My Wrekin
Access cover being installed

Unipak and Uniform FAQs

Unipak installation guide

Assumptions made in the following advice:

  • The chamber top construction on which the UniPak system will sit is in a robust condition and is suitably prepared (dry and clean with a textured surface for good bonding).
  • Installation operatives are familiar with and trained in the conventional method of highway ironwork installation. E.g. Frame tamping.
  • Installation operatives are competent in using mechanical mixing techniques with mortar materials.

How many 25Kg tubs of Unipak mortar do I need to install my manhole cover?

There is no definitive quantity of mortar, the amount needed depends on the volume or size of the gap below the frame that needs filling and whether other adjustment materials are to be used in the bedding construction. The general rule for calculation is based on a cured mortar density of 2,000Kg/m³.

Are wet conditions problematic for Polyester Resin based mortars, like Unipak?

Ideally, chamber top slabs should be in a dry condition when receiving a bed of UniPak mortar in order maximise the likelihood of bonding with the overlaying bedding mortar. However, whilst this should always be attempted (e.g. by force drying), it is sometimes impractical to expect UK climatic conditions to allow this scenario. But with over 20 years history and experience of Polyester Resin’s successful service in highway civils situations, there has been no definitive evidence of particular sensitivity to moist environments.

Cured Polyester Resins are known to be resistant to all types water (e.g Sea, Distilled, Fresh, etc), so this would suggest that simply protecting the unmixed ingredients from direct, excessive moisture (e.g. heavy rain) will afford all the protection the material needs to fulfil its expected requirement.

Note: Good practice should always be to prevent constant water immersion of bedding materials as the water could contain salts that are detrimental to such bedding.

The instructions describe compaction of the as-laid mortar bed(s). Is this important?

Yes, it’s vital. In order to achieve the optimum bond strength between resin-coated granular particles, those particles need to maximise the contact area between them. i.e. be in intimate contact. This is effectively achieved through compaction and can result from conventional Frame Tamping operations and/or manual compaction.

The instructions describe the need for a clean chamber top/slab surface for the Unipak mortar bed. Is this important?

Yes, this is an important preparation step as the Unipak mortar has high adhesion properties, which means that it will stick to the first solid material it comes into contact with. If that is dirt, dust or loose debris, that’s what the Unipak mortar will stick to… not the chamber top/slab.

Note: Grease and Oil chamber top contaminants are particularly detrimental to mortar adhesion as these are used in the moulding industry to deliberately prevent the materials they’re using from sticking to the moulds.

The instructions describe that it is advantageous to have a roughened or textured chamber top on which to apply the Unipak bedding mortar, why is this?

This is a particularly useful preparatory step in optimising the bedding construction as roughened (but clean) chamber top surfaces increase the contact area with the bedding mortar, thereby increasing the likelihood of adhesion between the two.

Additionally, a textured surface also allows mechanical interlock between the mortar and chamber top so that lateral movement between the two is prevented, even in the event of loss of adhesion.

Can I mix less than the recommended 1:1 (tin-to-bag) ratio?

No, as any variation from this ratio will; affect the mortar’s expected mechanical and physical properties, extend the curing time or even adversely affect its ability to fully cure.

The blend for the 1:1 mix ratio has been carefully selected to achieve the optimum balance of properties.

Can I dispose of unmixed Unipak mortar ingredients in landfill?

No. Only mixed (in a 1:1 resin-to-powder ratio) and cured Unipak mortar may be sent to a landfill as in this condition, it forms an inert, non-hazardous material. Ideally, any excess ingredients should be mixed and used in the ironwork installation.

Note: Unipak mortar’s packaging containers may be recycled where suitable facilities exist (contact Wrekin for details of materials employed in same).

Polyester Resin mortar is known to have a characteristic odour so do I need to take any particular precautions in using it?

Always wear appropriate PPE and read the Material Safety Data Sheet (MSDS) before using a particular material, working in accordance with its safety guidelines. Unipak’s MSDS is available at the bottom of this page and further directions are located on its packaging/mixing tubs.

Additional to this, apply logical practical actions. E.g. stand on the upwind side of mixing tubs, close opened resin containers where possible, avoid wiping uncured mortar on clothing, limit dust generation of the powder component in the mixing tub by slowly adding it to the resin or using the resin as a seal on top of the powder, etc.

