Sure, you can, but if you do, the locking mechanism is likely to break due to the added flex that it's not designed to deal with.

It might work but since they don't recommend it, if it fails, you're on your own. Marble, tile and wood are all successfully glued down over 6mm thick cork so my feeling is that it would work, except that it looks like you're using 8mm product. That's a mark against it.

Why do you want the additional layer of cork?

I'm trying to avoid having a 'cIicky/hollow' sounding floor (as much as you can with a laminate floor, anyway).

I was considering adding a 6mm cork underlayment because the laminate I'm using is only 8mm (with a 2mm attached foam backing).

Any suggestions?

Thanks

Cork underlayment is much denser than foam products, so you may be OK doing what you propose. There would be very little additional movement that would negatively affect the laminate locking system, in my off the top of my head opinion. You will void the manufacturer's warranty should you add anything not accepted by them, but...hey!...it's your floor! Floor warranties were a joke when I was selling retail and I have to believe that little has changed in that area, or am I mistaken in that assumption?

Make sure you have a perfectly flat substrate to within the manufacturer's guidelines and you will avoid most 'hollow' sounds. Your floor probably will exhibit a 'clicky' sound no matter what you do to prevent that; after all, the plastic laminate over the fiberboard core is a 'hard surface' product, so top surface noise is just in the nature of the beast.

Hi Glen-Could you please give me your opinion of this reply that was posted on another forum?:

"First off, NEVER add more loose underlayment for any floating floor system you use other than what the manufacturer calls for, even if it is pre-attached. It usually voids the warranty and is simply not needed for installation purposes."

"And quite honestly, too much underlayment jeopardizes the integrity of the planks locking together. This can lead to separation and failure of the floor. This is the reason why you can't use extra underlayment."

"With that said, you can still use a pre-attached underlayment on your floor over a GLUED-DOWN cork underlayment. As long as the first underlayment placed down is glued directly to the subfloor, then you are okay. It's only the loose underlayment that can't be put with another."

"As long as you glue down the underlayment above, you can place a flooring with pre-attached underlayment on top of it."

"At minimum, you can use a pre-attached underlayment that comes with your floor, but do not place any added underlayment to it unless it is firmly glued down first."

Thanks, again.

If you are going to go to the trouble and expense of gluing down cork, you might as well glue down real wood as well rather than plastic imitations of wood. You're kinda talking bout putting cool whip instead of whipped cream on top of a home made chocolate silk pie in a gourmet restaurant. It's using a premium underlayment for a non premium topping. And it doesn't make good sense.

Your 8mm product may be heavy enough to hold the cork firmly to the substrate and prevent any vertical compression and the possible damage to the locking system that is the main concern. However, adhering the cork down with the approved adhesive will give you a firm and secure base over which to place most any flooring product and remove any doubts in that area.

I've done it both ways and you do have a slightly better 'sense' of firmness when installing over cork that is firmly attached to the substrate, as opposed to cork that lays loose.

Since the product you're using has underlayment attached, installing it over cork will do little or nothing to affect the "clicky" sound. To minimize the objectionable sound, it would probably be better to use a thicker product, laid over one of the higher density underlayments like Floor Muffler or Silencer.