How to prepare subfloor for hybrid flooring?

[Ieda7]

Hi all,

We have recently purchased a unit that was built in 1980. The floors are vinyl/lino (not sure) in the kitchen, tiles in the bathroom, and carpet to the lounge and bedrooms.

I'm looking to replace the carpet with hybrid flooring and redo the vinyl in the kitchen. We've pulled off the carpet and underlay in one of the bedrooms and found this:

From what I can see, this floor looks to be particle board. My initial thought was that the black area was mould (we found black mould underneath the skirting boards on the gyprock walls that backed into the shower and our building/pest inspection noted mildew on the floor of the crawl space), but it doesn't wipe off easily. So the second thought was that it was glue for the carpet underlay, however, 1) it's not across the entire board as the joins aren't discoloured, 2) the underlay came up without a fight, and 3) there are no tears or glue on the underlay either.

I'm also not confident that we've reached the subfloor itself as the above looks different from what the inspector photographed from the crawl space itself (below). I don't really want to rip these out in the event that there isn't another level beneath them.

If the particle board is the subfloor, then we need to clean and level it before we can install our hybrid flooring. My question is how to clean them off? I'm aware that some adhesive glues from the 80s had asbestos in it, so I'm reluctant to just get in and sand it back. I'm also reluctant to just put the black plastic over the top of it without cleaning as if it is mould/mildew, I don't want to just neglect that and end up with air quality/health issues.

Would welcome any thoughts/advice.

Cheers!

[EricL]

Hello @Ieda7 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about preparing your subfloor.

I suggest your first order of business should be to make sure that your floor does not contain asbestos. I propose having it tested professionally to make sure that it is safe to dismantle. If the results come back negative, you'll need to decide if you should rip out the flooring and replace it with yellow tounge or take your chances with sanding it down. I'm aware that you're not keen on ripping the floor apart. But from a safety perspective, I suggest replacing your floor as the mould in your current flooring is unpredictable.

It could be deeply seated, or it could be just surface mould, either way should you happen to miss a small hidden section of mould the entire exercise of sanding it down would be wasted as the mould will spread through the flooring again. I propose engaging the services of a mould specialist and getting their opinion on the severity of the infestation. Should an alternative be offered, then the general steps for floor layout preparation will be the same.      

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

[Dave-1]

Morning @Ieda7 

When I removed the lino and then masonite from my kitchen and the carpet and underlay from the dining room years ago I had the same colouring on top of my floorboards, it was fuzzy but smooth. For my place it was a glue that was laid down before carpet underlay is what teh sanders told me and came up very easy when I had it sanded.

I would possibly hit up some floor sanders to see if they have come across this before or go for what @EricL has suggested and get it tested. Going over your photos again, I would head towards a test at the very least it wil stop you worrying down the track.

Dave

[Ieda7]

Hi @EricL,

Thanks so much for your reply. We have sent a sample off for testing today and are attempting to find someone to come and do an inspection on the mould.

Regarding replacing the subfloor: just wondering if you suggested the yellow tongue rather than ply solely for the price difference, or were there other reasons as well?

[Ieda7]

Hi @Dave-1

Thanks for this info - it's nice to get validation!

Will definitely look into floor sanding contractors pending the asbestos test and mould inspection results.

Cheers!

[EricL]

Hello @Ieda7 

I suggested Yellow Tongue as it is one of the most common floor coverings used in construction.  However, you are free to choose plywood if this is your preferred material. My best advice is to take into consideration installing flooring insulation and a moisture barrier while the floor frame is open. 

If you need further assistance, please let us know.

Eric

[Ieda7]

Thanks for clarifying @EricL. Adding insulation is definitely part of the plan in the event we do need to take the floor up (and probably mechanical ventilation too). Hopefully strata agrees to the install!

I found the advice on this thread from March really useful and was intending to follow it:

https://www.workshop.bunnings.com.au/t5/Whole-of-House/How-to-add-waterproof-membrane-under-timber-f...

As for which type of insulation to go with, that's still undecided. I saw on another community post that polystyrene was the best material to deter rodents and is easier to cut, so we may go that way (https://www.workshop.bunnings.com.au/t5/Whole-of-House/How-to-retrofit-underfloor-insulation/m-p/181...).

Thanks again for your advice - it's appreciated.