How to: Building a block arch.

[Big_Eddy]

There have been a number of threads asking how to build a block arch.

I've been running this setup for 20 years, taking it down and setting it back up each season. I've pretty well got it as good as I think I can. Thought I would pull together a quick thread with pictures showing my usual setup.

Details - 2x3 mild steel flat pan.
Standard solid Concrete blocks
7" chimney.
Boils at 5-6 CDN Gals an hour (6-7 USGals/hr) consistently.

Pictures were taken over the last couple of years.

Build the arch.

Find a relatively level spot. Up to 4" variability is workable.
Lay a foot wide bed of sand or gravel where the blocks are to go, leveling as best you can. I keep a couple of buckets of dry sand in my shed so they are not frozen in the spring. Gravel works too.
Lay the first layer of blocks, starting with a full block at the front of each leg and level as you go. To level, tilt a low block up on edge and add a little extra sand under it. Run the arch about 18" longer than your pan and make the gap between about 2" narrower than your pan.
Lay a second row, starting with a half block on each side.
Toss broken blocks and stones in the back half of the arch to fill the arch up to about 2" below the top of the blocks.


I use a flat plate to support my chimney. Over the years I have tried elbows, exiting the back, gaps in the blocks, but this plate is the simplest and most effective. It is a 1/8" 24" x 12", with a 7" hole hacked in the middle, and a ring of 1"x3/16" flat bar welded to it. This gives a secure base for the chimney and makes building the arch simple. Chimney is supported with 3 guy wires to concrete blocks on the ground.

I built a grate out of 1/4" angle iron which keeps the fire off the ground.

Finally, drop the pan on the blocks, bring it to the front, and adjust the rear plate so that it is flush with the back on the pan.

[Big_Eddy]

I use a simple piece of sheet metal for a door on the front. I place a couple of blocks on the ground in front and space them a couple of inches apart to allow air under the grate, then place the sheet metal on top of those and trap it with a couple of blocks on the sides. Not sure that the picture shows it well.
Even this simple door makes a HUGE difference to the boiling rate by preventing a cold draft from running under the pan.

My chimney is about 12' of 7" standard stove pipe. I use 3' of wire at the top, then ropes out to concrete blocks to support it. I run one out to the rear and one to each side. If you are going to walk near them, FLAG THEM!!!!!

I build a small ramp and platform next to the arch and back my sap trailer up onto it. Filling is a simple as opening the valve, and I leave it cracked at a trickle when I am boiling.

Firing is every 10-15 minutes with a handful of sticks under wrist size. I have the good fortune of having a young woods and each year I have plenty of young 3-4" diameter trees that didn't make it. I collect them by the trailer load, and place them on the sawhorse to buzz through in bulk. I have no idea how much wood I use each year, but the pile shown might last a weekend.

[Big_Eddy]

With a flat pan, it's a batch operation. I usually run 3-4" deep in the pan, depending on whether I am standing guard, or off doing stuff. Firing is every 10-20 minutes. 6 sticks every 10 minutes will boil more off than 12 every 20 mins, but when I need to go collect or .... I jam it full and come back later. I can boil off about 1" every 20 mins if it's under 4" deep, so if I plan to leave I make sure there is enough to cover the time away. If the pan gets over 6" deep, the evaporation rate drops off substantially.

A batch for me is 60-80 CDN gallons, which is a good days boiling. Any less than that and it is impossible to take it to syrup in the 2x3 flat pan. Each cm of depth is 5.5liters of syrup, or roughly 55 Gallons of sap.

I've done this long enough, I can tell when I am close enough to take off. I don't bother with a thermometer. When the pan is down to 1cm, I have 70 gals in, and it looks like syrup, I stop firing with wood and move to handfuls of twigs every couple of minutes until it seems just right.

To take off, I rotate the pan 45 degrees over the fire, place a 20l stock pot beside the blocks, and pour out the corner. The fire needs to be OUT or almost out, or as soon as the syrup pours off the pan, the sticky will burn on. A couple of handfuls of snow into the arch will kill the fire. I remove all the ash from under the grate each time I start a batch, and just dump it in the rear of the arch amongst the rubble.

