Concrete Mix Design

This is for a six sack foundation mix for floors, driveways, etc.,
not for Monolithic Domes which require a 7-9 sack mix.

Mix Design for 3/10's of a cubic yard --

Shotcrete mix design varies from job to job due to different types of materials and other conditions. However, we have found a mix design that works well in most areas. These mixes are formulated especially for the Monolithic Portable Concrete Mixer, but they would work well in most 9 cubic foot mixers.

Cement — 188 lb. Two sacks of standard Type I or II or I-II Portland cement. This is what the lumber yard will carry. It is not mortar mix.

Water — about 80 lb. (10 gallons.) Water must be clean (potable). This will vary from job to job and must be adjusted. The water in the aggregate will cause a difference in the amount of water needed. Adjust to a proper slump. 2" to 6" as needed.

Concrete Sand — 690 lb. (Ten, 5 gallon buckets is a good approximate measure).

Pea rock — 140 lb. (Two, 5 gallon buckets.) The amount of pea rock is adjusted per gradation of the sand. If the sand is high in larger aggregate the pea rock may be left out. If it is low, then more may be needed. This is a place to start for maximum strength. The total of the sand and pea rock should equal the 830 pounds (twelve, 5 gallon buckets). Usually, the pea rock is left out of the final coats to provide a smoother finish.

Kel-Crete — use 2 oz. minimum per batch. Try up to four ounces per batch. Adjust between for best results. We normally use 2.5 ounces. Add the Kel-Crete additive in with the water for easier dispersion. If the Kel-Crete is not added, another 1/3 of a bag of cement should be added.

Kel-Crete is a highly concentrated liquid magic:

It helps the shotcrete to pump easier. This reduces wear and tear on the equipment. It often means the difference of whether a shotcrete mix will pump or not.
It adds air entrainment. Most concrete and especially shotcrete should have an air entraining compound added for flowability and most especially freeze/thaw protection.
It is a water reducing agent. Concrete is generally stronger if made with less water. Kel-Crete reduces the amount of water needed in the mix.
Costs less than other additives both to purchase and to handle. It is highly concentrated. The one gallon (128 oz) containers can be shipped easily. It is non corrosive. The dosage rate is from 1 oz to a maximum of 7 oz per yard
Long shelf life. It can be stored for years and still work

Nylon Fibers — use 1/3 lb. per batch. These fibers are made of single strand (monofilament) fibers that easily mix into the matrix with minimum clumping. They are alkali resistant and specifically designed for use in shotcrete. A single pound contains millions of fiber —13 times more than fiberglass or polypropylene. Shrinkage and crack control tests show fibers to be a superior product.

Leave the fibers out for the last coat. Fibers are optional; some swear by them others swear at them. You try, you choose.

When to use What

Obviously, if the job uses thousands of yards of concrete, a ready mix plant is the only way to go for ordering shotcrete. But for the small jobs using the small pumps, we suggest you consider mixing on site. Mixing on site with small mixers must be well organized.

The mixers can be a skid-loader mixing unit, or a plaster mixer, or small line concrete mixer. The biggest advantage of on site mixing is the ability to control speed and delivery. There is nothing worse than waiting a few hours for the ready mix truck and then immediately have a breakdown that prevents unloading it.

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Concrete Mix Design

This is for a six sack foundation mix for floors, driveways, etc., not for Monolithic Domes which require a 7-9 sack mix.

Mix Design for 3/10's of a cubic yard --

When to use What

This is for a six sack foundation mix for floors, driveways, etc.,
not for Monolithic Domes which require a 7-9 sack mix.