Ronabond HB25 – Pre-packed lightweight concrete repair mortar
Ronabond HB25 – Pre-packed lightweight concrete repair mortar. RonaBond HB25 is a prepacked mortar used for repairing concrete on vertical and overhead surfaces where ease of application is as important as high strength. It can be applied in relatively thick sections to walls and soffits and, depending on the nature of the repair, in layers up to 75mm deep in pocket repairs. RonaBond HB25 is supplied prepacked requiring only the addition of water. The cured mortar bonds well to concrete, steel and other building surfaces. It offers long term performance and protection to structures.
Ronabond HB25 – Pre-packed lightweight concrete repair mortar can be used in most weather conditions and at air, material and substrate temperatures between +3°C and +25°C. At high ambient and material temperature, the working time of the mix will be reduced; it will be increased at lower temperatures.
Preparation of concrete and steel
All concrete identified for removal must be removed back to a suitable substrate that is sound and stable and which will accept the repair mortar.
Reinforcing steel in the repair area must be exposed, and concrete cut back along the length of the steel to expose clean uncorroded steel. Loose rust and scale must be removed. Cut around the periphery of spalled areas to a minimum depth of 6mm at 90 to avoid dished edges and feather-edged repairs.
The concrete must be removed to allow no less that 15mm of repair mortar to be placed around the steel. Corroded steel must be replaced where necessary.
All removal of concrete and steel must be carried out in accordance with the specifiers’ recommendations. When repairing chloride contaminated concrete the method used to prepare and prime surfaces may differ and the Ronacrete Technical Department should be consulted.
All surfaces must be cleaned to remove loose dust, debris and surface contamination which may prevent adhesion of the repair mortar to concrete and steel. Surfaces to be rendered must be cleaned and mechanically abraded to provide a key.
Damping and priming
Following the preparation of concrete and steel, thoroughly damp all concrete surfaces to be repaired with clean, potable water. Remove any standing water. Brush and apply Ronacrete Standard Primer as appropriate to the steel and allow to become tacky, not dry. When the priming coat on steel is tacky, brush a single coat of the same primer on to the damp concrete and a second coat on to the steel. Ensure that the first priming coat applied to the steel is not removed during the application of the second coat.
RonaBond HB25 must be mixed mechanically in a forced action mixer (e.g. Creteangle pan mixer) or using a slow speed drill (typically 500 rpm) with a paddle attachment (do not use a free fall mixer).
Pour the dry powder in to a mixing vessel containing approximately 2.8 litres (but not more than 3.0 litres) of clean potable water. Mix to produce an even consistency to suit the requirements of the applicator. Generally a drier mix can be applied in thicker layers; a wetter mix can be used to achieve a smoother finish.
Use complete packs to ensure consistency, uniform dispersion of pack contents and accuracy of powder:water ratio. To avoid a false set in warm working conditions store materials in the shade and use cool water.
Ronabond HB25 – Pre-packed lightweight concrete repair mortar must be applied on to the wet or tacky primer before the primer dries. If the primer dries it must be thoroughly scarified and reapplied. Apply the mortar in layers to achieve the required thickness and to reform the original profile of the concrete and cover reinforcing steel. Layer thickness will vary according to the shape and size of the repair, the nature of the substrate and the mixing and application technique. Application techniques include hand packing the mortar on to the surface; this method allows faster build up and the ability to feel that the mortar has been packed around and behind reinforcing steel.
When applying multiple layers to achieve the total depth these can be built up monolithically (wet-on-wet) or after previous layers have firmed up. Keying and priming (with Ronacrete Standard Primer) between hardened layers is necessary to ensure total adhesion through the repair. Finish the repair with a wood float, steel trowel or leave with a sponged finish as required. If applying a protective or decorative coating, leave the final layer with a sponged or float finish to aid adhesion.
Cure with Ronacrete Curing Membrane or tight fitting polythene as soon as possible and as quickly as is practical to prevent rapid and excessive early moisture loss and minimise the risk of resultant cracking and crazing. Curing is more important when working in direct heat, sunlight, in a drying breeze or wind, or a combination of these. Note that maximum application depth per layer is dependent on the size and profile of the repair or render area, the consistency of the mortar and the skill and technique of the applicator. It is not always possible to achieve high build application, especially when working on larger areas.
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