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Understand the Three Main Wood Floor Adhesives

By Joe Hostler and Eric Wymer
October/November 2010
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In order to have a successful wood flooring installation, it helps to understand the types of wood flooring adhesives and how they work. This requires an understanding of both chemistry and bonding; here's a short primer.

Essentially there are three types of adhesive chemistries: modified silicone polymers, polyurethanes, and acrylics. Each has its place, and in order to understand how they work, you must first understand this: An adhesive can create a chemical or mechanical bond. A chemical bond is when molecule A combines with molecule B to form a new molecule, C. A mechanical bond consists of molecules interlocking but not chemically changing. Both types of bonds can be quite strong.

MS+

Modified silicone polymers (or MS+), which are relatively new, are considered hybrids. They create a mechanical bond with wood and thus penetrate into the cell structure of the wood. However, should adhesive end up on top of the finished wood, the outcome is much different. The MS+ will not bond well to this coated surface and will clean off easily. This gives MS+ adhesives excellent long-term cleanability.

With concrete, MS+ products form a chemical bond. MS+ polymers are unaffected by water when cured. They are also typically zero-VOC and very ecologically friendly. In my opinion, they are the future of wood flooring adhesives (full disclosure: we sell all three adhesive types).

Polyurethanes

Polyurethanes combine with the lignin (complex chemical compounds found in wood that form parts of the cell structure) to create a chemical bond. Polyurethanes create a mechanical bond with the concrete. They are enormously strong and form an elastic bond that has allowed the industry to bond ¾-inch solid wood to concrete. These adhesives are unaffected by water when cured. The biggest drawback is that a polyurethane adhesive will form an incredibly strong chemical bond with the polyurethane finish on top of the wood flooring. This makes trying to clean that spot on top of the floor you didn't notice during installation an absolute nightmare, so they must be cleaned when wet. Polyurethanes contain diisocyanates, are low-VOC and generally contain solvents.

Acrylics

Acrylic adhesives usually consist of polyvinyl acetate emulsions. (They are also sometimes called "latex," which is a term for natural and synthetic rubber resin materials, so the correct term is "acrylic.") Acrylic adhesives are highly filled polymer dispersions in water. The typical curing occurs when the water leaves the dispersion with the help of solvents. The polymers coalesce, or fuse, creating a particle entanglement or matrix. Acrylic adhesives are highly susceptible to moisture and usually require a flashing off period prior to floor installation. They clean off easily with water because of this, but will fail easily in a wet environment. When installed properly, they are an effective, proven option for engineered floors. Unlike the other two adhesives, which are waterproof at full cure, acrylic adhesives are always susceptible to dilution from water or water vapor. On the plus side, acrylics have a rebonding capacity: Contractors can weight a section of floor and have it bond after the rest of the floor was installed. Acrylic adhesives generally are low-VOC and contain solvents.

You don't need to be a chemist to understand how adhesives work, and understanding them is fundamental to any successful installation. One thing is clear: Demands for innovation and ecologically friendly or green adhesives will continue to drive the industry.

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What to Use

Here's a quick guide from the authors for which adhesives are usually recommended for which types of wood flooring products:

¾-inch solids: Polyurethanes
¾-inch shorts: Polyurethanes, MS+ Polymers
5/16-inch solids: Polyurethanes, MS+ Polymers
Engineered plank and strip: Polyurethanes, MS+ Polymers, Acrylics
Parquet: Polyurethanes, MS+ Polymers, Acrylics


Joe Hostler is business manager-wood floor bonding at Lyndhurst, N.J.-based Sika Corporation. Rusty Winters and Ondrej Masek of Sika Corporation also contributed to this article.



Wood floor adhesives            Installing wood flooring                   

 Comments:

The article states ''The MS+ will not bond well to this coated surface..''. Does this prohibit its use when gluing products that are sealed on all 6 sides?
Kevin  floorman  11/16/2010 9:26:29 AM

I personally would not use it. There are 2 issues with sealed products on all sides. The first is the chemically very weak bond as I discussed in the article. The second is typically there is no specification for the mil thickness of the coating on the bottom and sides of the board when run through a bath. Remember you are only as strong as the surface you are bonding. If I attach my adhesive to a polyurethane finish with an uneven mil coating, the floor may fail in some areas and not in others if the wood begins to move. My advice is to mechanically fasten any product sealed on all six sides.
Joe Hostler  National Sales Manager-BASF  11/18/2010 4:56:12 PM

Every factory finished bamboo manufactured floor we have ever used; Mannington, Teragren, Johnson, US Floors, D&M and Mohawk have been sealed on all six sides. All have bonded well to the concrete using urethane. Some floor man is going to read this article, decided the future is now, and end up in failure gluing bamboo with MS+.
kevin  floorman  11/19/2010 11:58:12 AM

I have a stained And sealed hardwood floor. I need to add a stained and sealed hardwood floor reducer onto it. What brand and type adhesive should I use
mark  stained and sealed  3/22/2013 8:17:29 AM

Can bamboo plywood flooring be glued to a concrete slab containing infloor heating piping? Or does the flooring need to float over a floor with an infloor heating system?
Neil Nelson    6/12/2013 8:56:42 AM

I am trying to use a friends extra 3/4" Brazilian cherry pre finished hard wood for a platform that will be 10' x 12' in two sections (one) 6' x 10' and (two) 4' x 12' it will be built out of aluminum and will act as a tray to hold the wood in place. I wanted to glue the tongue and groove wood together and let it act as the entire floor. In other words, no sub floor. What adhesive should I use?
kevin McGraw  building owner  11/18/2013 9:39:36 AM

What would you advise I use to glue a plywood (teak & holly) panel, 1/4" x 4' x 2.5', to a flat plastic (gelcoated) surface on the cabin floor?
Bob Aitchison  boat owner  1/16/2014 10:58:44 AM


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