Ardex RA56 Rigid Polyurethane Crack Repair Adhesive

Description

ARDEX RA 56 is an ultra-low-viscosity, two-component hybrid polyurethane adhesive used to repair cracks and spalls in concrete where minimal downtime is critical. Its low viscosity lets it penetrate deep into hairline cracks to form a structural repair, and mixing it with dry bagged aggregate turns it into a spall repair mortar that is ready for grinding and open to traffic in under an hour. Manufactured by ARDEX Australia.

Two numbers explain where it is used. At 60 centipoise it flows into a crack that a conventional repair mortar cannot enter, and at 33.8 MPa compressive strength after one hour the repair is stronger than the slab around it before the shift is over. That combination is why it turns up on warehouse and factory floors that cannot be closed overnight. Also written ARDEX RA56.

Technical Specifications

Coverage varies with the depth of the fill area, so it cannot be quoted as a rate per square metre. Estimate from the crack or spall volume, remembering that at least 12 mm of product depth is needed on top of any backer rod or sand layer.

Where to Use

• Structural repair of hairline and fine cracks in concrete slabs
• Spall repairs from 12 mm to 75 mm deep, mixed with sand
• Warehouse, factory and industrial floors that cannot be taken out of service overnight
• Joint and crack rectification ahead of ARDEX waterproofing membranes
• Repairs that need to be ground flush and reopened to traffic within the hour

How to Apply

1. Prepare the substrate – old concrete must be clean, completely dry with no moisture present, and profiled or textured. New concrete must be at least 28 days old. Remove all dust, dirt, grease, wax and oil, mechanically roughening smooth surfaces with a wire brush or sandpaper. For spalls, cut the edges at 90 degrees to the surface with a dry diamond or tuck point blade – never feather them – and blow out all debris with compressed air or a vacuum.
2. Set up the cartridge – keep it upright to prevent leaking. Shake vigorously for 10 seconds and stand upright for 1 minute. Insert into a caulking gun, hold at a slight upward angle and dispense a small amount into a disposable container until both materials flow evenly. Fit the flow control and mixing nozzle, threading clockwise. Purge air bubbles by pointing the nozzle up, bringing product to the tip, then dispensing one full stroke at 45 degrees into a container.
3. Set up the bulk kit – have everything ready first. Pre-measure sand at approximately 2 parts to 1 part product by volume. Mix 50% of Part A with 50% of Part B using a small drill mixer at low speed for a maximum of 20 seconds, while a second person swiftly adds the pre-measured dry sand until the mortar is homogeneous and lump-free, scraping the bottom and sides of the pail. Mix no more than half the kit at a time.
4. Fill cracks – on horizontal slabs, place the mixing nozzle tip directly over the crack and inject, letting the adhesive penetrate and topping off as needed. Insert backer rods or a layer of sand in larger, deeper cracks, keeping at least 12 mm of product on top. Clean, dry, medium-grade sand can be broadcast over the finished repair to add texture matching the surrounding concrete.
5. Fill spalls – place mixed material within 5 minutes at 24 degrees C, sooner in warmer conditions. Pour and finish trowel immediately, and do not over-trowel – the product cures fast.
6. Finish – remove excess by scraping or levelling with a blade shortly after application. The crack surface may be ground smooth one hour after application, at which point the area can be reopened to traffic. Clean tools with white spirits, mineral turps or an aerosol dewatering agent before the product hardens.

Important Notes

• ARDEX RA 56 is moisture sensitive before cure – the substrate and environment must be completely dry. Once cured it can be exposed to moisture.
• Do not thin with solvents; this will prevent cure.
• Do not reuse mixing nozzles between cartridges, and never force adhesive through a hardened nozzle – fit a new one to avoid rupturing the set or mixing improperly. If a leak develops, stop and change to a new cartridge and nozzle.
• The cartridge is fully dispensed when the plunger reaches halfway.
• Where the work environment or substrate is below 21 degrees C, condition the product to 21-24 degrees C before use. Cold product cures more slowly.
• Colour changes during cure from black to light grey. In exterior applications the product may take on a greenish tint after cure from UV exposure; it can be painted or coated for appearance, but the cured surface must first be roughened and the dust wiped away, and a test area run to check compatibility.
• If a levelling compound is to be laid over the repair, broadcast clean dry sand into the wet surface or mix sand into the product before installing it in the crack.
• Adding aggregate may extend curing times.
• Shelf life is 12 months; if recapped and stored properly the product may be reused.

Frequently Asked Questions

How long before you can drive on an ARDEX RA 56 repair?

ARDEX RA 56 is ready for grinding and open to traffic in 1 hour. It gels in 2 to 3 minutes at 24 degrees C and is tack-free in 12 minutes, and the crack surface may be ground smooth one hour after application. Adding aggregate may extend curing times, and cold product cures more slowly.

Does the crack need to be opened up before applying ARDEX RA 56?

Usually not. Because the viscosity is only 60 centipoise, the adhesive penetrates hairline cracks without the crack being cut or widened. Opening it is only necessary where you suspect the crack is very deep and want to insert backer rods to stop product running away. The crack must be dry and clean – wire brush out loose concrete and dirt, then blow or vacuum away the dust. For larger, deeper cracks, insert backer rods or a layer of sand first, keeping at least 12 mm of product depth on top.

How do you use ARDEX RA 56 for a spall repair?

Mix it with clean, dry, medium-grade sand at approximately 2 parts sand to 1 part product by volume. Prepare the spall with a dry diamond or tuck point blade so the edges are at 90 degrees to the surface – a feathered edge leaves the concrete unprotected. Minimum spall depth is 12 mm and the maximum repair depth is 75 mm. Once mixed, the material must be placed within 5 minutes at 24 degrees C, so only mix what can be placed in that window, and pour and trowel immediately without over-trowelling.