calculating 4 different corner depths for self levelling compound help

[Chippee]

Hi all I'm struggling to work out how many bags of deep base self levelling compound I would need for me room as all 4 corner run out differently. For example
Too left corner = 3mm -- Top right = 28mm
Bottom left corner = 20mm bottom right = 38mm

I thought it was to add all 4 values then divide by 4 so my answer with the above info would be 3+28+20+38÷4=22.25mm

I know theres a way to calculate an average depth with the info above but I just don't remember how to do it.



If anyone could aid me with this it would be very much appreciated.

 

[Fred61]

Yep pretty much that’s the way I would work it out. You could divide the room in to many small areas and calculate each of them then add up the answer. But it really won’t make a great deal of difference. Fred

 

[Doggit]

How did you measure the 3mm though, and where's the lowest point. Another way of looking at it, is the 3mm is your base level, so subtract 3 from all the figures, and then add them together, and divide the total by 4. But this method doesn't tell you how large the 3mm area is, or how small the 38mm area is.

At the end of the day, you'll either do it in stages, or get about twice as much as you think you need, and just keep adding it. Now as SLC doesn't actually self level, do you know to do this job.

 

[Fred61]

Or you have 20+ years of experience look at the job and say how many bags you need to create the finished floor you need.

If not you are back to an appropriate calculated guess.

 

[Chippee]

How did you measure the 3mm though, and where's the lowest point. Another way of looking at it, is the 3mm is your base level, so subtract 3 from all the figures, and then add them together, and divide the total by 4. But this method doesn't tell you how large the 3mm area is, or how small the 38mm area is.

At the end of the day, you'll either do it in stages, or get about twice as much as you think you need, and just keep adding it. Now as SLC doesn't actually self level, do you know to do this job.

This whole floor is being levelled to another as a wall was removed so all 4 depths mentioned in my original post needs to be raised. I ran a level off the higher floor and placed multiple packers along each line until I got to the end of the room which left me with 3mm in the one corner. the packers where measured in a 1m2 grid formation along the entire floor area so all packers are perfectly level both in x and y directions and diagonal. Basically this entire floor needs to be raised and slc seems to be the best bet rather than a very thin screed. I am also considering plying the one have of the floor so it levels it out a bit and saves on slc bags.

Also another idea was to place screws at 1m2 grids and set those to the correct levels so I could gauge off them.

 

[Doggit]

I believe there is a trick of adding sand to the first few bags to get a bit more volume out of it (but I'm not sure if it's mixed in, or just thrown in as you go); and if you're doing concrete, I've seen bricks thrown in to pack it out. Having got the first attempt to within about 20mm to the height you want, then you'd drill and set in rawlplugs in a metre square pattern, and then set in screws leveled to the height you want to achieve. You'd then add maybe an extra half a litre of water per bag to allow it to move easier, and then trowel it to the top of the screws.

 

[Fred61]

No don’t use ply this will cause you lots of potential problems. Stick with the bags of compound it takes time but you get the best results in the end. Many shops won’t take returns of unused powder compound as they don’t know how well you have stored it. This generally isn't a problem to the trade but could be for you. So best to be a little cautious with you needs. Fred.

 

[Doggit]

Wickes is fine for returns, and isn't overly expensive on some of their pack deals. But going back to your measurements, as one of them is 3mm, make sure that the SLC you use can be feathered to that thickness. Some of the cheap ones will say 5mm to 50mm etc, and some will feather edge down to 2mm. You can use wickes acrylic primer on the existing floor before you lay the SLC.

 

[Fred61]

Dogget posted as I did. Adding sand is a cowboys way of saving money. You end up with a floor that is softer than it needs to be. We regularly make up floors of this depth no site. We just use self level compound. Normally on a Friday so it has the weekend to harden. If not we make it up out of several lavers.

 

[dazlight]

Been adding sharp sand or granno chips to Screeding compounds for years and in no way does it make it softer ?
Most Screeding compounds go to anything from 3mm to 6 or 12mm. By adding granno you can bulk it out to 30-50mm. Great way of building levels up if you can’t us concrete.