Quick answer. H250CR PU binder uses an A:B mixing ratio of 2:1 by weight, followed by a nominal stone-to-mixed-binder ratio of 30:1. That equals 20 kg of Component A, 10 kg of Component B and 900 kg of clean aggregate for a representative batch. Preserve permeability by excluding fines, keeping the stone surface dry and placing each batch inside the verified working-time window.
For procurement teams, the ratio is only the starting point. Aggregate grading, moisture, batch temperature, mixer geometry, layer compaction and cure protection determine whether the finished surface drains water or develops foam, blocked pores and loose stones.
What the H250CR Mixing Ratios Mean in Production
The published H250CR two-component high-permeability PU glue data specify A:B = 2:1 by weight and stone:adhesive = 30:1. “Adhesive” in the second ratio means the combined mass of Components A and B after proportioning, not the mass of either component alone.
At 30:1, mixed binder equals 3.33% of dry aggregate mass. Expressed as a share of the complete stone-and-binder mixture, it is 1 ÷ 31, or approximately 3.23%.
| Dry aggregate | Mixed H250CR binder at 30:1 | Component A at 2:1 | Component B at 2:1 | Total placed mixture |
|---|---|---|---|---|
| 300 kg | 10.00 kg | 6.67 kg | 3.33 kg | 310.00 kg |
| 600 kg | 20.00 kg | 13.33 kg | 6.67 kg | 620.00 kg |
| 900 kg | 30.00 kg | 20.00 kg | 10.00 kg | 930.00 kg |
| 1,200 kg | 40.00 kg | 26.67 kg | 13.33 kg | 1,240.00 kg |
Use calibrated scales rather than pails, drum counts or visual estimates. The published densities differ: Component A is 1.00 ± 0.10 g/cm³ and Component B is 1.20 ± 0.10 g/cm³. A 2:1 volume ratio would therefore produce a different reactive balance from the required 2:1 mass ratio.
The current product page lists 10 kg packaging for both components while also specifying A:B = 2:1. A buyer should therefore confirm the net fill weight and kit configuration on the quotation, pro forma invoice and packing list. Equal drum counts must never be treated as proof of a correctly proportioned kit.
The nominal 30:1 permeable stone binder ratio is a production baseline, not permission to change binder loading without testing. At 28:1, binder consumption rises to 35.7 kg per 1,000 kg of stone; at 32:1, it falls to 31.25 kg. That 4.46 kg difference can alter film thickness, pore bridging and resistance to stone loss.
Run a three-point aggregate trial before ordering project volume
Screen the actual local stone and test 28:1, 30:1 and 32:1 stone:binder ratios. Produce panels at the intended layer thickness using the same mixer, trowel release method and compaction pressure planned for the site.
Record mixed-batch mass, mixing duration, placement time, ambient temperature and aggregate temperature. Reject a ratio that leaves visible pools at the base, seals connected pores or releases aggregate under the project’s abrasion and traffic simulation, even if its neat-resin laboratory values appear acceptable.
Aggregate Grading Controls Permeability More Than Extra Binder
A polyurethane pebble binder forms a film around stone contact points. Water still needs a connected path between particles, so a continuous distribution of dust, sand and small chips can fill the voids even when the resin itself cures correctly.
Washed, narrowly graded aggregate is the normal starting material. Example screening bands such as 2–4 mm, 3–5 mm or 4–6 mm can be evaluated, but they are trial ranges rather than H250CR specifications. Particle shape, absorption, packing density and required traffic load must be tested with the locally sourced mineral.
Document grading by sieve analysis instead of accepting a supplier description such as “3–5 mm decorative stone.” A shipment can satisfy a nominal label while containing enough sub-size material to reduce interconnected voids. Record the retained mass on every relevant sieve and set contractual limits after the approved trial.
Permeability cannot be purchased as a binder value alone. The U.S. EPA describes permeable pavements as complete systems in which water passes through the surface into an open-graded bedding or base layer that can temporarily store runoff. Its permeable pavement guidance also identifies sediment accumulation and unsuitable site conditions as system-level concerns.
A permeable H250CR surface installed over an impermeable slab without drainage openings will still retain water. The buyer’s specification should therefore separate four acceptance points: surface infiltration, bedding permeability, reservoir capacity and subgrade drainage or underdrain discharge.
