Laminate floor underlay questions

[Mike-B]

Hi all,

I've got 30m2 of laminate flooring (Inovar) to lay over some concrete (thankfully is old, sound and flat).

Anyways, I have a question regarding the underlay. It's a rubber 2 or 3 mm underlay with a gold moisture barrier on one side. So, does this sort of underlay still need to be laid right to the wall, slightly up the wall or stop the same distance from the walls as the floating floor (10mm)? Some instructions I've read still suggest using builders plastic sheet to run a bit up the sides of all walls, others don't. Is the plastic sheet on these 2in1 underlays a good enough moisture barrier for sound concrete? It seems to be the same material as those 'space blankets'...

Cheers,
Mike

[Ken-67]

I don't know why you would want to run it up the walls, The underlay is not intended to waterproof a room; it is intended to stop moisture rising up into the flooring. If you know the concrete was layed on a waterproof barrier, there should be no need of additional plastic sheeting under the underlay.

[Mike-B]

It seems the idea of running a vapour barrier 30-40mm up the walls is to reduce the chance of said vapour getting into the unsealed ends of the boards. Just wondering if anyone's bothered to do this with a 2in1 type underlay...

[Chris@Phoenix]

No need, just straight underneath the flooring will be fine :) The underlay you've bought is an acoustic product and it's there for pretty much just that, give you a nice feel and sound to walk on! They put the foil on as just a bit of an extra protection for rising moisture from the concrete, in an old (10 years+) house the concrete will be fully set and wont have any escaping moisture.

Laminate flooring isn't super sensitive to moisture like a solid timber is, very different product!

[Mike-B]

Cheers Chris, just what I wanted to hear.

[Levey]

I agree with Chris except for the "Laminate flooring isn't super sensitive to moisture like a solid timber is".
In some cases I have found that Laminate flooring can expand more than timber flooring after installation, and that is why an expansion gap is required everywhere.
All solid timber flooring should have an expansion gap around walls etc but it is now common (in WA) to cut the boards neatly around door frames and with no problems unless excess moisture changes the conditions.
Some sort of moisture barrier should be used on all flooring installs regardless of the age of the concrete slab, cheap insurance in case of a problem.