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Double stick installation has been around for many years but it seems that retailers and installers shy away from these types of installations; why is that? Before we answer that, we need to know what a double stick installation is. Double stick is where a high-density cushion designed for double stick is adhered to the substrate with either a pressure-sensitive adhesive or a multi-purpose adhesive depending on the manufacturer’s recommendations. Once the cushion is fully adhered to the substrate, carpet is glued directly to the cushion, thus a double stick installation. So why are there concerns?

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• Type of carpet backing

• Recommended adhesives

• Proper trowel notch and proper use of trowel

• The proper amount of  open time

• Proper roller weight

• Type of maintenance

• Type of traffic  

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 These are all important factors to look at before proceeding with this type of installation. (Photo 1) Shows what happens on a failed double stick installation. This installation was approximately 2 years old when the end user noticed the carpet bubbling in the traffic areas. One or several of the bullet points could be factors involved with the bubbling.

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In this article we’ll cover some tips that will assist you in a successful installation.

(Photo 2) Shows two backings commonly referred to as “Action Bac”, that have different “Pics.” The backing on the left is a lower pic backing. This means that there is a larger space between the warp (length) and weft (width) wires compared to the backing to the right. What this means is that there is more potential for adhesive to get up into the backing, which leaves less adhesive on the cushion and weakens the bond strength of the adhesive. A higher “pic” backing allows for better bonding of adhesive to backing and cushion by keeping more adhesive between the two surfaces.

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(Photo3) A 1/16”x1/16”x1/16” square notch is the proper trowel notch to use for cushion to substrate; follow the manufacturer’s recommendation for the type of adhesive. (Photo 4) Full spread the adhesive to the substrate; install cushion at a right angle to the carpet in the longest lengths possible, or offset a minimum of six inches if running the same direction as the carpet. Do not use tape at the cushion seams; net fit the seams with no voids. (Photo 5) Use a broom to flatten and push out any air bubbles.

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Photo 6 shows a top row cutter without a bottom plate and one with. Be careful when using a row cutter to trim seams; if you are using a top row cutter without a bottom plate, use scrap cushion between the installed cushion and the carpet as cutting into the cushion may cause issues over time.

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 (Photo 7) Seal all seams after carpet edges have been trimmed. Some manufacturers state that a 1/8” bead of seam sealer is sufficient for seam sealing. I make it a point to use a hot melt seam tape under all double-stick installations to ensure better integrity of the seams. There are several manufacturers who make hot melt tapes designed for double-stick applications; we’ll just cover a few here. If I have a room that has a small fill, rather than fight the small fill piece into the glue, we will seam the fill piece onto the main breadth (full width) trowel adhesive to the cushion, and then lay into the adhesive.

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Photo 8 is a “designer” carpet tape. Area rug fabricators use this type of tape for seaming area rugs; this type of tape also works well for double stick installations. Construct the seam with the designer seam tape using the traditional hot melt tape method, and when the seam cools, pull the carpet back, remove the paper carrier, trowel on the adhesive, allow for proper open time and then lay into adhesive.

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Photo 9 shows a system using radio wave technology. This type of system uses a special non-silicone hot melt tape placed underneath the seam; the tool sends radio waves that create a reaction with the foil which causes the adhesive to melt. This type of tape generally does not stick to the cushion because heat buildup is kept to a minimum compared to that of a hot melt seam iron. Trowel on the adhesive, allow for proper open time, then lay the carpet into the adhesive. The two seam tapes mentioned DO NOT HAVE SILICONE on the backs of the tape. Silicone backed seam tapes will not bond to the multi-purpose adhesives.

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(Photo 10)  This type of double stick seam tape is installed directly to the cushion and held in place with pressure sensitive adhesive on the back. Place and align tape under the seam and remove the carrier paper and then press the seam tape onto the cushion. When troweling on adhesive, make sure to place adhesive just under the tape and also on the exposed paper on the top. This type of seam tape requires that you apply adhesive to the cushion and then hot melt construction of seams.

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(Photos 11 and 12) Another seam tape designed for use with double stick installations is the radio-wave technology (Double Stick) DS tape.

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This tape also has a pressure sensitive adhesive and uses the Radio wave tool (Photo 13). Once the carpet has been placed back into the adhesive, seam the carpet together. As with all hot melt seams, seal seams, use proper seam roller, and seam weight.

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(Photo 14) Approximately three feet of adhesive that has been properly spread with an 1/8”x1/16”x1/8” U notched trowel.

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(Photo 15) See the excess on the right side of the photo? The same trowel was used but the difference was that more pressure was applied to the trowel, which flattened out the adhesive ridges; the result is an improper amount of adhesive even though the proper trowel was used. Make sure to use light pressure on the trowel to maintain round shaped ridges of adhesive.

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See the difference between the two trowels in Photo 16? The trowel on top is the 1/8” U notched trowel. The U shape uses double the amount of adhesive as the 1/8” V notched trowel pictured on the bottom of the photo. Make sure you allow for the use of more adhesive in your bids. Many installers will start with the U notched trowel but realize they are using a lot of adhesive and will switch to the V notched trowel, and once again, the amount of pressure on the trowel handle can influence the amount of adhesive left on the cushion. Will the carpet bond to the adhesive? Sure it will, for about 18 to 24 months until bubbles start to appear in traffic areas, which takes me back to Photo 1. Spray applications are also being used for double stick installations; check with the manufacturer for recommend systems and procedures.

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Open time of adhesive is critical as you are applying double the amount of adhesive. Indirect air movement can help in reducing open time of adhesive. Do not place air movers to where air is moving directly over the top of adhesive. Instead, aim the air movers towards the ceiling, reducing the amount of direct air which causes the adhesive to skin over and can create loss of bond strength. In some parts of the country, it may require the use of de-humidifiers to maintain an acceptable level of relative humidity in the areas to be installed. Use adhesives recommended for double stick. These are adhesives that have a higher solids content which means less fillers and water. They cost more than regular multipurpose adhesives but they perform much better.

(Photo 17) Two different rollers; one is a lightweight lean-on roller, the other is a 75-pound roller, so which one do we use? The lightweight roller is the one to use or a roller that does not exceed 35 pounds. We are trying to get transfer of adhesive, not rolling all the adhesive into the carpet backing.

Installers must follow ALL recommended installation procedures for double stick installations. Not enough adhesive, no open time, to heavy a roller, immediate foot traffic, all lead to a failure.

Sales personnel must understand the differences between a direct glue down and a double stick installation; they are two different installation systems and cannot be bid at the same price!!! Pre-qualify the installation and flooring products to determine the proper installation method.

There are many successful double stick installations without any concerns whatsoever but, these types of installations are installed by qualified installers, and retailers who know the parameters for a proper double stick installation.

For a detailed description of proper double stick installation techniques you can log onto the International Certified Floorcovering Installers Association website: www.cfiinstallers.com

For proper double stick cushion, log onto Carpet cushion council website:  www.carpetcushion.org