetic issues as a result of the moisture.
Many pavers are not subject to these issues. But some are. Material which is a light, consistent color could become blotchy as a result of efflorescense.
Materials that should not be set over concrete in sand
- Porcelain Tile or Ceramic Tile (as opposed to porcelain pavers).
- Marble Tile (as opposed to marble pavers).
I am constantly warning clients who take samples home not to walk on them. It’s a normal reaction. People want to see what the material will feel like under foot.
If there is any debris under the tile, it will act like a fulcrum and the tile will snap.
Once tile is glued to the floor, this does not happen.
The same goes for thin marble.
A porcelain tile needs to be at least 2 cm (a little over ¾ of an inch) thick in order to be set in sand. Marble is generally thicker – 3 cm.
Also, there are some do’s and don’ts when using tile outside in freeze thaw areas. Click here to read more about the differences between porcelain and ceramic tile.
So while it is ok to install many types of pavers over concrete. Not every paver is a good choice for this application.