38" Pompeii build

[Frenchie]

Working only with a brick bolster and a 9” grinder has its limitations so my cuts are not the most accurate or clean. I’ve been getting by though, using wedges to plug big gaps between bricks in a course and sometimes between courses.

on the last course I’ve tapered and bevelled the bricks but as we get closer and closer to closing the dome I’m afraid much of the material will be mortar or screed and not firebrick.

Therefore I have lapped 2 layers of full bricks together in opposing directions to prefabricate a keystone. The bricks were ‘keyed’ before joining with mortar. I will cut the 4-brick block down to suit the final opening in an attempt to minimise mortar. Will it be okay?



I plan to handle this keystone by drilling in plugs and fashioning a handle, the plugs later to be removed and mortared

[Frenchie]

Keystone has been marked, cut and trial-fitted.
ready for aesthetic fettling and mortar tomorrow, and a few tapered wedges on the cardinals.

[mongota]

It's always a great accomplishment to get the dome plugged. Congrats in advance on getting that cap wedged and mortared in place.
Just when you celebrate that feat, the real work begins!

[Frenchie]

Haha, yes there’s much much to do. One suspects such a project is never truly completely finished

[Frenchie]

Cleaned up yesterdays joints best I could - left them a little too long

[rsandler]

Congrats on closing your dome!

If the excess mortar is bugging you, scrubbing with vinegar and a wire brush can remove stubborn excess bits of mortar (one can use stronger acid, but using HCl or muriatic in an enclosed space gives me the heeby-jeebies. YMMV)

[Frenchie]

I found a few hours last saturday and managed to build the outer arch.

For the chimney transition, I was going to build a brick platform on top of the arch to create a level surface - HOWEVER, I just can't cut the bricks properly - so will save the remainder of my firebricks for an outdoor barbecue or firepit.

Instead of the bricks I will cast a flat plinth in-situ using either Vitcas Heatproof Screed, or Refractory Castable.
Then on top of this, I will place my transition piece.

The transition piece will use a rectangular to round duct converter as a form, making the transition out of castable refractory.

[Frenchie]

If one uses 3 layers of 1" fibre blanket insulation, is the v/p-crete layer still required or can we go straight to stucco on top of the insulation?

If the v/p-crete is required, what thickness on say, 2" or 3" fibre blanket please?

[Giovanni Rossi]

I believe you'll find the stucco/render is easier to apply over the pericrete vs. over the blanket for a few reasons. The springiness of the blanket make it difficult to trowel a smooth layer of stucco unless you are quite skilled. The stucco layer is not so thick and will make it difficult to get a smooth layer over the lumpiness of the blanket. Plus, the blanket will pull moisture from the stucco, decreasing working time.

The same issues pertain to the pericrete. Some builders have been successful at using one thick layer of pericrete, but that has its challenges in getting the right consistency to prevent slumping while maintaining the dome shape.

Most use thin layers of pericrete that can be troweled on quickly. After the first layer, each subsequent layer allows for working the surface to correct/maintain a proper dome shape.

I don't think there's any hard and fast rule for the final thickness of the pericrete. It can depend on how much room you have on your slab and the look you're trying to achieve. I was trying to maximize my dome insulation and had planned for 2 inches over my 4" of blanket. I did it in 3 layers and that seemed to work fine. I probably finished with a bit more than 2". I'm not that skilled with a trowel, but I was able to get a good result. Take a look at my build. I believe it was david s who suggested using a wire brush lightly on each layer before it cured to provide a good substrate for the next.