I swapped to a new sand mix for our greensand molds last week.

We usually use a 50/50 blend, but I tried a 60/40 mix with more new sand on a small batch of gear castings. The molds held shape way better during pouring, but the surface finish came out rougher than I expected. I think the extra new sand didn't bond as well with the clay. Has anyone else run into this with a higher new sand ratio?

4 comments

4 Comments

zaranelson2mo ago

Yeah, you need a touch more clay to glue that extra new sand together.

skyler_johnson322mo ago

Sounds like your clay content is too low for good bonding.

casey2682mo ago

Disagree, sometimes less clay means fewer cracks. Skyler_johnson32 ever try a lean mix on purpose?

mitchell.thomas3d ago

Huh, Skyler might be onto something, but I've had good luck with low clay content if I really pack it in. A leaner mix can actually make the surface harder once it's compacted right, less cracking if you don't overwork it. I do a 12-15% clay range and just really work the material with a tamper, especially around the edges. The key is getting it wet enough to mold but not so much it turns to mud. That extra sand just acts like filler if you don't have enough clay to glue it, so Skyler's point stands in some cases.