How Much Water for a 25 lb Bag of Grout?

A 25 lb bag of standard sanded cement grout takes about 2 US quarts (1.89 L) of water: Custom, MAPEI and LATICRETE all print exactly that, and TEC prints 1.75 to 2 quarts. A 25 lb bag of standard unsanded grout takes far more, 3.6 to 5 quarts depending on the brand. High-performance grouts sit in between. Use the figure on your own bag, measured, every batch.

Water per bag: 12 data sheets side by side

The table collects the mixing water printed on current technical data sheets (TDS) and one manufacturer FAQ. The last column converts each figure to water as a percentage of powder weight, which is the number that lets you compare a 17 lb box with a 25 lb bag and mix any partial amount on a scale.

The pattern is plain. Every standard sanded grout in the set lands at or just under 2 quarts per 25 lb. Every standard unsanded grout lands between about 3.6 and 5 quarts. The LATICRETE 1600 figure looks like a misprint next to Custom's, but it is not: the current data sheet gives 4.5 to 5 quarts per 25 lb and 1.4 to 1.6 quarts per 8 lb, and the LATICRETE FAQ gives 5 quarts.

Why unsanded grout takes so much more water

The "about 2 quarts" figure that circulates online is a sanded figure, repeated for every cement grout. It is right for sanded and badly low for unsanded.

The reason is the aggregate. In a sanded bag, much of the weight is graded sand, and coarse grains need only a thin film of water to wet. An unsanded bag swaps the sand for fine mineral filler, so per pound there is far more fine powder surface to wet and far more cement paste to make workable. The sanded vs unsanded comparison covers what that does to shrinkage and joint width.

High-performance products blur the line. PERMACOLOR Select NS is unsanded, yet its FAQ figure (0.9 quart per 8 lb) works out to roughly a quarter of the powder weight, closer to the fine-aggregate grouts than to standard unsanded. Ultracolor Plus FA and Prism, both built on fine aggregate, sit at 22% to 31%.

Weigh it: the most accurate method

A US quart of water weighs about 2.09 lb (946 g), and a liter weighs 1 kg, so any data sheet figure converts to a weight you can mix on a scale.

1. Find the percentage. Divide the water figure in liters by the bag weight in kilograms. For a 2 quart (1.89 L) per 25 lb (11.34 kg) sanded grout, that is 1.89 / 11.34 = 0.167, or about 17%.
2. Weigh the powder. Scoop dry-blended powder into a tared bucket and note the weight in grams.
3. Multiply. Grams of powder times the percentage gives grams of water, and grams of water equal milliliters. 2,000 g of a 17% grout needs about 333 g (333 mL) of water.

The method checks out against the data sheets. Five pounds (2,268 g) of Keracolor S at 17% gives about 379 g of water; MAPEI prints 13 oz (384 mL) for 5 lb.

Mixing a partial bag

MAPEI's guidance on partial units says its grouts are designed as full units and that color consistency is not guaranteed when several small batches are used in one area instead of the whole bag. When you do split a bag, three rules come from the data sheets:

• Dry-blend first. MAPEI and TEC both tell you to blend the dry powder before taking a portion, because pigment settles during shipping.
• Use the printed small-batch figure where there is one. Custom prints 1 pint per 7 lb, which is about 10% leaner per pound than the 25 lb figure scaled down (scaling gives about 18 oz). If your amount matches a printed line, use it.
• Otherwise scale by weight. Use the percentage from the table.

MAPEI also gives volume ratios of powder to liquid for partial bags: 4 to 1 for Keracolor S, and 3 to 1 for Keracolor U and Ultracolor Plus FA. It calls these starting points that may need slightly more or less powder or liquid. They are a coarser tool than weighing.

To work out how much powder a section of floor needs before you split anything, use the grout calculator or the grout coverage table.

A range is a ceiling, not a target

Where a sheet gives a range, the top end is the limit, not the goal. TEC's Power Grout sheet is explicit: start with the low end of the water range, mix for at least 2 minutes before adding more because the grout loosens as it mixes, and do not exceed the recommended range.

The same sheet names the two situations where the top of the range is the correct choice: hot weather, where more water gives more working time, and very absorptive tile such as bisque or thin grout lines, where the tile pulls water out of the joint. For other conditions, see grouting in hot and cold weather.

Single figures are different. Custom's sanded sheets give a flat 2 quarts with no allowance; its Non-Sanded sheet allows up to 0.2 pint (0.1 L) more per 10 lb, "if needed". Every splash beyond the figure ends up as pore space, and the science of excess water explains why that costs strength, raises absorption and causes the blotchy color covered in grout discoloration and shading.

Do not retemper

Retempering means adding water to grout that has started to stiffen in the bucket. Custom's wording is to remix periodically "but do not add water, which can weaken the grout, cause color variation" and possibly shrinkage, cracks and pinholes, and to discard grout when it becomes too stiff to work. MAPEI's Keracolor sheets say to remix without adding any liquid, and the Ultracolor Plus FA sheet says plainly: do not retemper the grout by adding additional water.

The fix is batch size, not water. Mix only what you can float and clean within the product's pot life, which the data sheets put at about 1 hour for Keracolor S, 30 minutes to 1 hour for Ultracolor Plus FA, and 1 to 2 hours for Polyblend Sanded. The full sequence is in how to mix grout.

When the liquid is not water

Some grouts can be mixed with a liquid additive. On these sheets it replaces water rather than going in on top of it:

• LATICRETE 1776 Grout Enhancer: 2 quarts per 25 lb of 1500 Sanded and 5 quarts per 25 lb of 1600 Unsanded, the same amounts as water. The 1600 sheet says not to use other grout additives with it.
• TEC Acrylic Grout Additive: used in place of water to take AccuColor sanded to ANSI A118.7 performance for exterior, freeze-thaw and similar jobs.
• MAPEI UltraCare Grout Maximizer: a stain-resistance additive for Keracolor S and U that replaces the entire amount of water.
• MAPEI Ultracolor Plus Extend: a pot-life extender; if you want a firm mix, withhold about as much water as the additive you put in.

Do not add a latex additive to a polymer-modified grout unless its own sheet names that additive. For built-in stain resistance without an additive, see stain-resistant grout.

Where these figures stop applying

• Epoxy grout: no water at all. Resin and hardener come in fixed proportions, and MAPEI says its epoxy grouts should never be mixed in smaller batches because any deviation can stop them setting properly. See how to apply epoxy grout.
• Premixed and urethane grout: ready to use from the pail, no water. Stir, do not dilute. See premixed grout.