stucco advice Getting Started Discuss stucco advice in the Pizza Oven Design and Installation forums; Hi Does anyone have any advice on the final stucco/render layer? In particular - what proportion of sand, portland cement ...

[mieno]

Hi
Does anyone have any advice on the final stucco/render layer?
In particular - what proportion of sand, portland cement and lime is best?
Is it applied in several layers and what sort of consistency should I aim for?

Also, I have used several layers of ceramic blanket and a rigidizer to harden it up instead of a vermicrete layer over chicken wire. Do I still need to put the chicken wire over the blanket for the stucco to grip to or can I just start rendering over the hardened blanket?

Has anyone tried the new flexible polymer type renders?

Thanks in advance for any advice.

[gjbingham]

Stucco scratch coat: 3 parts sand, 2 parts portland cement, 1 part masonry cement, water

Finish coat: 1 part lime, 3 parts sand, 6 parts white cement, water

[RCLake]

Originally Posted by gjbingham

Stucco scratch coat: 3 parts sand, 2 parts portland cement, 1 part masonry cement, water

Finish coat: 1 part lime, 3 parts sand, 6 parts white cement, water

Is there a difference between masonry cement and white cement? I have a bag of white Portland cement left over that was used for the grout for the stone work on our house.

sorry to rob this thread but I'm planning on putting stucco over the blanket as well, at least for the short term. Eventually I will enclose it with stone but I'm itching to cook

[gjbingham]

RC,
Probably, but I'm not really 100% sure. I was just quoting from the book Black and Decker Home Masonry. Since they are very specific about the recipie, I would assume that they are different animals.

Personally, if I were you, I'd just buy the stuff at Lowes or Home Depot. They should have it in Texas and it's not very expensive. Not so here in the NW.
G.

[CanuckJim]

RC,

Portland is way too hard, too brittle for what you want to do. If you can't find "white" cement, which has a high proportion of lime, use Type N. It's much more flexible and water resistant than Portland, what with the Sealbond and other additives in it. I'd really urge just about everybody to steer clear of Portland for oven use; just too hard and unforgiving.

Jim

[gjbingham]

More good advice Jim, once again too late

[carioca]

Originally Posted by CanuckJim

<snip>
I'd really urge just about everybody to steer clear of Portland for oven use; just too hard and unforgiving.

Jim

NOW he tells me!

Cheers,

LMH

[mieno]

Thanks for the tips.
Jim, just to clarify that a traditional stucco of 1 Portland : 1 Hydrated Lime : 2.5 to 4 Sand will be too hard / brittle right?
I will need to replace the Portland with a White Cement with a higher lime content. Unfortunately our white / ivory cements here are described as white portland and I can't find any reference to type N.
Would a traditional lime plaster (just lime and sand) work if the oven was sheltered? These seem to be used on earth/clay ovens that need to breathe.

Thanks

[CanuckJim]

Mieno,

If I understand you properly, the addition of hydrated lime to the Portland mix will avoid the brittleness issue because the lime adds elasticity to the mix, as well as better stick. Type N is relatively new on the North American market. I use it for sticking on veneer stone in vertical applications; well, because it's "sticky" and is good at shedding water. It's difficult to know for sure, but I suspect that your white Portland is the same as what's called here white cement. It was commonly used in the old days to make up a white putty for decorative brick pointing of the last quarter inch or so in a joint. Usually, a beading tool was used to make the resulting joint convex. White cement, however, is expensive.

To clarify, using straight Portland in a vermic mix is fine, but using it straight, full strength in places where expansion and contraction take place isn't. If used, it has to be tempered somehow.

Using a lime/sand mix alone will not be waterproof. I wouldn't use it in my climate; not sure about yours.

As an addendum to brick laying questions and cracking, I further suspect that some cracking that builders have experienced has to do with dry joints, where the mortar never really forms a bond because the firebricks are not wet enough and the moisture is sucked out of the mortar. Although the mortar will probably stay in place, the bond is either not strong enough or nonexistant, hence cracking. Using wet bricks and wet mortar can get messy, I know, but just have a bucket of clean water and a sponge nearby. It's also crucial to finish point the joints, front and back, so that the mortar is forced deep into them, with no pockets or air gaps, and the remaining water pushed toward the bricks and drawn to the surface. Done properly, the resulting joint should be shiny from the tool work. Fill any resulting gaps with a dryish mix, and push it in.

In the Photo Gallery, there's a pic of most of my masonry tools, including a collection of pointing tools. They're cheap at HD, and everyone should have them. The exception is my beading tool, which is hard to find and not necessarily cheap.

Jim

[Mojoe]

Portland cement (white or gray) and masonry cement are different with the exception of they both get hard when water is added. Masonry cement uses the same clinker (small balls resulting from cooking raw materials in a 2700 F rotary kiln) as Portland cement but it is ground finer and has hydrated lime added during the milling process. The finer grind and lime addition makes the product weaker more pliable than Portland cement.

There is also a product known as PCL, portland cement and lime, which is typically used for at or below grade applications or when high strength is needed. Many government jobs spec this material when constructing schools, jails, etc when laying the cmu's. We produce this product either in the mill or we blend the portland with the hydrated lime in our mixer.