castable refractory

[mr g]

Re: castable refractory

Hi all, just a quick report on how the entrance casting went over the weekend. As a lot of people hinted the castable was pretty tricky to work with. The difficulty was the vertical walls. It seemed like it was either too runny or too dry but we quickly rigged up some forms and it all seemed to go quite well. It is obvious now that the dome will have to have outer forms for the verticals.
Other than that it was a success as far as I can tell. I ended up using a product called Silacast 145 which is the equivalent of the Densecrete 145. I added about 11% water by weight for best results. I didn't spend too much time
vibrating the concrete for the entrance but I'll definitely do that for the dome.
I'll spend some time casting the dome this coming weekend.

Cheers.

[david s]

Re: castable refractory

It will slump if you use too much water. Just get your mix right. Don't mix up too much in one go, it goes off pretty fast and is expensive to waste it. It's also thixotropic which means that it will go more runny with a little agitation. Follow Johnnys advice on the consistency.

[mr g]

Re: castable refractory

Thanks Johhny, will let you all know how I fare tomorrow.

[Johnny the oven man]

Re: castable refractory

Perhaps mr g might want to give me a call, we are in the same town. 95604477.

[pacoast]

Re: castable refractory

I'm not disagreeing with anything that Johnny just said. But mr g, I think you'll find that the castable will slump, that is shift downwards before it sets even if you tried to mix it thick. I haven't seen any castables that are thick like putty.

I hope that it works the way you want & you may have found a thicker product than I have seen. But perhaps give it five minutes thought as to how you will handle it if it doesn't go according to plan. Perhaps a partial second form or something that would help if you run into problems.

Best of luck on the pour!

.

[Johnny the oven man]

Re: castable refractory

Castables should be mixed to a consistancy that is niether runny or too dry. If you can get a ball of the mix in your hand, it should not ooze through your fingers when squashed, and should not crumble when thrown in the air about 2 meters and caught.

[mr g]

Re: castable refractory

Hi Pacoast, yes that is the big question - will the castable simply run down the sides and not hold. I'm casting my first one tomorrow so I'll post an update soon. What I intend to do is cast the entrance part first which will only take two to three bags so if things go bad I haven't lost too much money.

Regards,
Mr G.

[pacoast]

Re: castable refractory

I'd be really interested if you figure out a way to reuse your sand forms. It might work if you mixed enough cement into the sand to hold it together - but that is just speculation, I haven't tried such.

Sand is often used as a form e.g. for low domes. And sand molds are used to cast metal pieces. In which case a reusable pattern is used to set the next sand mold up quickly. I suspect that you want a reusable form. I think that if you "glue" the sand together with more cement than is usually used, it might be reusable. But are you sure that your refractory mix is stiff enough to simply apply it to the sand form? The castable refractories that I've used are runny like concrete and need a female form (second shell) to hold the refractory in place until it sets.

.

[david s]

Re: castable refractory

diy,
The product information I was given on castable refractory says that it does not require extended curing like portland cement. It uses calcium aluminate cement which, unlike portland, only needs 24 hrs to set hard before going through its heating schedule. It's chemical process is different.The clay content in the mix has already been fired (grog) so the shrinkage is zero.

[jonkendall50]

Re: castable refractory

I may have missed this earlier, but what kind of castable are you using? I went to a local place and they had insulating castable and non-insulating. I was thinking that it might be smart to use non-insulating as the dome, cover it with a thermal blanket then a layer of insulating castable.

[diy]

Re: castable refractory

Proper refractory castable should dry out very slowly so then it won't crack

[mr g]

Re: castable refractory

Hi David, it sounds like you make these domes regulary ? Is that right? If so
I have a few questions for you.

Regards
Mr G

[david s]

Re: castable refractory

Mr G,
I think you'll be very lucky to release a casting from a sand mould without damaging it. I have to use a hammer and screwdriver to release my castings. If you are doing a one piece casting it's going to be extremely heavy.

[sonomacast]

Re: castable refractory

Excellent, Good luck and keep us informed and up to date Mr g.

[mr g]

Re: castable refractory

Hi Sonomacast, yes I'll be using a couple of outer templates similar to what I used for the sand dome only 3" bigger to guide me. Yes, we will be making the first one in three sections - two pieces for the dome and one for the entrance. It may be that two pieces for the dome will be too heavy so there is a possibility that the next ones will be in three/four pieces. I'll post some pictures when I have the outer template and separators ready. There's a good chance that the first dome will be cast this weekend.

Cheers
Mr G