stucco questions

[PhoenixStucco]

I'm planning to tackle the stucco stage of my Pompeii oven build soon, and I'm leaning towards using a pre-mixed acrylic stucco for convenience. However, I've seen some recommendations for adding a scratch coat before the finish coat. Is a scratch coat necessary when using pre-mixed acrylic stucco on a Pompeii oven, or can I apply it directly to the oven dome?

[Prairie Valley Bread]

Re: stucco questions

I have some problems with my stucco coat.
I don't think I got the insulation/wire tight enough to the dome before i stuccoed. So now there are a couple of soft spots were it moves.
Can I just build up the stucco, or should I try and slice up the existing stucco layer and tighten it up? I don't expect anyone to lean into it.
Cheers,
Tom

[jimkramer]

Re: stucco questions

I did the first layer of stucco. I bout two bags of stucco labelled "fiber base coat" - worked great, fibers made it easier to put on. Before I started, I feared I didn't have enough and went to a closer store this Sat. That guy said I'd be better with a mortar mix, no fibers, which would be stronger and more water proof. I had only enough stucco w/fibers to do the dome, then put the mortar mix on the vent. The mix w/o fibers was much harder to spread.

So my question is, since the bag said "fiber base coat," is it still okay to use the fiber mix for the brown (second) coat? Since it's much easier to spread evenly, I'd rather to that. It's also smoother, which will probably look better under the final coat.

[kbartman]

Re: stucco questions

......I'm going to do a regular 3 coat. I've read I need to wait at least 24 hours in between coats. That sound right? Also, do I need to hydrate if for a day or two after applying a layer? I'll be doing the first layer this Sat, with temps in the high 60's, then they drop to the 50's. Not sure if the lower temps negate the need to spray it down.

That sounds good. Temperature low, that could be low humidity though. Some low temperatures bring very dry air masses with it. I would be on the safe side keep her hydrated, aleast tent her after she setup some.

[jimkramer]

Re: stucco questions

Thanks, got it. Okay, now that the vent is figured out...I'm going to do a regular 3 coat. I've read I need to wait at least 24 hours in between coats. That sound right? Also, do I need to hydrate if for a day or two after applying a layer? I'll be doing the first layer this Sat, with temps in the high 60's, then they drop to the 50's. Not sure if the lower temps negate the need to spray it down.

[Gulf]

Re: stucco questions

Right, I was vague. Sorry, I don't have a pic yet (at work) but I'll try to describe it better. I have a piece of steel pipe 1/2" diam, 4" long. It's threaded (on both ends), and can fit into a (roughly) 4" diam round flange that I got to help the pipe sit in place, like a base. However, seems I might not need the flange, and maybe a shorter piece of PVC is better.

So just to get this right...If I go with 3 coats of stucco (not sure if I'll do that, or 1 coat "process" of several coats) I put the 2 layers of stucco down, then the vent pipe sits on top of that, then the waterproof coat goes on top? Wouldn't it be better if the vent pipe extends to the insulation? That way It can let out vapor from the oven. Or does that then keep the stucco moisture trapped?

Just to the top of the insulation layer. It only has to extend through the stucco. You can't really do much better than that to relieve the mosture from the oven. Don't put any more hardware in there, than you need to, to secure the vent opening to stucco layer at the apex of the dome. That goes for stucco, directly over ceramic fiber insulation, and for stucco applied over a vcrete layer which is on top of a ceramic fiber layer. For the latter, I formed a hole in the vcrete with a beer can. That hole was filled with cfb scraps. But in either case, the hardware of the vent should only extend through the render. I don't advise deviating from the "age old" scratch, brown, finish coat. If I were to apply stucco to a flat wall tomorrow, that is what I would do. However, I did not find that technique fast enough for the compound curve application on a dome. But, I dried, fired, cooked, and inspected my oven's render for several weeks before I applied the brick veneer. The firebrick in the oven has a few cracks. The render has none .

just sayin'

[kbartman]

Re: stucco questions

So just to get this right...If I go with 3 coats of stucco (not sure if I'll do that, or 1 coat "process" of several coats)?

Jim,
Your need to do no less than scratch and brown coated. Unless your using a 1 coat type stucco. Varying the aggregated to stucco cement ratio is very important, otherwise you could end up with cracking. Attached is a good article that explains the stucco process and cracking. I found it very informative.

Too big to post the pdf file here's a link http://c.ymcdn.com/sites/www.nibs.or..._011_WB4-2.pdf

[david s]

Re: stucco questions

Hi David,

Why would he need to vent, if he has already cured his oven? The outside of my oven only reaches ambient temperature and that would not cause any problems with the curing of the render, would it?

The idea of a vent is to allow some communication between the insulation layer and the atmosphere. If the oven has already been dried out then the vent won't be of that much use, but if the oven is out in the weather and the insulation gets wet again then the vent will help it dry.

[Laurentius]

Re: stucco questions

Yes it has to extend into the insulation layer.

Hi David,

Why would he need to vent, if he has already cured his oven? The outside of my oven only reaches ambient temperature and that would not cause any problems with the curing of the render, would it?

