Alginate- The Key to Mixing Well

Alginate- The Key to Mixing Well

Some people call us to complain that their alginate mixed poorly. Our mixing instructions are carefully written, but we feel terrible when customers fail. Complaints are generally:

  • Too thick
  • Too thin
  • Lumpy Mix
  • Too fast setting
  • Never set

In every case, the customer claims to have "followed the instructions perfectly". We're sure that they believe that, but we can pretty much always find a problem with their mixing technique that caused their problems. 

I'm going to share with you everything I've learned about alginate mixing over the past 30 years so you don't have to go through this.

Problem- Too Thick or Too Thin

Measuring your alginate and water is crucial to a good result. Just being "off" by a little can adversely affect your project. Fortunately it is pretty easy to get it right. You just have to understand one concept:

"Volumetric vs. Weight Measurement"

Volumetric measurement refers to measurement done with a cup or scoop or some other container. If you put in three scoops of water and two scoops of powder- that would be a 3:2 volumetric measurement. While this method is more convenient (not requiring a scale), it is less accurate because alginate is a compressible powder and can be in any one of a number of density states at any one time. "Fluffed" alginate can weigh as much as 40% less than "Compressed" alginate.

Weight measurement refers to the actual weighing of the water and powder on a scale. If you use 40 grams of water and 10 grams of powder- that would be a 4:1 weight measurement. This is the MOST accurate way to measure and will never let you down. The main problem with telling people to measure at 4:1 by weight is that they ACTUALLY measure 4:1 by volume and since water is MUCH heavier than powder, that works out to be about 11:1 by weight- obviously waaaaaaay too thin.

Problem- Lumpy Mix

A few lumps in your alginate isn't a problem. If it is like cottage cheese- that IS a problem as you will be unable to make an accurate mold.

A lumpy mix can be caused by several factors:

  • Poor mixing technique
  • Too thin a mix
  • Too thick a mix
  • High phosphates or calcium in your water (hard water)

There are good mixing techniques and bad ones.

Unfortunately, the most common error is attempting to mix the water into your alginate with your hand. This rarely results in better than mediocre results.

Accu-Cast's exclusive Mix-In-The-Bag technique is good, but it must be done the right way to work well. This VIDEO shows the right technique. It is crucial to do a second "burp" of the bag to remove all the air prior to finishing the mixing.

Mixing with a kitchen whisk is very good for up to about 1.5 pounds of alginate. Don't "whip" the mixture, but stir it firmly. Use a small whisk for small amounts and a big sturdy one for larger amounts.

If you are attempting to mix a large quantity of alginate- up to about 3 pounds, use an electric drill with a paint mixer attachment on it. Run the drill in reverse (anti-clockwise) for best results.

Too thin or too thick a mix can cause lumpiness. If the mix is too thin, there isn't enough internal friction to work out the dry spots in the mix. If the mix is too thick, there isn't enough water to do the same. Careful measuring is critical.

Hard water adds one or more additional chemicals to the mix and can have unpredictable results. Lumpiness is one. If you feel good about drinking your tap water- its most likely fine to mix with your alginate. If you filter your water or drink bottled water- probably best to use that water to mix with your alginate to minimize problems.

Problem- Slow or Fast Setting Time

There are several things that can affect the setting time of alginate:

  • Thin mixtures set slower, thick mixtures set faster
  • Using warm water makes alginate set faster- cold water makes alginate set slower
  • Poorly mixed alginate will have both thick and thin spots which will set unevenly
  • Using water with calcium in it (hard water) will cause your alginate to set faster
  • Using water with phosphates in it will cause the alginate to set slower
  • Applying alginate to a cold surface will make it slower
  • Taking too long to mix will make it seem like the alginate is setting quickly.


Measure carefully, use good water and a good mixing technique and you'll be fine. We test our alginates rigorously and we don't let bad product out of our warehouse. 99+% of the time, problems fall into one of the categories above. 

Have fun with it.