Paving Pedestal System or Mortar Bag for Patio Slabs
You would like to take the terrace construction with natural stone slabs or slabs made of porcelain stoneware into your own hands and you already have a concrete slab on your terrace? A good prerequisite – this gives you a substrate that is sufficiently load-bearing and frost-resistant. If you already have a concrete slab instead of soil, in addition to loose laying (patio slabs laid on a bed of chippings), partially bonded laying (slabs laid on a bed of chippings with grouting) and bonded laying (patio slabs laid with a natural stone adhesive), there is another interesting variant for installing patios: laying the slabs on paving pedestals, mortar bags or slab bearings. Particularly practical with this type of installation: if necessary, slabs can be quickly and easily replaced here in the future! If you want to lay natural stone slabs, you should choose hard stones such as granite, basalt or quartzite for this type of installation.
Laying terrace on supports has advantages
There are good reasons to choose paving pedestals. Especially for balconies or roof terraces, this type of laying is ideal. For one thing, weight is saved because no bedding material such as chippings or gravel needs to be used. Also, it is not necessary to pay attention to the slope of the laid terrace slabs, since the rainwater runs off through the approx. 0.16 in wide cracks between the individual slabs – however, the concrete slab underneath must have a slope, be sealed and, if required, be supplemented with balcony or terrace profiles to drain off water.Since the slabs are not grouted when paving pedestals, there is also no need to renew grouting material – another plus for this laying variant.
Another advantage: if it is desired to raise the level of the terrace, this can be easily achieved by paving pedestals. The laying method is also helpful if a new terrace is to be built over the existing one without removing the old one first. Dimensional tolerances of slabs can also be well compensated by paving pedestals.
Tip: When paving pedestals, the weight of the slabs is distributed over several support points. Therefore, hard stones such as granites, basalts or quartzites are particularly suitable for this type of installation.
What is the load capacity of slabs?
Since when paving pedestals tiles rest on the bearings at their corners, and there is a cavity under them, the question of load-bearing capacity arises. In the case of slabs made of porcelain stoneware, you can be completely unconcerned. The flexural strength of these extremely robust slabs is very high and can easily bear loads weighing several tons. The stability of natural stone is also very high, especially in the case of hard stone. However, each stone is different, and in the rare case of a very high load, the veining may cause the slab to break. In addition to the four paving pedestals support points at the corners, at least one additional paving pedestal should be placed in the center for stabilization.
Important: The basis must be right!
Before you start laying the stone slabs on paving pedestals, slab bearings or mortar bags, you should check, for example with the help of a spirit level, whether the existing concrete slab has a slope of 2-3%. This is necessary so that rain and meltwater does not collect under the stones and can drain away unhindered. If the slope is not present, you can create it yourself after priming with a suitable cementitious mortar. To prevent water from penetrating into the concrete slab and the adjacent house wall, this should be followed by waterproofing with a sealing slurry. Once the floor coating has been applied, you can start laying the terrace slabs on paving pedestals.
Paving pedestals- that’s what you should know!
When paving pedestals, the slabs are arranged in a cross-joint bond, as the punctual concentration of the weight is distributed best in this way. You have the choice between slab bearings, paving pedestals or mortar bags. Slab bearings are flat stud elements with a fixed height and with an integrated cross joint, into which the slabs are inserted. Care should be taken to ensure that the slabs are of uniform thickness. Paving pedestals, which are also called terrace bearings, offer, in contrast to slab bearings, a higher possibility of erection, and they are also available in height-adjustable versions. Therefore, they are also able to compensate for existing unevenness of the base. In addition, they have attached spacers to create a uniform width of the joints. As a rule, paving pedestals have four separable fields, with which you can divide them into corner and edge pieces.
Tip: A cheaper and less time-consuming alternative to slab bearings and stilt bearings are mortar bags – these are plastic bags that are filled with a mortar mixture and laid under the slabs when damp with earth, after which the slabs are aligned. The advantages of this type of laying, besides the low price (you only need standard freezer bags and a cement mortar with trass cement), are the uncomplicated alignment of the slabs on the not yet hardened bags. In this way, unevenness in the substrate or stones can be quickly and easily leveled.
With all variants of paving pedestals, it is essential that a slab joint spacing of 0.16 in is maintained to ensure water drainage. Also plan for sufficient movement joints to prevent possible stress damage.
The basics for laying stilt on a concrete slab
- Concrete slab: Slope of 2-3 % available? If not, make and seal it yourself
- Slab bearings, paving pedestals, mortar bags: these support variants are available
- Square, practical, good: arrange slabs in cross joints when paving pedestals
- Keep a joint distance between the slabs of 0.16 in