Planning to overboard the existing floor with ply prior to laying a new engineered wooden floor.

Problem is that part of the floor is old concrete/cement where a range used to be. It’s breaking up slightly on the surface and seems quite, errm, crumbly underneath.

I thought about using wall type fixings to try and anchor the overboard down as I don’t want it to ‘rattle on the concrete area.

Equally, I don’t want to end up with the whole lot coming loose after a fortnight.

So, dig out the top few inches and lay a screed over it or just go with the wall fixings/anchors approach?

From your description I’d go with a screed. Better for the long term, assuming the base layer is stable.

[sucks teeth]Depends[/sucks teeth]

What width and thickness are your new boards? How are you fixing them?

Few options:

Lay the ply over it with shedloads of expanding foam underneath, weigh the whole area down and have everything pre-cut and ready to plop down before squirting the foam.

Drill and screw the ply down (probably what I’d do) with screws and rawlplugs.

Scabble out half an inch and latex to level with floor (bit of a dusty shitty faffy job and not worth the hassle for such a small area) where the planks would probably span it anyway.

It’s this stuff.

http://timbafloor.com/18mm-tg-engineered-oak/

Being laid as a floating floor (just gluing the t&g bit together) on green foam underlay stuff.

I have 15mm ply to go over the existing floor with this on top of that.

The concrete area is probably 3ft x 6ft and (due to previous changes to the room layout) is in front of a door so will be a high traffic area.

I did space blanket- pink gripfill , 15mm ply and 60mm hammer hits at 100mm centres into my concrete floor. Before tiling over.

Hasnt moved.

Possibly a stupid question – why is the ply needed? Why can’t you just use the foamy underlay stuff?

It’s not how I’d fit it, but anyway, that’s not what you want to hear. 🙂

Moving on…

Is the concrete roughly level with the rest of the floor? If so, then the ply should just float over it anyway – maybe use some flexible (Sika T52/Bone R850 in sausages) adhesive between the ply and concrete. Or drill and screw it for belt and braces approach. Use No. 10 screws, approx 60mm long with brown plugs. If it’s a high traffic room in general, then maybe have a think about floating it at all.

The existing floor isn’t brilliant tbh, it’s the old kitchen floor and has had various holes cut in it, boards lifted etc over the years.

Boarding over the whole thing will give a solid, level, basis to lay the new floor on.

A guy in B&Q once asked me if I wanted flooring……….

What’s under the concrete?

We had the same thing at ours – concrete plinth where a range used to be.

Turned out the concrete was laid over a mound of wet earth, through which damp was spreading up the wall. Proper nuisance.

So, our solution was to remove the whole deal, re-joist the area, new boards etc, proper below-floor air circulation.

Worth checking out?

If it’s a high traffic room in general, then maybe have a think about floating it at all.

‘the bloke in the shop’ said it would be fine 🙂

tbh, if it’s ok for a few years then that’s enough and as an amateur it’s probably the easiest method. It’s a continuation of this floor through from another room;

I think I’ll try and lay the plywood over what’s there and leave it a week or two before putting down the main floor to make sure it doesn’t start shifting.

As long as you have room for the 15mm ply (15mm ply + 18mm flooring + underlay is nearly an inch and a half higher than you currently have – I assume you’ve taken all this into account for doors opening into the room etc.).

Here’s how you should do it:

Get your ply down – lay the long side of the ply perpendicular to the direction of the existing boards.
Forget the underlay and get a kit of a box of R850 sausages + free gun + nozzles.
Lay the floor using liquid batons (posh way of saying strips of adhesive applied to the floor approx. 12″ apart, perpendicular to the direction of the new floor).
Don’t glue along the tongues and grooves – let the timber be free to expand/contract a little with seasons.
Liquid batons is a doddle and gives you plenty of time to get the first few rows right whereas PVA will be cured in around ten minutes meaning any gash-ups will be harder to put right.
Buy/rent some flooring strap clamps.

EDIT: I know plenty of people will happily recommend gluing on the T/G but it’s not really correct practice for full thickness flooring. You’re better off adhering it to your subfloor which in this case is your ply.

I’ve also got a floor question (OP let me know if you want me to delete this and start my own thread, I don’t expect to take up much of your space though)

I am looking at buying a house, it has been recently renovated and finished fairly well. One odd thing though is the use of Wallmate under the floor instead of on the wall. Does anyone know if this is ok or will it cause a problem. Will the weight of the floor/being walked on be too much for it?

Any advice greatfully received.

DD – thanks I’ll look into that solution.

I realise that it’ll raise the floor a fair bit (my recent plunge saw purchase makes door trimming a doddle!).

Alternative is to lift the existing boards and dig out the concrete and then lay a t@g chipboard floor and then the new floor, I guess?

dirtycrewdon, no worries 🙂

Alternative is to lift the existing boards and dig out the concrete and then lay a t@g chipboard floor and then the new floor, I guess?

Yes – that would be a prawper job, although tbh, I wouldn’t bother unless you really need the height that much. They look like Victorian boards to me and lifting them (and jerking joists out of the spot where they’ve been nestled for a century-ish) often causes more problems than it eliminates. They’re happy enough where they are. Btw, 15mm ply might be a bit overkill – 9mm would be plenty. Often, I just overboard with 5.5mm if needed.

BTW, the liquid baton method is easier than gluing on the T/G…honest!

is the height going to match up with the flooring in the next room?

is the height going to match up with the flooring in the next room?

it’ll be pretty much ok on one side and it’ll join the floor in that photo. bit of a step on the other as it’s sanded boards!

May go for thinner ply 🙂

given I’ve glued the previous lot will switching to the baton method at the doorway cause problems if it does expand and contract?

given ‘ge glued the previous lot will switching to the baton method at the doorway cause problems if it does expand and contract?

No, not at all. Tbh, if you’ve T/G glued the previous lot, then go ahead and do it on this one too…I don’t mean to scare you. It’s just that when you’re doing it for a living, you have to do it the “best” way to justify the ridiculous charges. 🙂

It was probably the easiest floor I’ve ever laid, tbh.

Easy to get the boards together (easier than Quick Step, certainly).

Lots of nice straight runs ending under the kitchen units and just dropped the skirting on in the places it needed it.

Will look at thinner ply to avoid too large a step at the other end, though.

Im now a firm believer in not gluing the t&g togethor after using tongue tite screws on a floor recently ,plus if anything goes wrong underneath its easy to take up without damaging the boards

Tongue-tites are a great little invention! Really useful little things to have. (Although bugger all use over concrete).