Remove Air Bubbles from Refractory Cement

[david s]

Re: Remove Air Bubbles from Refractory Cement

Once the mixture has "gone off" (begun to harden) it will act as an accelerant when you make up the next batch. That is your next batch will tend to go off even faster as some of the previous batch present begins the reaction again more quickly. This also happens with plaster of Paris and fiberglass resins I have noticed. It is a good idea to wash out your barrow before making the next batch. It is a bit of a pain, but will increase the working time of the material. In hot weather I also use chilled water to help increase working time. The material I use has aggregate only about 1-2 mm and I find it easy enough to work with unlike the stainless needles which makes you have to handle the mix carefully. The aggregate used is fired and crushed fire clay (grog) I have crushed quite a few fire bricks to make up a castable mix and it is slow hard work doing the crushing and sieving.

[david s]

Re: Remove Air Bubbles from Refractory Cement

"The aggregate used is fired and crushed fire clay (grog) I have crushed quite a few fire bricks to make up a castable mix and it is slow hard work doing the crushing and sieving."
I should have added that proprietary mixes already have the aggregate mixed in to the correct proportions so all you have to do is add water. You could ask your supplier for a different mix with a finer aggregate, but if you've already bought it then it may be too late or too much trouble to exchange.

[Oven_Man]

Re: Remove Air Bubbles from Refractory Cement

Hi Guys
Hope all are well.

Its been a while since last posting here but since my last post, I haven't worked on my oven until today.

Never the less, I've managed to cast a second piece of my oven (Busy drying in the mold). I've learned a lot from the first piece so I guess it wasn't too difficult. I also became a little more familiar with refractory material so I knew just by feel when it was at the right consistency but time will tell whether this piece has been more successfull than the first.

Coming back to my first piece, I tried the tip of mixing a little bit of cement in a more liquid form so I could easily fill the voids in my cast but this didn't work as I planned for it to. The cement is just too coarse and has a lot of stone, probably the crushed firebrick in it. The mix wasn't as smooth as I hoped for it to be so it didn't easily fill the voids and was too rough to work with.

I even checked with suppliers whether they have a refractory cement that is less coarse than the one I already have and I can't seem to locate any.

Is there any way I could crush the current cement I have further, making it almost like the consistency and smoothness of portland cement?

I'm a little worried since I don't know how my second cast will end up and if it has voids like the first, then I would have the task of doing this to both casts and even possibly all the casts.

Please help guys, I'm panicking here. Spent too much time casting this two pieces that I can't even let the thought of ridding these casts cross my mind. I have to fix them. I've had too many hurdles along the way with this project and overcame all of them, at times almost giving up but I kept pursuing and I've come a long way already so I'm sure there's a fix out there.

I look forward to hearing from you guys.

Thanks
Regards
OM

[Neil2]

Re: Remove Air Bubbles from Refractory Cement

"the recommended amount of water "

This will usually be the minimum amount. You generally will have to add a little bit more water. Just enough to be workable, err on the dry side.

[Oven_Man]

Re: Remove Air Bubbles from Refractory Cement

Hi Neil

Thanks for your response.

I've managed to find the right mix ratio of water/cement. Initially when I started, it was the first time I've worked with refractory cement and finding the right mix ratio took a few tries but still after finding the right mix, my first casted piece still had voids.

I used the same mix ratio for my second piece and I'll know once it's fully dried and removed from the mold, how well it took and whether any voids formed or not.

For now, I have to find a way to fix the first piece, and subsequently the rest of the casts should the same problem arise.

Thanks
Regard
OM

[Oven_Man]

Re: Remove Air Bubbles from Refractory Cement

Hey Guys

Haven't got any more responses regarding this.

Please help in any way possible. I really appreciate it.

Thanks
Oven-Man

[dmun]

Re: Remove Air Bubbles from Refractory Cement

Part of the problem of forging too far ahead of standard procedure is that you aren't going to have people with experience with your specific refractory product. There's really no such thing as standard castable refractory: every vendor has it's own specific proprietary formula. You really need to get help from your dealer, or the manufacturer that they get their stuff from.

I haven't answered your question, not because i'm ignoring you, but because I don't have any experience with castable.

[JoeyVelderrain]

Re: Remove Air Bubbles from Refractory Cement

pictures would help also :/

[david s]

Re: Remove Air Bubbles from Refractory Cement

hi oven man,
What you need to do is put a little of the refractory mix into a sieve and shake it a bit so that it will remove the courser aggregate. Add a tiny bit of water to the sieved mix so that it makes up a paste, then rub it into any small voids with your fingers. This is what I do all the time and it works really well.
Dave