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Resin Bound Knowledge Base

Resin Bound Knowledge Base

Frequently Asked Questions

● Some resin systems are a FeRFA compliant 7.5kg size?


Suppliers claiming to sell FeRFA compliant systems are not members of FeRFA and FeRFA do not suggest that any system is compliant with their guidance notes. The FeRFA resin bound guidance notes are designed to promote best practice. Star Uretech are founding members of the FeRFA Resin Bound Technical committee and the guidance from FeRFA is that whilst a 7.5kg kit is desirable (this is to prevent low quality resin being used in low quantities) each manufacturer’s guidance should be followed. StarScape ULTRA is sold in a 6.5kg kit size and is significantly stronger than many systems sold in 7.5kg kits. Several years of testing have confirmed the optimum level for StarScape ULTRA is 6.5kg with 7.5kg offering no benefits in physical properties. High performance systems formulated by skilled polyurethane chemists, using the very best raw materials do not benefit from additional resin content whilst low quality or poorly formulated systems require more resin content.

● White spirit or WD40 should be used to clean mixers.



The high level of C7 hydrocarbons in WD40 make it incompatible with polyurethanes and the less volatile, variable contents of generic ‘off-the-shelf’ white spirit are not suitable for use with an aliphatic resin system. Any products used to clean mixers, tools or as a trowel lubricant should be sufficiently volatile as to leave no oily residue after 30 minutes. We only advise the use of a products containing C9 aromatics such as StarScape SOLVENT.

● A resin bound surface will be completely smooth, flat and level.


As with any surface application there can be a lot of confusion regarding the terms flat, smooth and level. Should a resin bound surface should be specified as flat, smooth or level. As with any non-self-levelling screed surface, a degree of imperfection is inevitable but what is the difference between expected imperfection and a poor installation?

If we look in various dictionaries, smooth, flat and level can have almost the same meaning which can be confusing. 

Smooth:    having an even and regular surface; free from perceptible projections, lumps, or indentations.

Flat:             having a level surface; without raised areas or indentations.

Level:         a horizontal plane or line with respect to the distance above or below a given point.

In relation to the resin bound surfacing industry, the three words are applied to certain aspects of the surface and have very different meanings.

Smooth:    Is typically used to describe the surfaces slip resistance. I.e. the surface is too smooth and requires                                               additional slip resistance.

Flat:            A resin bound surface should be flat, meaning no obvious or significant lumps, or indentations.

Level:        Used to describe the overall placement of a resin bound surface in relation to another point such as an                                        edge, adjoin surface or parallel to the horizon. 

A resin bound surface should not be too smooth, should be flat and can be level.

So what is the difference between expected imperfections and a non-flat resin bound surface? When viewed in normal day-light a resin bound surface should have no obvious imperfections. Any trowel marks, sharp inclines or imperfections (typically greater than 4mm) that are positioned away from an intentional edge are not to be expected and should be rectified.


Any slight change to the surface height that is less than 4mm and only visible at night should be expected and is not an installation or product failure. A resin bound surface is not a self-levelling system and is applied by compacting the firm aggregate/resin screed to the desired application depth. This can result in unavoidable, small variations in the surface. Such variations should not be visible unless they are brought level with the eye line or they are side lit at night.

A simple test to confirm that a resin bound surface has been laid to an acceptable standard and tolerance is to use a one meter long aluminium ruler or straight edge. When placed on the resin bound surface there should be no unintentional indentations or height changes greater than 4mm.

● The addition of sand increases the strength of a resin bound surface.


In some cases, the addition of sand to each mix can increase the overall strength of the cured system however this is dependent on the aggregate selection used and viscosity of the mixed resin components. The addition of sand into some aggregate blends will reduce the overall matrix strength. A highly viscous resin can result in the sand particles clumping together when mixed in a force action mixer. Any build-up (clumping) of sand in a specific area can result in a low strength, fracture point. The microporous nature of some stones allows them to act like sponges and soak up resin. When combined with the additional surface area introduced by sand this can significantly reduce the strength of the system. 

● A resin bound surface is SUDS compliant because it is porous.


Simply because a surface is porous does not mean that it is SUDS compliant. Sustainable Urban Drainage Systems (SUDS) are systems of drainage that provide an alternative to the direct channelling of surface water to drains and through networks of pipes and sewers to nearby watercourses. It means that it is suitable for use in a wider SUDS compliant system. The installation of a resin bound surface directly onto a non-porous substrate does not provide a SUDS compliant surface and it must either be installed onto a porous base or direct rainwater onto an area in which the water can drain naturally. A non-porous surface such as a resin bonded system can also be installed as part of a SUDS compliant system if it directs water away from drains, prevents water entering nearby watercourses and directs water to an area in which the water can drain naturally such as a lawn or garden.

