Stage floor levelling - options?

[Ynot]

Don't think there's going to be anything practical we can do here but worth at least an ask.

Our stage floor is, as per the pic below, floorboards nailed to a sub-frame of heavy timbers, which we cover with 12mm MDF boards, which we replace every few years. 

In general it's fairly level but there are areas where it dips a little - enough so that rolling our mobile scaff tower around can be a little worrisome as occasionally one wheel can suddenly be in a bit of fresh air until it makes contact again the other side of the dip. 😮

We'll be re-boarding this coming weekend and we've been looking at whether/how we might solve the problem, but sadly nothing has really presented itself as a solution. The sub-frame isn't something we can affect to make any changes at all, not that we can see. I've contemplated some sort of self levelling fluid, but have been advised against that for a couple of reasons. 

It's not at all easy to see where the floor dips, so not an easy option to pack it out with anything, and it'll be hard to judge how thick that packing might need to be and ultimately could mean we make the situation worse by introducing rises as well as/instead of dips. 😞

We have already used a thin underlay before (seen here being rolled up) to mainly stop the boards creaking, but that didn't help the dips.

So - anyone ever used anything LIKE self-levelling to solve a similar problem?

Any other thoughts?

[sunray]

Lift the floor boards, level the subframe timbers replace boards.

[Ynot]

18 minutes ago, sunray said:

Lift the floor boards, level the subframe timbers replace boards.

Sadly don't have the time to do that, although it was suggested. 

[J Pearce]

Screwfix sell a good bag of mixed packers. Grab a long straight edge and pack boards as you go, though if you're only replacing the 12mm MDF you may struggle to pack under the 12mm and retain sufficient strength. There's no easy answer alas, beyond lifting the floorboards, levelling the subfloor, then reboarding (I'd probably go for 24mm ply instead of floorboards at that stage).

[Ynot]

2 hours ago, J Pearce said:

Screwfix sell a good bag of mixed packers. Grab a long straight edge and pack boards as you go, though if you're only replacing the 12mm MDF you may struggle to pack under the 12mm and retain sufficient strength. There's no easy answer alas, beyond lifting the floorboards, levelling the subfloor, then reboarding (I'd probably go for 24mm ply instead of floorboards at that stage).

The 12mm MDF is already on site and waiting the team to lay and screw...

 

[kerry davies]

You have the extra long spirit level (though a laser level might be better). Now all you need is sacks of packing ply and hardboard of varying thickness and endless patience. It was the part of stage building I hated but then we were doing it in fields in the rain, as often as not. There is no short cut that I ever found, it is just a long-drawn out, PITA process.

[sunray]

I have had the situation in a farm building conversion where the floor was very rough sawn planks on very rough sawn joists on tree trunk timbers and variations of up to 3" (75mm) across the 60ft (18m) length. This was originally a hay loft with very wide gaps between the boards and the conversion simply filled in the gaps with more random boards.

The only way we considered levelling was to remove the boards and send away to be planed/thicknessed, added packers between the worst trunk/joist points and added 4x1 to the side of the the joists to get a level top surface.

[Dave m]

Basically, as said. Use a big straight edge/level and create a series of stacks of shims to create a sort of grid of new reference points.

Then do the same again, reducing the size of the grid of points.  Once you have a decent idea of low spots you could use floor levelling compound depending on depth.

If time is precious, forget it for now but screw and c/s the boards down so they can be lifted later .

[Jivemaster]

I have bought sheets of thick solid card from Staples before, these were available from 1 to 3mm thick and about a short meter (not quite) square. These would do for packing low spots. The real problem is defining the low spots without just moving them round. Could you hire a laser level, and measure and map the floor level vs intended level, considering any intended rake?

[Ynot]

13 hours ago, Jivemaster said:

I have bought sheets of thick solid card from Staples before, these were available from 1 to 3mm thick and about a short meter (not quite) square. These would do for packing low spots. The real problem is defining the low spots without just moving them round. Could you hire a laser level, and measure and map the floor level vs intended level, considering any intended rake?

Have a (couple in fact) laser level and plan to try and pack the boards as we lay them this weekend.

I was sort of hoping someone would tell me of some levelling compound that might work, but of course that was a vain pipe dream...

[sunray]

52 minutes ago, Ynot said:

Have a (couple in fact) laser level and plan to try and pack the boards as we lay them this weekend.

I was sort of hoping someone would tell me of some levelling compound that might work, but of course that was a vain pipe dream...

I woudn't try packing MDF with any sort of shim, it could end up as lumps.

 

If you are intending to use a levelling compound I'd say it has to be latex, in my very limited experience of cement based compounds they cracked and broke up when fixings went through them so only suitable for glued coverings.

 

Make sure nothing is in the slightest bit damp when adding the MDF, it will draw the moisture, swell and fall apart.

[Dave m]

Also,

 

it IS “fireproof” MDF?

we buy our timber from

https://www.creffields.co.uk

[Ynot]

On 8/9/2024 at 12:26 AM, sunray said:

I woudn't try packing MDF with any sort of shim, it could end up as lumps.

We've basically concluded that we have to just suck it up and accept the slight variations.
ANY attempt to 'fill' the dips with strips under the boards were clearly going to be counterproductive, certainly in the limited time we have now to sort it.

😞

[Ynot]

On 8/9/2024 at 11:48 AM, Dave m said:

it IS “fireproof” MDF?

That's a rather OTT thought tbh.

We've had MDF stage flooring (with at least two coats of stage floor black) for years, and regularly use pyro at floor level...

NEVER had even the slightest issue with hot fallout causing issues.

And if your stage floor is on fire, I'd sincerely hope that it's taken long enough to get to that stage that there's noone even close!!

 

[Dave m]

We aren’t allowed to do any structural work that isn’t fire resistant.

we could make stuff out of normal MDF, but if it is screwed down/up then it needs to be resistant.