Doing my first brew this morning and just started my mash with 18L but it has around 4KG of malt, wheat and MO in it, the mash seems really dry pre sparge, is that normal?
The usual ratio is 2.5L/kg, so for 4kg that would be 10L of water. If you used 18L that is a ratio of 4.5L/kg which might affect fermentablility a tad but otherwise is perfectly fine. A thicker mash allows for a longer sparge which improves efficiency a bit, but don't worry it won't have any noticeable effect on your beer.