Your question. Our answer.


  • Rated value - Which values are interesting for structural planner / structural engineer?

    Maximum permissible compression strength fcd.

    In principle, a structural engineer can again use only the rated value of maximum permissible compression strength fcd as basis for calculations of the structure. The compression strength value specified many times with 10% compression is a value from the test standard and is not relevant for static calculations.

  • Load bearing capacity of a thermal insulation layer as foundation bed - How do I prove this ?

    The manufacturer specifications and the values declared in permit shall apply for the loadbearing capacity of an underlay. An informative proof of the loadbearing capacity is difficult to achieve with reasonable effort on the construction site.

    The actually existing loadbearing capacity of an underlay can only be verified by means of a load plate test. With elastic panel insulation materials, it is also possible to check only the construction pit plane under the broad layer. The manufacturer´s specification of the compression strength and thus the loadbearing capacity of the entire underlay situation is not verifiable for this type of construction on the site with reasonable effort.

    The underlay of a building founded on cellular glass gravel is also influenced by the properties of underground as well as that cellular glass gravel. Both the layers interactively create a certain underlay modulus. This is measurable on the construction site by means of a special load plate test. Based on the grain size of the cellular glass gravel, a load plate test on the insulation layer only with a load plate of more than 600 mm diameter results to reproducible results.

    There is no urgent need for such a test.

    If the loadbearing capacity of the underground is proved using the load plate test before beginning the cellular glass gravel work, it suffices to check the compliance with compaction  factor of 1.3:1. This way, the remote-monitored rated value of maximum permissible compression strength can be provided.

  • Load plate tests - Are they practical on cellular glass gravel ?

    No. As the general construction permit of GLAPOR cellular glass gravel SG 800 P does not require further proofs, a conclusive load plate test of a correctly installed cellular glass gravel layer is on a verified sustainable underground.

    Basically, it is only possible to prove the actual conditions of a building bedding by means of a special load plate test. However, since cellular glass gravel is a relatively coarse grain mixture, tests with lightweight drop weight tester and a 30 cm load board are unsuitable fro foam glass gravel according to DIN 18134. Useable results can only be achieved with 600 or 720 mm load boards. In addition, for practical reasons, it is necessary to adapt these load plate tests in detail to the coarse grain size.

  • Compaction factor - is it possible to choose a higher / lower compaction factor to increase the loadbearing capacity of cellular glass gravel ?

    No! The compaction factor is regulated by the building construction permit inspectorate approval; a deviation due to, for example, manufacturer information is not permitted for this application.

    Cellular glass gravel is an unregulated construction product, which requires a common construction permit for its use as thermal insulation fill in Germany within the scope of the state building regulations. It is only there that it is regulated which compaction factors are permissible. As cellular glass gravel is used as a load-carrying layer under the foundation slabs, it is necessary to use only building supervisory recognised rated values of maximum permissible compression strength for static calculations. A deviation from the permit, e.g. by manufacturer releases of higher or lower values, is inadmissible in Germany for the application under load-bearing foundation slabs and entails a liability of the planner or executing company with itself. If deviations are planned, this is only possible by agreement in individual cases.


  • Compaction factor - How do I prove it ?

    The easiest way is to measure the height before and after, the filling height and the finished dimension, which is best determined with a laser. Please pay attention to recommended compaction equipment!

    First, the construction pit plane is created with the necessary evenness and load-bearing capacity. The plane height serves as a starting point for the measurements. The filling height of the cellular glass gravel is now determined using laser, in which the plane thickness is multiplied by the compaction factor of 1.3. This would result in a finished thickness (planning thickness) of 30 cm and a filling height of 39 cm. Subsequently, the surface of the cellular glass  gravel is compacted down to the planning thickness using suitable compaction equipment (see: LINK processing instructions). While doing so, it is important to pay attention to the maximum permissible thickness of 30 cm finished dimensionon per work process. The maximum permissible total thickness is 60 cm.

    We recommend recording the height measurements and the compaction check conducted by the site foreman / site supervisor in the daily construction records.

  • Thermal conductivity value - Which value must be used to calculate the thermal insulation verification ?

    Lambda: In Germany, only the rated value for the thermal conductivity, characterised by λ, may be used to calculate the thermal insulation verification. For other EU countries, on the other hand, the value λD forms the basis of assessment, sometimes with a supplementary facto. For the use of the material as a thermal insulating material under load-bearing foundation slabs in Germany, only the rated values of thermal conductivity, characterised by λ, are applicable. The values λD or λ are not relevant for thermal protection calculations in Germany and would lead to incorrect calculation results.

    The basis of assessmet, sometimes with a supplementary factor. For the use of the material as a thermal insulating material under load-bearing foundation slabs in Germany, only the rated values of thermal conductivity, characterised by λ, are applicable. The values λD or λ are not relevant for thermal protection calculations in Germany and would lead to incorrect calculation results.


  • Unloading and loading - Are special measures necessary against dust from cellular glass gravel ?

    In principle, no. For exceptions see below.

    Dust from GLAPOR cellular glass gravel does not contain carcinogenic substances. However, in case of a large amount of dust formation (e.g. strong wind during unloading), we recommend carrying standard safety equipment (mask/safety googles) for avoiding mechanical irritations. If it is possible that uninvolved persons (pedestrians, residents) or their properts (e.g. cars, laundry) could come in contact with dust, we recommend moistening the cellular glass gravel falling out of the vehicle during unloading with a broad water jet. The thermal conductivity values in areas outside the rated value of the German permit do not deteriorate.

