Metal lath or backerboard? Special waterproof stucco necessary?

[Chris]

I?ve got the steel frame put together and anchored down. Studs are about 16 inches on center, although I got a little creative with the front, since I couldn?t run track across the opening.

I initially built the frame with a 0.25/12 pitch, planning for a flat roof covered with ceramic floor-tiles. I later decided to just use some leftover metal roofing. This called for a steeper pitch, to keep water from pooling or running back under the overlapping pieces. So, I cut a 2?4 on the slant and screwed it to the frame from below. The wood rafter at the front of the oven will be separated from the flue by 4 inches of perlite-concrete, so it will be ok.

The walls will be stucco. I?m debating whether to use a backerboard, or expanded metal lath. Does it matter?

Most people here seem to use concrete backer board. Any reason not to use metal lath?

I plan to use a basic lime/portland/sand stucco mix, possibly tinted. I'd rather not paint, as I'm going for an antique look. If I flash behind the lath/backerboard, does it matter too much whether or not I use a special waterproof stucco?

The only problem I can see is at the front of the oven. The chimney will be covered in perlcrete and stucco, and I can't figure out a really good way to flash the seeping water away. Plus, the "adobe" bricks I bought soak up water like a sponge. I can see this moisture making its way into the perlcrete layer eventually.

On the other hand, if I use the basic breathable stucco, perhaps any water that finds its way in will eventually seep out again. It's not especially damp here in Austin, but we get our share of thunderstorms from time to time.

Thanks for any tips or advice!

[CanuckJim]

Re: Metal lath or backerboard? Special waterproof stucco necessary?

Chris,

First off, I tend to overbuild everything, so bear that in mind. If I was asked to do your job commercially, I'd use cement board, then lath, then waterproof stucco. Lath on its own can be tricky to work with unless you have experience. It must be stretched tight to prevent bellies. You'll need more coats because it will squeeze through the mesh for the first one (which is a good thing, makes it hold), but if it's stretched over board, you won't need as many coats. Take the moisture out of the equation by using waterproof stucco, and be sure to vent the enclosure.

Jim

[Chris]

Re: Metal lath or backerboard? Special waterproof stucco necessary?

It seems that some builders on this forum apply the stucco directly to the cement board. I'll probably go this route, and use the lath for the corners and around the chimney.

The instructions on the back of the stucco bag indicate that if using lath, a 3-coat process is required, while for concrete board and masonry, you can get by with 2 coats. This seems to make sense, because once you apply the scratch coat to the lath, you've got a surface similar in thickness and rigidity to a hardibacker.

[james]

Re: Metal lath or backerboard? Special waterproof stucco necessary?

Hi Chris,

This sounds right. I have always thought that using concrete board was the best way to create flat and linear surfaces. It goes up quickly, and it is smooth and level. In that way it's like drywall; you screw it in place and tape the joints, and it is ready for the finish coats. The process of building the enclosure (which you have done), is the same as drywall, with studs on 16" centers, concrete board joints centered on the studs, taped joints, etc.

The advantage of rebar and stucco lathe is that it lets you create a more organic shape. Which will work for you around the chimney.

You are lucky -- you get to do both.

James

[jahysea]

Re: Metal lath or backerboard? Special waterproof stucco necessary?

Chris,

I applied stucco directly to the wonderboard product. It adhered instantly. Too well in fact, I found it much easier to apply if the wonderboard was wetted significantly before application.

It's only been since November/December, but I have no cracks or flaking as yet.

I used two coats for most areas. Some of it 1 coat.

[james]

Re: Metal lath or backerboard? Special waterproof stucco necessary?

Hey JC,

How's the oven cooking? Is it spring in the wine country, with the vines starting to bud out?
James

[jahysea]

Re: Metal lath or backerboard? Special waterproof stucco necessary?

Hey JC,

How's the oven cooking? Is it spring in the wine country, with the vines starting to bud out?
James

Hi James! Oven's great. Lamb cutlets and potatoes last night, Pizza tonight. Found San Marzano tomatoes in the area, but no caputo flour just yet. I'll have to order a bag from fb.com.

It's very springy here in the wine country, been 80+ in SH Sat and Sun. Of course I've spent much of it inside laying 500sft of travertine.

Weeds are up, many trees blooming, but no bud break just yet, at least not on the 18 cabernet vines I have along my fence. Got to happen soon as warm as it's been. I hope Italy's been as nice.