How to Lay a Slab or Flag

There are a number of ways to lay a flag, each depending on received loads, what lies beneath them and the style of flag used. To lay flags to a patio area for example which will receive medium loads such as people and furniture, the following method is best adopted.

Photo Credit: Designlazy.com

Steps

1) When laying flags if there is not one in place already it is best to lay a foundation, this will provide a solid base for flags to sit on and minimise the risk of subsidence and movement.

2) Start at a chosen corner and lay one of the flags on a 15-20mm bed with your trowel. This bed size helps you overcome any bumps in the foundation and varying flag depths. Level the flag in both directions with a spirit level. Lay flags in the in the corners at 12 and 3 o’clock, these must be perfectly square and will simply act as a ‘dead man’, meaning you will lay the flags towards them and lift them up once you reach them and relay to suit. 

3) Set up a string line in both directions and begin to lay your flags making sure that you stick to the line and follow the level of the tile in front. Joints are best kept at 10mm. A gentle shake or the use of a rubber mallet are best for reducing the flags on the mortar bed. Once you reach ‘dead man’ at 3 o’clock it can be removed and relayed to suit the positioning of the previously laid flags. This then allows any cuts to be placed all at one end rather than in the centre which is undesirable. Any cuts should be done with an electric grinder.

4) Move to the second of slabs and lay a flag at the end next to where the dead man was, but this time the bond has been achieved so it can laid following the flag next to it. Set the string line up again and work toward the end slab. Complete this process and you will work your way out of the corner. 

5) Once the flags have set they must be jointed which can often cause staining when not correctly. If wet mortar is to be used then when each flag is laid the joint on the receiving  flag should be in placed, and a jointing iron to form a half-round joint. A semi-dry mix can also be used, sometimes being the same colour as the flags, this is usually packed hard into each of the joints. 

Tips

If putting in the foundation yourself, make sure it is level and has no bumps this will minimise the risk of errors when laying the flags

Always place any cuts at one end

Be sure not to stain the flags when pointing