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You are on the [OvenRepairs] page of folder [Dufferin Grove Park]
For the cover page of this folder go to the Repair and operating issues
smoke damage to insulation and roof
During the fall/winter of 2011/2012 the Dufferin Grove bakers noticed occasional little bit of smoke curling out from under the oven's roof overhang. In April, when the snow was gone, they got a carpenter to take off the shingles and open the bottom part of the roof where the smoke seemed to be. Indeed the roof insulation was blackened in places. The bakers pulled out that insulation and replaced it with new insulation. There seemed to be no actual fire damage, and there was no effect on the baking. The carpenter put fresh plywood over the spot and re-shingled the roof. Since then there has been no more smoke leaking out.
Oven builder Alex Chernov suggested to us that there have been design improvements since our oven was built. He said the when the insulation is packed in like in the Dufferin Grove oven, over time the heat communicates from the oven dome through the insulation to the wooden roof.
the blackened insulation near the front was replaced
the plywood was replaced
hearth and shelf damage, probably due to wet mopping; crumbling chimney bricks
smaller oven, hearth uneven, bricks worn down
bigger oven -- shelf bricks worn down
smaller oven, shelf slab worn down
The smaller oven door was built by a city welder, who billed $900 for the job. The door is solid but has always been sticky. The water damage on the hearth is annoying but it's primarily in the middle, so the bakers work around it. The corroded parts of the shelf in either oven don't interfere with baking -- they just look worn down.
crumbling brick on bigger oven chimney
The chimney pipe is also cracked. Some ovens don't have chimneys at all, so this factor also doesn't interfere with the baking. But it would be nice to make it look right again.
Oct.23, 2014
Two staff from Facilities and Real Estate Division (FRED) came to look at the oven shingles and chimney. The bakers showed them the damaged hearth as well. The FRED staff asked for information about a builder who might be able to fix the hearth, and we sent them a link. No follow-up so far.
July 10, 2015
A longish thread of staff requests about the work orders that might be necessary to get the ovens fixed.
July 12 2015
Jonathan White at Dufferin Grove
Jonathan White, a cheese maker and baker who lives on a farm an hour from NYC in New Jersey, had emailed us about our oven (his oven is also designed by Alan Scott). After some back-and-forth on email, he took a Porter flight from Newark and came to visit. He took a close look at both ovens and said he intends to come back on September 14 to repair the little oven hearth and door, in memory of his friend Michèle Cherrington.
Jonathan said he had some concerns about the bigger oven's dome as well, but some of us feel that this is not the time for CELOS to undertake major oven repairs -- too much uncertainty about recreation staffing of oven programs.
August 4 2015
An email query to Alex Chernov of Stovemaster (about the possibility that the oven dome might be unstable) came up with the surprising information that city staff had asked him to come on a Wednesday to assess what needs to be done to repair the ovens. We wrote to him to explain that there is always fire in both ovens on Wednesday, so he needs to come very early or on a different day to assess the ovens. The bakers were added back in to the email thread.
August 8 2015
Took photos of the inside of the big oven.
brick descended at the front
two bricks seem to be resting on oven door ledge
view to the back, old crack along top middle
hearth
August 18 2015
Alex Chernov visit
Alex Chernov, the city's consultant oven builder, came to inspect the two DG ovens today, and gave his suggestions. He felt that the big oven might just have the two bricks put back in securely with new mortar, not a good idea to take off the roof at this point, and no sign of actual oven collapse. Park baker Heidrun said she might try doing it, with scaffolding and various safety helps.
Alex also had an alternative suggestion for the hearth of the little oven. He said that much of the hearth looks like it's not in great shape.
Alex says he's had good success in the past just putting a layer of 3/4 inch refractory kiln tiles over an existing damaged hearth, i.e,. over the entire surface. He says that these could be pushed in without someone squeezing inside the oven. Alex pointed out the the oven door is very narrow and it would be quite difficult for someone to get in there to remove the most damaged bricks and level in the new ones.
Also Alex said it ought to be fairly simple to re-mortar the loose front brick back in, so the oven doesn't leak so much heat -- photo #37 of the photo record shows the way it fits in.
Jonathan replies:
I'm not sure what he has in mind here. When the arch was built, the bricks were dry-set against a wooden arch, and then mortar was applied from above. A dry brick that has fallen out can be pushed back up into the cavity whence it came, with difficulty I might add, but I cannot picture how you would get mortar in between the replaced bricks and the adjacent brick. I have used refractory cement on the top of such a brick, with some success, but without bonding to the adjacent bricks, that brick is going to come right back down with time. Maybe I should talk to him, maybe he has a trick I don't know.
Again, I can't picture how you could securely lay tiles on such an uneven surface. Even if you succeed to get them to lay evenly without rocking, the air gaps below the tile where brick mass is missing could create cold spots, which would seriously affect the baking.
I rebuilt the hearth on our old oven without "going in": I pried the farthest bricks out with a chisel stuck into the end of a length of steel pipe, and used a mallet and a 2x4 to put the new ones in. It takes time, but I'll have all day, and part of Tuesday if need be. Alan, of course, skinny as he was, would probably just slither in. I miss that guy!
Brick advice from Alex Chernov
KX-99 is a low porosity super-duty firebrick. In general, lower duty (medium-duty) more porous brick is preferred for hearths in bread ovens since high density low porosity brick tend to overcook bottom of the bread b/c of higher thermal conductivity.
