How to Fix Loose Paving Slabs and Joints
By the end of this guide, you will know How to Fix Loose Paving Slabs and Joints. Our guide covers removal of the old joints and paving slab bed, mixing up mortar and PVA, and re-installation of the paving slabs. Please note this guide assumes your issue is due to a breakdown of your mortar paving slab bed, or high foot traffic over your effected paving slabs. If you suspect ground movement, then please consult your local builder for advice. Before we tell you how to fix loose paving slabs, you will first need the appropriate safety wear and tools.
Safety Wear Required
How to Fix Loose Paving Slabs Guide
Step 1: Remove the Failed Grout Joints
Before removal of the loose slabs, you will first need to remove the pointing around them. This can be done using a club hammer and masonry chisel. If you have a section of pointing missing, then this is a good starting point. Place the chisel where there is a break or gap in your pointing, then start to chisel around the perimeter of your loose paving slab. Working along the pointing, knock away the pointing with the hammer and chisel. Only use necessary force when extracting the pointing, and be careful not to disturb the neighbouring slabs (as they can also become loose).
Once you have removed all the pointing around the failed slabs, give the area a sweep. Brush the edges of the slabs with a hand brush to clear the remaining loose debris in-between the slabs.
Step 2: Decide which Slabs are Blown Underneath
If the pointing has failed, it doesn’t mean the slab is loose. The best way to determine which slabs have failed is to knock on them with your fist, then listen to the sound. If there is a hollow echoing sound, then it means the slab mortar bed has failed underneath, and will need to be re-done (re-bedded).
Step 3: Remove the Loose (blown) Slabs
Once you have identified which slabs are blown underneath, you will then need to carefully remove them. The best way to pull up the slab is to gently slide a shovel under the centre of the slab and lift the front up, to get your hands underneath. Do NOT put the shovel under a corner of the slab, because you risk breaking the slab. It is possible the next slab could be disturbed in the process. If the next slab does become loose, then pull that up too.
Step 5: Remove the Mortar Bed that was underneath the Slab
Remove any loose parts of the mortar bed first. The best way to remove hard parts of the mortar bed is by using an electric chisel. We recommend an SDS drill. You can buy SDS chisel attachments. Electric chisels enable you to break down the mortar bed in seconds. Once done, you can then shovel the mortar bed pieces into your rubble sacks. Be careful not to damage the neighbouring slabs when using the electric chisel. Also, you only need to chisel to the depth of the mortar, leaving the concrete base intact. Once you have completed extracting all of the affected areas, make sure all the holes are debris free and the patio is clean.
Step 6: Prepare the Mortar Mix for the Slab Bed
The ratio for standard patio mortar mix is:
2 parts sharp sand.
1 part soft sand.
1 part cement.
It would be advisable to use a bricklaying trowel or shovel to stir the mix. Place your mixing board away from the patio, or place some protection underneath the mixing board to prevent staining the patio. You will need to mix the sand and cement together dry, before adding the water. Care must be taken with this part, to ensure too much water isn’t added to the mix. If you have a very thick bed to put in, it is important you don’t make the mortar mix too wet. The best way of adding the water to the dry mix is to use your bricklaying trowel to make a hole in the middle of the pile, gently tip some water into the hole. Then use your shovel to cover the hole back in, turning the mix over and over. If the mix is a bit dry then repeat the process again until you have the right consistency.
Step 7: Prepare the PVA
You will need: A bucket, PVA and a masonry brush.
A standard PVA mix is: 50% PVA, %50 water.
Pour some PVA into the Bucket (about 1/4 full). Then pour the same amount in water. Use your masonry brush to mix the PVA and water together. This PVA will eventually be applied to the underneath side of your slabs. PVA creates a perfect surface (or key) for your mortar to bond too. If this step is avoided, then it is likely your mortar will not bond to your slabs!
Step 8: Apply Mortar to the Paving Slab Bed
Fill the hole for the slab with the wet mortar mix that you prepared in Step 6. Completely fill the hole, just over the bottom lip of the adjacent slab. Avoid over filling the hole, because the mix will rise through the gaps in the slabs and spill out on to the patio. Avoid getting any wet mortar on the patio as it will stain it. Once you have filled the hole, you will need a bricklaying trowel to evenly distribute the mortar mix within the hole.
Step 9: Insert the Paving Slabs onto the Mortar Bed
Before you place the paving slab back into the hole, you will first need to brush the PVA that you mixed up in step 7 onto the underside of the slab. Once done, carefully hold the opposite corners of the slab with your hands, then place if flat on top of your wet mortar bed. Make sure you lay the slab slightly higher than the existing slabs in all four corners. If one end is slightly low, you will need to take the slab back out and lay more wet mortar at the low end. The flatter you can put the slab into the hole, the easier it will be to lay. Using a spirit level and rubber mallet, tap the slab down to make it level with the existing patio. Check continuously that the slab is level. If you hit the slab too hard, you will break it or knock the slab down too low, so care needs to be taken on this part. Complete this process doing one slab at a time until all your loose slabs have been relayed.
Leave the slabs to set for a minimum of 48 hours before you move on to the next step (repointing).
Step 10: Re-Pointing
Only start this step if your patio is dry, and the weather conditions are also dry.
Standard mix for pointing is: 3 parts building sand, 1 part cement.
Again, you need to use a mixing board and mix the sand and cement together dry before adding water. You only need a very small amount of water, so the mortar isn’t dusty. If you make the pointing mix too wet it will stain the slabs. The pointing mix should be hard and clumpy and feel slightly damp.
You will now need a pointing trowel, pointing iron and a soft brush.
Pour the pointing mix into the grooves between the slabs, and use the pointing trowel to work the mix into the grooves so it is evenly spread. Then use the pointing iron to compact the mortar to make it solid within the grooves between the slabs. Try and copy the pointing profile that is on your good slabs. it will likely have a flush or curved profile. If curved, then you can create a curved mortar joint using the curved edge on your pointing iron.
Once you have completed the pointing, make sure any loose mortar is swept from the patio. Once all work is complete try to stay off the repaired areas for another 48 hours to allow setting time.
We hope you have enjoyed this comprehensive guide on How to Fix Loose Paving Slabs and Mortar.