Level very uneven tenement floorboards

[AkiraDIY]

My central heating is on microbore, which is blocked in places and most the rads are full of sludge, so the system needs gutted. I know in the living room, the microbore pipework was just jammed between a gap in the floorboards, wouldn't surprise me if the rest of the flat was in a similar shoddy state. Since the floorboards and carpet need to come up, I figure it's a chance to sort out the floor too.

My flat is in a 200 year old tenement building on the 3rd floor and the floorboards feel dreadful through the carpet. They're uneven, creaky, and there's dips in the carpet like chunks of the floorboard are missing and the previous owner just foam underlay and carpeted over it.

I'm guessing replacing all the floorboards will be expensive (can you mix and match original tongue and groove floorboards with modern floorboards or they different sizes/thicknesses now?).

I was thinking to just nail down any loose boards, replace the worst looking ones, 6mm plywood on top screwed down, caulk the joins of the ply sheets, a self levelling compound over the top, underlay, then laminate on top.

Does that sound like the best way to do it?

 

[tell80]

Maybe not the best way to do it.
Lift all coverings to show only the bare boards.
Now begin to remove all or some of the heating installation. You will have to lift boards to some of the pipework. Be careful, dont destroy the boards as you lift them. Re-"nail" using screws only.
Design a new c/h system. Think positions of boiler, rads & pipe runs?

Be sure your joists are firmly fixed with noggins at the correct span before blaming floor boards.
Whats the final floor, the FFL, going to be? You need to know before building up the under the FFL?
Laminate will butt the skirtings or go under them?

 

[AkiraDIY]

Sorry for the late reply, work exploded this week. Been running around daft.

I've got my rad locations and pipe runs pretty much figured out, the locations aren't too far from the original locations, all on the same wall. Biggest change will be the bathroom (back of the flat, pretty much in the middle) as the pipes to straight up into the loft, run across to the back left of the flat, then drops down into the boiler. I'd prefer it to go below the floor, through the wall towards the boiler somehow (hoping there's an existing hole somewhere nearby) so the high point isn't 6m of pipe in the loft.

Final flooring is going to be mainly laminate (carpet in the bedroom possibly). Would prefer it to go under the skirting but it looks like original skirting and probably impossible to remove without taking parts of the wall with it. Most likely just end up butting it.

I've not seen the joists, I can only assume the noggins have been done correctly but won't know until I start lifting boards. I've pulled some of the carpet back before and the floorboards are a right state. A lot of them are cracked, split, warped, bits missing, gaps filled with what looks like mortar, etc.

What's the most cost effective way to level the floor without it being a cowboy job?

 

[foxhole]

6mm ply too thin to support screed .

 

[Harry Bloomfield]

Would prefer it to go under the skirting but it looks like original skirting and probably impossible to remove without taking parts of the wall with it. Most likely just end up butting it.

You could use a multi-tool to trim the bottom of the skirtings and door frames, without needing to disturb them.

 

[AkiraDIY]

You could use a multi-tool to trim the bottom of the skirtings and door frames, without needing to disturb them.

I've bought a flush-cut saw to do this in my mothers house before as a multi-tool would have taken at least a week and countless blades. Don't really want to do that again as it still took ages and butting it doesn't look that bad. Not worth the effort imo.

6mm ply too thin to support screed .

why would 6mm ply be too thin to screed when the old floorboards will be underneath? Is it because the ply will eventually warp and conform to the state of the floorboards?

Then what's the best way to get this floor level before laying laminate / carpet?

 

[foxhole]

I would use anything less than 18mm sheet to give a floor flat enough for laminate , if carpeting then thin ply will be sufficient .

 

[Deleted member 174758]

why would 6mm ply be too thin to screed when the old floorboards will be underneath? Is it because the ply will eventually warp and conform to the state of the floorboards?

Then what's the best way to get this floor level before laying laminate / carpet?

When I've done this for floorers, they normally specify something like 12mm plywood minimum, screwed down at 150mm centres, and they often put an SLC over the top to take out any residual hollows. How thick you go with the plywood sort of depends on how bad the original floor is

 

[AkiraDIY]

I would use anything less than 18mm sheet to give a floor flat enough for laminate , if carpeting then thin ply will be sufficient .

You wouldn't use anything less than 18mm? 18mm sheet is thick enough to be a subfloor by itself is it not?

I was only planning to put a new layer on top of the existing subfloor, I didn't want to remove the floorboards if it can be avoided as it sounds like a lot of work that might not be necessary.

When I've done this for floorers, they normally specify something like 12mm plywood minimum, screwed down at 150mm centres, and they often put an SLC over the top to take out any residual hollows. How thick you go with the plywood sort of depends on how bad the original floor is

Ideal world would be just 3-5mm underlay and 12mm laminate although I think the sub-floor isn't flat enough, it feels pretty bad through carpet. I thought/hoped 6mm ply and SLC might be enough to get it acceptable but looks like I need to remove the whole carpet and see the state of the subfloor before I can figure out the most suitable option. Maybe a full subfloor refit is required but hopefully not

 

[Deleted member 174758]

Ideal world would be just 3-5mm underlay and 12mm laminate although I think the sub-floor isn't flat enough, it feels pretty bad through carpet. I thought/hoped 6mm ply and SLC might be enough to get it acceptable but looks like I need to remove the whole carpet and see the state of the subfloor before I can figure out the most suitable option. Maybe a full subfloor refit is required but hopefully not

You can get a rough idea by taking something like a 4ft or a 1m level and plonking it across the floorboards at different points with a light source behind the level. five millimetres or so here and there in the boards (e.g. cupped or crowned boards or board ends high) can sometimes be taken out with a power planer or a big belt sander and P36 or P40 grit belts. Laying plywood over that just smooths it out further (and reduces sound transmission, draughts, stops SLC seeping through if you need to use that, etc), so if after you've sanded/planed the sub-floor it is pretty good all it might need is a layer of 6 o, 8mm plywood - screwed at 150mm centres - it all depends on how flat the sub-floor is before you ply it. 12mm covers a multitude of sins, and conforms to the sub-floor less than the thinner stuff, making for a faster job and meaning that you can often get away with nothing more on top, but again you need to check with a straight edge and light source

 

[AkiraDIY]

thanks for the advice. I'd be amazed if my floorboards are warped less then 5mm but I'll definitely check once the central heating is getting replaced. Maybe some new screws will get it to 5mm for sanding but I'm not holding my breath. If I was going to use 12mm-18mm ply and not sand the floor, would it be necessary/advisable to soft underlay that as well or is screwing down and underlaying the laminate enough?

I don't want to be that neighbour that lifts the carpets and then the neighbours hear every footstep or drag of a hoover (like the neighbour at my mothers house. She has to move after 35 years of living there cause it's so bad but I digress)

 

[Deleted member 174758]

The exact how you do this depends on how bad things are to start with... One thing I will say is that with old boards you don't stand much of a chance of screwing the cup out of them and trying to do so too 'vigorously' often results in cracked or split boards - which is why power planing or belt sanding the worst of the cup out followed by over plying (12mm, or even 8mm if your sub-floor isn't too bad) is a quick way to get results for a modicum of work. The more uneven the floor is to start with, the more work or the thicker the ply needs to be to correct any issues

 

[AkiraDIY]

Thanks, looks like I'll be getting a pro in to sand/plane the floor at some point then. Is it recommended to underlay the ply and the laminate or is just underlaying the laminate enough?

(if it doesn't hurt and I can get my hands on decent underlay for a reasonable price, I'll probably do both for maximum sound proofing)