● The overall performance is dependent on the type of aggregate used.

The resin is a key element in the overall performance of a resin bound surface however it is not the only factor. Different aggregates result in very different properties and this is not always reflected in the aggregate specification such as its crush strength or polished stone value. All of the StarScape ULTRA aggregate blends are tested to provide accurate performance information.

● Bound surfacing resins are DIY products.


Bound surfacing resins should never be viewed as ‘do-it-yourself’ products. Only fully trained installers have the knowledge and skill-set required to handle the chemicals, source high quality materials and successfully install a resin bound system. It is illegal to sell aliphatic isocyanates (the ‘B’ component) to DIY users and this is stated in section 1 of the products safety data sheet. 

● Some bound surfacing resins can be installed in the rain.

No polyurethane-based resin surface should ever be installed in the rain or damp weather conditions. The nature of the chemistry requires a resin to isocyanate cure however, the isocyanate will react with water before the resin and this reaction creates a brittle, urea rather than the desired urethane.

● All bound surfacing resins are the same.


There are different types and qualities of bound surfacing materials available in the UK. The five most common systems are:

Aliphatic: The highest quality and best choice due to its combined strength/flexural properties and UV resistance. Both the isocyanate and resin components will be clear or have a very slight yellow hue.

Aromatic: A low-cost system that discolours (turns a mucky brown) and becomes brittle due to UV degradation. It is less flexible than aliphatic systems making it prone to reflective cracking. The isocyanate component is usually a brown colour and mixed kits look yellow/buff rather than clear/white.

Aromatic Hybrid: This can be a blend of aromatic & aliphatic isocyanates with UV stabilisers which are incorporated into a resin. Typically used with a natural castor oil-based resin component, this delays the discolouration and strength degradation but does not prevent it. The isocyanate component is usually a light brown and the resin component is often yellow.

Epoxy: Rarely used and superseded by urethane resins due to its chemical hazards and history of problems.

Aspartic: A relatively new development in resin surfacing (patented by Star Uretech) and very much in its infancy. Current costs exclude this from being a competitive system.

If you are unsure as to the chemical nature and quality of a resin this can be confirmed by consulting the products safety data sheet. In section 3.2 of the isocyanates data sheet (typically part ‘B’) a UV stable product will only list Aliphatic and Hexamethylene Di-Isocyanates. A non-UV stable product will list Diphenyl Methane Di-Isocyanate.


● It is essential to premix the resin components.

With some systems it is essential that the components are pre-mixed prior to being added to the aggregate in the forced action mixer. This is usually required because the component viscosities make them immiscible or the resin component contains an additive which separates from the main polyol. StarScape ULTRA has been specifically formulated to make the components highly miscible and use any moisture trapped in the aggregate particles as part of its back-end curing process. As such the StarScape ULTRA ‘A’ component is added to the aggregate prior to the ‘B’ component and pre-mixing is not required. 

● Whitening or Blooming is always caused by water.


Most instances in which a surface is affected by whitening are caused by a reaction between moisture and uncured resin however this is not the only cause. Some cases of whitening have mistakenly been attributed to moisture when the cause of the problem was solvent evaporation from a tarmacadam base course. A tarmacadam surface cures as the solvent content evaporates and this process is greatly affected by the ambient temperature. When a tarmacadam surface is laid in cold temperatures the solvents evaporate at a much slower rate and if a resin bound surface is laid prior to the evaporation of solvents these can leach into the uncured resin and result in whitening of the surface. As this typically happens in the winter months the problems are easily misdiagnosed as moisture/frost damage. A tarmacadam which contains solvents and is not fully cured can look identical to a surface that is fully cured and it is essential that a minimum of seven days (ideally 14 days) is allowed prior to the installation of a resin bound system.

● A high-performance system requires less resin than a low-quality system.


StarScape ULTRA is formulated by the UK’s best polyurethane chemists, using only high specification raw materials and requires less resin than a low-quality system. Our approved suppliers list ensures we only purchase the very highest quality raw materials and our formulation remains unchanged. The only time our formulation would change is to improve its performance and not increase our margins. This would only happen after notifying customers and a minimum of 12 months rigorous testing.


● Resin diluted with solvents can be used as a bound surface overcoat.


Resin systems intended for binding stone should not be used as a restorative or repair coating and this is especially important if the resin is diluted with solvent. Undiluted resin is purposely formulated to a relatively high viscosity and can significantly reduce the surface’s porosity. Resin which is diluted with solvent or white spirit will attack both the resin surface and a tarmacadam base which can result in delamination of the bound surface. Products such as StarScape RESTORE have been formulated to ensure they will not react with (attack) the bound surface or base and to a specific viscosity which allows it to both cover the surface and flow through the existing bound matrix in order to strengthen its bond to the base.

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