It is best to clean your darby as you are using it and as soon as you have finished. It is much quicker and easier this way.
The best way to clean a darby is to use warm water, a mild detergent (washing up liquid would be suitable) and a soft brush.
Simply wet, soap, brush and rinse.
Try to ensure your darby is clean after use. Any concrete or plaster residue that dries on may crumble off when you next use it and mix with the newer materials, ruining your project.
Don’t worry, though – it’s not impossible to remove dried-on debris: there are a couple of methods to try.
You can try gently rubbing off the dried-on plaster or screed with sandpaper or wire wool. You may also try using a dull chisel.
However, Wonkee Donkee recommends wire wool, as sandpaper and chisels can scratch the aluminium.