Measure the installed surface, not a loose stone sample
ASTM C1701/C1701M-17a(2023) measures the field infiltration rate of in-place pervious concrete. H250CR resin-bound stone is not Portland-cement pervious concrete, so any use of the ring method should be written as a project-approved modified procedure rather than a claim of automatic ASTM conformity.
The ASTM page states that a result represents only the tested location and that several locations must be averaged to characterize a pavement. Apply that principle to resin-bound work: agree on the number of test points, conditioning state, water head, reporting unit and minimum result before shipment or installation.
Keep a baseline reading after full cure and repeat measurements at the same marked locations. A falling infiltration rate may indicate sediment loading, pore bridging by excess resin or contamination during adjacent construction. Surface washing cannot correct a sealed lower interface, so cores may be needed to locate the obstruction.
| Observed condition | Probable mechanism | Evidence to collect | Corrective decision |
|---|---|---|---|
| Resin pools below the layer | Excess binder, slow placement or low-viscosity drainage | Batch ratio, aggregate temperature, placement time and cross-section | Reduce batch size; repeat ratio trial; do not dilute the binder |
| Water ponds on the surface | Fines, excessive compaction or blocked base | Sieve report, infiltration map and core inspection | Identify the blocked layer before cleaning or replacement |
| Loose stones after cure | Low binder coverage, dusty stone or off-ratio A:B mixing | Scale records, retained aggregate and cured witness panel | Quarantine the batch and test adhesion before traffic release |
| Foam or white bubbles around contacts | Moisture reacting with the isocyanate side | Aggregate moisture result, dew-point log and opened-drum history | Stop placement, dry the aggregate and protect open containers |
Moisture, Pot Life and Cure Must Be Controlled as One Process
The H250CR technical data report Component A viscosity of 3,500 ± 100 mPa·s, Component B viscosity of 210 ± 50 mPa·s, 95% solids and a 15-minute pot life measured on a 100 g sample. The stated mixing time is 1–2 minutes.
A 100 g laboratory pot-life value does not guarantee 15 minutes in a larger bucket. Polyurethane reaction heat is retained more readily in a deep mass, while higher material and ambient temperatures accelerate reaction. The site method statement should establish a smaller operational discharge limit through a witnessed trial.
As an initial production rule, plan to mix, discharge and finish within about two-thirds of the verified working window. If a crew can place 150 kg of total mixture in 10 minutes, that batch contains approximately 145.16 kg of stone and 4.84 kg of mixed binder: 3.23 kg A plus 1.61 kg B.
Do not add solvent to restore flow after viscosity rises. Dilution changes film build, reactive balance and emissions while failing to reverse polymer formation. Expired material should be isolated according to the SDS and local waste rules.
Control aggregate and substrate moisture
Water can react with isocyanate groups and generate carbon dioxide. In a pebble-bound layer, the resulting bubbles interrupt the resin film and may leave porous, pale or weak contact bridges.
Check aggregate moisture by a documented drying procedure. ASTM C566 covers total evaporable moisture in aggregate by drying and explains that the result includes surface moisture and moisture in accessible pores. Use the current project-specified edition and establish an acceptance limit from H250CR trials because the public product data do not publish a universal moisture percentage.
A clean-looking stone pile can still regain moisture overnight. Store aggregate under cover, off the ground and away from wash areas. Record the stone temperature, moisture result, air temperature, relative humidity and substrate temperature immediately before batching.
Check the substrate against dew point rather than relying on touch. Condensation can form on a cooler base even while the surrounding air appears dry. The project engineer should define the minimum substrate-to-dew-point margin and the response to rain, fog or falling evening temperature.
Separate cure stages from traffic release
Published H250CR values identify initial cure at 3 hours, basic cure at 24 hours and final cure at 7 days. The operating instructions also give an 8–36 hour cure range depending on temperature; this broader window reflects field exposure rather than a universal release time.
Do not translate “initial cure” into permission for pedestrian or vehicle traffic. Release criteria should name the minimum elapsed time, surface condition, ambient history and any witness-panel result. Protect the area from rain, dust, leaves, irrigation and turning vehicle loads until acceptance.
