How Is The Resin Bound System Mixed?

Mixing of Resins

It is important that the resin supplier's guidelines on quantities and mixing are followed precisely as this can affect the workability, finish and longevity of the system.

The resin is usually supplied in two parts. The resin and an activator. These require mixing together on site prior to adding to a mixer. The two parts should be mixed together thoroughly for approximately 1 minute until the resin becomes homogenous, usually using a drill and paddle mix attachment.

The mixed resin is poured into the mixer containing the aggregates, this should also be mixed for about 5 minutes to ensure products are fully coated but also that the resin is dispersed through the mix evenly. Poorly mixed mixes will leave areas or the surface weak or resin rich, this is where the resin is too heavy and fills all the voids between the stones creating a shiny patch.

In very hot temperatures it is essential to work quickly, some resin manufacturers will state upper and lower application limits, for example 10-35 degrees surface temperature as a maximum however at these maximum temperatures, you have maybe 8-10 minutes to lay, spread and trowel before the resin starts to set and thicken and this can lead to problems. The most experienced contractors can adapt to these conditions and  do so by often starting early in the morning and stopping when it’s too hot or by using retarders to minimise any potential premature setting. When applying in extremely hot conditions, the resin can expand making a cracking noise which can be heard as it expands. Also the relative humidity when laying and curing is essential and the resin supplier will state the tolerances for this as well typically RH 30-85%.

Resin quantities to aggregate vary, however a general rule is 7-15% resin by weight depending on the stone size, depth of layer and strength required. A blend of stone sizes 2-5mm and 1-3mm will give a terrific increase in strength or allow a lower resin ratio. This however creates a compact finish, whilst many prefer the 2-5mm alone as it creates a preferred gravel like appearance. However a thorough blended mix, that has the majority of the cavities in the mix filled, will produce a longer lasting surface and it is a more cost effective way than increasing the resin content to get the same effect.

To achieve a non-slip surface, two things can be done, the first is to introduce a small bag of C52 sand into the mix which will give a gritty finish to the resin or secondly, broadcast some C52 sand onto the actual surface before the resin sets completely.

When the resin and hardener are mixed with a drill paddle-mixer this should be for several minutes to ensure everything is combined thoroughly, it is at this stage if an accelerator is required, for example in cold temperatures below 15 degrees or if there is a chance of dew or light rain overnight, it should be added. An accelerator is used to fast cure the resin if temperatures are expected to drop below the recommended temperature, (as stated by your resin supplier) in the curing period or moisture may be expected. In summer and warm temperatures setting times could be vary between 2 and 4 hours, however in the autumn and winter months, the resin could still be tacky the next morning, therefore adding an accelerator prevents the resin being affected overnight when the temperatures drop and the moisture increases.

Download our Resin Bound Advisory Notes