Installing hardwood floors directly onto a concrete slab is a common process, and a full trowel glue is the preferred method for installing hardwood floors on concrete. This method provides a strong, permanent bond between the wood and the concrete subfloor.
Preparing the Concrete Subfloor
Before any flooring is laid, proper preparation of the concrete slab is crucial for a successful installation.
- Cleanliness: The concrete must be thoroughly cleaned. Remove all dirt, debris, grease, paint, or old adhesive residues. A clean surface ensures the glue adheres properly.
- Levelness: The concrete surface should be flat and level. Check for dips or high spots using a straightedge. Uneven areas may need to be ground down or filled with a self-leveling compound specifically designed for flooring.
- Moisture Testing: Concrete can hold significant moisture. Excess moisture can cause hardwood floors to warp, cup, or buckle. It is essential to perform moisture tests (such as calcium chloride tests or relative humidity probe tests) to ensure the concrete's moisture content is within the acceptable range specified by the hardwood flooring manufacturer and adhesive manufacturer. A moisture barrier or sealer may be required if levels are too high.
- Curing: New concrete slabs need sufficient time to cure, typically 30-60 days, before flooring is installed.
The Full Trowel Glue Down Method
As the reference states, a full trowel glue is the preferred method for installing hardwood floors on concrete. This technique involves applying a specialized adhesive directly to the prepared concrete subfloor.
Step-by-Step Process
- Acclimate the Wood: Allow the hardwood flooring planks to acclimate to the room's temperature and humidity for the recommended period (usually several days) before installation. This helps prevent expansion and contraction issues after installation.
- Layout: Determine the starting line for your floor, often the longest wall or a central point, factoring in doorways and transitions. Snap a chalk line as a guide.
- Apply Adhesive: This method involves troweling a mastic glue over the concrete subfloor before laying the wood planks. Use the specific type of adhesive recommended by the flooring and adhesive manufacturers for solid or engineered hardwood on concrete.
- Trowel the Glue: The glue is applied to the concrete subfloor using a notched trowel, creating a ridged pattern that helps secure the wood planks. The size and shape of the trowel notches are crucial and specified by the adhesive manufacturer to ensure the correct amount of glue is applied for adequate coverage and bonding. Work in small sections that you can cover with flooring within the adhesive's open time (the time it remains workable).
- Lay the Planks: Begin laying the hardwood planks along your starting line, pressing them firmly into the wet adhesive. Stagger the end joints of the planks to create a strong and aesthetically pleasing floor.
- Check Alignment: Periodically check that the rows are straight and the planks are fitting together tightly. Use tapping blocks and a mallet if needed to seat the planks into the adhesive.
- Roll the Floor: After a section is laid, use a roller (like a 100-pound floor roller) to ensure full contact between the wood planks and the adhesive. This helps eliminate air pockets and ensures a strong bond.
- Continue Laying: Repeat the process of applying adhesive and laying planks until the entire area is covered.
- Expansion Gap: Remember to leave an expansion gap (typically 1/2 inch or as recommended by the manufacturer) around the perimeter of the room and at all vertical obstructions. This gap allows the wood to expand and contract with changes in temperature and humidity.
- Curing: Allow the adhesive to cure fully according to the manufacturer's instructions before walking on the floor or placing furniture.
Pros and Cons of Glue Down
| Pros | Cons |
|---|---|
| Very stable and secure installation | Can be messy |
| Reduces noise (less hollow sound) | Requires significant subfloor prep |
| Suitable for solid or engineered wood | Difficult to repair or replace single planks |
| Permanent bond | Adhesive fumes can be strong |
While other methods exist, such as installing a subfloor over concrete or using a floating floor system with engineered wood, the full trowel glue down method is often favored for its stability and feel, particularly for solid hardwood.
Ensuring proper concrete preparation and using the correct adhesive and trowel notch size are paramount for a successful glue-down hardwood floor installation on concrete.
