Tech Help

Website Introduction to Technical Help

This is our Technical Help Page where commonly asked questions are included with links to the Reference RMS Specification R178 Revegetation which is the Industry Standard Specification.

You are free to use this facility to help you to understand what the Hydromulch process is all about by reference to the Specification, RMS technical Notes, and/or Works Completed in accordance with specification requirements.

There are no systems in place to record your enquiry or use of the website information which would result in a contact by us to promote a sale.

All materials used in the process have been proven in use over the last 30 years or so and are freely available from commercial outlets.

There are no special materials only available from restricted manufacturers or suppliers of materials which do not have full SDS and conformance certification. Valley Hydramulch are not material manufacturers or suppliers, all materials used in specification conforming applications are freely available from various commercial outlets.

Answers to Typical Questions are based on:

  • The Reference Specification RMS NSW R178 – Revegetation
  • RMS Guideline for Batter Surface Stabilisation April 2015
  • VHR Works in compliance with the above and approved by RMS NSW since 2005

Questions and Responses

1. What Technical details or Specifications of the Hydromulch Process are available for reference?

See Introduction to Technical Help.

2. Is Hydroseeding the same as Hydromulching?

RMS R178–General 1.3 Definitions, Table R178.1 Application Rates for Materials,

Hydroseeding is an application which includes grass seed, fertiliser, green dye and water and is usually used for temporary revegetation of soil stockpiles to produce a temporary grass cover for mid term erosion protection until stockpiles are reused in the works

Hydromulching is hydroseeding with the addition of a cellulose fibre and binder.

Additional fertilisers can be added to this mix following testing in accordance with clauses 2.1 and 2.1.1 of R178 August 2018

3. How does Hydromulching Work?

RMS R178 Cl 3.4.3 – Hydromulching and Hydroseeding

Success with Hydromulching is not due to black magic or some force from a galaxy far far away. It is based on RMS experience over many decades of roadworks, agricultural practices which have been adapted for rehabilitation works and plain common sense.

Successful hydromulching is easily achieved by working backwards from the desired end result in order to determine the application requirements.

What you need for initial and long term germination and growth is;

  • An Adequate Seed Bed
  • Nutrition
  • Suitable Seed Varieties
  • Moisture
  • Sunlight

Seed Bed – RMS R178 – Cl 1.5 Personnel;

Cl 2.1.1 Topsoil from Site;

Cl 3.1.2 Slopes;

Cl 3.2 Topsoiling

Must be able to retain seed and moisture. For example, if the soil and preparation is not adequate for direct laying of turf, Hydromulching will not give you the same result as turf laid on and adequate seed bed.

Nutrition – RMS R178 – Cl 1.5 Personnel;

Cl 2.1.1 Topsoil from Site;

Sufficient nutrition needs to be available for initial germination, short term growth of cover crop grasses, as well as for germination and the long term growth of perennial grasses and native plants. Again, if the soil does not have enough nutrition to produce healthy plants, it will not produce a successful result. The soil requires amelioration and a loose, furrowed surface preparation.

Seed Varieties – RMS R178

Cl 2.3 Seed;

Table R 178.1 Application Rates for Materials;

Proven in local area and sown in sufficient quantity to provide for short and long term requirements.

Moisture – RMS R178

Cl 1.4 Timing of Work (c) Note at end;

Cl 8 Maintenance

Sufficient nutrients available for short and long term growth. The role of the very fine softwood cellulose fibre used on RMS works for many decades up to about ten years ago was to form a paste on the surface to hold the seed and additives in contact with the ground and take advantage of the fact that the fine softwood could absorb up to ten times its mass of rain water received and then release it over a longer period to assist in germination and plant growth. In the last decade introduction of sugarcane mulch and finely chopped straw as the cellulose fibre for hydromulching resulted in this loss of this water storage capacity because the coarser cellulose fibres were hydrophobic, that is, they were unable to absorb and store rainwater.

