42 build in queensland

[david s]

Thanks David, the wires are around 0.3mm. I looked at one of the manufacturers in Australia (antec or something like that), and at the specs of theirs when trying to work out what size wire to get. The only way I could get near the size was the cable option.

Thanks for the tip on filling the mould with sand, I had thought previously about filling it with water, but I knew that would just leak and be no help, can't believe I didn't think of the pile of sand I have laying here spare... I used under 27litres of sand filling the mould, and I have 3 bags of castable. The seller told me it takes 4 to 5 bags to to a 1m by 1m by 50mm slab, so that works out to be 10 litres per bag, so I have 30 litres of castable to play with.

Does the motor oil/kero mix stain the castable, or more to the point, would it affect painting it afterwards. I'm guessing I'd have to use a strong detergent to clean that off once the castable has cured enough, or does it not really leave any residue on the castable.

Sounds like your wire should do the trick. I get my stainless extract fibres from Antec
The reason I use motor oil diluted with kero is so I don't end up with the casting coated in oil, it comes away pretty clean, but I do apply it fairly sparingly. Unfortunately plaster is very absorbent, so the wax is probably a good idea to seal it first, then apply the oil. If you're not wanting to make anything stick to the casting then it doesn't matter. If you are planning to either cover the flue gallery casting in blanket or vermicrete then you won't even need to clean the surface.

[SirClutzz]

ok thanks, I'm still worried about the oil as we want to paint the flue gallery for the final finish.

[david s]

Just scrub it with some detergent and rinse off

[david s]

Just scrub it with some detergent and rinse off. But don’t paint it until you’ve had many firings or your paint can blister from the moisture being pushed out by the heat. The same goes for the outer render.

[SirClutzz]

All done, now we wait..That stuff was really heavy to mix. How long do you think I need to leave it before demoulding?

[david s]

Wait 48 hrs. 24 might be sufficient but 48 is safer. You have a far better solution than attempting a flue gallery top made of brick.

The advantages are
1. no joints to fail from thermal expansion issues.
2. less weight on the large radius unbuttressed arch.
3. reduced labour (although in your case considerable time has been invested in creating a mould)
4. reduced volume of material, saving in costs.
5. smoother smoke flow to the flue pipe.

If you have any castable refractory left, do not leave it in its bag and store it on the concrete floor of your shed, it will go off. Empty it into a plastic bag and store it in a bucket with a sealed lid.

[SirClutzz]

ok cool, I'll probably wait until Wednesday afternoon then, I'll have time to pull it out then.

I prefer the look tbh, and was always worried about the thermal expansion around the flue. I have enough left over bricks to have done it in bricks. Thanks so much for your help and input.

My next question is...

Cleaning the bricks, as much as I cleaned up as I went, so there's not chunks of mortar sticking around, I do have a whitish (I assume lime) haze that I'm trying to clean off. I'm trying vinegar atm, which I think is helping, but its a bit of a painful process. I have have some pencil marks that I cant seem t shift.
The bricks also have a blue stamp on them and I can't seem to clean off. Any suggestions. Vinegar did nothing, tempted to try Hydrochloric acid (muriatic acid), but laying in the oven on my back using that is probably not a great idea.

[SirClutzz]

So I'm wondering if the castable has failed, and why it might have done so. I've started to demould it, and can see strong colour differences from the different bags of the castable, in the pics, the darker gray castable on the left of the pic is nice a strong and the surface is barely able to be marked, while the lighter stuff in the middle I can mark with a finger nail, and scratching it away from the formwork in the middle there, it just crumbles. I had initially intended to break the mould to get this out, but right now, I'm half expecting the whole thing to crumble away so I don't want to sacrifice the mould. I've reached out to the supplier, but waiting feedback from them atm. I am wondering if they have sold me different castable or if some was older and no good. I did purchase 2 bags, then worked out a week or so later that I needed a 3rd, that 3rd bag is the hard/different colour castable.

Pretty shattered atm..

[SirClutzz]

heres a video I uploaded to youtube to show how soft and crumbly it is

https://www.youtube.com/shorts/_kDn_VXtPzo

[david s]

It’s hard to say but it sounds like the product has failed. Was it lumpy when you mixed it? Are you sure it was dense castable and not insulating castable. The different colour suggests it could have been a different product.

[SirClutzz]

other then the different colour, I didn't notice much difference, but I can't really remember. I do know the bags looked different, like the manufactor had changed their graphics slightly, made me think some might have been old, and there was a date of 2020 on the older bags, so unsure if that means anything.

The supplier has asked me to let it cure for another day, as when it's thin it sometimes takes longer to harden, but I think he is being hopeful, as the it soft anywhere that mix is, even where it 80mm thick I it doesn't harden up, he's offered to replace the bags, then I just have to work out how to save my mould so I don't have to start from the beginning all over again..

Thanks

[david s]

Some folk say not to use castable that is over 12 months old, so it could well be off. I've had a bad batch and the supplier replaced it, so it's not an uncommon problem. For the temperatures we use, much of the ingredients used in castable refractory are not required. The homebrew, which is almost as good is far cheaper and easier to work with, but does need the burnout fibres added and a week of damp curing, whereas the proprietary castable has the fibres already mixed in and the different chemical reaction of the calcium aluminate cement only requiring 24-48 hrs to achieve full strength.

If you have to start again, it would be far easier to mix some perlite or vermiculite with some cement or plaster to make a weak brew that is easy to break away. Create a hump mould over which you can trowel a new batch of castable. Damp sponge the outer surface to remove all tool marks and you're done. Throw away the hump mould. Even easier is to cast gallery in situ, that way you don't even need to move and mortar it into position.

[SirClutzz]

the suppliers has replaced the castable, so that's all good. Getting the failed castable out of the mould was... not fun. The unset castable would rather break up, then come out clean. In the end I cracked the mould and then resorted to some controlled cuts. Contemplating dumping the mould at this point, but decided to see if we could repair it, and it went quiet well, and we should be casting again today. I didn't take photos of the mould in a pile of 50 pieces, I didn't want a photo memory of that one... But I do have pics of the back in the box, ready to be repaired.

[SirClutzz]

Castable pour went pretty well I think, but now we wait...

[SirClutzz]

looks good, will demould tomorrow afternoon