I remember on AA, metalbynevin (a guy with a good number of successful lost foam pours under his belt) had a theory that polystyrene vapour residue builds up in the sand, and that once it reaches a certain concentration, it can cause or aggravate sand float defects which sometimes occur if you pour the soup can Kush tool too full when the pattern isn't buried under a heavy enough load of sand to counteract the hydraulic pressure. If true, I can see how it would be easy to misdiagnose as such. I don't know if there is any validity to that, it was only briefly discussed, but if so, maybe it is possible the sand may need to be replaced (or burned clean?) every so often. If that is a real thing, perhaps it is only of concern if you've been pouring cool enough to see a lot of those tell-tale sand lumps? Jeff
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