There is also a problem on construction sites where the amount of water required to initiate germination and ensure long-term growth is usually not available and also impractical to apply.

If artificial watering is used to achieve initial germination, what usually happens is that once the artificial watering ceases, plants dieback as they have become “soft” and unable to survive in a harsh climate.

The amount of water required can be calculated using basic agricultural principles and the following link contains a basic spreadsheet calculation of the amount of water required based on expected rainfall and soil types and conditions.

Water requirement in warmer seasons is usually somewhere between 15 and 50 mm per week. For 100,000 sq. m of application the water requirement is somewhere between 1.5 million and 5 million litres per week.

Also the rate of application of this water has to be controlled to prevent surface wash-off and allow time for absorption into the surface. As a result, fine sprays are specified which dramatically increase the time and cost of the application.

Water carts cannot be used as this usually requires tracking over the surface application which destroys the application and causes compaction of the surface and retarding of germination process.

The RMS specification under Clause 8 Maintenance requires that revegetated areas are to be maintained “for 12 months after all sowing is complete or until the actual contract completion, whichever occurs first.” And also to “water areas where and when directed by the principal. Water by means of a fine spray which causes minimal disturbance to seeded areas.”

The control processes required are as follows;

Seed Bed

  • must be deep enough to have a measurable storage capacity,
  • be porous enough to absorb rainfall and
  • be not compacted

All to comply with RMS 178 Clause 3.2.


  • The topsoil should be tested using an NATA accredited testing laboratory to ascertain its suitability for use in revegetation…….. And to determine soil amelioration requirements (if any).

Soil testing to RMS Cl 2.1.1 will ensure adequate nutrition for the short and long-term requirements of the proposed revegetation program.

Seed Varieties

  • Must have proven success rates in the site soils and climate and so should be site-specific based on local knowledge.
  • Must be commercially available at relatively short notice in sufficient quantities for the project.
  • Must include quick germinating, colonising species to maintain surface cover until natural regeneration of the indigenous varieties not available for collection at the time of the works.


  • Seedbed preparation, surface preparation with furrows aligned with the contours are all specified to ensure maximum capture of rainwater and absorption into the soil surface.

Sunlight – Required for Photosynthesis.

  • Sunlight cannot be controlled.

Considering that each has an equal role, and that Moisture and Sunlight cannot be regulated, the other 60% of the limiting factors have to be managed to make up for the 40% that cannot be controlled.

4. How much does it cost?

The Cheapest Cost to get the Required Result is the Cost to do the Application the Right Way the First Time

Cost will depend on type of soils, quality of soils, type of long term cover required, location, area to be treated etc.

5. What surface preparation is required to ensure a good result?

See 3. How does Hydromulching Work? Above.

6. Why does Hydromulch sometimes germinate quickly, establish a reasonable ground cover of emerging grasses and when the grasses grow to about 75 to 100 mm then go yellow at the tips then die back and weeds proliferate in the exposed soil surface?

Grasses and plants will usually germinate when flooded with water and spread roots into the surrounding soil to get the nutrition required for ongoing growth once the nutrition in the seed hull is exhausted. If insufficient nutrition is available in the soil the plant will yellow off and die.

7. What type of grasses are used in Hydromulch and why does the grass germinate and grow so quickly?

Annual grass varieties, which only grow once and do not regenerate from seed heads, are referred to as sterile grasses and are cereal crops with summer and winter varieties.

Perennial grasses are long-term grasses which regenerate from roots in the ground after die-back or heavy grazing.

Annual grasses germinate quickly to provide erosion prior control and act as a nursemaid grass for the merging perennial varieties provided that there is sufficient nutrition in the soils for short and long-term germination and growth.

8. How often does the application have to be watered?

A standard Hydromulch Application to RMS R178 on ideal soil, with good preparation, would not have to be watered. Rainfall will induce germination and growth.

