Density of Concrete
The following are the types of concrete used in construction with their acceptability to receive the Parabit Duo Hot Melt System:
- In-situ Concrete: Structural concrete will have a density of 2,160 kg/m³ to 2,500 kg/m³ and will retain 3 to 5% moisture by volume when cured. Concrete with high moisture content requires a minimum curing period of 28 days to ensure adequate drying.
Low density concrete (less than 1,850 kg/m³) will create adhesion difficulties due to the friable / dusty nature of the surface.
- Precast Concrete: Where the pre-cast concrete units provide a smooth and level surface, the joints between the units can be
grouted in readiness to receive the specified PARABIT Hot Melt system. Joints should be locally reinforced using a strip of the
PARABIT SOLO Angle Reinforcing Strip embedded into the PARABIT Hot Melt Compound. Where the surface of the units are
not acceptable, a structural concrete layer above the pre-cast units will be required.
- Concrete Block: For vertical applications, concrete block is acceptable. Joints should be flush pointed. A strip of the PARABIT
SOLO Angle Reinforcing Strip should be installed into the 90°angle using PARABIT Hot Melt Compound.
- Lightweight Structural Concretes are considered acceptable substrates when the density is between 1400 kg/m³ and 1800 kg/m³; retaining 5% to 20% moisture when cured.
- Lightweight Insulating Concretes are not acceptable substrates.
The concrete surfaces shall be of sound structural grade, and shall have a wood float or fine broom finish, free of fins, ridges, voids or entrained air holes. A steel trowelled finish or shiny surface is not acceptable. All knots and dust must be removed.
Laitance: Loose concrete towards the surface of the concrete must be removed.
Concrete shall be cured by water curing method. Pure sodium silicate curing compounds are acceptable.
Contamination: All contaminants must be properly cleaned before application of the Parabit Hot Melt System can commence.
Concrete shall be cured for a min. 28 days.
Voids, rock pockets and excessively rough surfaces shall be repaired with approved non-shrink grout or ground to match the un-repaired areas.
Form Release Agents used to facilitate removal of formwork from cast concrete can be transferred to the face of the concrete once the formwork has been struck. Such agents can detrimentally affect the adhesion of the monolithic membrane. As a result all agents transferred to concrete must be removed prior to application of the membrane. Furthermore, accelerators within the concrete can migrate to the surface leaving a shiny surface. These should be removed.
Two-stage drains shall have a minimum 75mm flange and be installed with the flange flush and level with the concrete surface.
- Plywood: All plywood substrates should be in accordance with BS EN 636, BS 5268-2 & BS EN 13986. All interlocking board joints should be locally reinforced using a strip of the PARABIT Angle Reinforcing Strip embedded into the PARABIT Hot Melt Compound.
Before the Parabit Hot Melt Membrane is installed an adhesion test must be conducted to ascertain the suitability of the concrete surface. Bond tests are advised to the area to be coated that day prior to the main application.
To complete the bond test, apply a small amount of primer to the cleaned and prepared area and allow to dry. Apply a small amount of the PARABIT SOLO Hot Melt Membrane and allow it to cool and embed a prepared section of Power Elastomeric 250 Sanded membrane into the hot compound, leaving an overhang of membrane to facilitate the pull test. If it is not possible to separate the hot melt sample from the substrate (resulting in destruction of the membrane), the adhesion is considered satisfactory. If the membrane can be easily peeled away from the deck, then the substrate is not ready and may require further preparation works.
If the test patch is acceptable, protect the patch until the main area material is to be applied. The test material will re-act with the new material maintaining a monolithic membrane.
|Example 1: Successful bond test
||Example 2: Unsuccessful bond test
Common reasons for peel test failures:
- Surface laitance – loose, friable surface concrete that will require mechanical removal
- Damp substrate – wet concrete will impede adhesion. Efforts should be made to reduce the retained volumes of water within the slab. A high penetrating primer (eg. Siplast Primer) may also be required.
- Damp substrate – evaporation from moisture retained within the concrete slab can lead to peel test failure and blistering. A high penetrating primer (eg. Siplast Primer) may also be required.
- Surface contamination – dirt, debris, dust curing agents, form release agents can all impede membrane adhesion. All should be removed prior to repeating test.
- Smooth surface finish – power floated concrete finishes will be too smooth and will require mechanical scabbling.
- Primer – the primer should be allowed to dry naturally. Do not attempt to dry the primer using gas torches.
Prime all areas to receive the Parabit Duo or Solo Hot Melt System using Icopal Siplast Primer and allow to dry. Apply a thin coat and avoid pooling. Allow to dry thoroughly before over coating.
The primer should be applied to the prepared concrete surface by brush or roller at an approximate coverage rate of 0.25 L/m² (coverage rate will vary subject to substrate porosity).
Drying time for the primed surface will be 1 to 3 hours dependent upon ambient conditions and substrate porosity.