Concrete needs time to harden before it can be troweled smooth. Troweling too early can weaken the surface and create defects. However, waiting too long can make troweling difficult and reduce the quality of the finish. Finding the right timing is crucial for proper concrete finishing.
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When can you start troweling concrete?
The timing for when to start troweling concrete depends primarily on the concrete mix design and weather conditions. Here are some general guidelines:
- Standard concrete mixes – Wait about 4-8 hours after pouring and let the bleed water evaporate before troweling. This allows the concrete to harden sufficiently.
- Fast-setting concrete mixes – These can often be troweled after just 1-3 hours. They gain strength quickly so you can trowel sooner.
- Hot weather – Concrete sets up faster when it’s hot. Wait about 2-4 hours before troweling in temperatures over 80°F.
- Cold weather – Colder temperatures slow the curing. You may need to wait 8-12 hours when temps are below 60°F.
- Low slump concrete – Stiffer mixes can be troweled sooner, usually within 2-4 hours.
- High slump concrete – More fluid concrete may take 6-8 hours or longer before it’s ready to trowel.
Do the “thumbprint test” to help determine when the concrete has hardened enough. Push your thumb into the surface about 1/2″. If it indents without crumbling, it’s generally ready for troweling.
Steps for troweling concrete
Follow these basic steps when troweling concrete:
- Let it set – Allow the concrete to reach the proper hardness as outlined above before troweling. Soft concrete will get damaged.
- Remove bleed water – Sweep or blow away any bleed water sitting on the surface before troweling.
- Hand trowel – Do an initial troweling pass by hand to smooth and level the surface.
- Fresno Trowel – Use a fresno-style trowel for the second pass to further smooth and shape the concrete.
- Edging – Trowel and shape all slab edges and control joints.
- Final troweling – Make a final troweling pass with a power trowel to finish and hard-trowel the surface.
The number of passes and exact tools depend on the desired finish. But always wait until the concrete has set enough before starting the troweling process.
Troweling stages
Concrete troweling is generally done in multiple stages as the concrete continues to cure:
Initial troweling (soft trowel)
The first troweling pass is done by hand shortly after the concrete has hardened sufficiently. This levels and smooths the surface and embeds large aggregate just beneath the surface.
Second troweling (scratch trowel)
About 30-60 minutes after the first pass, a second troweling is performed with a jitterbug or fresno trowel. This further levels the surface and creates texture to aid in the final finish.
Final troweling (hard trowel)
The final troweling pass is done once the concrete has hardened enough to support a power trowel, usually 2-4 hours after pouring. This brings cream to the surface and creates a smooth, durable finish.
Edge troweling
All slab edges and joints should be hand troweled using an edging trowel. This compacts and finishes the edges for proper curing.
Trowel types
Many types of concrete trowels can be used depending on the stage of troweling and the desired finish:
| Trowel | Use |
|---|---|
| Hand trowel | Initial leveling and embedding aggregate |
| Fresno | Smoothing and texturing the surface |
| Jitterbug | Roughens surface and removes imprints |
| Edger | Finishing slab edges and joints |
| Power trowel | Hard troweling and final finish |
Troweling tips
Follow these tips for best results when troweling concrete:
- The surface should be hard enough that your foot leaves only a shallow print.
- Keep trowels clean and smooth for best finishes.
- Overlap each troweling pass by half the trowel width.
- Trowel until the surface is smooth and free of defects and trowel marks.
- Go slowly on edges to prevent breaking them.
- Minimize walking on the slab to prevent imprints.
- Allow 7-10 days curing before heavy traffic.
Timing considerations
Besides the concrete properties, consider these factors when timing the troweling process:
- Weather – Hot, dry, or windy conditions can accelerate curing. Adjust timing accordingly.
- Bleed water – This must fully evaporate before troweling can begin.
- Curing compounds – If used, these create a time limit for finishing the surface.
- Tools – Have tools ready and staged to begin troweling on schedule.
- Texture – More open finishes like brooms allow slightly earlier troweling.
- Size – Schedule troweling in phases for large slabs.
Testing readiness
In addition to timing, check the concrete visually and physically:
- No bleed water or sheen on the surface
- Thumbprint no deeper than 1/2″
- Footprint no deeper than 1/4″
- Does not flatten or crack around rebar when pressed
- Trowel leaves only minimal marks
Performing these simple tests helps identify when troweling should begin for ideal concrete finishes.
Issues with early troweling
Problems that can occur if troweling is started too soon include:
- Surface tears, pits, and unevenness
- Weak top layer that powders and delaminates
- Aggregate pops out leaving voids and blemishes
- Irregular and uncontrolled setting and hardening
- Increased shrinkage cracking as it cures
- Difficulty with later finishing steps
Even minor troweling while the concrete is still plastic can have detrimental effects on the final durability and appearance.
Issues with late troweling
Delaying troweling too long can also cause problems:
- Increased effort required to cut and finish the harder surface
- More difficult to blend repairs and blemishes
- Reduced quality of surface finish and smoothness
- Edges cannot be properly finished and compacted
- Curing compounds cannot be applied in time
- Loss of creaminess and surface gloss
- Increased wear and dusting over time
Troweling late wastes effort and can reduce the final durability and aesthetics of the concrete surface.
Conclusion
Timing is critical when troweling concrete. Wait for the concrete to stiffen adequately, but don’t delay too long and make finishing difficult. Test the surface hardness, and consider the weather, concrete properties, and desired finish. With the right timing, you can achieve a beautiful and durable concrete surface.