Stucco

[mokomon]

Having trouble for some reason finding info in the forums on mixing my own stucco mix and appling it for the outside of my pizza oven . Some guidance would be greatly appreciated. Thanks

[david s]

There are a number of solutions. (In Australia and the UK we refer to stucco as render)
1. use a bagged proprietary cement render. It comes dry in a bag and some has confusingly marked as “polymer modified.” These usually also contain a degree of waterproofing that makes them partially waterproof. Reinforcing is advisable because the outer shell is subjected to considerable stress from thermal expansion and steam pressure build up. Chicken wire is a traditional reinforcing material but is difficult to form over compound curves. Alternatively, some reinforcing fibres can be added to increase strength and are far easier to use and more effective than chickenwire, but more expensive. Commercial renders are also usually designed to have some acrylic added 50/50 with water to assist application and also enhance strength.

2. make your own with sand, lime and cement. Hydrated lime imparts flexibility and crack self healing properties. Thermal expansion and steam pressure challenges the strength of the hardened mix so the lime is a good ingredient, but wearing gloves to handle the wet mix is mandatory. Graded sand also assists in strength so a mix of grain sizes is advantageous.
A pretty good mix is 4:1:1 graded sand, Portland cement and hydrated lime.

3.A 100% acrylic render is another alternative, comes wet in a sealed bucket ready to apply and has the advantage of being 100% waterproof as it dries to an impervious layer. The drawback is that it is expensive.

I think it is best to gently drive off all the contained water in the inner oven and insulation layers before applying an outer rendered/stucco shell as accumulated moisture in the insulation layers can be damaging.

[mokomon]

Thankyou for the info