£144.95 per m². Prices stated below are per pallet containing 4m², this is our minimum order quantity and is exclusive of VAT and delivery charges. Trethowel Grey is a traditional Cornish slate facing stone and comes in a variety of sizes and finishes. This stone is particularly popular with stonemasons due to the ease of working and the stunning results. It has a range of uses and can be used internally or externally depending on your project, whether it’s a time-honoured barn conversion, a contemporary new build or anything in between then this walling stone could be just what you’re looking for. This is a relatively soft slate with a unique blue / grey colour which weathers in colour over time, pulling out some rustic and yellow shades depending on exposure to UV and sea air.