How to level cracked outdoor slabs?

Welcome to the Bunnings Workshop community @Jacqueline23. It's sensational to have you join us, and many thanks for your question about levelling a slab.

I'd recommend using Lanko 20kg 173 Floor Leveller, and the primer for it is Lanko 1L Ultraprime 124 Surface Primer. Make sure the concrete is cleaned thoroughly with a pressure washer before priming. The floor leveller with do up to 25mm thick. Remember that outdoor slabs are typically graded and sloped away from the house so water runs off them. If you level them, you could cause water to pool if they are exposed to the weather.

Regarding the slabs being previously painted, is there paint remaining on them? If so, it must be removed for the primer and floor leveller to adhere. I am unaware of a primer that will adhere to a painted surface for overcoating with a cement product.

For the cracks, you can use Gripset Betta 1L Concrete Crack Filler. However, if the cracks are fine, then the floor leveller will fill them for you.

Please let me know if you have any questions.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/31244#Comment_31244

Amazing. Thanks Mitchell.

Yes, there is paint and what looks to be stain on the slab. Besides pressure washing is there a product that will remove the paint? There’s brand new lawn directly off the slab which I don’t want to damage with harsh chemicals.

https://www.workshop.bunnings.com.au/discussion/comment/78076#Comment_78076

There's no particularly easy way to remove paint from concrete @Jacqueline23. In some instances, it might be easiest to have the slab ground back and re-surfaced by removing material.

How badly do the slabs need to be levelled?

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/103153#Comment_103153

Quite badly unfortunately. They have been poured terribly.

https://www.workshop.bunnings.com.au/discussion/comment/118587#Comment_118587

I've done some investigating @Jacqueline23, and if it is water-based paint on the slab, then you can prime it with Sikafloor -14 prep and prime and level with Lanko 20kg 133 Pro Level Floor Leveller. However, if it is a solvent-based paint, it must be abraided and removed. To test if it is water-based, apply some methylated spirits to a rag and wipe it over the paint. If the cloth becomes stained with the paint colour, it is a water-based paint.

The Sikafloor -14 prep and prime is a somewhat specialised product and must be ordered for you through your nearest store's Special Orders team.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/127748#Comment_127748

https://www.workshop.bunnings.com.au/discussion/comment/133740#Comment_133740

It’s a bit hard to show the significance of the uneven parts due to furniture being on it but this gives you an idea. Thanks Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/137459#Comment_137459

Is it the brushed concrete textured finish you are referring to @Jacqueline23?

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/140010#Comment_140010

No, but that will need a finish as well. There’s up to more than centimetre difference in some places, water pools right where the outdoor kitchen will go etc

https://www.workshop.bunnings.com.au/discussion/comment/141808#Comment_141808

Let me know how you go with that paint test @Jacqueline23. It will make your life a lot easier if you can prime the painted surface instead of removing it.

Mitchell

https://www.workshop.bunnings.com.au/discussion/comment/143150#Comment_143150

Soooo…. the rag had slight colour but when I tested it on another piece with known water based paint I didn’t get any colour removal. Maybe I might just have to hope it’s water based.?.?.?

https://www.workshop.bunnings.com.au/discussion/comment/144103#Comment_144103

Hi @Jacqueline23

I'm sorry, but would it be possible for you to redo the test? You might have hit a soft spot where the paint was loose. If you find another spot where the paint does not come off odds are it is solvent based. If you have a grinding tool, I suggest having a look at using Josco 75mm Twistknot Cup Brush. This is designed to strip rust and paint. Please let us know what the results are and we'll continue from there.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/144823#Comment_144823

Hi Eric and Mitchell

Thanks again for being so helpful. Tried some other spots and it’s come off. My life should be a little easier now 🙂

https://www.workshop.bunnings.com.au/discussion/comment/145371#Comment_145371

Hi @Jacqueline23

That's good to hear. Please remember to put a slope on the slab when you re-level the surface so that any rainwater will flow away from the house.

Please remember to wear personal protection such as gloves, goggles and a mask when working on your project.

If you have any other questions we can help with, please let us know.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/145796#Comment_145796

Hi Eric and Mitchell,

thanks heaps for this info. Wondering if the process will work as well for an internal floor? The floor does have some issue with moisture coming up from below so I was wondering about the need for a two way sealant or negative sealant below the primer?

I was also hoping to paint the floor white hoping you can recommend a suitable product.

thanks!

https://www.workshop.bunnings.com.au/discussion/comment/146244#Comment_146244

Hello @JackP

Welcome to the Bunnings Workshop community. It's sensational to have you join us.

Your comment about moisture coming up through the concrete has me a little bit concerned. When moisture comes through the slab it's either coming from the sides or the slab does not have a moisture barrier and water is coming through the slab itself. If not properly sealed it will keep coming and cause mould and mildew infestation. If it is a living or bedroom area, I suggest engaging the services of a professional to properly seal your flooring area.

Just in case you are curious as to what type of product can be used on the cement floor, I suggest looking at the Dunlop 4L Damp-Proof Moisture Barrier. But before using it, it's best to consult a flooring specialist.

If you need further assistance, please let us know.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/146495#Comment_146495

Thanks Eric! Totally fair about the concern. It’s a half finished basement section of the house that we are just looking to convert into a usable spare room. The concrete job is average at best and tbh long term the whole thing would need to be pulled out and redone. We are just looking for something that will clean it up and last a couple of years.

For clarity the issue is not so much rising damp and there isn’t mould present but that in exceptionally heavy rain (over 80-100mm) we get water coming though a section of the concrete.

https://www.workshop.bunnings.com.au/discussion/comment/146706#Comment_146706

My plan was to clean it with a crommelin degreaser, fill the big cracks with backing and sika concrete filler, prime with the crommelin damp-stop, use a floor leveller to even it out and fill small cracks and the paint it.

Let me know if that sound reasonable? And if you recommend using the Dunlop or similar instead of the crommelin. If so would I need to prime the Dunlop product before moving onto the leveller?

https://www.workshop.bunnings.com.au/discussion/comment/146706#Comment_146706

Hi @JackP

Thanks for adding that extra bit of information. If water does enter that section of the basement floor then it will need proper sealing as a damp proof coating will not be enough.

Eric

https://www.workshop.bunnings.com.au/discussion/comment/146873#Comment_146873

Ok sweet, given it’s a small area, the water enters through just one spot, is there something you could recommend trying without engaging a trade. Our place is on Dangar Island so trades can be a little difficult and hoping to have the space at least functional by the end of the year.

Or would you recommend treating the rest of the floor to deal with cracking etc and leave that section for a professional to look at?

https://www.workshop.bunnings.com.au/discussion/comment/147009#Comment_147009

Hello @JackP

I recommend leaving the flooring area as is until you have enough resources to repair the floor properly. Patching that particular section will not be effective as water will simply work its way around that patched section, it will look for the easiest path around it and look for the weakest most vulnerable spot around your floor. All of a sudden, another section is flooding where water has never out of before. I don't advise doing small section repairs especially when it involves flooring and water leaks.

Eric