Another Minneapolis WFO

[Sixto]

Just catching up on this..I did the same thing with my chimney anchor bricks...

Thanks Mongo, your build was the inspiration for my chimney anchor layout - though I did not want to handle 6 bricks at a time, so I did end up playing quite a bit of "tap, tap" with groups of 3. Right now the rear two sets of 3 are mortared-in waiting till that's set to tap the two front sets. I also did not trust myself to set the bricks into a form, so I'm just going slowly and tackling other things like fiber insulation while the 4 sets of 3 bricks sat inside plastic garbage bags over the weekend to build some bond-strength in the mortar joints for these critical sections.

There will be another layer of bricks with 1/4" s.s. bolts to tie into the stainless flue, and a sloped cast cement top to shed water and snow off the whole thing.

Here are some photos:from earlier today. I started to add perlite to the base of the dome. Its quite crumbly when wet, even at 8:1 perlite to cement ratio, with 2 parts water added to the mixed dry ingredients in the wheelbarrow. I mixed just a little to test it, seemed to be a good consistency with no pooling of water at the bottom. I'm glad I tested since adding any more perlite to the base would have slumped-off the top. I got about 4" high so far, we'll see how it dries tomorrow and whether I need to get some chicken wire to hold the perlite on to the vertical surfaces till I reach the more tapered, horizontal sections of the dome...

next day edit.... the perlite stiffenned-up quite nicely overnight, should be able to continue adding today..today, but i got a roll of chicken wire to see if that will let me work a little faster by providing something the perlcrete can hold onto.

[MarkJerling]

Looking great Sixto!

[Sixto]

HELP!!! Perlcrete is not going well
(and thank you Mark for the encouragement, I need it today!)

Even adding chicken wire did not help the perlcrete stick together on the more vertical portions of the dome. The stuff goes on like a dream when the dome starts to go horizontal, I can lay it down with a trowel and pack it down into the chicken wire with no problems, but when I try to do that below that zone it just crumbles away.

Is there any additive I can add to the water to help the perlcrete stick together? flour, elmer's glue, old paint??? I just need some more viscosity... I can ball it up fine, and I can add one ball at a time, but when I press on the ball to flatten it against the wire, it just crumbles apart...

Edit: I just read this thread: https://community.fornobravo.com/for...ket#post443399
Good information there, I will try adding some clay to the mix, and shape myself a curved trowel to help hold the stuff on... we'll see.

[david s]

Don’t add more cement or you’ll just drastically reduce the insulation value. To make it more sticky, just add a handful of powdered clay for every litre of cement. When placing the mix, start at the bottom going all the way around the base, and make a flat ledge on the top to take the next row. Also the correct amount of water is crucial. Too little and the mix is too dry and crumbly, too much and the water washes the cement off the grains and pools in the bottom of your barrow. You can do a low wall say 6” high, leave it overnight to dry and it provides a more stable base for the rest the next day. You can also carve it back a bit if required.

[Sixto]

Adding powdered clay helped us get two more batches of perlcrete on today Yay!

But we still had trouble with the vertical parts....will give what we placed time to stiffen up and see if we can place more tomorrow....
Part of the problem is that the chicken wire moves under the perlcrete when a handful of fresh perlcrete is added, disturbing the cohesion of recently placed sections even when using a big, curved trowel.

Will play with the clay ratio tomorrow,and also will try to be more patient when I'm working on the difficult parts.

Another positive development was the placing of all the chimney bricks, and the stainless steel base plate. Photos soon.

9/1/2022 Edit - added photos and comments below.



My wife's gentle persistance (Bless her patient heart!) finally got through to me... she kept saying "if the perlcrete is crumbling off, why don't you add a form to the outside? I'm realizing that often success comes when I can (temporarily) dislodge my own head out of my backside... or in business-speak... think outside the dome?

I'll just pack the form full of wet perl-crete from the top, let it set, move the form up 6" and do it again. You can also see the issue created when I added the last layer of fiber blanket on the very top, there is a bit of a vertical undercut. I hope two layers of carboard cinched tight with moving straps will be the solution I've been looking for...(now that I'm adding clay to the mix) I may have to add a bit of plastic sheet between, to make sure the fresh perlcrete does not stick to the cardboard...Fingers crossed!

Oh and I agree with David's comment below... the chicken wire is not doing much, but two days ago, it was cheap,- it gave me a glimmer of hope, and now that it's on there with perlcrete on top, I'm not about to take it off. I did go around the whole section of exposed wire, and using needle-nosed pliers I twisted almost all of the horizontal parts of the wire hexagons to tighten the mesh further against the blanket and reduce the flexing that I've been complaining about.

[david s]

Adding powdered clay helped us get two more batches of perlcrete on today Yay!

But we still had trouble with the vertical parts....will give what we placed time to stiffen up and see if we can place more tomorrow....
Part of the problem is that the chicken wire moves under the perlcrete when a handful of fresh perlcrete is added, disturbing the cohesion of recently placed sections even when using a big, curved trowel.

Will play with the clay ratio tomorrow,and also will try to be more patient when I'm working on the difficult parts.

Another positive development was the placing of all the chimney bricks, and the stainless steel base plate. Photos soon.

Chicken wire between the blanket and vermicrete is a waste of time IMO. Apart from the problem you mentioned and the time required to fit it, you are left with a conductive material in the middle of the insulation layers, which seems counterproductive to me. The chickenwire will do little to reinforce an already weak 10:1 vermicrete layer.

[fhausback]

I found that handfuls separated by a few inches stuck fairly well. A handful at a time, I’d put 15 handfuls on, then go back and fill the gap between with another handful. The few minute gap gives the first handful time to settle before knocking it loose with more. This makes a very uneven surface, but once the first layer is dry, the next layer holds to the oven very well.

