28" homebrew cast oven in walled enclosure Belgium

[david s]

Yes, you’ll probably need to cut at least 100 mm off the bottom so you can manoeuvre it out the oven mouth. The sand holds everything in place.

[Kris S]

Quick question: after casting the dome with homebrew, do I cover it in cling film for a week to keep moist? Or use wet blankets?

[Petter]

Cling film since it prevents evaporation.

[david s]

You will need to fill voids in the casting while it is still moist so removal of sand and newspaper after about 48 hrs after casting is called for. take some dry home-brew mix and sieve out the coarse sand which will give you a finer mix to force into the voids. add just enough water to make a peanut butter (smooth not crunchy) consistency. Then cover the whole casting with wet hessian or wet blankets (if that suits your personality better ), then cover with plastic sheeting or cling wrap.

[Kris S]

I'm a little confused now, so is this procedure correct please:

after I cast tomorrow I cover the the cast directly with cling wrap or plastic sheeting
--> or do I need to wait 48 hrs before wrapping it in cling wrap?
--> do I need to first cover with wet blanket and then cling wrap or plastic sheeting?

48 hrs later I remove the sand and fill any voids as suggested by david
--> what if the paper is stuck to the cast and I can't remove it to inspect for voids?

5 days later (so one week after casting I remove the cling wrap (and / or plastic sheeting)
(I presume this won't be stuck to the dome by then?)

Then I wait for at least 2 weeks before starting the slow 5 day curing fires.

In the meantime I can cast the flue gallery


Thanks so far for all the help guys!

[david s]

I'm a little confused now, so is this procedure correct please:

after I cast tomorrow I cover the the cast directly with cling wrap or plastic sheeting
--> or do I need to wait 48 hrs before wrapping it in cling wrap?
--> do I need to first cover with wet blanket and then cling wrap or plastic sheeting?

48 hrs later I remove the sand and fill any voids as suggested by david
--> what if the paper is stuck to the cast and I can't remove it to inspect for voids?

5 days later (so one week after casting I remove the cling wrap (and / or plastic sheeting)
(I presume this won't be stuck to the dome by then?)

Then I wait for at least 2 weeks before starting the slow 5 day curing fires.

In the meantime I can cast the flue gallery


Thanks so far for all the help guys!

Directly after casting it will be quite wet. Wait for the casting to set before covering. After 48 hrs the casting will still be quite moist. The voids need to be filled when the cast is somewhere between wet and dry to get a good bond. If the newspaper is hard to remove attack it with a scrubbing brush. Once you've filled the voids you can then start the gallery. Build the sand form in front of the oven mouth and cast the gallery. Then keep both dome and gallery covered for at least a week to damp cure. Don't start any fires while the dome and gallery are damp. Wait until both are dry, then insulate and after the insulation has dried you can start the drying fires. Fires in an uninsulated cast is inviting cracking.

[Kris S]

Allright thanks David!

Just finished casting the dome, all went well I believe. Pictures will follow.

just to be sure: we're having typical varying spring weather right now and next week: 15-25°C winds up to 60km/h and sunny and rainy spells...

It's very likely to rain in the next 48hrs, so should I still leave the cast uncovered for 2 days??

[david s]

"The voids need to be filled when the cast is somewhere between wet and dry to get a good bond" I'll let you be the judge as I I don't know your weather conditions.

[Kris S]

I presume you mean the voids on the inside of the dome, after removing the sand 48hrs after casting.

I'm worried about protecting the outside of the dome from the rain...

Anyway it's raining now and I've covered the dome with a plastic sheet...

[Kris S]

Building the sand castle was fun, much easier than I anticipated.
I first shortened the central stick as suggested by David to assist it's removal when I will empty the sand.
Put some bricks and styrofoam blocks to save on sand.
Still ended up using about three 25kg bags of ~ 1 - 2 mm fine white sand.
Using the quarter arch pivotting on the screw on top of the stick made it easypeasy to shape the dome.

[Kris S]

Next step was super frustrating: getting the strips of wet newspaper to stick on the dome was nearly impossible with winds up to 60 km/h.
Had to call the missus to assist and after a stressy 20 mins we managed to get the dome covered.
Used more layers of paper than I had planned (a little extra weight so it wouldn't blow away immediately) I also ended up with quite a lot of wrinkles... curious to see what the inside of the dome will look like on tuesday...
Then I immediately covered the dome with a wet blanket and a plastic sheet for the night.

[Kris S]

Next day was casting, I used the 3:1:1:1 homebrew mix with PP fibers, but no SS needles.
I first mixed all the dry components before adding water. I worked with batches of ~ 10kg dry and added about 2,5 L of water.
Starting at the base and working up to the top, went quite easy. I tried to push/press onto the newspaper in the hope to get a as clean as possible inside without too much wrinkes and voids...
There was quite a strong wind throughout, so fearing the newspaper would dry out and blow away I always kept the moist blanket on top as I worked my way upwards.

[Kris S]

Looking at some pictures of the casting stage from other forum members I get the feeling my homebrew looks a lot dryer when I put mine on...
I was cautious not to wet it too much, fearing it could sag under it's own weight.

[david s]

You will find out when you remove the sand. It looks ok from the pics though. Too dry and you'll get more voids, too wet and the castable will slump and perhaps get some shrinkage cracks.

[Kris S]

I removed the plastic under which the oven was covered last night and today.
I expected to see the underside of the plastic covered in condensation, but this is not the case...

Should I be worried about that?

Should I give it a good hose?
I didn't do that yesterday, should I have done so?

here's a close up of the surface. I don't see any cracks or crumbly bits...