[david s]

Re: stucco questions

Yes it has to extend into the insulation layer.

[jimkramer]

Re: stucco questions

Right, I was vague. Sorry, I don't have a pic yet (at work) but I'll try to describe it better. I have a piece of steel pipe 1/2" diam, 4" long. It's threaded (on both ends), and can fit into a (roughly) 4" diam round flange that I got to help the pipe sit in place, like a base. However, seems I might not need the flange, and maybe a shorter piece of PVC is better.

So just to get this right...If I go with 3 coats of stucco (not sure if I'll do that, or 1 coat "process" of several coats) I put the 2 layers of stucco down, then the vent pipe sits on top of that, then the waterproof coat goes on top? Wouldn't it be better if the vent pipe extends to the insulation? That way It can let out vapor from the oven. Or does that then keep the stucco moisture trapped?

[cobblerdave]

Re: stucco questions

G'day
I just wrapped a piece of cereal box cardboard around the fitting and taped it to get the size. The cardboard tube was the set in the render. I removed it just on the point of the cement setting. The cardboard tube was damp and easy to pull to pieces. A brass 1 inch plumbing end cap was silasticed into position when dry.
I've bricked the dome over since and used the same method again and refitted the same fitting. A chain has been fitted to the cap to prevent little fingers from taking the prize piece away.
Regards dave

[Gulf]

Re: stucco questions

Thanks Gulf. Thanks to your post, I was able to use the metal cloth. I started by wrapping a 4' section around the dome, then making slits every 10". After seeing your post, I redid it using an initial wrap around the bottom of the dome only 24" high. Worked much better.

I'll look into the single coat process for mortar, since I might have only one-two days this coming weekend before temps fall below 40 at night. Though I'm also worried about moisture. Regarding a vent, I already bought a 1/2" pipe with a flange. Would this suffice, you think, If I just set it on the top of the dome, on top of the metal cloth? I was thinking I could also grind in some grooves on the bottom of the flange to allow more steam to escape. How did you do your vent?

Jim,

I'm very glad that it worked out easier for you. I'm not sure about the "1/2" pipe with a flange". Can you send me pic or post one on your thread? I have adapted my origional vent, somewhat. The last one that I designed hasn't been installed yet. I used a 3/4" to 1/2" threaded (inside and out) PVC fitting. I sandwiched, and glued about a 5" round piece of 1/2" mesh in between two adapted pvc fittings. The same thing could be more easily done with this [B]bulk head fitting[/B]. I did not get a pic of the this rough "jury rigged" contraption. But maybe, Merlyn can. It is designed to secure the vent into 1" of rendor. Mine was designed to tie the mesh opf the vent into the existing mesh for the dome. It woold work great in either case. But, it should not extend any further than the bottom of the waterproofed rendor.

I hope this helps .

[jimkramer]

Re: stucco questions

Thanks Gulf. Thanks to your post, I was able to use the metal cloth. I started by wrapping a 4' section around the dome, then making slits every 10". After seeing your post, I redid it using an initial wrap around the bottom of the dome only 24" high. Worked much better.

I'll look into the single coat process for mortar, since I might have only one-two days this coming weekend before temps fall below 40 at night. Though I'm also worried about moisture. Regarding a vent, I already bought a 1/2" pipe with a flange. Would this suffice, you think, If I just set it on the top of the dome, on top of the metal cloth? I was thinking I could also grind in some grooves on the bottom of the flange to allow more steam to escape. How did you do your vent?

[Gulf]

Re: stucco questions

Jim,
I think that you can apply the stucco any time after you install the insulation. But, then I believe in intalling a vent. For applying the stucco (this may not be best practices), but I did not go with the traditional scratch, brown, finish coat method. Also, with this method, by the time one coat is appled you can start back over where you began with the next coat.

Below I copied a comment of mine from another thread. I think that it was mentioned in another post that I used an acrylic fortfier/bonding additive to my stucco to help with waterproofing. I also used it between each coat of stucco to help with bonding.

"I used a 12" short handle sheetrock seam (taping knife) trowel.



It has a slight curve built in to it. It will take a little pratice to figure how much stucco to load on to the trowel. Forget the handle, grab it by the ends. Start at the bottom and apply in a vertical motion. It will apply about 3/8" to 1/4 " for about 16 to 18 inches verticaly. Go all the way around the dome overlapping the runs about a couple of inches. Now go back to where you started. If it has dried out, you will need to apply some more fortifier by brush. Overlap the bottom run by about 4". Each horizontal run gets shorter (and faster) as you go up the dome towards the apex.

If after completing one complete layer you decide to stop for lunch, or the day: (before doing so) Take a course sponge and wet it in a bucket. Wring it out and start at the bottom in the driest areas. Wet a small area with the sponge. Use circular motions to knock down the high spots and fill up the low spots. Rewet the spong and repeat until you have covered the entire dome.

Before applying another layer, apply another coat of fortifier.

It takes 3 to 4 applications of stucco to get 3/4 to 1" of thickness on the dome. But each coat is much quicker than the one before.

This method will add and lock in water to your oven's insulation. I very much advise installing a vent at the apex of your dome. At least temporarily."

Hope this helps