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Expansion Gaps & Adhesive Recommendations

Matt emailed with two questions…


1. Why is there a need to provide the ½” perimeter expansion for glue down application?  If the product moves that much wouldn’t it break the glue bond?

2. Could you provide compatible adhesive/vapor barrier & retarder manufacturers?


The reply:




I’m assuming you are doing a full spread, glue-down installation. Is that correct?

Here in the U.S. we have a dozen or so types of environments. Teragren has to speak to all of these. ½ inch around the perimeter in many situations, is the thickness of the sheetrock or the base molding. Minimal space that’s otherwise unused.


In floating floors that move as one large unit, it’s a key element in ensuring that as seasons change, any expansion/contraction the flooring might encounter, has the ability to utilize that ½ inch. If the floor can’t move freely it will separate at the seam or buckle trying to do so. Separations are the result of tension that is greater than the t&g glue bond. Buckles are caused when a floor tries to expand and can’t. Either way, that expansion gap is critical to the long term success of the install.


Nail down or glue-down floors, restrict that movement on a large scale. But, the material still expands/contracts at a measureable rate. It just does so per plank instead of per room. The individual plank seams will gap or compress through the seasons. Most people don’t notice it because it happens so gradually. Eased, beveled and micro-beveled edges help mask it as well.


The take-away


a ½ inch gap isn’t normally going to hurt. But, if the floor buckles or pinches, you’ll waste time and money doing repairs after 6-9 months (a couple season changes)



Do you have a moisture meter? Know what the substrate moisture content is. Keep a record of it. If it’s high, you’ll want to ensure the adhesive manufacturer warrants the product for that moisture content. Teragren products have been tested by the following;


Flooring Adhesives: Resource list


Franklin Flooring Products:


811 Advantage Urethane Wood Flooring Adhesive

821 Premium Urethane Wood Flooring Adhesive

741 Ultimate Wood Flooring Adhesive

531 Plus Concrete Moisture Control System

571 Sound & Moisture Control System



DriTac 7700 Easy Clean Premium Green Hybrid Urethane Adhesive

7500 Eco-Urethane Premium Green Urethane

DriTac 7000 Moisture Control System

DriTac Golden Bullet



Ultrabond ECO®:





Teragren doesn’t warrant adhesive. We warrant Teragren Flooring.


Do a google search for the products above with “pdf” following the title. You’ll usually get a specification sheet that will tell you the permeability ratings, MC & RH allowances, warranties, etc. Good to research before you commit to one.


****This is where most installations go south****


Follow installation guidelines to the letter. Use the appropriate tools, trowels, products and methods.


I want you to have great success. This is the best way I can help. I try to provide the data and the possible risks so you can make informed choices. Let me know if I can help further.


Take care,


Technical Manager