Ideal soils are very, very rare.

9. If no water is carried out how long does the application remain viable?

A standard Hydromulch Application to RMS R178 on ideal soil would remain viable for several months at least and then respond to adequate rainfall.

Again, Ideal soils are very, very rare.

10. What stops the application from being washed off the service during heavy rain?

A batter chain or implement which will produce furrows which follow the contours will collect the rainfall in the furrows and it will be absorbed to the depth of the loose surface.

If the application consists of microfine to very fine ingredients they will all be washed into the surface and grasses will germinate.

11. What type of glues or binders are used in the application and for how long are they effective?

Bitumen Emulsion was used as the binder when hydromulching was first introduced to Australia in the 1950’s.  This was a messy operation with adverse environmental effects, and frequent severe blockages when the emulsion reacted with the ingredients in the application and coagulated. Hammer milled newsprint was used as an alternative to wood fibre and the cellulose in the paper provided the binding effect. Use of paper alone was discarded as the resultant Paper-Mache surface was impervious and tended to shed rainfall. Wood fibre/paper mixes were used but the paper content had to be increased on slopes to be an effective binder and impervious surfaces resulted.

Guar gum was introduced about fifteen years ago when available binders were not proving to be satisfactory. This was the preferred binder until about four years ago when crop failures restricted availability and as guar gum had been introduced as a drilling agent in the mining industry prices increased dramatically and the mining industry absorbed most of the available supplies.

Recently Polyacrylamide binders have been widely approved for use in hydromulching and have proven successful when the finer wood fibre cellulose fibre is utilised because as they are re-wettable and the binder loses its adhesion when re-wet, this allows microfine and very fine ingredients to be absorbed into the soil layer. The wood fibre is also absorbed and increase the organic matter in the soil layer.

When the heavier sugar cane and chopped straw cellulose fibre is used, especially in heavy layers, the binder becomes ineffective when re-wet and the heavy cellulose fibre tends to wash off the slopes or float away on the flat areas as the fibres are hydrophobic.

12. What Degree of surface cover should I expect initially in the longer term?

Long term surface cover development depends on the amount of long-term nutrition available in the soil, and as there are really no slow release fertilisers available which extend out more than about 6 months there must be some mechanism to provide additional nutrition in the longer term.

This is achieved when applications contain large amounts of calcium, gypsum and fine organic compost to AS 4454 “Composts, Soil Conditioners and Mulches” as these combine to work their way down through the soil layer releasing nutrients locked in the untreated soils and the microbiological action of the compost encourages root growth and take-up of these nutrients.

The appropriate soil test, not a grading test or a standard agricultural test for pH will identify these “exchangeable” nutrients by type and quantity and the application can be designed to suit.

The standard RMS hydromulch mix as applied has low sort term nutrient levels as it is the basic mix to which the ameliorants determined by soil testing are added to become a site specific mix. There is no standard mix which could be expected to be successful on all soils in all locations across the State.

See 6. Why does … Failure of the cover crop allows weeds to predominate as weed seed is present in most topsoils and in accordance with the r-k theory poorer classes predominate in poorer environments, better classes predominate in better environments.

13. How do I know that the application will be effective and produce the result required?

As with any commercial arrangement, if you are not an expert in the particular field you either attempt to become an expert or rely on what is supposedly expert advice to obtain the results you require. This then becomes a matter of trust between the parties involved and this trust should be enforced by references and details of similar completed works over a long period of time with large variations in area treated and climatic conditions. The applications and the application processes should conform with some industry standard specification so that both parties can be assured best practice methods have been adopted.

Documentation or statements submitted to support the viability of the applications should have independent technical backup to confirm compliance with industry standards, and care should be exercised when publications and website information relates more to the short-term application process showing a green dyed surface immediately after application rather than long-term results showing dense perennial growth after several years.

