#11  
Old 08-07-2010, 09:20 PM
david s's Avatar
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Default Re: Remove Air Bubbles from Refractory Cement

By the way, 24 Hrs is all you need to cure the castable. You do not have to keep it moist for a week like concrete. It is a different chemical reaction. Normally remove from the mould after 24 Hrs.
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  #12  
Old 08-07-2010, 09:37 PM
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Default Re: Remove Air Bubbles from Refractory Cement

I have mixed about every type of bag mortar, cement, and concrete. I have only followed the manufaturers water/mix ratio one time (sand mix for a shower liner). Every other time it has always needed more water (usually nearlly twice as much). I'm not going to dispute the manufacturers claims, somehow they can make it work, those of us in the real world are not idiots, we are just adjusting so that we have a workable mix.
I have built or laid thousands of ft of brick. block. cement slabs, and every type stone or tile. NEVER a problem with loosening up the mix with water, would not worry about that aspectyou are good to go

RT
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  #13  
Old 08-07-2010, 11:03 PM
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Default Re: Remove Air Bubbles from Refractory Cement

Yeah, it often depends how dry or wet your sand and aggregate are too. Maybe it's an arse covering exercise by the manufacturers so they can say the product failed because too much water was added. Check out Cosmotron from Ability Building Chemicals. It's great stuff.
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  #14  
Old 08-08-2010, 10:08 AM
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Default Re: Remove Air Bubbles from Refractory Cement

Hi Guys

Thanks for all the encouring words.

David s the oven is being built at a friends house and th next time I'm back there is a week from now.

I was wondering whether it would be a problem to leave my cast in its form till then or is it strictly 24 hours and must be removed.

I pictured the building of the oven as a breeze but I now know I was mistaken. Its a painstaking task but the joy I get out of success after so many failures is truly unexplainable and I love a challenge.

Wish me luck guys, I hope to have the next piece casted soon and once all 4 are done, its of to the next step.

Thanks guys
Regards
OM
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  #15  
Old 08-08-2010, 01:40 PM
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Default Re: Remove Air Bubbles from Refractory Cement

There should not be any problems leaving it longer. The first casting is always the most difficult to remove. Subsequent castings release more easily. I use 50% motor oil and 50% kerosene as a release agent, but other methods are ok too.
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  #16  
Old 08-08-2010, 03:25 PM
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Default Re: Remove Air Bubbles from Refractory Cement

Thanks david

I just hope that certain parts of my cast don't get stuck to my form and my attempts to remove it doesn't damage my form or the cast for that matter but when the time comes, I'll only know.

I'll try your method for casts to follow and maybe even try using oil to loosen the current cast from the form should it get stuck.

Guys, please feel free to provide any other tips.

I'll let you guys know how it goes

Take Care
Regards
OM
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  #17  
Old 08-12-2010, 05:19 AM
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Default Re: Remove Air Bubbles from Refractory Cement

You may need to drive some wedges between the mould and the casting to assist removal. Be patient the first one is always the hardest to remove. Sorry have I already said that?
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  #18  
Old 08-12-2010, 05:40 AM
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Default Re: Remove Air Bubbles from Refractory Cement

You've already poured the 'crete, but another option, for future readers is a hammer drill. I chucked a bolt into the hammer drill so the head was exposed and then placed that against the form and pulled the trigger. WOW!! It would create huge vibrations pulling the 'crete into the bottom of the form!
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  #19  
Old 08-12-2010, 06:05 AM
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Default Re: Remove Air Bubbles from Refractory Cement

You have to be somewhat careful. There is an ideal frequency that will remove air bubbles, consolidate the material but NOT lead to aggregate segregation. Hand orbital sanders are as close as you can get without spending a good chunk of change to rent or buy an actual immersed or form vibrator.
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  #20  
Old 08-12-2010, 10:20 AM
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Default Re: Remove Air Bubbles from Refractory Cement

Hi Guys

Thanks for all the replies. You guys have been undoubtably helpfull.

Today I reached my friends house to remove the cast from the mold and got a surprise of my life.
I just felt like I've wasted a load of money and time but I know someone here probably has a solution.

Never the less, here's the problem.
My mold is in 2 pieces. First I have a 1/4 sand dome ontop of which I built a form from wood. The plan was to place the form over my sand dome and pour the cement in since I heard the cement would be very runny. Anyways now when I opened the top mold being my wood form, I got a shock. My cast was completely filled with voids and holes. The perfect example to compare with is a Bee Hive. The cast was filled completely with holes and looked just like Hive. Sorry I know I'm repeating myself but I'm just so frustrated and upset right now.

Anyways, I've taken pictures of the Cast to better explain the situation I am in.

The first picture shows the bottom left hand side of my cast. This side was where I initially started my cast. This was the first or possibly second batch of cement that I made and I was still learning about refractory cement in particular and how to use it.

The second picture again was the bottom of the cast and also is the first few batches of cement when I realised I needed more water and the consistancy of the cement just wasn't right.

The third picture is that of the top most part of my cast which was the last part of my cast I completed. This was after few tries with this cement that I found to get the right consistancy, I needed to increase the water contact by 50%. So instead of the recommended 100ml of water per KG of cement, I needed 150ml of water per KG Cement.

I also noticed the steel fibres are just pulling loose from the voids and holes in my cast.

Right now, I've removed the wooden form, but my cast is still sitting over a sand dome made from concrete and I can already see issues releasing the cast from this concrete.

I thought, before proceeding further, let me first sort out the voids and then I can try to remove the cast entirely.

Guys, I'm at a loss here and in great panic right now. I just don't know what to do or try to sort this out.

Really looking forward to hearing from everyone.

Take Care
Regards
OM
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