Concrete subfloor - needs repair?

Lifted an old carpet in my study. Concrete subfloor underneath. Want to fit solid wood flooring (using leftovers from previous project where I bought too much). Tongue & groove flooring to be glued in place with Laybond Floor Adhesive.

The subfloor is nice and level but has some hairline cracks in it and in places feels a bit hollow. It feels like the surface has blown in some places. It’ll be about 20 years old.

Tell me I’m not going to have to get the subfloor repaired before I get started! I’m going to have to get it repaired, aren’t I? If I don’t, I’ll regret it later, right? Ugh

You don't mention damp so, no, no and no.

Blup

Hairline cracks generally aren't an issue and are fairly normal in mass concrete , it's only when the get wider than 3 or 4mm that you need to consider stitching them (e.g. dig out crack area, lay mesh over the top then refill the joint with resin)

blup said:

You don't mention damp so, no, no and no.

Blup

Click to expand...

Ah ok. No, I don’t think there’s any damp around (I’ve got a moisture test meter in the back of a cupboard somewhere so I’ll be using that soon to check). In that case, might I be ok?

Floors need a moisture meter like a Tramex to get an accurate reading. Moisture meters designed for wood are at best inaccurate, at worst downright misleading. Tape a couple pieces of thick polythene to the floor and leave overnight. If you lift them in the morning and find condensation, you have a DPM/DPC issue. Either way before putting any wood floor down it is always a good idea to put a liquid DPM onto the concrete. That's what I'd expect a trade floor fitter to do