Double Glue Dos and Don’ts, Revisited

Regular carpet installation (pictured here during a recent INSTALL training session) and Double-Glue carpet installations are different animals. Make sure to familiarize yourself with the proper procedures and read all the manufacturer’s instructions once and once more before going in.

Double Glue? “Sounds easy enough,” the installer says, “just like doing two direct glues... one for the pad then another for the carpet, right?” Not exactly. There is a bit more involved to these tricky little beasts than meets the eye, everything from trowels to rollers and all the stops along the way. Let’s take it from the top – or actually, the bottom – and begin with pad.

Not just any pad can be used for Double Glue. Rubber Double Glue pads are either made of a closed-cell construction or coated so as to not allow the adhesive to soak into them like a normal pad designed for stretch-in installation. They are also much thinner; usually no thicker than 1/4”, and very dense with rebonds starting at 10 lb and sponge rubber pads at 20 lb. Some nylon felt pads are also designed for Double Glue. In a traditional Double Glue installation the pad is glued to the floor with a pressure-sensitive adhesive. These adhesives are quite often mistakenly called “release adhesives.” Not accurate, as what they do is remain tacky when dry. How well they grab depends on the amount used and how much pressure is applied. A small amount of this glue goes a long way. It’s applied with a VCT notch trowel or a roller, or sometimes the flat side of the trowel. Flat troweling is risky and not recommended.

Allow the adhesive to dry to its translucent tacky state with no transfer when touched. After laying the pad into the glue, use a stiff push broom, a carpet tube, or light roller to smooth out the bubbles and press the pad into the glue. Trim the pad net to the wall, leaving no gaps or excess.

Think of it as installing a subfloor made of rubber. The whole idea is to have just enough adhesive to hold the pad in place, making removal “easy” when replacing the carpet. Having cussed many a Double Glue off the floor with elbow grease and scrapers, I can attest that it doesn’t always work. Going into it even just a little wet and you’ve got a permanent, and I do mean permanent, bond akin to sticking two pieces of duct tape together. 

Many different types of Double Glue pads are on the market, requiring different adhesives and installation techniques. It’s important to read carefully and follow the manufacturer’s installation instructions. Once the pad has been installed it’s easy to think, “OK, just do a direct glue bing-bang-boom, and we’re outta here.” Don’t be fooled. This is where Double Glue gets tricky. Remember these tips.

Type of Glue. You will need a premium, high-solids content adhesive approved by the manufacturer for Double Glue. Generally these adhesives are referred to as firm-set; they don’t dry hard but remain flexible. Even though Double Glue pad is thin and dense, there is enough movement to break down an adhesive that doesn’t remain elastic and flexible.

Amount of Glue.The recommended trowel sizes for double glue are: Smooth-back carpet, 1/8(width) x 1/8(depth) x 1/16(space); and Rough-backed carpet, 1/8(width) x 3/16 (depth) x 1/8 (space) Unotch. You might look at these trowels and say, “Holy mud! I’m installing carpet not doing yard work! Let’s see if I’ve got this straight: Use the best glue I can get and put it on with a rake! OK, see ya, I’ve got work to do.”

More on Trowels. Let’s stay with the trowels a bit longer. First, new trowels will chatter and jump on the pad because of the burrs left from the notches being stamped out. This is not something you would ever notice doing direct glues. A quick and easy solution is to buff them off with a wire wheel on a bench grinder or with a piece of sand paper.

Also, while applying the adhesive, if the same pressure is used as you would on a direct glue, the pad will bulge into the notches, cutting your coverage by as much as 40%. Light pressure is the key, just enough to push the glue pile around, allowing the trowel to measure the correct amount out (remember, trowels are a measuring device). From my experience the above-mentioned trowels (1/8x1/8x1/16 and 1/8x 3/16x1/8 U-notch) will give you coverage of four to five sq. yd. per gallon and a 1/8x1/8x1/8 U-notch will yield six to seven sq. yd. per gallon if held properly. When pricing a job, figure adhesive costs of at least $1.50 to $2.00 per sq. yd.

Moisture. You have just applied an enormous amount of adhesive to the floor. It’s important to get the excess moisture out of the glue before the carpet is laid into it for a couple of reasons. First, the carpet or the fillers in the latex used to laminate the primary and secondary backs will absorb the moisture, causing the carpet to expand.

Here’s the scenario: The job is installed (cut to fit), looks great and you’re on your way. A few days or weeks later the adhesive cures, the carpet gives up all the moisture it’s absorbed and it shrinks! Well, not really, unless it was wool or jute backed. What it has done is contract, just like anything does with heat and humidity changes.

