Laying Karndean on ply subfloor in bathroom

24 Nov 2015
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United Kingdom
I am having a small bathroom redone and want to lay Karndean da Vinci wood effect planks in the bathroom but am struggling to get sensible answers to some questions as follows -

1. The current subfloor is damaged chipboard. This will be replaced with 25mm WBP ply as part of the refit. The area to be Karndean'ed will be a single 8 x 4 sheet of ply. Can Karndean be stuck directly to the ply using their Universal Adhesive? I don't see why not but Karndean says overlay with 6mm ply which seems daft ...

2. Does ply need to be sealed on top side before spreading adhesive?

Thanks in advance for any help.
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No need for another layer of ply, however joins and screw heads should be covered. I can't remember what it was called but there was a karndean product I used which did the job, primed and filled.
The guy I asked who lays karndean and amitco for a living said their tech spec used to say fill with a sandable filler and prime with PVA and he never had a problem, but he now uses the product I mentioned as its what they guarantee now.
Thanks Chappers - I think I said somewhere that the ply should be sealed with an acrylic sealer on the underside and edges. Is this true? And also does the top of the ply need to be sealed other than where it has been filled / smoothed?
Yes you need to cover with 6mm plywood then a coat of feather finish screed.
The 25mm with move over time so that's why you overlay with 6mm.
You never prime with PVA!!!!!!!
It's not a floor primer!
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Karndean's own instructions say nothing about having to ply over ply here
As I said the guy who I asked said that their instructions had changed so he no longer uses PVA, however there is still plenty of stuff around the net saying to still use neoprene or PVA such as here and they appear to have a Karndean certificate
It might not but about 15-20 company's make LVT and will have different ways of fitting. I've done the Karndean and Amtico advanced course. And know then you ply over 18mm plywood or about.
You don't use PVA as I said before. Ring karmdean tech tomorrow and ask them.
Or prime neat and use a fibre screed like level flex, stopgap 700, Ardex FA20 etc
I wasn't arguing with you about the PVA, but I also bet if you rang Karndean they wouldn't guarantee it if you used another manufacturers screed either.
As for the ply are you saying that if the 25mm ply you mention moved that the 6mm attached to it at 150 centres wouldn't too, especially as Karndeans own spec sheet says it isn't necessary. I can only speak from experience, but the karndean I laid about 6 years ago direct on 18mm ply is as good as the day it was laid barring a few nicks and dents.
They would. Karndean recommend most top manufactures screeds. Karndean sell a skim coat( which they don't make) but they don't make a fibre screed.
I'm just saying the way I'd do things. It's a Diy forum and up to the person asking the questions how to proceed.
I'm just giving my opinions, they might differ from other people which is fair mate.
But I've been to Ardex , Fball, Uzin, who alol say never use PVA.

You can get away with lots of stuff. I've laid over 18mm plywood and the joints have should through due to movement because that's what I was told to do. Never done it again.
Whatever Karndean say I don't see why I need to overlay a new 25mm WBP subfloor with 6mm of ply when the (small) area to be covered in Karndean is a single 8x4 sheet of ply - ie with no joins. Other than the guarantee (which I am not bothered about) what risk am I running?

Also any suggestion for the best adhesive in this situation in a bathroom which is prone to puddles of water being left on the floor? I cannot tell which adhesives are waterproof in the event that a bit of water seeps through joins in the tiles.
If no joints go for it.
Put a coat of feather finish screed on top.
Most glues are OK for bathrooms.
You can use their PS or Universal which is a high temp adhesive buy goes off quick so best to cut floor in then lift out and glue area then place Karndean in.

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