How to level cracked outdoor slabs?

[Jacqueline23]

I am wanting to level two separate outdoor slabs. Both have some cracks and have been painted or stained in the past. I plan to paint and stencil them when they have been levelled. What are the best crack fillers, primers and levellers to use? Thank you

[MitchellMc]

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

[Jacqueline23]

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.?.?.?

[EricL]

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

[Jacqueline23]

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

[EricL]

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

[JackP]

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!

[EricL]

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

[JackP]

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.

[JackP]

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?

[EricL]

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