Bulking up self levelling compound

[derek.j]

I need about 20 backs of slc to sort a utility floor out. It's concreted but all over the place

0 one side of the room to 30mm the other with a dip of about 50 in the middle

Has anyone bulked it
Up with gravel or ordinary cement to save a few ££

[fat80b]

20 bags seems like a lot!

I had a very similar problem when I did my utility 2.5 x 2.5 with a 10mm drop at one end and an 80mm drop at the other.

I put a concrete screed that I mixed myself and added fibres in first to bring the level up to closer to the finished floor height feathering it down in thickness.

I then used 2 bags of the expensive stuff to level it on the top of that and it made for a perfect finish.

The problem I had was that if you read the internet it’ll tell you that you can’t have a screed less than 50 mm which might be true but makes it tricky if you need to do what you are doing.

I deliberated for ages but I’d go down my route again.

[Panamax]

I thought the whole point of SLC is that it's pretty liquid so flows to a natural horizontal. If you clog it up with other stuff it won't be able to do that.

50mm is a lot. Sounds as though the floor needs properly skimming.

[paulwirral]

Read the instructions on the rear of the bag , you can add sharp sand to self levelling compound , at least you can to certain ones .

[marksx]

Would it be cheaper to do a first layer with normal concrete gravel mix. Cut into the existing layer. Than SLC over the top.

[derek.j]

Cheers for the replies. I'd read you cant screed to 0 otherwise I would have screeded it much closer to the required level then slc over that

As for it not levelling it would be ok because I would only be bulking out the deeper bits first

[T1547]

Panamax said:

I thought the whole point of SLC is that it's pretty liquid so flows to a natural horizontal. If you clog it up with other stuff it won't be able to do that.
.

Exactly. Manufacturers of these products spend a lot of time developing them to behave in a certain way (strength, flow, set time etc). If you add cement or aggregate it will affect the properties of the product.

If you Google ‘deep levelling compound’ there are products ready to use suitable up to 50mm depth.

[Biggy Stardust]

I had an uneven floor with a 50mm maximum deviation. I put/stacked some old wall tiles in the worst depressions and used the SLC over the top.

[biggiles]

Biggy Stardust said:

I had an uneven floor with a 50mm maximum deviation. I put/stacked some old wall tiles in the worst depressions and used the SLC over the top.

This is a good approach. Normal SLC will take AGES to dry if you use it deeper than recommended. Rather than "bulk it up", use something practical and solid to reduce the depth required.

[Fatboy]

biggiles said:

Biggy Stardust said:

I had an uneven floor with a 50mm maximum deviation. I put/stacked some old wall tiles in the worst depressions and used the SLC over the top.

This is a good approach. Normal SLC will take AGES to dry if you use it deeper than recommended. Rather than "bulk it up", use something practical and solid to reduce the depth required.

I'd agree with that, but would add to use some tile adhesive to hold them in place so you have a nice solid base for the self leveling (tile adhesive is nice and cheap and sets quickly)

[KTMsm]

30 - 50mm

I'd screed it

Whilst you can't screed to 0 you can screed to a couple of mm and then use self levelling

if it's carpeted screed would be good enough but if it's vinyl then yes it has to be spot on

I use SBR - both on the floor and it the mix, it's fantastic stuff

[chippy348]

Did this 20 years ago in our office, the guy doing the floor used pea shingle to bulk up. It worked very well.