Self-levelling compound suggestions

[Adrian]

We've got an outbuilding that I'm refurbishing and bringing back into use as a studio for SWMBO's artistic and creative purposes. Originally built in the '70s as a commercial kitchen, the concrete floor's been painted several times over the years.

It's in two rooms, one of which has a higher floor than the other. We were looking to screed the lower floor, bringing the two level, but a bit of laser-level investigation has revealed that the lower floor... slopes.

The highest point is about 2mm over the height of the other floor. The lowest point is about 100mm lower. This room's about 3m x 5m, the other room about 4m x 5m.

I'm told that a screed isn't going to work terribly well - it'd just be too damn thin at one end, and would break up in no time. Putting some kind of a "dam" in place and screeding everything over ~25mm depth would leave about a third of the floor untouched.

There's a (let's call it semi-structural) dividing wall between the two, with two doorways through it. One of them has a ~50mm step, the other a ~80mm badly-done and fairly steep ramp, which will probably be getting cut off. The floor paint on the upper floor is peeling badly, mostly just the top layer, but several bits have worn through to bare concrete. The original plan was to leave the floor as painted concrete, because there's a reasonable chance of spills etc.

What would the assembled masses do? There isn't enough depth below door sills to screed the ENTIRE floor, both rooms, to 25mm+.

[Adrian]

I should say that the thread title came from the suggestion to just do the entire lower floor in ~3mm-ish SLC. Whoever laid the original concrete in the lower room did not do a very good job of it. It is... textured.

I am a bit sceptical of that suggestion, not least because it would still leave us needing to add some kind of wear layer to the floor surface.

[fred]

In article , Adrian writes

Could you stretch to adding 43mm to the floor? If so I'd be tempted to switch from a solid to a suspended floor and add an inch of celotex under 18mm sheet or boards to make it warmer under foot. That would of course leave you needing to add a floor covering or use reclaimed floorboards for a rustic look.

Perhaps not the best given the possibility of spills but hey, it adds character.

If that's not to your liking, I'd follow your damming idea to get the floor area semi-level using screed down to its minimum thickness as it tapers out (for lowest cost) then add a self levelling area over the top for the whole area using the minimum thickness achievable on cost grounds (a large area wont be cheap), then paint.

I'm sure Tim Watts will be along shortly, he did a lot of homework on large areas of screed before doing his (IIRC) entire ground floor.

[Tim Watts]

Here's what I did in similar circumstances:

Read the technical doc here:

Soak the whole floor

Clean (degrease/dewax if required) all the floor and soak in diluted SBR as a sealant (see sheet). Allow to dry - may be left for as long as needs be.

Mix a screed as per sheet plus a pot of bonding slurry.

Paint slurry and immediate apply screed. Deal only with the parts which are > 5mm too low. Do not be a perfectionist - as long as you have no high spots, it will get dealt with in the next phase.

Use P131 primer and Stopgap 300 HD.

Calculate the mix volume and mix with the max water permitted. Pour in one go if you can get help or dam the floor and divide into sections - but you will not match the levels better than 1mm in practise - 3x5m is going to be about 4-6 bags worth.

You can mix 3 bags each into one of the massive plastic tub buckets that some places sell - you will need to borrow/hire a plasterer's power mixer to handle that volume.

Kick the buckets over, wear wellies (wet soles of wellies first - P131 remains very tacky). Use a t bar made of 2 bits of wood with 2 round head screws set into the bar to allow the wood to ride 3-5 mm above the floor substrate. This can be used to very quickly push the wet mix around to approximately the right level.

Use a spiked roller and long handle to work the 300 all over and remove air - this keeps it mobile and it will self level. Walk backwards and roller your footprints out.

You have 20 minutes to do this max. Escape, hose wellies, buckets and tools immediately or they will set like iron.

In my case I got a kitchen floor that was >25mm out to within 2mm all over - very nearly perfect, That was about 4x5m.

[Adrian]

Not without lifting doorways...

[stuart noble]

The two part screeds where one part is 5L of milky stuff work well and will feather down to a very fine edge. Most BMs will stock

[Adrian]

Oooh, interesting... Thanks for that.

[Tim Watts]

And IME will not be as good as the F Ball stuff - I tried both.

I am not sure if Stopgap 300 is fundamentally better or if it more acase that sealing and priming with P131 (a neoprene paint) first stops the water getting sucked out of the Stopgap 300 and thus renders it more fluid.

My very limited experience with the generic stuff is that it is adequate in small areas if you can shape it with a float. For a large area you will not be able to float it off that easily.

[Capitol]

I'd adjust the door sills to get the 25mm or allow the doors to open outwards.

[harryagain]

Chisel off (mechanically) the high bit so it's say 30-40mm below proposed finish level. The paint wil have to be got rid off (more chiselling?) Screed the lot with added PVA at the thin bit.

OR Install a timber floors with tapered "joists" and chipboard. High point will still have to be chiselled off.

[Adrian]

About 5m2

About 35m2

[js.b1]

Many issues here...

Is the DPC functioning? Many SLC & indeed bagged screed mixes are for above DPC.

Primer & surface preparation is important. This is particularly true where you are going thin, even SLC that go 2-3mm in fact need the surface & primer to be spot on otherwise they will fail. Loose material needs a diamond cup grinder for example, can be v.quick.

Water content re mix consistency is CRITICAL. This is so often "varied on the day" and the result can be "dig it up".

Generic SLC tends to hairline crack. Better branded stuff tends to flow better, level better, bond better.

Deep area sounds ideal for an unbonded screed (bonded is typically 10-35mm) . Note there is a drying time which is 1mm per day, if this is a problem yo u can use special screeds from Mapei & others (with or without selected agg regate). Note day joints need 2-3mm stainless bar - keep all same height ot herwise you create internal stresses. A cement mixer is really necessary fo r large areas, or a barrowed delivery if really big.

A "cheat" would be say tile insulation board to bring the level up, but thi s gets expensive quickly for a large area. Then SLC over the lot (mesh tape joints).

So perhaps bring the too-deep areas up, then prime whole with SBR, then SLC over the whole lot. You can buy yellow self adhesive foam partition strips for pouring SLC - some people just use expanding foam as easier to get up.

[Adrian]

Probably.

Seems to be, yes. The building was completely unused, but full of crap, for ~4-5yrs, but there's no signs of moisture in there at all.

Interesting, ta.

[harryagain]

Yep. A builders life is a hard one.

Or take the whole floor up and replace it. You could put insulation beneath then. That would be a proper job. Everthing else is just a bodge that may fail in the future. A builder would insist on this as nothing else can be guaranteed.

I can see you are a Southern Poofter. Never done a hard days work.

[Tim Watts]

Good point that - and if the OP's is below or the DPC is broken, I have help there too!

Indeed - the F Ball instructions are adamant on this point. But general builders are not known for reading data sheets, which is why I always regard screeding including SLC as a specialist job.

And strangely the quality stuff hardly costs any more IME than the crap the sheds sell.

[JimK]

Not without lifting doorways/q

?? Are they notably low now? Or are you notably lanky (now)? :-)

Jim K

[Adrian]

I was thinking more of the other end of the doorway.

43mm - or even 25mm - more floor height is going to have the floor higher than the door ledge.

(and 43mm may very well bring me close to banging my head, but since this is SWMBO's womancave, and she's 5'2", she'd probably regard that as a benefit...)

[JimK]

/43mm - or even 25mm - more floor height is going to have the floor higher than the door ledge./

Wassa door ledge?

Jim K

[stuart noble]

If the next person to occupy the house isn't a midget, then what? You don't mess with door heights