The published cured-material values are Shore D 70 ± 5, tensile strength 15 MPa and tear strength 50 N/mm. These characterize the cured polymer under its test conditions; they do not establish pavement compressive capacity, wheel-load classification or substrate adequacy.
Procurement and Factory Qualification for H250CR
Manufacturer-direct purchasing provides access to batch records and application adjustments, but every requested change must be validated against the 2:1 reaction ratio and the approved aggregate system. A longer pot life, lower viscosity or different color can affect cure rate, drainage and UV appearance.
Issue the request for quotation with the project area, layer thickness, stone type, grading curve, aggregate bulk density, expected temperature range, traffic class, mixing equipment and target shipment date. Without those inputs, comparing quotations by price per tonne hides differences in binder consumption and installation risk.
Request a matched-component sample and test it with the project stone. The pre-shipment control plan should record appearance, component viscosity, density, mix ratio, pot-life method, cure schedule and retained-sample identification. Batch values should be compared with the approved technical limits rather than a sales description.
Ask for the current TDS and SDS before the trial. OSHA explains that isocyanates used in polyurethane production can irritate the skin and respiratory tract and can cause occupational asthma; its isocyanates guidance directs employers toward exposure evaluation and controls. PPE, ventilation, spill response and waste handling must follow the supplied SDS and local regulations.
Do not assume a regulatory certificate from a product family applies to H250CR. For an EU order, request a formulation-specific compliance statement and supporting documents for the destination and use. For other markets, name the required chemical inventory, labeling, VOC or construction-product documents in the purchase contract.
The public H250CR page does not state an MOQ or export lead time. Obtain both figures in writing, together with shelf life at dispatch, manufacturing date, shipping temperature limits and the permitted remaining shelf life on arrival. The published storage period is one year under general indoor warehouse conditions, so a buyer should contract for traceable batch dates rather than accept an undated stock statement.
A manufacturer-direct approval package should contain the signed specification, golden sample, aggregate trial report, batch coding format, certificate-of-analysis fields, packaging configuration and change-notification requirement. This creates measurable acceptance criteria if raw materials, viscosity targets or drum fills change during repeat orders.
- Confirm A:B = 2:1 by mass on the order and site batch sheet.
- Confirm that stone:binder = 30:1 refers to dry stone and combined binder.
- Resolve the component packaging configuration before calculating container quantities.
- Approve permeability and stone-retention results using the buyer’s actual aggregate.
- Keep unopened and opened-drum storage rules in the installation method statement.
- Require written approval before any formula, raw-material or packaging change.
FAQ
Q: What is the correct H250CR permeable stone binder ratio?
The published ratio is 30 parts dry stone to 1 part combined H250CR binder by weight. The binder itself is prepared at 2 parts Component A to 1 part Component B by weight.
Q: How much H250CR is needed for one tonne of aggregate?
At 30:1, 1,000 kg of dry aggregate requires 33.33 kg of mixed binder. That mixed binder contains approximately 22.22 kg of Component A and 11.11 kg of Component B.
Q: Can the binder ratio be reduced to improve permeability?
A lower binder dose may leave contact points under-coated and increase raveling. Test a controlled series around the nominal 30:1 ratio and accept a result only after measuring infiltration, cure and aggregate retention on the project stone.
Q: Why did a permeable stone surface foam during curing?
Aggregate moisture, substrate condensation or moisture entering an opened component container can react with the isocyanate side and release carbon dioxide. Check moisture records, dew point, drum sealing and batch timing before changing the formulation.
Q: Is the 15-minute pot life the guaranteed installation time?
No. The published 15 minutes is based on a 100 g sample. Larger batch mass, a deep mixing vessel and higher temperatures can shorten the usable window, so contractors must validate batch size and discharge time under site conditions.
Q: When can traffic be allowed on H250CR paving?
The data list initial cure at 3 hours, basic cure at 24 hours and final cure at 7 days, while field cure may range from 8 to 36 hours with temperature. The project specification must define traffic release; initial set alone is insufficient evidence.
Q: Does H250CR automatically make an impermeable concrete base drain?
No. The resin-bound surface, bedding, stone reservoir, subgrade and any underdrain must function as one drainage system. A sealed base needs engineered outlets or another approved drainage design.