Metal Casting Zone

I thought I read a post stating that blasting sand was undesirable for green sand or refractory use.

you can buy "playsand" at lowes that should be fine for your refractory. I think the grains are too large for a green sand mix though. It might work, but i think you'd probably run into some issues with mold stability.

According to the Navy Foundry Manual, for the highest green strength a rounded grain is the best, however you sacrifice permeability (the ability for gasses in the poured mold to vent through the sand). They pack together tighter.
As far as sand availability, I have the same issue up in the Great North Woods here. I started out with fine mason's sand from HD (it says fine mason's sand right on the bag) and I sifted it through a bacon spatter screen from Wally werld. It gave acceptable results, had decent green strength and I got reasonably good surface quality. I am always on the lookout for a supplier of finer stuff, I did check out blasting sand, I got a bag of 00 mesh (ask for double ought) that was about as fine or finer than the sand I am using now (somewhere around 60 mesh or so), and it is obviously a sharp sand. It seemed to ram up fine, and it cast okay, but it had quite a bit of dry strength and was kind of hard to shake out. I added that batch into my regular sand to maybe improve the qualities a bit.
The secret, I guess, is use whatever you can lay your hands on at the moment, sifted through the finest screen you can find. It can always be used as fill in your backyard if it doesn't turn out right, and you won't be out much money. Most anything will work for the backyard caster, unless you plan on making parts for the space shuttle you are building or something.

That's interesting .. the HD here doesn't carry that stuff. But I get the gist. But what you said that really interests me is the mention of the Navy Foundry Manual! Can I download that in a PDF for free. Being a Marine veteran, I have many hard copy/digital military field manuals and this would be a perfect addition to my collection.

Today I bought 50 lbs bag of bentonite clay from a well drilling supply store! When I picked it up they mentioned that they had double ought sand (00 sand). He gave me a 100 lbs for free because the bags were busted. The kind of bentonite I purchased was this --> http://www.wyoben.com/WBassets/z-downloads/product_sheets/extrahighyield.pdf ... After I found the clay supplier's website I found this --> http://www.wyoben.com/WBAssets/z-downloads/product_sheets/bighorn_fnd200.pdf. So I'm just wondering if the stuff I got will work ... I'll say this much. When it gets wet it's slicker than snot! It's used for directional boring and well drilling.

One other question. How do I dry out my sand? It's been outside and is very moist. I want to make sure it's dry before mixing to make green sand.

sounds like you have some good stuff there!getting the sand dry is a curse in bad weather. its taken me a yr to slowly but surely build up a supply! some powder the clay in a mill/blender but i mix small amounts to a complete slurry and slowly dry it off in the sun little bit by little bit! you can use a hotplate on the bbq or a tray in the oven if you are desperate!! been there done that! this is why i advise others to start with their sand and whilst its drying build the furnace.remember the idea is to coat each grain of sand with a coating of clay. this is why the sand must be as fine as possible to start with!

Finally! the man got his sand! and clay to boot. Put the sand in a coffe can and put it in the oven and set to its higest temp for a few hours to dry it out.

Heh ... it's been a long time since I had a coffee can. I buy whole bean coffee. But I'm sure I'll find something. Bake it for a couple of hours eh? Wife's gonna like that one. Do I need to strain/sift the double ought sand before I start to make green sand?

And here is the recipe for the refractory. http://www.backyardmetalcasting.com/refractories.html This one calls for Portland cement whereas the Gingery recipe does not. Any ideas which is the best?

That Bentonite looks like good stuff. Make sure you mix it and the sand dry or it turns to a lumpy mess.
I picked up some foundry sand from a big pile where we knocked down the storage silo. I dumped it out on a tarp on the garage floor and just stirred it a couple times and it dried right out. It was winter and the humidity was low so it may take longer now. If it's clean it seems to dry out fast.
As far as the portland cement, I had to go look at that. If you mention it in the BYMC forum all you hear is spalling, explosion and DEATH!!!
It isn't ideal but will work for up to Aluminum temps maybe Brass. I spent the $40 for a bag of 3200 F. refractory for the hotface. I backed it up with Kaowool in one furnace and Fireclay/foam bead mix in the other, it sounds like the clay/foam is breaking down. I get a crunching sound when I move the furnace. The lid already collapsed, I didn't have enough support in it.

I just used the sand fire clay and pearlite mix, its works out well but after about 10 burns i have noticed a little bit of wear but not enought ot worry about for probably another 10 or 15 burns then im going to add a commercial hot face to it. The portland cement from what I understand doesnt work well for hi temps.