Installing Hardwood Floors On Concrete

The installation of hardwood floors on concrete offers several Illustration plywood on concretetypes of applications. Over the last twenty years newer forms have all but replaced the older, more dated sleeper on slab system. Now with advancements in adhesive and manufacturing technology, floating floors and engineered wood floors glued direct to concrete (right) have become viable alternatives.

See glue down methods with cost analysis on concrete.
See floating floor methods also with cost analysis on concrete.

For those seeking to install solid wood flooring without a wood sub floor system, changes are slowly taking place when considering gluing directly. Upon closer examination, thinner solid hardwoods, shorter length products, and parquet patterns have been used successfully for years. Unfortunately the explosion of manufacturers in recent years trying to stimulate sales of solid wood floors on concrete created a plethora of problems, namely by inexperienced installers and salespeople.

The Older Method. Sleeper On Slab System

The sleeper system that entailed fastening 2' X 4's to the concrete laid on their side has faded from use. The application involved adding a poly film and/or #15 asphalt felt laid into messy cutback mastic over the slab for moisture protection.

Finished Floor Was Too High

While the sleeper on slab application is not widely used today, it created vertical height concerns. Final heights are in the 2 1/4" range after the actual hardwood floor is nailed. This can cause problems with exterior door entries and other fixed objects. In some cases 3/4" plywood is used above the sleepers, adding another 3/4" or a total overall height of three inches is created. By using this method in new construction, one should plan well in advance to avoid vertical height concerns from one floor covering to another.

Recent Methods. Plywood Only

Over the most recent thirty years the most popular method of installing solid 3/4" hardwood on concrete was a plywood subfloor attached to the slab (illustration right). Using a minimum 5/8" CDX (3/4" recommended) plywood, the material is installed over the same moisture barriers (mastic excluded) but attached by way of concrete fasteners. A variety of fasteners are used, including masonry cut nails, tapcons (concrete screws), and Hilti types. Methods vary from one region to another, or what professionals are accustomed to.

Update 2010- The above procedure is losing credibility due to the loss of moisture protection through direct fastening. Read more.

Newer Methods. Floating Subfloors

Other methods of using 3/4" solid wood floors on concrete would be a floating subfloor. Yea...really...what's a floating subfloor you ask? The same moisture barriers (without mastic) are used but with two layers of 1/2 or 5/8" plywood. Plywood is installed opposite of one another, overlapped at the seams, then stapled or screwed together with shorter fasteners The preference here is not to puncture the moisture barriers.

Considering the reliability and performance in relation to keeping moisture at bay we expect this application to gain more prominence and use as time moves forward.

Or. Glue Plywood To Slab

If the floating subfloor doesn't work, another method calls for gluing the plywood direct to concrete. In this situation a premium urethane adhesive (troweled) is recommended. Keeping the plywood adhered or flat can cause problems. The solution here is establishing Sika Acoubond kerf cuts on the backside of the plywood with a circular saw giving it better flexing properties.

Traditional ¾ Inch Hardwood Glued. No Plywood Sub Floor

For more traditional hardwoods or ones that are longer in length, the largest disadvantage of gluing has always been material that is not milled straight or may not lay flat. This creates problems trying to close up gaps, whereas nailing to a wood sub floor forces gaps to close by the sheer force of the nailing tools used. Other common problems include wrong adhesives, or incorrect amount used.

Other methods of installing solid ¾ inch hardwood without a wood sub floor system include a product named Elastilon, currently sold through Lumber Liquidators and Home Depot. One more product to the mix is the Sika Acoubond system (above) that also provides some sound dampening properties for apartment or condominium dwellers. As mentioned previously, any successful installation using the these products requires very straight material.

Cost Analysis With Different Applications - 2015

CostsBased on 1,000 square feet. No angled walls

The following analysis provides a general idea of what to expect when adding a plywood sub floor to concrete in preparation of installing a traditional ¾ inch nailed or stapled floor. Keep in mind the material costs are not hardwood contractor pricing but average retail (sales taxes not included) at home improvement centers or flooring supply stores in the continental USA. They should also be considered general as regional differences can affect the pricing. The only factor that could vary noticeably from below is the labor cost. Furthermore, labor costs reflect individual contractor pricing only. Retail store pricing may be higher.

3/4 Inch Plywood Fastened To Concrete

Description
Quantity
Cost
Total
Plywood (material)
33
$ 28.00
$ 924.00
Visqueen 6 mil (material)
1,000
50.00
50.00
#15 Asphalt Felt (material S/F)
1,000
.04
40.00
Tapcons (material) ¹
1,056
.14
147.84
Installation (S/F)
1,000
1.50
1,500.00
Total
$ 2,661.84

3/4 Inch Plywood Glued To Concrete

Description
Quantity
Cost
Total
Plywood (material)
33
$ 28.00
$ 924.00
Adhesive (material) ²
7
180.00
1,260.00
Installation (S/F)
1,000
2.00
2,000.00
Total
$ 4,184.00

Floating Sub Floor (2 Layers 1/2 inch plywood)

Description
Quantity
Cost
Total
Plywood (material)
66
$ 20.00
$ 1,320.00
Visqueen 6 mil (material)
1,000
50.00
50.00
#15 Asphalt Felt (material S/F)
1,000
.04
40.00
Staples (material) ³
1,056
.02
21.12
Installation (S/F)
1,000
1.75
1,750.00
Total
$ 3,182.12
 S/F - Square foot

What's Not Included Above

Moisture protection from concrete is getting more attention these days. Only 15 years ago there were no solutions outside of using glued sheet vinyl for glue down hardwood applications, or the older horrible gooey mastic approach with sleeper system. Today there are mastic type moisture compounds that many professionals use if initial concrete testing shows unacceptable concrete conditions. Still more, some professionals simply add in the cost of these systems out of sleeping better. If conditions warrant their use, another $ 1.50 per square foot (labor and material) should be added to the above numbers. If this relates to your situation the visqueen (plastic sheathing) and asphalt felt paper can be removed.

Floor preparation is also not included above. Prior to the installation plywood, sub floor conditions should be addressed and corrected. See floor prep on concrete.

¹ Based on 32 per plywood sheet. 1 3/4" x 3/16" size
² Bostik's Best Urethane (5 gallon) with #4 square notch trowel. 30 S/F per gallon
³ 18 Gauge crown staples