Concrete Isn't A Material You Want to Make Mistakes With!

I recently received an email regarding how to repair a cracked patio slab. The writer said she had found my website through the listing in Google for my webpage Concrete vs. Cement: What Is The Difference?

Though patio concrete repair falls outside the realm of garden art projects, I was able to offer her some sound advice, as I have a relative who used to work in the commercial concrete industry.

I thought I’d post here on my website what I shared with her, as the information about repairing with concrete given to her by the salesperson at the local hardware store was so wrong it wasn’t funny! Really … it was sad.

The salesperson told these people to spread a thin skim coat of Portland cement (mixed with water of course) onto the surface of the cracked patio slab and that would do the trick! WRONG!

What a mess these poor people were left with. The Portland cement was cracking and flaking right off.

So, if you are contemplating a patio repair like this, here are some things to think about before you even begin. You might be able to tackle a small DIY concrete repair on your own, but in most instances, I would say get a quote from a professional.

Concrete is not a very forgiving product. The mishaps garden art crafters have when making even simple projects happen all the time.

I’d hate to jump head first into a big crack repair project, and realize half-way into it that I should never have begun it in the first place! Think about it ... it’s pretty darn hard to scoop up and dispose of a large area of oozing, wet concrete.

My Concrete Repair Reply

Anyway, in an edited version of my answer to her, here are the things I told her she needed to be aware of. I hope these help you if you are in the same predicament.

Sue wrote:
Hi Claudia: I have encountered a problem on my patio. After much research your site was the only one that made it clear there was a difference between concrete and cement. We have a slab in our back yard (like a river rock slab), we wanted to skim it over with a smooth layer. We did so with what the hardware store told us to do it with (Portland cement). But it came out with lots of cracks and you can scratch your fingernail in it. Is it because we used cement and not concrete?

My reply was:

Hi Sue:
First, thank you for telling me how you found my website. Glad that page helped you.

Next ... the easiest way to explain cement vs. concrete: cement is the dry, powdery product; once it is mixed with water and aggregate, it is called "concrete". So no, your problem wasn't in the terminology ... your problem was a very ill-informed salesperson :-(

What a shame! You were given horribly wrong information!! Even I know that you shouldn't have used pure Portland cement. And I'm no concrete expert by any means.

A relative of mine was a professional concrete finisher and I picked his brain for you ... and in a nutshell, here is what I can offer you:

1. Portland cement CANNOT be used all by itself in this situation! it needs some kind of aggregate added to it ... so this was mistake #1;
2. You cannot just put a "skim coat" onto the slab ... you need at the minimum a 2-inch thick "layer" of concrete ... so here was mistake #2;
3. The slab must be prepped with a "bonding agent"; this allows the new concrete to adhere to the slab ... mistake #3;
4. There very well might be the need for the bonding agent to also be mixed into the new wet concrete before it's poured;
5. The slab might possibly need to be wet down, before the bonding agent is applied;
6. Use a 5-sack mix (called 5000 lb concrete);
7. Keep the newly poured concrete moist for 28-days -- it will reach about 90% of its full cure (hardness); spray with your hose every day & night to dampen -- this will help it to not crack and to cure properly;
8. And then seal it after the 28 days.

There will most surely be other things to take into consideration ... but I DO NOT know the particulars. There are many variables when it comes to concrete, concrete repairs and the specific project.

And before any new concrete can be laid, you are going to have to THOROUGHLY clean/scrape off all the flaking Portland cement.

***Bottom line ... I suggest you call a reputable professional concrete company to add the smooth "layer" for you. Forms have to be built along the outside edges to hold in the concrete; expansion joints may need to be added into the wet concrete; depending on the size of the slab, interior wire "mesh" might need to be laid to help it not crack; the top must be finished off correctly to make it smooth, etc.

Does this help you? I hate to hear of problems like this. If nothing else, you deserve all your money back for whatever supplies and such that you bought for this project!

Lots of luck!
Claudia

Here are a few of the concrete projects and helpful tips you can find on my website:

• Forms For Concrete Projects: Which Work the Best?
• What are "Release Agents": Which Ones Should You Use?
• Concrete Stains & Colorant Guides
• Safety Guidelines: Concrete & Cement are Caustic!
• Hollow Garden Spheres: Concrete SuccessTips
• Eggshell-thin Concrete Recipe For Waterproof Spheres & Basins