Clinker waterproofing
my preferred coating uses Eze-Kote made by Deluxe Materials. Used with glass cloth. Available from most good model shops or online.(www.deluxematerials.com/products)
I find it has advantages over polyester or fiber glass resins, as there is no noticeable odor and can be used in the house, which is good if you don't have a heated workshop. Hope this helps.
COLIN.