visual signs of weak concrete

Being able to pick the signs of a weak slab is not always easy. There are various mechanical means for testing the integrity concrete, like rebound hammer tests or tensile pull off adhesion tests, but you don't always have the ability to conduct these types of physical tests.

In this post, I want to share some photos to demonstrate a few quick and easy ways to pick if you're dealing with a weak slab.

In the first photo you'll see how easily a screwdriver was able to gouge the surface of this slab. If you're able to gouge the concrete as easily as this then it's a good sign you've got a weak slab.

In the second photo you'll note the weathering on one side of the roller door line compared to the other. In this case the house was less than 12 months old and to see this amount of deterioration is something that would set off a few alarm bells.

The third image shows a divot in the floor that has easily popped out down to the larger aggregate layer.

The fourth photo shows the rapid wear and tear of the floor directly outside the entrance. Even though it's only foot traffic in this case, the twisting of footwear was enough to cause significant damage.

The final photo shows a degraded area of a slab where the fine trowelled finish has quickly worn through and begun to pit the surface. The rate of deterioration is much quicker once you have loose aggregates and sand that tend to contribute to the grinding of the surface.

A special thanks to Tough Floors for sending me these great photos!

If you're asked to install a resin floor on a slab that's showing any of the signs of weakness above, take care to carefully analyse the concrete and determine the best way to prepare the slab and build some integrity back into the surface first.

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Mauricio Samiq Pisos wrote:
22 Aug '20 5:01pm
Gracias, muchas gracias por su gran colaboración a nuestra labor profesional, en mi caso en particular ya tenemos alguna experiencia la cual se pudo resolver con resina epoxi Sherwin Williams en tres capas la primera diluida al 30% la segunda al 10% y la ultima sin dilución, finalmente esto nos permitió aplicar resina epoxi de terminación, como dice Resin Jack mucha cautela con las garantías.

Muchas gracias por tan valiosa información que usted nos comparte.

un afectuoso saludo desde Santiago de Chile, y seguimos sonriendo.

Resin Jack
Resin Jack replied with:
24 Aug '20 12:51am
Hi Mauricio,

Thank you for your comment. I appreciate your input and agree with the fundamental approach to overcoming the problem.

About the only thing I would say is that I am not a fan of adding 30% solvents to clear solventless epoxies. Hopefully, you can achieve a satisfactory result with no more than 10% solvent and if you do add solvents then be mindful of solvent entrapment issues.

Thanks again for your comment.

Take Care and keep smiling.

Solomon Lamptey wrote:
21 Aug '20 12:12am
So if you encounter such problems what should I do Boss...what’s the solution
Resin Jack
Resin Jack replied with:
21 Aug '20 5:41am
Hi Solomon, thanks for the comment.

You will get a few different views on how best to tackle a weak crust slab. My view is to remove the weak layer by heavy grind, shotblast or even using bush hammers. Then use low viscosity epoxy resins to penetrate into the concrete to build some integrity back into the concrete. You will most likely need multiple coats as the substrate will be porous. At that point, you might need to skim coat the floor and then you can start on your resin flooring system. I would be cautious about what warranties you provide because most product warranty will stipulate a sound substrate.

Does that answer your questions?

Take Care and keep smiling