39 inch - 1000mm corner brick WFO build - Newcastle au

[david s]

Hi David, The percrete would be approx 50mm (2 inches) thick with another 10-15mm of builders render over. So far I have done 7 days of 3-3.5hr curing fires with gas burner on lowish flame, plus 2 wood fired curing fires of 3.5 hours so far. Hoping after a few more days of curing fires getting slightly bigger each time the moisture should be driven out of the oven. Thanks for the tip re plastic during firing to check moisture. Will test before sealing dome.

I'm not sure how much perlite you ended up using but at a guess of 3 X 100 litre bags, that would be around 120 litres of water added to the mix. About half will be chemically used up in the hydration process as it chemically combines with the cement, but it still leaves about 60 litres which is a lot to dry out. Covering it with a cement render reduces its ability for theeither the weather or heat from the fires to push it out. You will eventually get it dry, but it may take a long time. You should follow the instructions provided by the manufacturer of your kit. As an explanation of the drying of a p/v crete slab, read the attached experiment, which relates to a 5:1 underfloor slab, but the same principle applies. Water in the insulation layers drastically reduce the insulating ability as heat is easily conducted by moisture. If the outer surface of the oven's rendered shell feels hot then there's moisture there. It should only ever feel barely warm. With experience you'll find a hand held to the outside a particularly good indicator.

Vermicrete insulating slab copy.doc.zip