Concrete (resurfacing) advice

[nero44]

One for the concrete experts...

I am doing some works in a damp cellar and after digging up some more rubble, I found an old concrete pad in a corner. It's pretty beaten up with cracks, missing chunks, lots of unevenness and generally looks like someone just used different types of leftovers to build this patch. Anyway, I've put some timbers around it, some primer/pva, bits of rebar and layed a new slab on top, which is now curing. As the area will not be subject any foot traffic (storing boxes at most) and given general poor accessibility of the area I opted for a dry pour (yes haters gonna hate...), which seems to have worked quite well.

I did however underestimate the amount of bags needed, which meant that I could not fill the form all the way to the top and nicely screed it flat with a timber, which normally helps to push larger stones down/out and leave a nice flat finish. Did the best I could "by eye" and flattened with a foam paint roller and it's okay and could probably just leave it at that.

The form is still in place, so now thinking if there is a simple way to improve on this. It's a 1.7m x 1.2m shape and I have about 15-20mm space left to the top of the timber form. Could I just mix up a bag or two of self levelling compound/concrete to "topup" to achieve a flat finish? Would I need to use a float at the top or would self-levelling take care of this? More importantly, would this even stick or start to break/crumble? Any product suggestions welcome.

 

[blup]

I used bostik cementone repair cement, it comes in 10kg tubs from tool station. I bulked it out with a little gravel and it stuck fast to brick

 

[Ivor Windybottom]

Check the specs for the self-levelling compound. They all have a max and min thickness.

It's self-levelling but needs a bit of help to spread it around, a float or anything else that gives you enough reach will be good enough. If you're worried about the odd bubble you could get a spiked roller. Or just pop them with anything as it's small if you can hang around for half an hour.

Thoroughly wet your dry pour (eek!) concrete for a day or so before pouring over it, ensure it's very damp but not wet. If it's really porous then seal it with SBR and leave it to dry. Otherwise it would just suck the water out of the new wet compound and leave you with a right mess.

 

[nero44]

Finished this project now and it looks fine, thanks both for your advice. I used setcrete exterior for this job. My conclusions for any other future concrete novice DIYers:

- you can get around the max thickness by doing it in several coats and letting them dry in between. In fact it was much easier this way, as using a spiked roller on thick/deep pour does not work very well. I used 4 bags in total for 1.99sqm. Poured 2 bags first, but the layer was quite thick so could not get a neat finish. So I let it cure and then poured the 3rd and 4th bag individually in two thin layers. This worked much better for a nicer final finish
- spiked roller is essential! No way I could have achieved a smooth finish without it
- when mixing self-leveller, be sure to add powder gradually else you will get lumps. I added water first, then poured a bit of powder.. mix.. and again. For one 20kg bag I added its powder content in 5 batches to reduce the risk of lumps forming. Slow setting on mixer! And if you get lumps, they are much easier to flatten out with a spiked roller than with a float
- Despite using the roller I still got just a few bubbles. What I did was I rolled until I was happy and then went away to let it cure. I should've stayed around longer to pop the odd bubble as adviser by Ivor...

Last but not least >> Don't dry pour concrete...once I removed the timber frame I could see that water penetration was suboptimal. It will be fine for my purpose but generally I would advise against it. Do it properly