Can I put Stucco over Mortar?

[bradmtb]

On my Casa2g110 I have put the 3 layers of insulating blanket and covered it with a wire mesh/lath. I've read that most stucco/plaster should not be applied more than 3/4 to 1 inch thick. Since I will need to go thicker in spots to get the igloo the right shape, I was considering putting type-S mortar over the wire lath/thermal blanket first, then putting the stucco over the mortar?
Will that be ok?

[Tscarborough]

Re: Can I put Stucco over Mortar?

You don't really want the stucco to be over 1/2" per layer, The thicker it is, the more shrinkage cracks there will be. An ideal 3 coat system would be, base coat-3/8", scratch coat-3/8", finish coat 1/8-1/4", for a total thickness of about 1".

Type S mortar and stucco are almost exactly the same, generally the Stucco will have a larger aggregate.

[bradmtb]

Re: Can I put Stucco over Mortar?

Tscarborough,
When I picked up my oven kit at the Forno Bravo warehouse several weeks ago, one of the workers, who builds ovens, showed me a finished Casa2g110 like mine with a "marble glaze" smooth finish. He told me it was BMI "finishing marble", over stucco. So, I called BMI and found out a local place to buy it, and that person recommended BMI 690 Plaster first, then the BMI "finishing marble" which apparently has an acrylic for waterproofing.
So, since I need to even out my igloo shape, and I'm not doing the "3 coat system" you mentioned, but rather the Forno Bravo recommendation, I'm looking for something I can use to "build up" my igloo in a few spots where I need to go more than 1 inch.
Should I do a couple coats of stucco in those spots? The reason I need to go more than an inch is because when I formed my wire mesh/lath around the oven, there were some voids between the thermal blanket and the mesh that exceed 1 inch.

[Tscarborough]

Re: Can I put Stucco over Mortar?

Fill them in lifts. That is, build it up in layers.

[bradmtb]

Re: Can I put Stucco over Mortar?

Thanks for your help!

[fxpose]

Re: Can I put Stucco over Mortar?

Perlcrete or vermicrete form and take shape very well, and will be perfect to fill low spots or large voids. And they hand sand down to any shape using coarse sandpaper. I used percrete to form and sculpt over the entire dome and chimney. You can apply stucco directly over that.

The top half of my oven as seen below is entirely solid perlcrete (over blanket and wire mesh). I have yet to start applying stucco.

George

[Nic The Landscaper]

Re: Can I put Stucco over Mortar?

I'm not experienced with perlcrete or vermicrete but I grew up in the stucco industry and what Tscar said is spot on. Build up your low spots with maximum 3/8" lifts of stucco, or Type S mortar (virtually the same product, stucco usually has more sand in it, and coarseness of sand is usually up to the craftsman). You can use Type S mortar to do these lifts. As you complete each lift you should be scratching the coat with a 1/4" notched trowel so that the next coat of stucco can "key" into the previous layer until you get to the final base coat which will be your BMI base product. After you complete the BMI Base coat you should let the cement cure for 2 weeks before you finish coat it. Any cracks in the scratch or base coats will translate into the finish if it doesn't get a chance to cure well.

I didn't see the "Finishing Marble" on BMI's web site, is it a smooth product or textured? What kind of trowel and/or float are they recommending you use?

[bradmtb]

Re: Can I put Stucco over Mortar?

I decided to skip the vermicrete/perlicrete and use the BMI 690 plaster as a base coat. As I put the first coat over the wire mesh, it seems to be pushing through the holes in the mesh and pushing the insulating blanket down a bit resulting in at least a 1/2 inch layer in spots. Once I trowel it over the mesh, and the plaster falls through the mesh, I can't control it's thickness very well.
Is this going to be a problem? Do I have to wait 2 weeks for the next coat of BMI 690? After the 690, I'll put the Marble finish stucco (it's called BMI Stucco with Marble stamped on the bag) and it's smooth instead of textured.
I know nothing about trowels...what kind of trowel would I use with the marble finish?
Thanks for all the advise.

[Nic The Landscaper]

Re: Can I put Stucco over Mortar?

You want that first base coat to fall around the wire lath. It's called "keying" and basically it is how it grabs a hold of the surface. Wait 48 hours until your next coat, it will reduce cracking in successive coats.

For a very smooth surface I would recommend plastering it on with a regular hard concrete trowel and finishing with a bull nose pool trowel. The rounded ends will help you from marring the surface as you float it out smooth and the flexibility of the trowel helps reduce burnishing.

Good luck!

[bradmtb]

Re: Can I put Stucco over Mortar?

Nic and others, thanks for the tips and advise...I'm finally seeing the light at the end of the tunnel on this 3 month project. Can't wait to start cooking