I have been hired to correct marine synthetic teak decks, also referred to as faux teak, plastic teak or fake teak, that eventually opened up where the planks were glued together incorrectly. What I have witnessed is the obvious lack of Stelmax ( the bonding adhesive used directly in the tongue and groove ). Sometimes when the installer is connecting one plank another they fail to put enough adhesive to connect the planks together.
A common mistake I have seen is the installer applying the Stelmax into the groove. By applying the Stelmax directly into the groove you are taking a risk of putting too much in and once that happens the two planks will not fit together tightly due to the extra Stelmax in the groove. Once an installer sees that his planks aren't fitting tightly together his next move is usually to go light on the Stelmax from then on and then there is not enough Stelmax in between the two pieces to actually do the intended job of creating a sealed seam.
It is easy for an installer to think everything is fine because it looks good during the installation. After time, temperature changes, and humidity take their toll and the seams open up and become unsightly and compromised.
The easy solution to keep this from occurring is to not apply the Stelmax into the groove. Instead, apply a bead of Stelmax to both sides of the tongue. This will not put the Stelmax into the bottom of the groove which caused the first problem of not fitting together tightly. By applying the glue this way you will get the seam sealing action desired especially along the topside of the material where the failure usually starts.
When Ameriteak is hired to fabricate mats we do not use stelmax, instead we weld all of the mats together therefore alleviating the need for tongue and groove seam bonding glue.