[david s]

Another trick I use when making a lean brew is to mix perlite and vermiculite together 50/50 which makes a more workable mix.I currently use by volume, 5 litres of medium grade grade perlite, 5 litres fine vermiculite, 1 litre of cement and a handful of powdered clay mixed dry, then add 4 litres of water. The finer the grade of aggregate, the more workable the mix, but the more water is required. The water is best added slowly so the mix doesn’t get too lumpy. I usually start with these quantities then go for mixing up double batches.

[Sixto]

Heh, heh, I may not be too smart, but I married an F-ing Genius!

Thanks to David and Fhausback for your insight! I think the form helps me go faster, one layer at a time, and with a little more clay and a little more water, it went on like a dream. I got just perlite, but in two different grades: coarse and medium - mixed. I just had to pack it down from the top to make a flat surface.

The final recipe was this: (using 1/2 gallon bucket)
8 buckets of perlite
1 bucket of cement
1/2 bucket of clay powder
2-1/2 buckets of water added slowly while mixing in my wheelbarrow with a large hand trowel.

The added clay powder needed more water than I had originally used, but still with all this there was little to no wet cement residue at the bottom of the barrow after mixing it all well.

[Sixto]

If you drive out all the moisture from the vermicrete layer before rendering over it, some of the moisture from the outer render will be sucked back into the vermicrete. To reduce this loss I simply wrap the whole oven in cling wrap once the render has been applied, then leave it for a week. Little beads of moisture are visible under the cling wrap indicating that the moisture is being held in.

So the apex vent is on, and I'm almost done with the perl-crete layer. If I wait till the perl-crete is set, but not completely dry, then add stucco/render, wrap it with cling-wrap and wait a week for the stucco to cure (mostly) = do I run into any problems heating the stucco render with drying fires (it shouldn't crack because of the vent, but will heating it up slowly after a week cause any other potential problems?

Since the perl-crete took me so long (1.5 weeks) I'm pushing the Pizza! date out a week....I hope I can do the stucco/render in 3 days.


My wife (the potter) made the apex vent out of the same terracota we'll use for the tiles, It is a cylinder that sits on the top layer of blanket and it has vertical slits on the sides below the top of the perlcrete layer, it will be filled with stainless steel wool, and it will have a removeable, flanged cap (think inverted saucer) that blends in with the tiles and keeps the rain away from the opening and also hopefully keep the cap from blowing off in a strong wind...


The base plate was bolted on to 4 bricks that had been mortared together with 1/4" stainless through-bolts, nuts and lock-washers. Then the whole thing was set on top of the 12 shaped bricks. (but tapping the 4 bricks cracked the vertical joints between them - I'm ok with that - the fresh mortar under them is what's doing most of the work) Plus, I'm planning to cast a sloped-top concrete cap that comes all the way out to the 12 bricks with a slight overhang to shet water off. When I do, I will leave 1/4" gap between the concrete and the flue that can be siliconed later...

[david s]

No, don’t do that. The vermicrete layer is at least a third water. The excess free water needs to be largely eliminated before you can safely start any fires. It will dry from the outside if exposed to sun and wind, which will take around a week in ideal conditions depending on conditions and the thickness of the layer. Then the inside moisture can be pushed to the outside by gentle fires. It is better to do all this drying before applying an outer render, otherwise it will trap the moisture in. Wait until the inside of the dome turns white before applying the outer render.

[Sixto]

No, don’t do that. The vermicrete layer is at least a third water. The excess free water needs to be largely eliminated before you can safely start any fires. It will dry from the outside if exposed to sun and wind, which will take around a week in ideal conditions depending on conditions and the thickness of the layer. Then the inside moisture can be pushed to the outside by gentle fires. It is better to do all this drying before applying an outer render, otherwise it will trap the moisture in. Wait until the inside of the dome turns white before applying the outer render.

Ok, then I'll apply the fiber-reinforced layer on the gallery arch first (those bricks are dry) and wait for the perlcrete over the dome to dry before applying render to that... I was going to have a control joint between those two areas of render anyways, thinking they may move independently and crack there eventually. My drying fires will then move ahead on the schedule, while the drying of the render layer over the dome will move to the end... it's so difficult to wait at this stage!

Thanks for for the advice David!

Just to make sure i understand, I'll finish the perlcrete tomorrow. Then while I wait a week for that to dry I can start rendering the brick gallery (no perlite there). By the end of the week both the perlcrete on the dome and the render over the gallery should be dry enough to start the gentle drying fires. Once that is done, then I can render the dome.

Edit 9/4/2022: Never mind my previous question about firing the oven while the render is drying: I found a response on another forum from a member I think is David S. that states the following (with my emphasis) : "I also like to wrap the outer render layer in cling wrap for a week before using the oven because anything made from calcium silicate cement will be enhanced by extended damp curing, usually a week is standard." so I've adjusted my dates accordingly.

Pizza date is now 9/24/2022.


Edit 9/4/2022: Perlcrete over the dome is done!

[Mr. Slowhand]

This is project management at it's best!! 24/09, excellent planning!

[Sixto]

This is project management at it's best!! 24/09, excellent planning!

Thanks! some skills are useful even beyond retirement, but honestly, I though I was DONE making Gantt charts and my life was going to be one big improvisation! "Best laid plans!!!"
I guess now that's in writiing, the pressure is on - I only have 2 weeks between the first Pizza and my son's wedding. I better learn to work the oven fast!

[MarkJerling]

Wedding pizzas! Sounds like fun. Enjoy!