Paving Slabs FAQs

Tobermore slabs can be installed on the vast majority of pedestals offered by the various pedestal manufacturers. For confirmation please contact the pedestal manufacturer directly.

We recommend the following guidance:

Yes, Proprietary bedding and jointing mortars are now used frequently. There are numerous manufacturers of these products which meet and exceed the requirements of BS 7533.

To ensure surface water runs off the slab surface a minimum longitudinal fall of 1.25% (1:80) and cross-fall of 2.5% (1:40) should be incorporated.

Yes, download them here.

Yes, BES 6001 & ISO14001 – download from here.

No, Tobermore concrete slabs do not contain any Ground Granulated Blast furnace Slag (GGBS) and Pulverised Fuel Ash (PFA).

Once all full size slabs have been laid use cut slabs to complete the area. Where cut slabs are required avoid cuts which are less than a quarter of the original plan size. The use of in-board cuts can help to achieve this. Slabs should be cut using a masonry saw with water suppressant. Full PPE must be worn. When 25% of a slab needs to be cut the remaining piece should be cut from the internal corner of the cut to the external corner of the slab at an angle of 45 degrees.

For best practice cut the slabs away from the area being paved to avoid cutting dust staining the newly installed slabs.

Yes, please refer to our online Sub-base Specifier tool here.

To allow for the slabs dimensional tolerances and to create a gap to allow brushing in of kiln dried jointing sand slabs installed unbound must have joints between 2-5mm.

Important: Straightness of lines is dependent on workmanship and any differences in sizes of the slabs that result from the manufacturers permitted tolerances. Installing the slabs using a 2-5mm joint can help achieve straight lines.

Tobermore do not recommend butt jointing slabs. Butt jointing is when slabs are installed tight together, touching. This will make achieving straight lines more difficult and causes the edges of the slabs to spall.

Slabs installed bound should have joints between 6-10mm.

Mortar Jointing using a trowel.

Joint filling usually occurs 12 hours after the slabs have been laid on the mortar laying course.

Press the mortar firmly into the joints using a trowel. The whole joint should be filled with a compacted mortar to within 2-3mm of the slab surface. Finish the joint using a pointing iron. Extreme care should be taken to avoid staining the slab surface with jointing mortar. Clean any spills immediately using clean water. The strength of jointing mortar required will depend on the application. Please refer to BS 7533: Part 4. As a guide, typically a 1:4 cement/sand mix is used.

Slurry Mortar Jointing

Important: To avoid staining the surface of the slabs, extreme care should be taken when slurry jointing.

Slurry jointing mortars begin to set quickly allowing the paving to be cleaned shortly after jointing is complete. Determining the optimum time to allow the joints to start to set whilst still being able to remove the excess material is crucial. If left too long it will become much more difficult to clean off and there is a risk of staining the slabs permanently. Temperature and humidity will also affect the setting time. On very hot days, it may be best to leave jointing until late afternoon. We would strongly advise to construct a trial panel to determine the time required.

Completely soak the entire area of slabs with clean water. A suitable strength mortar slurry should be spread over the area. A squeegee should be used to move the slurry over the surface to ensure all open joints are adequately filled. As much of the excess slurry should be removed from the surface of the slabs and the joints should be allowed to firm up. Once the joints have begun to firm up any jointing slurry remaining on the surface of the slabs must be washed off carefully taking care not to wash material from the joints. For best results use a sponge grout roller machine. Alternatively a pressure washer can be used with care.

Concrete slab paving installed unbound is jointed with kiln dried jointing sand. The sand is brushed and vibrated into the joints using a plate compactor. Important: The paved area should not be cleaned by vacuum road sweepers for a minimum of 3 months. This prevents loss of jointing sand and allows sufficient time for the sand to self-stabilise. If necessary, the jointing sand can be stabilised immediately by using a sand joint sealant.

Concrete slab paving can be installed “unbound” on a bed of sharp sand which should be approximately 25mm after final compaction.

Concrete slab paving can also be laid “bound” on a bed of mortar which should be approximately 30mm after final compaction. Slabs with plan dimensions greater than 450 x 450mm are normally laid using the “bound” method.  Tobermore strongly advise against spot bedding as this can cause staining to appear on the surface.

Concrete paving slabs should be installed to BS 7533 Part 4.  You can download a simplified version of this here. 

BS 7533 states that a cut block should not be smaller than a quarter of a full-size block.

It is better to avoid this if possible however it can be done provided the existing base is in good condition and has no cracks. It is very important that the finished surface level of the paving remains below the DPC ( Damp Proof Course ) level.

No, slabs must always have a joint whether they are laid flexibly or rigidly. Slabs laid flexibly will have a 2-5mm joint and slabs laid rigidly will have a joint width of 6 -10mm.