Repair & Care
Installing Glue Down Hardwood Floors On Concrete
Gluing of hardwood floors represents a sizeable part of the hardwood flooring business with most of it installed on concrete in homes that are generally on grade (no basement).
Not For The Timid DIY
These types of installations are more prone to failure over all others. Some of the more common reasons include; improper or no floor preparation, wrong adhesives or incorrect amounts applied resulting in de-bonding of the material from the subfloor. This is why any glue down installation should be performed by someone that has the experience and know how. Adding to the difficulty is the mess involved.
How Are They Installed?
Gluedowns are installed by trowel spreading of adhesive on the subfloor in a pre determined area (shown above). Usually professionals will measure out three feet or enough for twelve rows to cover, using a three inch wide board as an example. Each and every individual board is placed one at a time into the adhesive until the glued area is covered. Once completed, another area is marked and laid.
Not All Types Of Hardwood Should Be Glued
Contrary to what you may hear, not all products can be glued easily. Put another way, gluing solid 3/4" hardwood has always been risky business, but some premium urethane glue manufacturers will warrant their use. The difficulty encountered with solid hardwood is the lack of flexibility compared to more common products that are glued; engineered flooring.
Common types used for gluing down are engineered hardwoods. Thickness vary from 1/4 inch up to 3/4" depending on the manufacturer. During manufacturing the bottom sides of many products are milled with relief cuts. This insures the flooring can bend to minor irregularities in the contour of the subfloor it is being installed, while increasing the bonding contact with adhesive at the same time. This is definitely not an excuse to skip floor preparation; stressed heavily on this site.
Pros and Cons Of Gluing
Most consumers prefer the solid feeling of hardwood floors underfoot. Floating floors for the most part do not offer this benefit unless a premium underlayment is used and a very flat subfloor is maintained prior to installation. After the addition some still complain of the hollow effect floating floors exhibit. A properly glued hardwood floor will feel and sound very much like a traditional solid floor.
Adhesives used for these types of installations do not come by cheaply. More preferred types recommended by many manufacturers can cost upwards of eighty cents a square foot depending on where it is purchased. With any glue down installation, do not take the suggestion of ill informed persons that any old glue will work while saving you bunches in the same breath. Skimping on costs in this department may very well lead you to our message board forum titled, "Yikes I Have Problems."
How Long Does It Take To Install? Are Adhesives Toxic?
Assuming you have a 400 square foot, square room with furniture moved and everything is ready to go, one experienced installer can complete a 3 inch wide glue down installation in 10 -12 hours. Adhesives used today are predominantly three types. Water based, urethane based, or acrylic, with the majority of manufacturers leaning towards the urethane.
Older more toxic adhesives are long gone, with newer more environmentally friendly varieties. If you are chemically sensitive it may be wise to vacate the premises when work is being done. With glue downs, curing time is typically one day or an overnight period before furniture can be moved back into place.
Case Study - Glue Down 3 Inch Engineered Plank
Few if any home structures will be square making it important to check any layout ahead of time and making necessary adjustments. On this job we got a measurement from two opposite wall lines and compared the two numbers. Depending on the width of the material, our starting area should be 30-36" from the baseboard or drywall. In our example by using a 3 inch wide engineered product we've multiplied 12 x 3 inches and added 3/8" for the expansion space that will be covered with shoe molding after the floor is laid. (measurement shown on the right should be 36 and 3/8 inches)
Expansion isn't as critical with glued engineered products as it is with floating floors or nail downs, but you will need some area to get those last few rows into place.
Not all products are created equal. We suggest placing twelve boards tightly together prior to the actual installation checking for size. Where it may be 3" in width, twelve boards may not equal 36 inches. This is common with lower quality products as the milling is not as refined. It may be a good idea to add another 1/4" on top of our example of 36 and 3/8 inches. Without doing so you may find yourself having to cut a smidgen off with the last board to fit the parallel wall area.
Getting That First Area Laid
Having marked two areas from our baseboard on each side of the working area, snap a chalk line. This will become our starting line. In this case our helper was nowhere to be found so a full bucket of Bostiks did the trick. Once we have our starting line, double check how it looks on the opposite wall with the tape measure. It's also a good idea to check against the starter wall area as some walls or baseboard may not be straight.
