Alginate and Hard Water - ArtMolds


How embarrassing! That batch of alginate impression material we mixed and provided to Roy Butler’s life casting workshop turned into a lumpy mess when it was mixed. I had egg all over my face in those earlier years. Mr. Butler, a well known sculptor, was none to pleased either. But as a consummate professional he muddled through his class, never to use our alginate impression material, again. Who could blame him either, as we almost single handily caused him a workshop catastrophe.

After his workshop, I hurried home to confer with our chemist as to what the problem might have been. He took an alginate sample from the same batch we had delivered in Nashville where the workshop was. He carefully mixed it, but no lumps were detected. In fact it was just as smooth as silk, just the way it was formulated to be.

Noticing my consternation, he then he explained.

Alginate formulas are composed of a number of ingredients besides alginate, including calcium, magnesium and other salts. These are the same materials that are often dissolved it the water we drink, too much and we call it “hard water.”

There in lies the problem. Alginate manufactures including ourselves test all formulas before they leave our facilities. But all mold making and casting materials consist of two or more parts (otherwise it would be set before it arrived in your studio). We manufacturers have great control over our formulation --- the powder part. But because we have so little control over the water quality used that the powder is added to, we use only distilled water for the quality control testing.

In fact, dental schools teach their dental students not to use tap water when they are mixing their alginate impression material. Why? Because alginate formulations are very precise. If water contains excess calcium or magnesium (the common ingredients in hard water) it will delay set time or in extreme cases prevent setting altogether.

The symptom of hard water – a lumpy or cottage cheese like mix. That knowledge was too late to help Mr. Butler. I could only apologize for my ignorance. But from there on I have been cautious in our instructions to our customs. In most instances tap water is soft enough to provide an acceptable mix. But I would estimate that in 15-20% of the cases, if tap water it is hard enough to have a negative impact on the mix.

So to prevent an embarrassment in your studio we always recommend that you mix a sample before any mold making session. The mix should be smooth and lump free after about 15-seconds of mixing. If it is lumpy – then that is your signal to go to distilled water. Bottled water is a second choice but sometimes it too contains excess materials. Keep a gallon or two in your studio for those days that your municipal water supplier fails to soften the water sufficiently. Oh, and if you have well water without a water softener, that is a red flag that you may not get a good mix. The Nashville studio was supplied by such a well.

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