Jap Slabs: Guidelines for Installation

Introduction

Jap Slabs are 60mm thick precast concrete paving slabs in sizes a 600 x 300mm and 300 x 600mm. The slabs have a smooth finish with a well defined bevel edge and can be laid in patterns according to the customers' choice.

Jap Slabs are made for pedestrian use and, depending on the preparation of the paving foundation, may take limited vehicle traffic. High frequency traffic will eventually wear the surface down.

Vanstone is not liable for the integrity of paving that has not been installed strictly according to the requirements and used within the limits set by this specification. If any doubt exists, the services of a qualified professional engineer with local knowledge should be employed.

 

Instructions for installation

Before starting the job survey the area and plan the installation while taking into consideration required drainage and position of lines and patterns.

For pedestrian Traffic

The substrata must be of a sufficiently sturdy and stable type like gravel, clay free soil or pure hard core filling. Expanding clay, silt, collapsing sand or other soils with poor bearing capacity or with unstable characteristics must be removed to a sufficient depth and replaced with suitable soil. Consult with an engineer if in doubt.

Loosen the subsoil to a depth of 150mm and re-compact at optimum moisture content to at least 90% of the modified AASHTO density to the required level. On top of the compacted layer, use a 20mm bedding layer of clean river sand or crusher sand, which is spread evenly over the surface and leveled. Ten percent of cement may be added to the sand to provide additional strength.

Lay Jap Slabs on the prepared sand and bed-down thoroughly by wriggling each slab a few times left and right. Test evenness of bedding by pressing down alternatively on opposite corners of each slab to determine if any seesaw-action occurs. Each slab must be bedded evenly over its whole base and no gaps may be left.

If straight lines, which are neater, are required, the slabs should be laid using a fish line or straight edge.

Jap Slabs may be laid with closed joints but it may be difficult to maintain trueness of line. It is better to leave joints of 10mm wide between slabs and grout with a semi-dry mixture of cement and river/crusher sand. Use a mix ratio of 1 cement to 3 sand. Work into each joint and compact to ensure that no voids are left. Smooth down the tops of joints by stroking firmly with a brick joining tool. Remove any excess jointing material.

Do not use wet brick mortar as this will stain the slabs if not washed off almost straight away.

For occasional Vehicle Traffic

This method is not suitable for high frequency vehicular traffic like busy driveways.

Prepare the substrata as above. On top of this cast a concrete floor slab of 75mm thickness. Use strength 15MPa concrete 15MPa or a 1:3:6 mixture and cast in panels not more than 4m in size nor with lengths of more than twice the width. Include expansion joints as required. Lay and bed Jap Slabs in a 20mm thick slightly moist bedding mixture of river/crusher sand to which was added 20% cement as above. Keep slabs clean while working. Bed-down as above and allow to cure for 24 hours before grouting and final cleaning. Observe movement joints to avoid cracking. Joints in the paving must coincide with the joints in the supporting concrete floor slab both in position and type of joint.

 

Important: Cleaning and Sealing

Immediately after a section of Jap Slabs has been laid and cement was used in the process, the paving must be cleaned off of all cement residues to prevent staining. This must happen within an hour or two as cement-setting will render cleaning very difficult. Use clean water and a sponge.

Jap Slabs may be sealed with a good quality water-based sealer suitable for cement tiles. The sealing may be done before laying, which will improve protection against staining.

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