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Sun 3-Nov-2019 Tech | 0 comments | Map

Wood-fired oven plans

Janet and I are in planning stages to build a wood-fired oven in the spring.  We plan to use it for cooking pretty much everything but mostly pizza and bread.  The thermal mass will not be too large to allow fast heating, and we won’t plan to bake multiple batches of bread in one firing.  We also want to smoke meat and fish.

As part of this project we will build a masonry paver patio behind the house where we currently have too much shade for grass to grow well.  The oven will go in the far corner of the patio facing the house so we can keep an eye on the fire from inside the house in bad weather.  The square block base will be used for an ash pit and the oven dome will be on a diagonal facing the corner.  The two adjacent sides will each have a 2’x4’ granite counter for food preparation and wood storage underneath.

The following is an outline for the design and construction.  Following that is a list of materials and drawings.  The design is in progress and I will continue to update this post as plans develop, then with photos after work starts, probably March 2020. Please add your suggestions, comments, and questions at the end of this post or on my posts on the Forno Bravo forum.

Abbreviations: IFB insulated fire brick 2.5x4x9, MFB medium density fire brick 25x4x9, RB red brick, FB Forno Bravo, RC refractory castable, WFO wood-fired oven.

  1. Foundation slab
    1. 6-inch rock base below slab, 1 foot outside of slab all around
    2. Make below grade deep enough to put 1” sand layer and pavers over it.  This will allow any water to drain below wood storage floor.
    3. Frame with 2×6 and stakes, 83” square, level with no slope
    4. Cover with 6 mil plastic
    5. Use both rebar around edge and 6” metal mesh
    6. Rent cement mixer
    7. Best to cure for a week
  2. Cinder block enclosure, no mortar, 4.5 high x 4 wide courses, 62.5 in square
    1. Fine tune height with short blocks +/-2” if needed
    2. Base will be 4” below grade and oven floor will be 11” above top of block, 42” above grade
    3. Make first course square, straight, and level with some mortar if needed
    4. Ash cleanout door 24×24” at bottom of back using 2x2x3/8 angle iron and metal door, so can go in there to remove 2×4 forms and to remove or level ash as needed.  Cut block with grinder to clear angle iron.
    5. Tabs in cracks to hold brick where needed front corner and counter sides
    6. Leave front corner open, 1.5 blocks missing
    7. Leave 1/8 gap next to 8” sections
    8. Vertical rebar in alternate blocks, stick up about 2”
    9. Fill alternate blocks with concrete, stuff others with bags 2” below top
  3. Slab above wall 4” thick with 2×6 frame
    1. Hardiebacker cement board on top of block with 2×4 support under it
    2. Leave about 2” open all around so some cement goes in holes
    3. Make sure form is level
    4. Make support frame with 2×4’s on their sides
    5. Suspend rebar 2” up on 12” centers, and tie where cross with rebar wire
    6. Weep holes with ½” PVC pipe through cement board to above top, cut off later
    7. Corner board to block off corner tipped 45 degrees inward for ash drop
    8. Put strap around form to hold in place
    9. Bang sides as pour to remove air pockets
  4. Insulated firebrick (IFB) on edge, no mortar, 4” high (“can’t have too much insulation”)
    1. Place small mosaic tile sections face down first for space for water to flow to weep holes
    2. IFB extends 2-3” beyond outside edge of where soldier MFB will go
    3. Later or now tile with mortar around edge and all area outside IFB; will be lower than oven floor
    4. Angle open hole in corner to edge of ash dump hole
    5. ??? need drawing Mortar 2 layers of MFB in front of ash hole in place of IFB to hold back sand and support arches
  5. Inside front arch cast from refractory castable
    1. Semicircle with 9” inner radius, 14” outer radius, 4” deep
    2. Make in advance on special form
    3. Mortar in place before setting perimeter wall
    4. Place on insulating firebrick plus 2x MFB
    5. Interior height 18”, opening height 9+3=12, ratio = 2/3=66%
    6. Tuscan style but with taller perimeter wall 9-2.5=6.5 above floor
  6. Perimeter wall
    1. Use standard size solid medium fire bricks on end soldier style
    2. Make sure it sits on insulating firebrick with 2” firebrick showing outside wall
    3. All space outside IFB covered with tile or red brick to edge
    4. Place in oval shape 36” wide, 42” long
    5. Angle to arch opening so no hidden pocket next to arch
    6. Bond in place with refractory air-set mortar
    7. Buttress wall with CR
  7. Half-inch layer of brickies sand and MFB floor
    1. Mix from fine sand and fireclay 1:1 and water
    2. Pack down well and groove it, check that ½” thick
    3. Cut to fit inside wall so replaceable later if damaged
    4. Place and cut edges MFB floor in herringbone pattern
    5. Tap to make surface even and level
  8. Front arch pre-made from full red bricks and half red bricks and rebar
    1. Semicircle with 9/5” inner radius, 14” outer radius
    2. Open hole at top 4×8”
    3. Mortar in place 1” thick insulating firebrick thermal break between the two domes, made by cutting bricks in half lengthwise to 1×4.5×9”
  9. Cast a chimney base support
    1. Hole size 4×8” square bottom, 6” round top, line with cardboard
    2. Cast in a plastic bucket, oil sides first
    3. Remove before completely set and smooth edges
    4. Cast will sit on top of 4×8” hole in arch with mortar
    5. Insulation will go around this cast
  10. Fill cavity and build up dome with wet sand
    1. Could make platform at bottom to reduce the amount of sand
    2. Sand could have some fireclay mixed in, especially on top
    3. Cover sand with wet newspaper
    4. Make height 18 inches above floor about 6 inches behind center of oval
    5. Oven should end up half-avocado shape
  11. Cover sand with bricks and a little air-set mortar to fix in place
    1. Keep wall about 4.5 inches thick
    2. Start with half bricks, then third, then half
    3. Cut bricks taller near front so rings stay at about even height all around
  12. Pour refractory castable in spaces between bricks and around chimney adapter
  13. Build up about ½ to 1 inch of refractory castable all over brick dome and second arch
    1. Let it cure for a few days
    2. Remove interior sand
    3. Start drying dome with heat lamp and small fires
  14. Cover dome and arch with several layers of ceramic blanket
    1. Wear protective gear
    2. Hold down insulation with chicken wire and wire ties
  15. Cover dome with 2 inches of Portland concrete protective cap, let set a few days
  16. Continue to fire oven, larger fires now
  17. Add a rendering coat (Watt p.71) over dome and back side of block and top of block
  18. Lay brick for counter support and wood storage with arched top
  19. Cast a base for in front of ash pit with thickness to lay tile to oven floor height
  20. Chimney 6”x48” stainless, single wall with cap and damper
  21. Place granite countertops 56×24” at about 36” high
  22. Consider making a metal cover for ash hole
  23. Make an insulated door with metal/plywood/foil/air/foil/plywood/wood handle to fit against cast arch
  24. Make an outside door with metal/plywood/wood handle with a 3” metal tube in the bottom and metal bottom to cover ash hole.  Purpose is to blow on fire to get started after warming chimney with a piece of burning newspaper.