Note: Mixed Unipak mortar forms an inert, non-hazardous material, so any excess ingredients should always be mixed (in a 1:1 resin-to-powder ratio) for use or render it safe for disposal.

When would I use Uniform Wedges?

As with any chemical reaction (curing in the case of bedding mortar), the speed of it is affected by temperature. Generally, a higher temperature will result in a faster reaction (i.e. a shorter curing/working time in the case of mortar).

Therefore, when working with Unipak mortar in elevated atmospheric temperatures, the mortar’s working time can be reduced to minutes. In these circumstances, it may not be possible to mix & lay a full bed of mortar and have time to Tamp ironwork frames into it before the mortar has ‘gone off’. In such conditions, Uniform wedges can be used to align an ironwork frame with the surrounding road surface (in lieu of frame Tamping), thereby allowing mixable volumes of Unipak to be mixed and applied sequentially under and over the wedge-supported ironwork frame.

Note: Uniform Wedges may be left in-situ as a set of 4nr are themselves capable of supporting a 400kN (c.40-tonne) load.

Will Uniform wedges need to be removed prior to trafficking?

Not necessarily, particularly if they’ve been fitted around the outside flange of the frame, rather than from the chamber-opening side of the frame. Leaving the wedges in-situ is permissible because they (like Unipak mortar) are also manufactured from polyester resin and form a coherent structure in cured polyester resin bedding structure.

If wedge removal is preferred, this can be achieved once a partial cure of the installed UniPak mortar has occurred by simply pulling the wedges out from under the frame or cutting off any unwanted protruding parts.

Where complete removal of the wedges has been carried out, the resulting bedding void should be filled with a fresh mix of UniPak mortar.

Note: UniForm Wedges may be left in-situ as a set of 4nr are themselves capable of supporting a 400kN (c.40-tonne) load.

Are there any characteristics of Uniform wedges that I need to be mindful of?

Yes. When laying the adjustment units into the mortar bed, they should not be tamped into it, only firmly pushed into the bedding using a side-to-side motion. This motion allows the adjustment unit to compact the underlying bedding and ensures that it also effectively interlocks with it.

Note: Tamping of adjustment units is not recommended as they can flex under this form of impact load and thus create a void in the bedding.

When I’ve mixed a batch of Unipak mortar, my mixing paddle is heavily coated with a residual mixture. How can I remove this for further reuse of the paddle?

Unipak incorporates deliberately-high adhesion properties which are indiscriminate in what they stick to, including mixing paddles. The remedy is to immerse the contaminated mixing paddle in a bucket or fine, sharp grit/gravel at the earliest opportunity following mixing, then simply replicate the mixing technique in the gravel until the UniPak is eroded off the paddle.

After applying the Unipak mortar on top of an ironwork frame flange, should I leave the surface float-finished?

Ideally no.

Whilst a float-finished surface looks neat, it is difficult for the intended overlying reinstatement materials to bond to it. Therefore, by all means, float the surface to ensure mortar compaction, but then lightly abrade it using for example; a stiff bristle brush.

This roughened bedding surface provides an increased contact area to bond with the reinstatement materials and also allows their particulates (e.g. aggregates) to ‘key’ or mechanically interlock with the roughened surface. 

Note: Where the overlying reinstatement material is Bitumen-based (e.g. Asphalt), such materials are themselves a derivative of Oil, which is also a lubricant. Therefore, to expect a lubricant-based reinstatement material to adhere well to a smooth, float-finished bedding surface is somewhat unreasonable. Hence, to improve the situation, a final float finish to bedding should be avoided.

Can I use the Unipak mortar as a trafficable surface. i.e. In lieu of asphalt, concrete, etc?

Whilst it is possible to use a cured mortar as a trafficable surface, we don’t recommend using Unipak in this scenario. Its polymer compound is not formulated to resist exposure to highly-abrasive environments, like trafficked surfaces.

Does the Unipak Mortar need to be laid in a particular bed thickness?

Yes, the minimum bed thickness should be 10mm and may be as much as 75mm thick where site conditions dictate. However, where a thick layer of bedding is required, it may not be possible to lay it in one pass and, indeed, many codes of practice dictate that multiple bedding layers should be employed.

Further, where a thick layer of bedding is required, it is worthwhile considering employing either a further course of Engineering Bricks or Uniform adjustment units as bulk fillers between separate beds of Unipak Mortar.

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