“So, what do I do, just stand around and watch the glue dry?” No, use fans, and I don’t mean bring one box fan on the job. Invest in at least two high-power fans. What you are looking for are fans that move between 9,000 and 12,000 CFM (cubic feet per minute) of air. The ones I used were the big 18” ones in the round silver cages called “Whole House Air Circulators.” They will cost you between $60 and $80 apiece for good ones.

I don’t recommend the more powerful hurricane fans used by carpet cleaners to dry carpets, because they project a concentrated stream of air instead of moving large blocks air over the glue field like the round fans do. For example, if two installers start in the middle and spread glue away from each other to the ends, set the fans at each end blowing toward the starting point. Set the fans at a 10- to 15-degree angle from the floor. This helps the glue set up evenly because you are not focusing the air stream on only one portion of the glue field, but moving large blocks of air across the entire glue field.

The desired condition of the glue before dropping the carpet into it is “tacky.” Touch a finger to it and you should pull “legs” 1 to 2” long.  By doing this you accomplish two things: 1. Most of the moisture is out of the adhesive (less for the carpet to absorb); 2. The adhesive has enough grab to stop the carpet from expanding from what moisture remains. Using the right fans will cut the set up time considerably and pay for themselves on the first job.

Spread some glue on a scrap piece of pad, drop a small piece of carpet on it and step on it immediately. When you pull back the carpet you will see the imprint of your foot with most of the glue forced into the carpet back, not enough left on the pad for a good bond. That is a good illustration of why it is important to let the glue set up.

Rollers. For the same reasons mentioned above, a light roller, no heavier than 35 lb., or a carpet tube is recommended to press the carpet into the glue.

Seams. Here’s a tricky deal. There are two ways of making Double Glue seams, and both are hotly contested. The first method is to seal the seam just like a regular glue-down. Make sure to cover both the primary and secondary backs, not just putting the bead of sealer on the pad at the base of the carpet. If you properly acclimatized the carpet, used the right amount and kind of glue allowing it to set up properly, used the right roller and restricted traffic for the recommended 24 hours, you will probably be fine.

Remember earlier when we spoke about the carpet contracting when it gave up the moisture it absorbed from the glue? If it does that and your seams aren’t properly sealed they could pull apart. If the carpet gaps at the walls you have lots of options to save the job: quarter round, cove base, even small strips as fill. With gaps in the seams, however, we’re talking big trouble. This brings us to the second method of making seams in Double Glue. Hot tape the seams. There are two methods of doing this: 1. Preseam, or 2. Seam it in place.

Pre-seaming is not practical for large areas. The only time I would recommend this is for adding fills to rooms. You can use regular seam tape for this, BUT (and this is a very big but) after the seam has cooled you must peel off the excess paper and scuff the silicone off the back of the tape, using heavy sandpaper i.e. 50 grit. If you do not follow this step, the glue will not stick to the silicone-treated paper.

Seaming in place. Lay out the carpet, seams trimmed and sealed with latex or thermoplastic seam sealer, and fold back one piece. Position the tape under the remaining piece, depending on which type of tape (there are two: with paper and without). The ones with a paper backing have a pressure-sensitive adhesive to hold them in place. The ones without paper, designed to stick to the pad when the seam is made, will need to be “tacked” in place with a quick smear from a hot glue gun.

Once the tape is in place, fold back the remaining piece of carpet and spread glue to the edges of the seam tape but not underneath the tape. Heat from the seaming iron can break down the multi-purpose adhesive. When the glue has tacked up properly, lay the carpet into the glue, make your seam and then roll the carpet. With either edge sealing or hot taping methods of seaming, you must have the seams set properly and be very careful not to shift them when folding the carpet back to spread the glue.

Whenever possible, begin the installation in the center of the room at a seam. Once the first seam is done you can work in both directions, using your fans to tack up the glue on one side while spreading adhesive on the other side. Working back and forth like this is an efficient use of time while adhesive is setting up.

This bears repeating: acclimatize the carpet and pad to the job site before installation and make sure to restrict traffic for 24 hours while the glue is setting. Bottom line is to always make sure you follow the manufacturer’s installation instructions, make sure the carpet and glue you intend to use are recommended for Double Glue, and keep in mind that some pads have different installation requirements than mentioned above.

When I was younger, and, uh, foolisher, my usual approach was: “When all else fails read the instructions.” Do yourself a favor and save yourself some aggravation. Learn the lessons the easy (and cheaper) way. Read the instructions first.