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I've recently bought a house and removed the existing laminate. I was told when buying the house that the downstairs subfloor was sealed concrete. After removing the laminate flooring I found the below. My questions are:

  • Could anyone confirm from the pictures that this is sealed concrete?
  • If so, does the sealer look worn out to you?
  • And if so, can I reseal by just cleaning and applying a new sealer on top or do I need to completely remove the previous sealer first?

I'd have expected a shiny/polished look if it was sealed concrete. Any help would be highly appreciated.

The reason why I'm asking is because when removing the laminate flooring that was there, the green padded tiles between the laminate and the concrete were quite mouldy and a bit damp. Not a lot, but enough to make me think there might be a damp/mould problem.

Thank you!

Subfloor

enter image description here

isherwood
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elmediano
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  • The sealer _may_ have been smooth and shiny when it was first applied, but I'd think that would be more evidence of an epoxy coating. The mottled look is the remains of the tile adhesive on the floor. If the concrete has a proper moisture barrier underneath (and wouldn't know that from above), what additional benefit are you looking for from the sealer? – FreeMan Apr 22 '22 at 11:10
  • Thanks @FreeMan. I think that's what I'm trying to ascertain, whether the floor has a proper moisture barrier. This is because when removing the laminate flooring that was there, the green padded tiles between the laminate and the concrete were quite mouldy and a bit damp. Not a lot, but enough to make me think there might be a damp/mould problem. Though it might just be a bit of condensation or the green tiles weren't suited for the job they were intended? I'm adding some LVT flooring so before I do this, I want to make sure the subfloor is suitably prepared. – elmediano Apr 22 '22 at 11:44
  • We aren't going to be able to answer from this. All I can see is old flooring adhesive. If you want to be sure, grind that away and re-seal it. – isherwood Apr 22 '22 at 13:24
  • Thank you all for your input, I appreciate it's not the best picture and even if it was, as you have mentioned there isn't an easy way to know. If you don't mind, I'd just like to point out that the bits where there isn't any adhesive (in front of chimney) and some other areas were the adhesive has come off, are dusty. I take it this still doesn't make a difference in telling if the floor was sealed back in the day? Instead of grinding and then resealing, could anything else be done to what's there in terms of damp/water-proofing? Thank you all! – elmediano Apr 22 '22 at 14:11

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You can not tell if concrete is sealed from a photo. The adhesive for the tiles could even damage some sealer’s. To see if you have a moisture problem take a piece of plastic like a trash bag and tape it to the floor. Wait 24 hours and remove the plastic. If the plastic is wet you have excessive moisture coming up. If just a slightly dark area on the concrete there is still moisture but that is closer to normal.

To really seal the floor the concrete has to be clean and that old tile adhesive is a bugger to clean, I have rented “shot blasters” to clean flooring like this then a muriatic acid etch and rinse followed by epoxy floor paint. It is an expensive way to do it but it effectively seals the floor with regard to normal moisture , a high water table will still find its way through even with a quality epoxy coating.

Ed Beal
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  • Thank you Ed. I actually taped some cling film on an area of the floor yesterday so I'll check tonight/tomorrow when I'm in the house next for moisture. Unfortunately, I won't be able to remove the adhesive like you mentioned because of current budget. Just crossing my fingers it isn't too bad in terms of moisture and that the flooring company can install the LVT flooring without problems. – elmediano Apr 22 '22 at 16:00