How To Mix Sheetrock 90


In the Court-Hampton Painting video below we teach you how to mix a batch of Sheetrock 90, 45, or 20.

At over 19000 Youtube views this has been a popular video about mixing Sheetrock 90 for painters and DIY enthusiasts!


How to mix sheetrock 20, 45, 90? Toronto painters Court-Hampton Painting show you how!

You will want to use a gypsum based compound such as sheetrock on your first coat of plastering patches or entire rooms. You can finish with a final coat of drywall compound if you wish. Sheetrock is stronger than pre-mixed compound and sets in 20 minutes, 45 minutes, or 90 minutes, hence the different names on the bags.

The mixing ratio is 3 parts powder to one part water. Only make enough Sheetrock to use in the time allotted. Hardening action cannot be prevented or delayed by dilution with water. In the video above we add water to powder to show visually the water to powder ratio. You can reverse it and add powder to water once you are comfortable with the ratios if you wish.

It is handy to have a wet rag available to wipe your putty knives and clean your tools if you are mixing multiple small batches of Sheetrock 90 as it can dry quickly on tools and is easier to wipe off wet. It is always better when plastering to apply thin coats and blade off excess Sheetrock on the wall or ceiling being plastered to avoid excessive sanding. Two to three coats of plastering is usually required so keep it thin! When sanding start on the outer perimeter of the patch and then gently sand to the middle. Wear a mask and vacuum up all dust.

Sheetrock 90 setting type compound is sold by CGC and they can provide Material Safety Data and Technical Data sheets.

Sheetrock 90, 45, 20, is humidity resistant and is great when painting or finishing bathrooms and kitchens.

Sheetrock 90 setting compound on wall
Sheetrock 90 on wall

It is also has more strength than premixed compounds. In the picture above we used mesh fibreglass tape and Sheetrock 90 to plaster an old doorway so the joints won’t separate.

Sheetrock 90 setting type compound
Sheetrock 90

If you need drywall patching or plastering on a plaster and lath home call Court-Hampton Painting Inc.

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  1. I’ve had a bag of Sheetrock 90 around for small jobs for ages and it has always worked well for me, but after replacing a severely bowed stud in a bedroom closet rough opening I was frustrated to find that it was taking over 8 hours to be sandable. Does this stuff have a shelf life?

    1. Hello Martin,
      Great question! I’m not sure what the official shelf life of Sheetrock 90 is but I do know how you store it plays a role.
      If stored where there is any humidity I’ve found it to compromise performance as humidity starts the chemical process I believe.

  2. I’m finding that the 90 is hardening to fast. 30 min. and it starts to solidify. I’ve tried everything and the only thing I can think of is my mixer is wrong. I’m using a speed mixer instead of a paddle type mixer. Could I be putting air into the fill with the speed mixer and causing it to speed up the hardening?

    1. Hi Sam,
      Could be the mix ratio, or the humidity/temperature. If mixing big batches try adding the water to the bucket first then the 90.
      Most beginners find it easier to visualize the ratio if you add the powder first then the water in small batches, that’s why I do it in the video but the best way is to add the water first. Thanks Sam hopes this helps!

  3. Trying to figure out how much to get. I can’t get it locally but don’t want to severely overbuy either. I need to patch where a triple wide was taken apart and put back together. Any rough estimate on how many linear feet I can get out of a bag?

    1. Hello Janelle, I think it really depends on how thick you apply it and your particular application. I’ve never tracked coverage on this product but a big bag will last me a couple of jobs at least just patching and painting. Hope this helps!

  4. Hello Michael does the cgc 90 make a strong enough bond that yo can get away without using tape? I seem to have trouble setting tape correctly and was wondering if yo can just fill the gaps with this and smooth out and sand the mud.
    Thank you

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