Sealing the joint between the Chimney and the Stucco with Rutland RTV Silicone Seal

The second coat of stucco is going on today with painting expected in a few days. My question - Does the area / joint between the side of the chimney and the stucco need some type of sealant like high temperature silicone to prevent water entry?

Also, is there benefit to adding a third layer of stucco using finishing stucco? We are out of time for warm temperature so have to just paint this year with hopes of adding either brick veneer or tile in the spring.

As always, thanks for all of your help and answers.

Before you paint the stucco, apply a thick layer of High-Temp Silicone Seal between the stucco and the chimney pipe or anchor plate to create a flexible, water-tight seal that’s resistant to high-temps. Once it’s dry, it’s safe to paint.

Rutland 500-Degree RTV High Heat Silicone Seal | Clear | 10.3 - Ounce Caulk Tube

As for adding a 3rd layer of stucco… it won’t add anything to the performance of the oven, but it will provide an additional layer of high-strength protection. So when your daughters annoying boyfriend decides it would be cool / funny to walk on top of your oven, he’s less likely to come crashing through w/ that 3rd layer of stucco.

I just added a third layer yesterday. As @BrickWood says, two is plenty, but in addition to strength, you can also refine your oven’s shape (ahem, looking in the mirror when I say that :slight_smile:). If you choose to do it, it adds a day to the required curing time. I know you’ve reported your nighttime temps are already reaching below 40°F, so you may decide to let it cure and get it painted.

We are adding a third layer of stucco this afternoon since we currently have a reprieve in the weather. The fire brick have been in place for several weeks so the final wait time is on curing of the stucco. The instructions state a specific number of days after stucco application before removing the form and then additional days prior to adding the exterior finish. Since it’s too late to add brick veneer, how long do I need to wait to remove the form and paint the exterior?

How long do I need to wait after the last layer of stucco to use the high heat silicone sealant?

You can remove the form now. Doing that will actually help draw out moisture (into the atmosphere) from the oven interior, and the form is not holding up anything now.

You can also add your chimney plate now. That’s a good reason to open the tube of high-heat silicone adhesive. If you have any kind of canopy over your work you will want to wait until you have removed it to add the pipe and chimney cap (just for clearance).

You can paint at the end of the seven day period. I am using the time until next Tuesday to assemble the oven door, clean up construction materials, put away the concrete mixer for the winter, and finish stacking the load of firewood that arrived Monday.

Then, provided the weather holds, I plan to paint two coats on the stucco next Tuesday, and allow it to dry overnight. The outdoor temperatures are definitely cooler now, but the atmosphere is drier (provided of course the Delta storm doesn’t come up the coast this weekend!).

I will be ready next Wednesday to start the curing fire schedule.

1 Like

I have just added the third coat of stucco too here in AZ - and yes I used the 3rd coat to “smooth” out my barrel with 3 layers of insulation! (evidently I am “dimensionally” challenged)! I had the same question of sealing around the chimney (notice a small separation between the stucco and chimney) before painting. Was going to tile the barrel with stone pebble tile, but running out of time (long story).

Couple of questions:

  1. Should I use high temp caulking for this (stucco/chimney interface)?

  2. How long should I wait for the stucco to dry (and higher pH) before painting?

  3. Should I use a waterproof masonry primer before painting?

  4. Painting - acrylic latex or elastomeric paint? - how many coats?

  5. I am putting mosaic tile on just the outer front ring and painting the rest of the oven- tile resting on the top of the fire brick arch and backing up to the stucco, can I use fire mortar, or stucco, or thinset grout? I think I would like to set the 1-2 inch tile (1/4inch thick) with either fire mortar or stucco - and not use thin-set and grout. But worried about heat in the front of the oven. If I use fire mortar, will I have a bonding problem with the mortar/stucco interface? Or should I just finish and mount the small tile with just stucco? Should I add concrete adhesive additive (moose milk)to the fire mortar to combat the problem of different cement products (ie. mortar/stucco interface)? Or is it even a problem…??

