Plastering on Laths
Firstly always make sure laths are clean.
Soak laths, best done with a hose-pipe set to a wide mist for some time, allowing the laths to soak up the water.
The laths must be damp at all times when you apply mortar so you will also have to spray as you go.
Knock back the mortar.
N.B. the water in the mortar bucket is to keep the mortar fresh and should not all be knocked back in.
The mortar must be haired for work on laths. If you are adding a pozzolanic to the mortar add the hair at the same time. You can add up to 10% by volume of pozzolanic to the gauge that you will be using in the next hour.
Do not try to use mortar that has become too hard as it will be weaker than required once set. The hardening time will vary - in general allow 24 hours.
Mortar has to be fairly stiff when used or it will crack.
Plaster across the laths pulling the trowel towards you making sure mortar is getting behind the laths to form a key.
Aim for 5 to 10 mm on this coat.
Spidery cracks that run in all directions are to be expected in moderation; as the mortar hardens just force them closed.
However, lots of crack running in line to the laths are a sign that the mortar was too wet when applied and may need to be re-done.
This can be done 1 or 2 days later depending on how quickly the mortar is setting.
Use a scratch comb to scratch this coat, making sure you do not go too deep with it as this will cause the mortar to fall from the laths.
Once completed allow this coat to dry, until completely set. Avoid vibration until completely set as this will break the key and the work will fail.
Next Coat (Scratched up ready for plastering)
When the scratch coat cannot be dented with a finger it is ready for the next coat.
Completely wet the scratch coat and allow it to draw up the water, then wet it again, otherwise the next coat will not adhere properly and will be much harder to trowel on. Again you will have to wet as you go.
This coat is much easier to apply and uses less mortar.
If you are trying for a level surface, I find a Darby much better to use than a feather edge. This coat will set a lot quicker than the first. Again allow this to set hard.
Again wet as before, knock back the lime plaster to a usable thickness and trowel on, until you have a fairly smooth finish.
Then apply a small amount of our super fine finishing plaster.
Allow to dry
P.P.E. MUST BE WORN
N.B. This sheet is for information purposes only and no responsibility for finished results is accepted