Q&A / 

Concrete Bleed Water Video

Hi, I'm Tim Carter from AsktheBuilder.com and I'm here on a job site where they are pouring a concrete slab. I want to show you something a lot of people don't get to see. It is really, really important to know because this is where a lot of concrete fails.

It is called concrete bleed water. Look at this. You can see the shine on the concrete. (This example is very light. Bleed water can be much worse than what appears on this job site. It can be large beads of water on the surface.)

What you are seeing is a really thin sheet of water up on top of the concrete. Now, what is that all about? Let's think about it for a second. What's the four ingredients that concrete is made out of? They are gravel, sand, Portland cement and what? Water.

Water is the lightest component of concrete. If you pour all the other ingredients into a bucket of water, they sink to the bottom. So concrete right after it is bull floated or screeded has the water come to the top. You have to make sure you don't float it into the concrete. It will go away on its own. But if you float it in, it will dissolve the cement paste at the top of the slab and it will make the upper part of the concrete very weak. That is one of the causes of spalling. So don't trowel bleed water back into your concrete slab.


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