  • Wetness - May cellular glass gravel become wet ?

    In principle, yes. The load-bearing capacity does not reduce in the wet state.

    The humidification of cellular glass gravel due to rainwater during storage and transport is not critical. cellular glass gravel absorbs water only to a small extent due to wetting of surfaces; complete grain moisture penetration does not occur in approved materials.

    The GLAPOR cellular foam glass gravel, which weighs just 160 kg/m³ on average, binds a maximum of 12% of its own weight of water to the grain surface even after 28 days of underwater storage. The comparatively high surcharge on the laboratory measurement values of the thermal insulation effect calculated is easily ensured even if GLAPOR cellular foam gravel were to be transported and installed during continuous rain.

  • Cellular glass gravel, cellular glass ballast or glass cellular granules - is there a difference ?

    The terms cellular glass gravel, cellular glass ballast or glass cellular granules mean the same material group. The names were freely selected by different manufacturers when finding a name of their products (mostly with common construction permit).

    A well-defined term in the sense of standardised name does not exist for these products. Today coarse, stress-broken cellular glass bulk materials are usually produced in the so-called dry-foaming process or wet-foaming process. There is no necessary correlation between the manufacturing process and the name.

    GLAPOR – cellular glass – granules comprise recycled sections of cellular glass boards and are used exclusively for performing tasks not related to approval such as light infills.

  • Foaming process, wet process or dry process - is there a difference ?

    Both the foaming processes are approved in construction and describe the physical state of foaming medium (liquid or solid).

    The wet foaming process that we use is a more technically demanding process. With this method, demonstrably better technical properties of the gravel products can be achieved.


  • Frost shield - Is it always to be design with 50 cm width ?

    No! The frost shield width depends on factors such as frost zone, soil class, cover with soil, etc. and is therefore determined depending on the application.

    The task of the so-called frost shield is to prevent a freezing by horizontal lateral projection of perimeter insulating material and thus freezing of the bearing building parts.

    A frost-free foundation for the building must be measured according to DIN EN ISO 13 793-4. A frost shield width of 50 cm as the sole specification is insufficient and represents only one specific case. The frost zone and thus to the depth of frost penetration at the objct site (information is given by the responsible civil engineering office), he soil class of the adjacent or covering soil, a certain minimum thickness of the frost shield (to prevent cold penetration) as well as the cover depth and the geometry of the frost shield must be taken into account.

    You will find a dimensioning aid under: Entries used: Compaction factor – is it possible to choose a higher (e.g. 1.6:1 or 2.0:1) or a lower compaction factor (1.1:1 or 1.2:1) in case of smaller loads in order to increase the load-bearing capacity of cellular glass gravel ?

  • Geotextile - Can you do without it ?


    The predominant task of (GLAPOR recommends a minimum quality of 150g/m²) is to prevent the penetration of fine parties of the adjacent soil during its usage time. If it is certain that this can be ruled out, the forgoing of geotextile is theoretically conceivable. This would be the case, for example, if an industrial building incorporates the material on an elevated, very firm surface between existing strip foundations.

    However, we still recommend the geotextile there as a separating layer for the individual layers and as clean edge finish for all applications, especially since its use does not present a problem from an economic point of view.

  • Underground pipes or supply and disposal pipes - can they be laid in the cellular glass gravel layer ?

    Actually, yes, although it is much more useful from a variety of perspective to lay the pipe systems underneath the insulating layer of cellular glass gravel.

    In principle, it should be avoided as far as possible to lay the pipe systems horizontally in the glass cellular gravel layer. If this is unavoidable because, for example, the necessary gradient up to the main collector is not sufficient or a deeper excavation is not possible for refurbishments, pipes can also be laid in the foam glass gravel. While doing so, it must be ensured that the pipe is fixed in its (vertical) position so that the necessary gradient is not impaired when compacting the foam glass gravel.

    The standard requires the pipe to be embedded in gravel sand, e.g. KG pipes. This can only be done successfully by completely coating the gravel bed in geotextile on cellular glass gravel, which has a very high processing cost. An alternative is special GLAPOR glass cellular boards, to which the pipe is fixed in its position reliably and without thermal bridges with a concrete bed.

    To avoid a load input, for example, of a floor board in the pipe, a minimum cover of the horizontal pipe must be provided in the size of the inner diameter of a pipe.

  • Potential equalisation and lightening protection - How do I secure this ?

    By using glass cellular gravel as a load-bearing element, the building actually stands on an isolator.

    To ensure lightening protection or potential equalisation, special measures must be taken.

  • Base board - Can it be dispensed with by using cellular glass gravel ?


    It is not possible to place building walls directly on compacted cellular glass gravel without appropriate foundation measures.

    Constructively, it would be possible to remove the building loads on strip or block or individual foundations and then overbuild the compacted cellular glass gravel layer inside only with a reinforced screed. However, this faces problems with regard to thermal bridging freedom, the freedom of design of building floor plans (variable positioning of partition walls) and general cost-effectiveness.

  • Inverted roofs - Can cellular glass gravel be used as an insulating material on inverted roofs ?

    No! Under building law, such a construction is inadmissible.

    Cellular glass gravel has the property of acting as a drainage layer. Therefore, rainwater can seep through the gravel layer almost unhindered and dissipate the heat from the realed building structure when draining. The thermal insulation effect would thus be severely limited. Under building law, such a construction is in any case inadmissible.