The starting area is the most important in any installation. If we're looking at a single room, the biggest concern is how square you are in that area. However, if the installation goes into other areas and your starting line is out of square to these areas you'll find yourself correcting as you go along. This is why we recommend a control line.
A control line is a reference point for the entire layout and should be utilized near the center. In this case find the longest parallel wall, measure out, and set a chalk line halfway across the room or nearer to the center of the entire installation. From here we recommend making reference points in other areas checking to see how square we may be from our control line. In other words, measure away from the control line and get another chalk line set. Check measurements against all parallel wall lines and make necessary adjustments. For more technology inclined, lasers can also be used for squaring up, but actual control lines should be visible at all times.
Back to the starting area. Measuring out 36 - 3/8" from our base we've snapped our starter line. Once the adhesive is spread we're ready to work off that line and towards the baseboard.
Place your first row directly on the chalk line, proceeding to add a few more rows staggered as much as possible as shown below. Once you have a few rows started use some scrap pieces to be used as backer boards to keep the installation from moving around in the adhesive. Attach them with concrete cut nails (3 1/2 penny or less) or tapcons. Some have noted hot gluing scraps to concrete may also work and be less troublesome. A very clean surface is important for this to work.
Working from left to right, continue to fill in the area where the adhesive had been applied. Don't forget about that can of mineral spirits and a rag. Your first experience with this adhesive will not be a treat and it's vital to cleanup as you go.
Keeping Adhesive Contained
Depending on how well you've spread the adhesive, you may get some ooze over the starting line. When spreading try to keep the adhesive 1/4 to 1/2 inches away from the line. If you should happen to stop for a day or two, make sure the area and the groove is clean of any excessive glue. Trying to engage the next row with a dried glue clog can be a frustrating experience. Always check before spreading any additional adhesive or when finishing for the day. Otherwise you will not get a tight fit of the old area to the new and gapping will be inevitable.
Moving In To Complete The First Area
If we've measured correctly, our last row should fit in nicely with a 3/8 inch space remaining. Place the last full piece while utilizing a pry bar against the base or wall (use a scrap or putty knife to protect from dinging) to pull the installation tight. Insert wedges into the area to keep the tight fit as shown below. At this point your starting area should be tight as a drum and should not slide out of place. However, I would keep a close eye on end joints for a few hours as they have a tendency to open up at will. They can also be tightened with the pry bar at perpendicular wall lines.
Other methods used for keeping floors tight include blue painters tape, but should be removed once the adhesive sets. Follow individual manufacturer directions as some do not recommend this procedure because it can affect the floor finish. Wedges can be made from scrap pieces on the power miter saw you are using.
Added 2008 - The use of strap clamps and blue tape have become the tools of choice with many hardwood professionals since this article was originally published in 2004. Strap clamps are an alternative to using floor fasteners, but can easily create more problems than needed if they are not kept out of the adhesive.
Cleanup As You Go!
Once you've completed the starting area, go over it thoroughly with a rag and mineral spirits. There's nothing more frustrating then having to clean cured urethane adhesive once the job is complete. In this particular job, and my attention to cleaning as I go, I still spent two hours on 1200 square feet cleaning spots that I missed or glue that got tracked from one ooze to another.
Continuing The Installation
Once our starting area is complete, remove our starter boards very carefully and measure out another area to be worked. Use whatever measurement you find more comfortable. 24, 30, or 36 inches (based on 3" width) away from the original starter line. Get another chalk line going and spread the adhesive again.
Knee Pads and Other Stuff
Obtain padded cloth types. Those with plastic caps will scratch your new hardwood floors. It's also a good idea to shake out any grit that may have been collected each time you put them on. Guys, all it takes is one piece of grit caught on a knee pad and you may be sleeping on the couch the next few days.
Have I mentioned how messy this adhesive is? By all means use your worst clothes and keep them separated from others when you're through for the day. You may be thinking.."if this stuff is that messy, why don't I wear gloves?" Frankly, I believe wearing gloves (medical types) is likely to create more problems. Why? You don't have the sensitivity to feel any adhesive opposed to being gloveless. Any contact with the glue while wearing gloves is ignored. You continue unknowingly and adhesive smudges multiply.
Go To: Getting Started. Staying square and tight