  1. Using the time to put the chimney plate on and cleaning up the brick. Also finishing up the door vents, thermometer and insulation…

  2. And Brick cleaning - there are some products out there - or should I try vinegar, then muratic acid? Or other ideas?

Whew!! Sorry !

I have really enjoyed this forum and have picked up very valuable points along the way. Thank you in advance and look forward to your answers, please!


Hi Don,

I’ve been away from the forums for a few days, so missed your reply and questions—sorry!

So I’ll answer in order:

  1. Yes. That area will warm up, so you need high-heat flexible silicone caulking as @BrickWood was describing above.
  2. Seven days. Even though the outside may turn a light gray, there is both a lot of moisture and a lot of curing going on under the surface. If you paint it too soon, you will trap moisture inside, which will find its way into the mineral fiber and then turn to steam. Not good. … Also, if this seems like an arbitrary number, I can report that my stucco still had dark patches on day 6, and they all disappeared the next day (for real!).
  3. No need. Your paint is all that is necessary (and see next answer).
  4. I used this product from Lowe’s. It is a polyurethane-fortified latex intended for masonry and wooden floors. It happens to be pre-tinted, but it was very close to the color I had wanted and it will work fine. You want to do two coats. In addition to the paint (and you will need one gallon) you need a 2 inch cutting-in brush, a paint cup, a roller tray set, and one or two ¾-inch nap roller covers. (One if you clean your covers, two if you dispose after use.)
  5. I will leave this question in the expert hands of @BrickWood. He can give you a better response on this.
  6. Yes.
  7. The easiest—and also slightly hazardous—way to do this is with muriatic acid. Here’s a link to a FAQ about it.

Hope this is all helpful, and not too late for your needs!

1 Like

Mr. Matt,
You are a good man!! Thanks for the care and detail in your response to my many questions of minutia.
I did use the high temp caulk for the chimney interface. Also, since the tile I chose for the front seemed to lend itself to a dry stack look, I used the caulking for securing the tile on the front. I did use a Behr concrete primer and sealer that dries clear (suspiciously, like moose milk), and now I am ready to paint with a Behr latex for two coats. Also, with some elbow grease, wire brush, wood rasp and 7% vinegar, my bricks are clean!
One final question - I was thinking of using a regular caulking all around the bottom of the barrel to seal the stucco/border brick interface. Anybody doing that or am I on overkill mode? Since I used firebrick for the border brick, I have been concerned about moisture getting into the bricks and migrating into the stucco or, even the oven proper. Maybe I should seal the border brick with a penetrating sealer? Any thoughts?
Not like I am trying not to finish - been at it on and off for 2 months(!) but believe it or not, at 6000 feet in Arizona, we get alot of freeze/thaw like y’all in the east. So I am trying to not have my hard work up till now go for nought, just cause I didn’t take care of the little stuff.
Again thank for all of the insights Matt !!- it doesn’t get said enough - but thanks for all your help and calm detail on this forum. As we say here in Gila County “you are quite the stud hoss”
Thanks pardner!


We agree! We are very fortunate to have Matt moderating and monitoring the BrickWood Ovens forum! He is a valuable addition to this growing DIY Pizza Oven community!

1 Like

Thank you for your kind words, Don! :slight_smile:

I am thinking the caulking around the bottom is, as you suggest, more than you need. When you are cutting in the paint around the bottom, just take some care that it gets in and even overlaps onto your border bricks just a bit.

Once your brick border is clean of any mortar stains—which you’ve done—it’s absolutely okay to seal it, top and sides. I’ve seen lots of folks veneer over those border bricks, and if you end up doing that, it will seal out moisture permanently from the bottom of the stucco. But in the meantime, yes, good to keep moisture out. (Any moisture in those bricks will be absorbed by the concrete slab underneath. That thirsty, thirsty, concrete…)

I’m sure the primer on your mortar did not go to waste, and will add to the protective qualities of the paint.

We’re all looking forward to seeing pizza baked at 6,000 feet, Don! Good luck with your finish.