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dixie53
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# Posted: 28 Apr 2026 06:19pm
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What are peoples opinions on using construction adhesive whe putting plywood on floor joists? Good idea or bad?
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travellerw
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# Posted: 28 Apr 2026 06:48pm
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Absolutely.
However, builders have begun switching from construction adhesive to foam subfloor adhesive. I used it when building my stairs and there is NO QUESTION that its much more robust than standard construction adhesive.
Costs a little more and requires a foam gun, however its what I will use next time.
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DRP
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# Posted: 28 Apr 2026 09:09pm
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I agree.
Pretty much any construction glue will creep over time under load, so does not add bending strength. It does make the floor assembly stiffer, and that is usually the controlling factor in making a good feeling, less bouncy, floor. Also, every joint is a potential squeak, air, and sound leak.
Look at Advantech vs plywood subflooring, its stiffer and handles construction wetting better. There is no better rain dance than breaking ground  .
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gcrank1
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# Posted: 29 Apr 2026 04:25pm
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Do I remember right that a strip of 'tar paper' over each joist before the p-wood is put down will stop the potential future squeaks?
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DRP
Member
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# Posted: 29 Apr 2026 10:34pm
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That's a new one to me. Flashing tape on deck joists is not a bad idea.
As I was just checking on the Forest Products Labs website I looked for the most important wood book in the country first, The Wood Handbook. That is not exaggeration. If you might ever have a use for wood info, I'd download it, it is a huge file. I have my FIL's 1953 early version. My first copy is from '76. It gets thicker through time as some old info drops off and much new info is added;
https://research.fs.usda.gov/fpl/wood-handbook
While I was checking the links I went to chapter 10 on adhesives and copied this short excerpt.
Strength and Durability
In building construction, adhesives that hold up the
building during its life are considered structural. These
adhesives generally are stronger and stiffer than the wood
that they bond. Structural bonds are critical because bond
failure could result in serious damage to the structure or
its occupants. Examples of structural applications include
glue-laminated beams, prefabricated I-joists, laminated
veneer lumber, cross-laminated timber, mass plywood, and
stressed-skin panels. Structural adhesives that maintain
their strength and rigidity under the most severe cycles of
water saturation and drying are considered fully exterior
adhesives. Adhesives that lose strength faster than wood
under severe conditions, particularly water exposure,
are considered interior adhesives. Between exterior and
interior adhesives are the intermediate adhesives, which
maintain strength and rigidity in short-term water soaking,
but deteriorate faster than wood during long-term exposure
to water and heat. Unfortunately, adhesives that are the
strongest, most rigid, and most resistant to deterioration in
service are typically the least tolerant of wide variations
in wood surface condition, wood moisture content, and
assembly conditions, including pressures, temperatures, and
curing conditions.
Semi-structural adhesives impart strength and stiffness to an
adhesive-bonded assembly, and in some instances, they may
be as strong and rigid as wood. However, semi-structural
adhesives generally do not withstand long-term static
loading without deformation. They are capable of short-term
exposure to water, although some do not withstand long
term saturation, hence their limited exterior classification.
Another semi-structural adhesive application is the nailed
glued assembly where failure of the bond would not cause
serious loss of structural integrity because the load would be
carried by mechanical fasteners.
Nonstructural adhesives typically support the dead weight
of the material being bonded and can equal the strength and
rigidity of wood in dry conditions. Nonstructural adhesives
often lose strength and sometimes stiffness when exposed to
water or high humidity. Two major markets for nonstructural
adhesives are furniture and cabinet assembly.
Elastomeric construction adhesives are categorized as
nonstructural but are normally used for field assembly of
panelized floor and wall systems in light-frame construction.
These adhesive joints are much stiffer than mechanically
fastened joints, resulting in stiffer panels. In addition to the
adhesive, mechanical fasteners are used to carry the load in
case of adhesive failure.
Some adhesives could be easily included in more than
one category because they can be formulated for a broad
range of applications. Isocyanate and polyurethane
adhesives are examples. Polymeric methylene diphenyl
diisocyanate (pMDI) with a low molecular weight develops
highly durable bonds in structural strandboard, even
though strandboard products deteriorate from swelling
and shrinkage stresses. One-part polyurethane adhesives
provide durable adhesive films, but as molecular weight
increases, adhesion to porous wood generally decreases
and bonds become increasingly susceptible to deterioration
from swelling and shrinkage stresses. Soybean-based
adhesives have limited wet strength on their own, but cross
linking agents are added to increase water resistance for
nonstructural uses
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DRP
Member
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# Posted: 29 Apr 2026 11:28pm
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You didn't ask, but in the same "connection"
For the nails, head to the fastenings chapter 8 in the wood handbook, the first couple of pages are about nails. The highlights are, that withdrawal strength is a function of nail diameter, depth of penetration, surface condition of the nail and wood density.
I typically shoot .128 diameter x 2-3/8" long ring shank nails in the floor. The classic 8 penny common, hand drive nail is .131 x 2-1/2". The specifics of fasteners and spacings for all the connections in the house for code are in, I believe chapter 6 of the codebook. (notice as you read code, they are reading the raw data from the wood handbook and writing the safety factored construction rules about spans and numbers of nails, etc. Read the strength tables in chapter 5 and you'll see the initial data for the engineering behind the code span tables)
The other biggie is pay attention that you are not overdriving fasteners... we get to renail it if he sees a bunch of overdriven nails. It really weakens the connection to blow halfway though the sheet goods. To get design strength you gotta make the design connection.
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toyota_mdt_tech
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# Posted: 10 May 2026 08:05pm
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Quoting: dixie53 What are peoples opinions on using construction adhesive whe putting plywood on floor joists? Good idea or bad?
At my cabin, all glued and screwed. No squeaks.
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