Use a notched trowel to spread the adhesive.
Too much glue hardwood to concretr.
If there are voids the boards can flex into them and make creaking sounds as they rub together.
Although this may be true they run out of the adhesive halfway through the installation process and lose precious work hours.
Installing engineered hardwood flooring over concrete too tight against a stationary object will not allow room for normal expansion and may cause a failure.
They use too much adhesive thinking that more is better and the panels will be more secure this way.
A vapor retarder is required for installation over concrete with a calcium chloride reading greater than 3 pounds a relative humidity reading of greater than 75 or a calcium carbide cm reading of greater than 2 5.
Glue forms the initial bond but without screws and nails the natural expansion and contraction of the wood can break or weaken the glue.
When you glue a hardwood floor to concrete the subfloor must be completely level.
The adhesive manufacturer should have instructions regarding specific trowel requirements.
When glue is used in conjunction with screws and nails the bond is strong enough to resist natural movement of the wood.
The weight of the glue and planks can become too overwhelming for the lightweight concrete or gypsum and ultimately lead to disastrous results.
Glued down floors are also not a good fit for below grade concrete or high moisture subfloors which are often found in basements.