The materials list below is a rough initial estimate as of November 2019. The cost estimates are US$.

ItemSize eachAmountCountCost eachTotal $
Base rock (12 yards)17 ton1750.00850.00
Sand, 2 yards3 ton340.00120.00
Patio pavers?500 sq ft5002.001000.00
Patio edging8′129.00108.00
Portland ready mix concrete60 lb bags40 cu ft803.00240.00
Rebar1/2″x10′155.0075.00
Rebar tie wire14.004.00
Cinder block 8x8x16 smooth on 4 sides7.62×7.62×15.62601.5090.00
Steel 2″ angle iron3/8x2x36212.0024.00
Hardbacker concrete board5/8x3x5213.0026.00
Insulated firebrick on edge so 4.5″ thick2.5×4.5×922 sq ft1502.00300.00
Fine sand60 lb bag 13.003.00
Fireclay60 lb bag110.0010.00
Oven body medium duty firebrick2.5×4.5×93002.50750.00
Red brick with 3 holes2.25×3.62×7.627590 sq in4000.50200.00
Air-dry refractory mortar dry mix50 lb bag260.00120.00
Type N mortar mix60 lb bag154.3565.25
Refractory castable dry mix25 lb bag1032.00320.00
Ceramic insulation blanket 1″x2’x25′100 sq ft279.00158.00
Chimney 6: stainless single wall6x6x48″155.0055.00
Rain cap for chimney6×6 126.0026.00
Damper for chimney6×6131.0031.00
Granite countertop24×52″252550.001250.00
Rendering coat on oven and block sides80 lb120.0020.00
Rental masonry saw per day369.00207.00
Rental cement mixer per day236.0072.00
Rental compactor per day253.00106.00
TOTAL6230.25

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