I finish on a propane fired burner and test with a hydrotherm. Half the time I'm almost there, half the time I need to thin with some sap.

[Big_Eddy]

Some additional comments.

I use solid blocks rather than hollow ones as they last longer. I lose a few every year, but they last 3-4 years before they crack and even if they crack, I don't change them during the season. I keep anything over a half brick and the rubble goes in the back.

Have been using the same chimney forever. I store it inside in the summer.

Some years, the ground under the arch will thaw after I have built it and the blocks will shift. A quick shovel full of sand under the low points and we're back to level.

The 3 guy lines for the chimney are just tied around solid blocks and placed on the ground. They keep the chimney vertical, and put down force on the base to stop it moving around. They have withstood tornado strength winds without issue.

Strong winds drop the evaporation rate to nothing. As does rain. Actually, the whole setup sucks in the rain and your evaporation rate goes the wrong way.


Let me know what else might be useful.

[happy thoughts]

Awesome, Big Eddy! Great details and pics. This is really going to help a lot of us get started. Thanks so much!

[Pibster]

What did you use to make your pan?

[Big_Eddy]

My pan is ~20 gauge mild steel. It's 2'x3' and about 8" deep, with 2 handles on each side. It was given to me by my dad 20 years ago and has withstood 20 years of boiling without issue. He has an identical one that he still uses too. At the end of the season I DO NOT clean it and hang it up on the wall in the garage. The soot and sugar protect it from rust. At the beginning of each season I hose off the major soot from the outside, and give it a brushing with a stiff brush on the inside.

We've had one "disaster" where the kids thought I was watching it and I thought they were watching it. We burned a whole batch to charcoal. I "cleaned" the pan by setting it back on the fire dry and leaving it there until the rest had burned to ash, then hit it with a wire brush. I have a slight warp in one corner but it has not been a problem.

[TapME]

you have done well with your arch. I only have half the time in mine that you have. Best thing is the end result is the same. Sweet nectar from the maple tree.

[boblangdon]

Gosh, Mr. Eddy, it's awfully nice of you to share all this stiff with us. Thanks!
:-)
Looks like I need to take a welding class this summer.

I HATE buying stuff... not because I'm cheap or poor (well, maybe a little of one ;-), but I have this "character flaw" that makes me want to do everything the hard way.
I suspect you understand.
;-)
Thanks again for all the GR8 DIY tutorials!

[tpallen]

Just wanted to use my first post to say thanks to Big Eddy. My new block arch was just put together this year based on his concept. Didn't fire it yet but plan on boiling this Saturday. 954295439544

[Big_Eddy]

tpallen
Glad to be of help.

I like what you've done. Your long narrow pan is going to be much more efficient than a shorter wide one would be. Your challenge with only ten taps is going to be getting enough sap to be able to get anywhere near to syrup in that pan. You will need almost 70gals in the pan if you want to take it close to syrup before taking off. Time to find some more trees :D

If you don't mind another suggestion, I would recommend you split your wood smaller if you can. It will burn hotter and faster if you do, and will speed up the process. You might end up using a bit more to boil off the same amount of sap, but you'll be done much faster.

Good luck with it, and post back how you make out.

[tpallen]

96169617

So I finished my first boil this last weekend and overall I'm really satisfied with the results. Big Eddy you are correct, my syrup output vs boil time was much better when I figured out that small chunks (wrist size) work so much better. First day (Saturday) I was cooking off about 3.5 gal/hr because after 6 hrs I called it quits and finished off inside with a 1/2 gal of syrup. Then on Sunday firing with small wood I finished with 1 gal of syrup boiling the same 6 hrs long. Pretty much had a pencil sized stream of preheated sap going in without throttling back on the ball valve. I was adding a couple chunks every 10 minutes and kept the depth in the pan to about 1 inch. The only down side to this was trying to play catch with the kid and keeping a close eye on the pan was somewhat challenging.
Again thanks for the info! Appreciate it!