How to Thin Latex Paint

Thinning and Stirring Latex Paint

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One of the benefits of using latex paint is its ease of use. As soon as you bring it back from the paint store in mixed condition, latex paint is ready to go. New, freshly mixed latex paint rarely needs to be thinned for most paint roller and brush applications. Thinning can be necessary for paint sprayers or for older latex paint that has partially lost water content due to evaporation. Since latex paint is water-based, it can be thinned with water. Successful latex paint thinning requires a reasonably precise assessment of paint viscosity and the addition of the correct quantity of water.

Tools and Supplies You Will Need

  • Latex paint
  • Room temperature water
  • Fluid measuring cup
  • Clean funnel
  • Paint can opener
  • Wood paint stirring stick
  • Electric drill (optional)
  • Power mixer attachment for drill (optional)
  • Viscosity cup (optional)
  • Fine mesh cone strainer (optional)

Instructions

Acclimate the Paint

Before you thin the paint, acclimate the paint to ambient room temperature between 50 F and 90 F. Cold paint will flow more slowly and does not require thinning. If the paint is too cold, it may give a false impression that it needs thinning.

Pre-Mix the Paint

Mix the paint thoroughly. If the paint has recently been shaken at the store, this step is not necessary. Over time, solids tend to gather at the bottom of the can, making it more difficult to gauge the true consistency of the paint. Chuck the power mixer attachment into the drill and mix the paint thoroughly. Run the wood stirring stick through the paint to test it. If the stick drags at the bottom, the solids have still not completely mixed through. If this is the case, run the power mixer in the can until the paint has the same consistency, from top to bottom.

Assess Whether the Paint Needs Thinning

To fully atomize paint, paint sprayers require paint that falls within a certain viscosity range. Consult the paint sprayer documentation for information about this range. For precise calibration when using a paint sprayer, invest in a small low-cost viscosity cup. A viscosity cup is essentially a long-handled funnel with a calibrated hole at the bottom. Industry-standard viscosity cups include the Ford #4 Paint Viscosity Cup and the Zahn Immersion Viscosity Cup. For a less precise but reasonably accurate way to gauge viscosity, dip some paint with a clean disposable cup and pour it through a kitchen funnel. Paint in need of thinning will clog the exit hole and either will not drain at all or will take an unreasonably long time to drain.

Strain Out Impurities

Solid paint chunks and film that have developed cannot be restored by thinning with water. Pull out large pieces with the hook end of a paint can opener. Remove remaining pieces and other impurities with an inexpensive fine mesh cone strainer.

Measure the Water

To portion out the correct quantity of water, use a fluid measuring cup, not a dry measuring cup. The amount of water to add varies according to the current consistency of the paint and the consistency that you desire. Four ounces of clean, room temperature water is generally a good amount to begin with; you can always add more as needed. Paint manufacturers tend to cap the quantity of additive water at 8 ounces per gallon of latex paint for spray applications. Consult the paint can label or online paint specifications for your specific latex paint.

Mix the Water Into the Paint

Slowly pour the water into the paint while gently stirring the paint with the wood paint stick. Test with the viscosity cup or funnel before use.

Tips for Thinning Latex Paint

  • Never use petroleum-based products to thin water-based latex paint. Any product called paint thinner likely is a petroleum-based solvent. Acetone and mineral spirits are types of paint thinners.
  • If you want to eliminate brush or roller marks, consider incorporating a paint additive like Floetrol instead of water. For roller and brush applications, add 8 ounces of Floetrol.
  • Adding water to paint dilutes the paint and thus lightens its color, so additional coats may be necessary to improve the color quality.
  • One telltale sign that latex paint has lost water through evaporation is when the lid of the can is encrusted with paint. Even a pinhole-sized gap between the lid and the can is enough to allow water-based paint to evaporate over time.