I'm getting ready to try my first mix of home made petrobond. Rather than do a ton of filtering I went to my local aquarium store and bought "the finest grain sand you have", then ordered a 5lb bag of bentonite clay powder off amazon. (Yes, I know it's not the most cost effective but I wanted to get going fast...) Looking at using synthetic motor oil and then using methanol (denatured alcohol) as a catalyst as per an article I read. Today I mixed 20 lbs of the sand with 2.5 lbs of the clay powder. The resulting mix was incredibly fine, as in pour through my fingers fine... Will that be OK? Holding off on adding the oil as my drill attached paint mixer I planned on using to mix/blend it has vanished and I have to go to the store or use a trowel manually.. What do you far more experienced folks think?
I'm concerned about the bentonite you've got, normal bentonite clay is used to make green sand, it is NOT what one uses to make petrobond. This, http://forums.thehomefoundry.org/index.php?threads/bentone-for-sale.1879/ is the stuff used in petrobond.
You might take a look at this thread. http://forums.thehomefoundry.org/index.php?threads/mixing-up-k-bond-sand-similar-to-petrobond.1759/ As Rocco said, Bentonite is NOT the clay you need for petrobond. Also, methanol is not the ideal (it will work) polar agent to use. It evaporates quickly. Glycerin is much better. Just came now in from molding with shop-made K-bond. Denis
I also think that for petrobond you need some other kind of clay. Well since you have sand, bentonite clay and probably water, you can make greensand. lol
I will probably roll this as green sand then and just deal with remoisturizing it from time to time then. Thanks for the catch everybody, like I have mentioned elsewhere, I'm something of a complete noob to this and still learning. Also, as much as I loved the fine nature of this sand it was over $1 a pound, so probably need to source good sand elsewhere here in Dallas.
You might give these folks a call to see if they'll sell you a small quantity of Green Diamond. They get it pre-mulled. https://www.claluminum.com/quality/quality_sand_control.htm
Thanks for the heads up Mach! I'll give them a shout. Now , I tried using this super fine sand (which literally poured straight through my sifter/strainer) and super fine bentonite clay powder (which also poured right through the sifter) with water. When I added enough water slowly while mixing it with a drill attached paint mixer it started clumping up. But now it clumps "too easily" and I cant get the resulting mixture through the strainer to do that "fine sand" first part for casting. I can still crumble it up in my hands decently, and then pack it, and it works , but it doesn't get the smoothness in the surface I'd like. I wonder if I put in too much clay powder (Around 10:1 sand/clay mix)
A common ratio of Bentonite to sand is about 1:25. Fineness of sand makes a little difference with fine sands needing a little more Easy to fix. Just add some more sand—-maybe an equal weight to what you have. Denis.
