Screeding is an important process in concrete floor construction that involves leveling and smoothing the concrete to create an even, flat surface. There are two main types of screeding wet screed and dry screed. Which is better for your specific project? Read on as we compare these methods in 2024.
What Is Screeding?
Screeding is the process of striking off excess concrete to leave a level surface. It is usually done by moving a straight edge across the surface to remove excess material. The two main types of screeds are:
Wet Screed
This involves screeding off the excess concrete in its wet state, before it starts to go off or set. Wet screed is the more traditional method.
Dry Screed
This involves placing a self-leveling concrete layer over the base slab once it has hardened. The fluid topping levels itself off to create a smooth finish.
So in simple terms:
- Wet screed levels out fresh concrete
- Dry screed levels out an additional concrete layer placed on top of set concrete
Now let’s look at how these two methods compare.
Installation Time
Wet Screed Is Quicker to Install
With the wet method, screeding is done in the same day as the concrete is poured. It is part of the continuous concrete floor construction process. This avoids delays and additional steps.
Dry Screed Adds Another Layer
Because dry screeding involves pouring self-leveling concrete over the top of an existing slab, it requires more time. You must wait for the base layer to cure before screeding, which adds days or weeks to the schedule.
Quality of Finish
Wet Screed Finish Varies
The quality of a wet screeded floor is heavily dependent on the skill of the concrete crew doing the screeding. If done carefully you can achieve a high quality finish, but there is potential for human error.
Dry Screed Is Consistently Smooth
A fluid self-leveling concrete will flow out evenly over the surface through gravity, achieving the desired smoothness. This gives very reliable, consistent results. The finish quality tends to be higher than a standard wet screed.
Leveling Ability
Wet Screed Limited By Base Slab
With the wet method, the finished surface will reflect any imperfections in the underlying concrete slab. Any high or low spots can transfer through to the finished layer. Achieving a perfectly level floor is difficult.
Dry Screed Can Compensate For Variations
The self-leveling nature of dry screed allows it to compensate for slight variations in the base layer to achieve a truly flat, level surface. As it flows across high and low spots it corrects the floor profile.
Curing Time Required
Wet Screed Ready Faster
Since it is applied directly onto fresh concrete, a wet screed can be walked on as soon as the concrete has cured enough to take foot traffic without damaging the surface often within 24 hours. This allows other trades back on the floor ASAP.
Dry Screed Needs Longer Curing
Being an additional layer that gets poured onto cured concrete, dry screed itself will also need proper curing time before foot traffic generally 1 week. This adds time before floor coverings can be installed or work continued.
Cost Comparison
Wet Screed Is More Affordable
Doing everything in a single concrete pour with finishing done by hand by skilled workers keeps costs lower. No extra materials are required beyond the concrete itself.
Dry Screed Adds Cost
Because it requires a second layer of special self-leveling concrete to be purchased and poured, dry screed is a more expensive process per square foot. There may also be added labor costs for pouring/finishing.
Thin vs Thick Applications
Wet Screed Thickness Flexible
Wet screeding can be done to various concrete thicknesses based on requirements anything from a thin 1″ residential floor up to a heavy duty 4″+ commercial slab. Any thickness concrete can be hand screeded.
Dry Screed Limited To Thin Layers
Self-leveling concrete should be poured thinner no more than 1 or 1.5 inches thickness typically. Thicker applications may not level out properly before curing, due to the fluid dynamics. Best suited for smoothening thinner slabs.
Cracks & Joints
Wet Screed Prone To Cracking
As concrete cures it shrinks slightly. With single layer floors this stressed can cause cracks unless properly jointed. Precise joint spacing and depth is required to promote planned crack control but random cracks may still form.
Dry Screed Adds Reinforcement
The self-leveling product used in dry screeding often contains added fibers and polymers to reinforce and strengthen it. This makes random cracking far less likely though properly spaced joints are still required. Fewer cracks!
Uses & Applications
Wet Screed Widely Used
Wet screeding is very widely used, it is a fundamental step of almost all concrete floor pours except highly polished floors. This versatility makes it very popular for all basic applications from residential floors to warehouses.
Dry Screed For Higher Standards
While suitable sometimes for residential use, dry screed is more popular in commercial settings where precise flatness is prioritized like industrial facilities, data centers, airports, retail stores. Provides top level smoothness!
Access For Other Trades
Wet Screed Gives Earlier Access
Because it can be walked on more quickly, wet screeded floors allow faster access for other trades to start their work like overhead MEP equipment installation, drywall framing, ceiling/lighting hangs.
Dry Screed Delays Work Slightly
The longer cure time before foot traffic means other trades may be slightly delayed as they wait for the dry screed application to be ready for workers & ladders to access without damaging it. A potential drawback.
Maintenance & Durability
Wet Screed Prone To Dusting
Over time wear from foot traffic and surface erosion can cause a wet screed to lose its protective top layer of cement, resulting in surface dusting issues. Periodic re-sealing is advisable for maintenance.
Dry Screed Increased Durability
The polymers mixed within quality dry screeding products provide increased density, strength and abrasion resistance compared to basic concrete. This improves durability and longevity, reducing maintenance needs.
Sustainability Benefits
Wet Screed More Eco-Friendly
With simpler materials and application process, standard wet screeding is generally seen as a greener construction method using basic concrete without further compound production/transport costs and impacts.
Dry Screed Allows Floor Recycling
An advantage is existing slabs can be overlaid with self-leveling products, salvaging the concrete below to avoid material disposal recycling the floor essentially. Though production does have impacts.
Who Does The Installation?
Wet Screed – Concreters
Wet screeding must be done promptly alongside the pouring stage by the concreters. Their basic tools like screed boards are simple enough for any experienced crew to use with proper technique.
Dry Screed – Specialty Contractors
It requires specialty skill and tools to correctly apply self-leveling products. Dry screed installation is generally done by flooring contractors specifically experienced with these niche polymer modified concrete mixes.
Conclusion
In summary, traditional wet screeding remains very widely used due to its affordability and good versatility for most basic concrete flooring needs. But for commercial sites needing precise flatness tolerances or thinner floor build-ups, dry screed provides unmatched smoothness, crack resistance, and long-term performance despite higher upfront costs. Evaluate your specific project requirements like schedule constraints, traffic loads, desired finish, and thickness to decide whether a wet or dry screeding approach better suits your situation in 2024 and beyond.
FAQs
Can you apply dry screed over existing concrete or tiles?
Yes, provided the base is properly prepared through cleaning, crack repair and application of a bonding agent. Dry screed levels out the floor to compensate for existing variations.
What thickness should a screeded floor be?
A typical wet screed thickness is 75-150mm (3-6 inches). Dry screed should not exceed 40mm (1.5 inches) to ensure proper self-leveling.
How long after screeding can you apply floor coverings?
Wait at least one week after dry screeding for moisture testing. With wet screed wait for the concrete to cure adequately per manufacturer