Using Ytong Outdoors: This Is How You Can Waterproof Aerated Concrete

Using Ytong Outdoors: This Is How You Can Waterproof Aerated Concrete

Ytong is a practical building material. The stones are big and light. It can be easily carved into any shape with a hammer, chisel and saw. That invites you to tinker and build. However, if the aerated concrete is to stand outdoors, measures must be taken. The stone is extremely sensitive to frost and moisture. Here’s how to use and seal Ytong outdoors.

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Sensitive material

The Ytong’s two worst enemies are water and frost. Ytong soaks up wet like a sponge. This is due to the internal structure of this brick: The millions of tiny gas bubbles have a strong capillary effect. Even standing water is inevitably sucked through the whole stone until it is completely soaked. That alone is very critical: aerated concrete loses its stability when wet and begins to dissolve. But it is very fatal when frost comes. Water expands by 10% when it freezes. If the water solidifies to ice in the aerated concrete, it literally tears the stone into pieces. So if you want to use Ytong outdoors, you have to take measures against the ingress of water. Unfortunately, that’s not that easy. Read how to proceed in this text.


Alternative to Ytong

Unless you have large quantities of aerated concrete blocks left over, there is practically no reason to use this building material outdoors. It is quite easy to edit, though. All in all, its outdoor use is quite delicate and always has a limited shelf life. In addition, aerated concrete walls are anything but attractive. In any case, they have to be disguised or plastered so that you don’t lose your good mood when you see them. We would therefore like to advise you to use a more suitable material for outdoor use:

  • Bricks, new or used
  • Concrete and structural concrete blocks
  • Natural stones
  • Solid sand-lime bricks

These offer only advantages in contrast to aerated concrete. They are decorative, waterproof, easy to work with and allow many creative design options. But if it is to be aerated concrete, then certain measures must be taken.

Using Ytong Outdoors – Tips

Solid, straight, watertight foundation

Aerated concrete needs a distance from the ground. That is the main reason for building a massive, watertight foundation. The aerated concrete must not come into contact with the floor, otherwise, in the worst case, the entire wall will become saturated with water. A foundation is approx. 10 cm wider on both sides than the aerated concrete wall should be. It is 80cm deep to ensure frost protection. After all, it has to be reinforced and made of water-impermeable concrete. To be on the safe side, the foundation formwork can be lined with pond liner on the inside. So you can be absolutely sure that no water can get in.

First shift: As straight as possible

Ideally, the foundation should be switched on 24 cm above the edge of the lawn. So it can be peeled off straight before it sets and you get the perfect substrate for the Ytong wall. If that doesn’t work, the first layer of waterproof concrete blocks has to be put in place. Concrete blocks have the advantage that they are very dimensionally accurate. There is also a bitumen sheet under and over the first layer. In this way, the future wall made of Ytong is guaranteed to be protected against rising damp.

Sealing aerated concrete – this is how it stays tight

If you want to use Ytong outdoors, you can’t avoid waterproofing. There are three ways to do this:

Epoxy-based nano-sealing

The epoxy-based nano-sealing is particularly simple and sustainable. You can apply the epoxy resin before the masonry and coat the stones with it. It is liquid like water before it hardens. As a result, it penetrates deep into the aerated concrete and provides a particularly lasting seal. To do this, lay the stones on a clean surface, for example on pond liner. Turn the stones over so that the outside is facing the sky. Now you can coat stone by stone 2-3 times with a brush and epoxy resin. Once the resin has hardened, turn the stones over and coat the back as well. You can safely use Ytong outdoors because the stones are now permanently waterproof.

However, the epoxy-based nano-sealing has one disadvantage: it is very expensive. With this solution you have to reckon with 25 – 50 euros per kilogram. Unfortunately, the consumption of sealing aerated concrete is very high, as a large part is sucked in by the stone.


Bitumen is viscous tar. It is heated for application. Then it becomes spreadable. Bitumen sealing is particularly useful in the basement area. When using Ytong outdoors, the main disadvantage of the bitumen coating is its black color. Bitumen is practically impossible to paint over. The already ugly aerated concrete becomes even more unsightly due to the bitumen sealing. Bitumen is therefore not really an option for garden walls, pond borders, walkways or sculptures. 

Sealing slurry

The sealing slurry, for example from PCI, is therefore still the best solution for sealing aerated concrete. It will be perfect if it is combined with a previous epoxy coating. So even small imperfections in the sealing slurry cannot harm the sensitive aerated concrete underneath. The sealing slurry is applied with a smoothing chip and distributed with a brush. It hardens quickly and offers permanent protection. The best thing about the sealing slurry is that it can be painted over. We recommend waterproof facade paint for color design. It offers additional protection when you want to use Ytong outdoors.

To seal aerated concrete with sealing slurry you need:

  • Primer (around 4 dollars per liter)
  • Cement (around 6 dollars / 25 kg sack)
  • Sealing slurry (around 30 dollars / 25 kg sack)
  • water
  • Mixing tub (around 10 dollars)
  • Powerful mixer (around 20 dollars daily rent)
  • Bucket (1 euro)
  • 2 x tassels (2-5 dollars each)

The Ytong is first coated with primer. While this is drying, the sealing slurry is applied. It is mixed with cement in a ratio of 1: 1. A powerful electric mixer is required for this. A household drill is definitely overwhelmed with this task. Plenty of water is added until the mixture is completely liquid. However, no water should settle on the top. The mixture is poured into the smaller bucket. Now the Ytong is generously coated with the brush and the sealing slurry. The process is repeated until no more aerated concrete can be seen. After the sealing slurry has dried, it can be painted over with facade paint. So you have a respectable and yet quite inexpensive result.