How to raise the height of concrete slab?

[Doug4822]

I need to raise the height of my slab underneath an entertaining area to facilitate run off. 20/30mm should do it. 

It's 8x5.5 and bagged mixes of formulated product like sika rapid patch are ideal but will cost an absolute fortune.  I expect a few $k but not 10k. I can use those mixes

 

for ramping the slopes but the main area needs a 30mm raise over a big area.  What mix/additives should I use? Final finish is intended to be stencil crete. Thanks for your help. Doug 

[JacobZ]

Hi @Doug4822,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

I can't say I'm aware of the necessary additives that would make this kind of job possible. 

As you've said, there are specifically developed products such as Sikafloor® Rapid Patch or SikaQuick 2500 (au) Rapid Hardening Repair Mortar, however they are quite pricey.

I imagine the best course of action would be to contact a concrete mixing plant and discuss your options in terms of mixing additives or to speak with a concrete resurfacing company.

Allow me to tag @Dave-1, @Nailbag and @Jewelleryrescue to see if they have any advice they can offer.

Let me know if you have any further questions.

Jacob

[Dave-1]

Afternoon @Doug4822 

I have not used any ramping concrete mixture as yet and when I went through looking at the specs of the sicaflex a bag will live a square metre by 12mm. So maybe it wont cost a huge amount?

I do like @JacobZ 's suggestion about contacting a concrete company as the overall price might be cheaper for a similar product.

Dave

[Nailbag]

Hi @Doug4822 

Again as with @JacobZ and @Dave-1 I don't have a specific solution sorry. 

However one thought would be to contact one of those driveway resurfacing/restoration companies. They specialise in laying a relatively thin layer of a range of durable finishes over old concrete, pebblecrete etc. 

regards Nailbag

[Jewelleryrescue]

Hi @Doug4822 

Sika is  too expensive  use  Regular  cement  as you arnt  driving cars on  porch  it can  be thinner.  Even it a  crack appears  later due to thinness then  use  a sika  rapid for less cost. Cement is quite forgiving. 

As your adding  stenciling on top no doubt you will be coloring it with powder.

That cement additive on top will harden your outer concrete shell making it  very  durable as a plus.

The trick is to not add too much cement powder it will make it super hard and  cracks  can form when  drying thinner than  usual. Just stick to the GP general  purpose cement for making garden paths  etc as a guide.

You  definatly can get away with  regular  cement mix (using smaller 10mm  stones ideally,  20mm stones  harder to screed flat in thinner beds.)  

I would go  40mm concrete thick the high end if possible dont go  below 15mm in thickness at low  end. General pupose cement has its thiness limits and remain strong. Worst case senario is thin end  cement busts up  so simple  repair it with  less bags of  sika repair  cement.

Do  follow instructions  for path cement mix ratio  ie  stones  sand and cement.  Or buy premixed sand cement bags. 

If your clever angle your stenciled lines  towards the fall to make mini water channels work for you as little drains.

Tips 1

Now unless your an expert screeder  we  will need some tricks to keep that new slab flat and following the down ward gradient.

I never used one but a laser level might help here if you used on before (remember we want a fall not flat)

Over the top of your current slab I might cut blocks of wood from  high to low used as  new cement height(thickness markers) from 40mm down wards.

Noting in your current slab has heighs and lows already)

These  35x 75 off timber off cuts are what you screed to.  ie start at thick end  and pull the cement towards you  so the screed  pole skims the next lower timber of cut custom measured and  placed so you know cement slab is on track. As you go pull timber blocks out.

To  restate this the timber  blocks a  dozen  of them are of different lengths siting on current slab some smaller over bumps some longer in any hollows but the tops are the  perfect height to guide your screed depth to form a down ward  slab.

So if you where to lay a long straight  egde on top of a line of these pegs/blocks  it would touch all to tops of them forming yur ideal sloped  screed path.

Tip 2

Use  full 5mm ply sheets laid on you freshly screeded  slab to allow you to walk on cement fresh with out sinking in much. As  no way you can lay stenciling into the wall corners like  on a  open drive way etc.

Hope this  helps.