Which Sand To Use?

[Dwisda]

Will any sand work (like play sand) or do I need fine sand (I've read pool filter sand for some mixes) for the 3:1:1:1 homebrew castable cement?

[MarkJerling]

Builders sand will work, but avoid sea sand as it's structure is too rounded and contains far too much salt. Play sand is usually much finer than builders sand. I'd avoid it as being too fine.

[Rosy]

Will any sand work (like play sand) or do I need fine sand (I've read pool filter sand for some mixes) for the 3:1:1:1 homebrew castable cement?

My brick mason friend uses Silica sand from home depot. The play ground sand grains are too rounded and microscopically do not stack up the same as silica sand

[wolfmoonex]

silica sand is recommended hands down

[Dwisda]

I read that silica sand is prefered for refractory Mortar, but may be too fine for actual castable refractory Cement. david s 's castable mix PDF specifies "coarse" so I was wondering if silica sand is coarse enough, or would all purpose sand be preferable? Note that actual sharp or coarse sand is very hard for me to source, while I can easily buy bags of quickcrete pool filter (silica) and all purpose sand.

[mrsrat]

I have found you can get medium and course silica sand at places that have supplies for sand blasting like Northern Tool.

[david s]

For mortar fine sand is better, but for a castable mix a range of grain sizes is preferred, so coarse sand works better.

[Dwisda]

Thanks! Im making a low budget ~ 300 dollar dome castable build with ceramic blanket + 10:1 vermiculite insulation. I plan on making a fiber glass mold over a 32" gym ball with 3-4 sections for expansion lines. Fire brick is crazy expensive around me right now, so I'm planning on using the near infinite amount of clay brick that I have in my garage for the floor + entrance, knowing this thing isnt going to last much more than 5-10 years.

[david s]

Making a fibreglass mould to produce one oven is a ridiculous amount of work. But if you plan on making a dozen the time spent might be worth it. Far easier, for a single casting, is the sand castle method used and well documented here in other oven types.

[fox]

The first fiberglass mold I made took about 100 -120 hours and was pretty expensive in materials too.

it lasted for around 20 castings all of which I either installed for customers or sold as a DIY projects. So it did pay for its self over a few year period.

i am building a new one at the moment but nothing has changed regarding the amount of work involved … not if you want to cast a 5 component interlocking dome anyway!

[Dwisda]

I have alot of experience with fiberglass and have a friend who will likely use it when I'm done. 2-3x 9 dollar fiber glass sheets + 10 dollars in resin and a day of waiting. But I may use the sand method. I just want to make a mold that allows for sectioning of my dome structure into a top section, and 3 lower ones as ive heard cracks occur during the curing process as the top heats at a different rate than the sides. If I find a good way to do that with sand, I may do that.

Edit. I'm pretty sure I can make section dividers on the sand dome with plastic wrapped cardboard so that's prob plan A.