If long term successful results cannot be demonstrated and only details immediately after application are provided, it is almost always because the results do not follow the hyperbole of the product brochures.

14. How do I decide on a preferred subcontractor?

You have to go through the usual commercial process which means that you trust the subcontractor to give you value for money and produce the result you require with a minimum of fuss. The legitimacy of the application can be checked by confirming the correct weights of materials are applied to a subcontractor supplied confirmation of the rates per hectare of the various materials and the amount of area covered in each load.

This is something a reputable and reliable contractor would supply without being asked and they would be quite happy to explain how you can be sure that the correct amounts of materials are being included in the loads.

If you are uneasy about the arrangements and have doubts that you are going to get the results you want you should seek independent expert advice prior to the work being carried out to avoid lengthy litigation post completion.

15. What should I expect from the application?

You should expect that the subcontractor will give you written confirmation of the ingredients in the application, advise you what your responsibilities are post application for a good result, a timeline of what you should expect and confirmation of what process would be adopted in the event of a dispute.

These items are usually included in a basic subcontract agreement and can be filled out by both parties and will avoid acrimony and costly litigation after the works are completed.

16. What are the indicators of an inferior application?

Before you received a tender for the works, you and the subcontractor should have discussed and agreed on what would be considered to be a successful result and also any latent or unforeseen conditions or circumstances which would affect the result.

17. How do I control weeds in the surface cover and longer term perennial grass cover or native plant cover?

The agreed application should make provision for availability of long-term nutrition to carry through at least to the time between the haying off of the annual cover crop grasses and the establishment of the perennial grasses and plants. It is difficult to impossible to selectively poison weeds out of a developing revegetated area and there are numerous publications confirming that competition with introduced grasses and plants the best form of weed control.

18. What conditions were subcontractor have in the tender for the works?

Refer to 3. How does Hydromulching Work?

The normal agricultural process to produce a viable crop to;

  • Poison any weed growth on the surface;
  • Deep rip the area to about 600 mm depth to produce a porous layer to absorb moisture deep into the soil;
  • Rotary hoe the area to a depth of 100 to 150 mm to provide a porous topsoil layer which will absorb and store moisture and nutrients;
  • Sow the seed with fertilisers and ameliorants by either by vicon spreader and harrows or seed drill;
  • Lightly roll the surface to assist in setting of seed.
  • Water area by irrigation with fine sprays until crop develops and become self-sufficient.

These operations are not practical or affordable on a construction site so an alternative method had to be developed and from this the idea of hydromulch originated. Over the years the Hydromulch application was developed to compensate for the parts of the above process which were either impractical or too expensive on batters and difficult to access areas common on construction sites. It was recognised early in the development of R 178 Specification that the condition of site soils encountered was predominantly unsuitable for a successful revegetation operation so a provision for soil testing was introduced along with requirements for seed bed and surface preparation. Deficiencies in subgrade soils were recognised and requirements for amelioration of subgrade were introduced which, to be effective required that the ameliorants had to be worked into the subgrade surface. This proved to be difficult on steep slopes so and spreading of the ameliorants, usually lime and/or gypsum was done by hand on the subgrade surface. Working lime and/or gypsum into the subgrade surface created an additional problem of excess loose material on batters which when saturated tended to slip off the batter and take the topsoil layer and Hydromulch application with it.

The best results are obtained if the subgrade surface is lightly scarified prior to topsoil application then the untreated site topsoil is spread and trimmed on batters with the finished surface having horizontal furrows aligned with the contours in a loose seed bed. The subgrade and topsoil ameliorants required following soil testing are then included in the Hydromulch application and applied to the topsoil surface.

Results obtained since introduction of these methods in 2005 indicate healthy short-term development of cover crop and perennial grasses, long term development of introduced native plants and effective weed control due to outcompeting of weeds which normally develop from the weed seed present in all site soils.

If this is not what the contractor has agreed will be provided, you should get his confirmation that his application will produce the same result