We've built two-thirds of my Pompeii oven dome from Refrax mortar from Forno Bravo, which we have mistakingly mixed with sand. When removing the plywood form from the entry arch, cracks developed in two mortar joints. I plan to use Refrax without sand for the remaining dome construction, but I worry that the mortar mixed with sand may not be strong enough and may develop problems in the future. At this time, except for the entry arch cracks, the dome seems to be sound. Any advice on how to proceed?