For this reason we use high-quality imported Austrian-made medium-duty hearth tiles or medium-duty Alsey firebrick. The first would not work for you in your proposed fix and the last could be used, although it is fairly soft and eventually will get worn. That being said, what you have there is low-duty Whitacre-Greer firebrick, which is even less strong....
For better strength and still acceptable porosity I suggest Alsey high-duty Jet-DP brick. These are available from the best refractory supplier in Toronto I use: http://www.alphatherminc.com/ Ask for Elvis there. They may also have KX-99. If not, they do stock some comparable super-duty brick, but I would not recommend it.
Also, keep in mind that Whitacre-Greeer firebrick is typically smaller than true 2.5", more like 2.25", whereas Alsey are true 2.5" thick, This means that Jonathan would need to cut some of the brick to fit in between existing ones.
Reply from Jonathan White
"...considering that the Whitacre-Greer 2.25" low-duty bricks lasted 15 years of water abuse, I think we should go ahead and use exactly what Alan used!"
Sept.4 2015: trip to Tucker's Pottery Supplies and Kreitmaker Inc. to buy hearth repair supplies
a tub of refractory cement
a bag of white fireclay
Hearth repair day for the smaller oven, Sept.14 2015
Jonathan White and his wife Nina flew up from New Jersey to make the oven repair happen. Jonathan and Mike Conway (from CELOS) started work at 9 a.m., getting all the tools together. Park baker Heidrun Gabel-Koepff spent most of the day as well, including climbing right in the oven (photo below) to vacuum out some of the dust.
Jonathan and Nina own the "Bobolink Dairy and Bakehouse" on their farm in western New Jersey, about an hour and ten minutes from New York City. They participate in many markets in NYC as well as having events at their farm. They have over a hundred milk cows. Jonathan does the dairy and Nina does the baking, in an Alan Scott oven not much different than the big oven at Dufferin Grove.
Jonathan came across the Dufferin Grove ovens on this website. He decided to help fix the smaller oven hearth to honour the memory of a friend of his youth from Toronto, Michèle Cherrington.
August 18 2015 -- hearth worse every day
The bricks came out easily. There was a lot of ash underneath, which Nina and Jonathan both felt might be the result of too much water use when mopping out the oven -- driving the ash right under the bricks.
starting the hearth-brick removal
progress
There were a lot of eroded bricks but Heidrun's count beforehand was correct -- we even had a few extra new bricks left over. Once the bricks were out, the bed of fire clay underneath was solid and level. One could still see Alan Scott's parging marks, from 15 years ago.
fire-clay bed from 2000 still excellent
a lot of eroded or cracked bricks!
Heidrun got into the oven and vacuumed out the rest of the ash at the back. Meantime, as more visitors from other public ovens came to see the repair work, Mike took the time to repair a market bench that had been partly broken for a long time.
brave baker Heidrun gets right in to vacuum out ash
repair assistant Mike fixes a broken park bench
Jonathan had spent time beforehand thinking about how to level the fire clay under the new bricks, so that the hearth would be level. But it turned out not to be a problem -- the fire clay from when the oven was built had hardened over time and the bricks sat level.
Park friend Pete Gaffney lent his masonry saw, so Mike was able to cut the final bricks to the right size for the front of the hearth under the door frame.
new bricks are level with no problems
Mike puts in sawed bricks under the door frame
visiting bakers had lots to talk about
The bakers from other public ovens who came by to watch, and catch up on oven issues over lunch: Dale Howey and Tania Davidson from Montgomery Inn oven, Zahrah Munas from Regent Park oven, Leah Houston from (former) Mabelle oven, and Gene Threndyle, from the Artscape oven at Queen and Crawford.
Jonathan readies the refractory cement
The final step was replacing the broken upright brick by the oven door, fastening it in with refractory cement. That's the end of the heat leak. Now the cement has to cure for a day, and then the oven is ready for use again.
replacement all done, like new
Jonathan and Nina are pleased, and no wonder
At 6 pm, friends and family of Michèle Cherrington, in whose honour Jonathan worked on the oven, came over to the park and later to the CELOS house, to celebrate over Bobolink cheese and bread and Portuguese wine, also provided by Nina and Jonathan. A very good day!
September 16 -- first baking day on the new hearth
The oven still has crumbling mortar above the door but it doesn't go right through and therefore doesn't seem to affect the heat.
fire at the back
some crumbling mortar above door
The oven didn't retain its heat very well after the first fire, so another, bigger fire was put in. That one took the temperature up to 600F.
second fire, to bring up the heat
Michael and Heidrun checking the temperature
first sourdough breads go in
first breads come out
The spelt rye came out looking just fine.
March 2016, Dufferin Grove Park
barriers to block the public -- but no repairs
New rule: when there's a fire in the ovens, they have to be blocked off.
Reason: so that no one can jump inside.
Effect: On a bread baking day, the bakers have to tend each oven around 10 to 15 times per oven and per firing. That amounts to 20 to 30 times per oven per firing for the two ovens. That adds up to 40 to 60 times of the bakers moving the barricades on Wednesday and 40 to 60 times on Thursday. In addition to that they have to set it up - moving 2 heavy barricades to position them in front of each oven, and afterwards to put them away again.
Note: this new rule appears to be modeled on the Riverdale Farm oven rules. That oven no longer has public use.
Content last modified on August 11, 2016, at 02:33 AM EST