This invention concerns methods and materials for the production of polymeric compositions, particularly, though by no means exclusively, suitable for use in the formation of impact absorbing surfaces or substrates to sports or play areas.

Known such impact absorbing surfaces comprise crumbs of a natural or synthetic rubber, such as EPDM for example, in a matrix of polymer, such as polyurethane for example.

The matrix may completely fill the spaces between the crumbs to give a non-porous composition or may simply coat the surfaces of the crumbs to cause them to adhere leaving the interstices between the crumbs void to give a porous product.

Either kind of composition may be laid to form a sports or play surface or to form a substrate to another surface such as that provided by synthetic turf for example.

The compositions are prepared on site immediately before use by mixing crumb, liquid polymer and if necessary a catalyst, to enable them to be laid, in the manner of asphalt, before polymerization has advanced

suff ciently to render them unworkable. Advantageously polymerization times are short to reduce the risk of damage to the finished surface before it has set.

The on site preparation and short setting time neccessitates expensive equipment and highly trained operators regardless of the size of the project.

It is an object of the present invention to provide a method and materials for production of a porous composite which overcomes the disadvantage aforesaid.

According to the present invention there is provided a method of producing a porous composite comprising the steps of :-

pre-wetting particulate material with a liquid curing agent medium to form a stable intermediate; transporting the intermediate to site; forming a shaped mass of the intermediate; and

applying to the intermediate a liquid polymer or pre-polymer, either immediately before or after formation of said mass.

The shaped mass may be a horizontal layer.

The liquid polymer or pre-polymer may be in the form of an emulsion.

The liquid polymer or pre-polymer may include an inhibitor or retarder to give extended shelf life.

The liquid medium may contain a catalyst or a chemical to neutralise any inhibitor or retardant present in the liquid polymer or pre-polymer.

The liquid medium may contain a coupling agent.

The liquid medium may contain a diluent.

The particulate material may be a natural or synthetic rubber crumb.

The intermediate may be mixed with the liquid polymer or pre-polymer for a predetermined short period before formation of the shaped mass.

The mixing may be effected using a conventional cement mixer.

The liquid polymer or pre-polymer may be applied to the shaped mass by spraying or pouring.

The invention also includes compositions for use in practising the methods aforesaid.

The invention will be further apparent from the following description, which concerns, by way of example only, the laying of a running-track in accordance with one method thereof.

In general the invention comprises pre-wetting a rubber crumb with a curing agent to form a stable intermediate, at a central facility. The intermediate is bagged for storage and transport to site.

Onto a suitable sub-base a base coat comprising the intermediate is laid using conventional concrete or asphalt laying techniques and equipment.

An emulsion of polymer or pre-polymer is then sprayed over the crumb surface so as to pass through the interstices of the mix to join the crumbs into a coherent mass. Excess liquid disperses into the sub-base.

In an alternative approach the intermediate is mixed with the polymer or pre-polymer for a predetermined short time using a conventional cement mixer to initiate polymerisation before the mix is laid.

In a specific example SBR waste rubber granules having sizes in the range of 2mm - 6mm are coated with 2% by weight of a liquid medium comprising a hydraulically stable organic polyol containing the polyurethane catalyst dibutyltin mercaptide and a coupling agent (silane). The mixture is bagged for storage and use at a later date. The shelf life of the bagged mixture is greater than 12 months.

A Diphenylmethane -4, 4' Di-Isocyanate based pre-polymer having a free (-NCO) of between 8.5% and

9.5% with a viscosity of between 2800 and 3400 cp is prepared and bottled. The shelf life of pre-polymer is up to 12 months.

When required the bags of pre-wetted rubber granules and bottles of pre-polymer are transported to site.

The pre-wetted granules and pre-polymer are mixed (1 litre of pre-polymer to 40 kg of granules) by tumbling in a conventional cement mixer for between three and five minutes.

The final mixture is then laid onto a prepared sub-base and allowed to polymerise.

Polymerisation time is controlled by adjusting the amount of catalyst pre-mixed with the rubber granules.

It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from the scope thereof as defined by the appended claims.

Whilst the specific example is concerned with a polyurethane resin system it will be understood that other systems such as epoxy resin systems might be used.

Again, for example, the particulate material may comprise cork crumb, gravel, chipped bark or any other material suited to the intended application.

Yet again, for example, the composition may include fillers, colouring materials or other known additives.