Hi everyone! We have a couple larger projects coming up that will require us to glue down 5/8" unfinished engineered. One is new construction over gypsum, and the other I am not 100% sure if it's gypsum or concrete cause we still need to remove carpet that is glued down. Although we have done some over the years these will be much larger then any we've done.. Most of what we do around here is nail down.

With both of these being in excess of 5000sf, I definitely want to be sure I do everything exactly right. Now on the new construction one the architect has asked me to specify the required psi for the gypsum and my supplier suggested that I specify 2800psi. So first I'd like to verify that this sounds right?

Next, I understand that I will need to check/monitor the RH and the moisture content of the gypsum/concrete and of the flooring.. However, I am curious if their is generally a recommended cure time for the gypsum? I'd have to assume it's at least a month? I believe the architect told me it was 1" thick gypsum..

Next, I am curious to know what adhesive you guys would suggest? I don't care about the price, I'd prefer to know that I am using the best stuff..

Any other recommendations would be appreciated..

Sounds like a scary proposition gluing to gypcrete or lightweight. Found this from Armstrong;

5. Concrete Compressive Strengths
Because of traffic loads anticipated for commercial and institutional
environments, concrete slabs should meet the requirements for ACI* class
2 or class 4 floors. For these environments, all concrete slabs, including
lightweight, must have a compressive strength of 3,500 psi or greater.
6. Lightweight Concrete
a. Armstrong resilient flooring may be acceptable over lightweight
aggregate concretes having dry densities greater than 90 lbs. per cubic
foot and cellular concretes having plastic (wet) densities over 100-lbs.
per cubic foot (94 lbs. dry weight), providing the surface is troweled to a
smooth, even finish. However, this is a minimum requirement for the
application of resilient floor covering. Concrete slabs with heavy static
and/or dynamic loads should have higher design strengths and
densities calculated to accommodate such loads.
b. Because lightweight concrete can retain significant amounts of moisture
within the slab, it is imperative that lightweight floors be tested for
moisture in accordance with ASTM F-2170, “Standard Test Method for
Determining Relative Humidity in Concrete Floor Slabs Using in situ
Probes.” DO NOT TEST LIGHTWEIGHT CONCRETE FLOORS USING ASTM
F-1869, “Standard Test Method for Measuring Moisture Vapor Emission
Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.” This test
method does not indicate the moisture condition deep within a slab and
can be especially misleading when used on lightweight concrete slabs.

More reading for you from Jason Spangler at Wagner Meters;
Understanding Different Types of Lightweight Concrete

http://www.wagnermeters.com/flooring/ra ... -concrete/

Then theres some really nice gypcrete self leveling systems out there with high compressive strengths. Most gypcrete I see here is all busted, cracked and powdery.

Ive been laying bamboo over gypcrete with ms plus adhesive for two years. No problems at all. If you have to replace a board you just need to cut the board into one inch strips so you wont tear up the gypsum when you pull up the old material. No primer just glued with a v notch trowel. You might consider a roll on primer/moisture barrier as insurance after your ca cl test and the usual 28 day curing period for new cementacious installations.