Concrete Roughness 1

[dik]

I have a concrete surface that will receive two coats of siloxane or silane to protect the surface and the protection will be applied annually or bi-annually.

I'm looking for a concrete surface that will have a degree of roughness... similar to a powerfloat or a light powertrowel with a light broom finish.

Is there a way of specifying a degree of 'roughness' as opposed to flatness that will give me the equivalent of something like 100 grit sandpaper?

Dik

 

[steellion]

Attach 100 grit sandpaper to the inside of your formwork, and when the concrete cures, voila!

 

[SKIAK]

Are you specifying for the surface of a slab or something inside formwork?

 

[dik]

It's the surface I'm concerned about. The sealers with a little water on a smooth concrete surface can be lethal!

Dik

 

[Ron]

dik...I assume these are vertical surfaces. Given that, you're stuck with "after the fact finishing" since casting such a finish would present form removal issues, unless you want to spring for expensive form liners.

You could specify a light sandblasting after form removal, using a 20-30 grit size.

Probably the easiest way to achieve that profile is to acid etch the concrete after form removal. I would use a citric acid solution rather than muriatic or other more aggressive acids. The citric acid is more controllable (mix the strength you want to achieve the result) and is more likely to be consumed in the process, so little or no neutralization would be required...just check the pH of the surface.

Ron

 

[SKIAK]

I've never seen a degree of roughness specified, although I've seen in the finishing section of the specs to leave surfaces in areas X, Y and Z rough for traction... that somewhat leaves it up to the contractor which may not be a good idea. In my area the concrete finishers are horrible and I have never had to worry about a surface being too smooth...

 

[JAE]

Since there is no "property" specification that I'm aware of for this so you probably have to specify mock ups to get to what Ron describes. Generally describe what you want, perhaps suggesting a couple of methods, and require two or three mock ups to be made prior to the actual work to verify you are getting what you want.

 

[dik]

It's a flat horizontal slab surface. The idea of casting a couple of test samples sounds pretty good. Acid etching is not likely a method due to final installed electrical equipment. I was thinking of a float finish or a light trowelling with a light broomed finish, but had no idea of spec'ing a roughness. Had actually considered using a comparible sandpaper grit.

Dik

 

[conceng]

Most qualified concrete finishers would understand the intent of a specification qualifying the surface to be a light broomed finish. A test panel is a great idea, specially if you can find a less important area for the contractor to cast it and leave in place even though the finish may not meet your expectations.

There is a macrotexture test procedure for measuring the texture of broomed pavements, but it may not be effective at evaluating a light broom finish.

Greg

 

[dik]

Thanks gentlemen... the project is about 600 miles from here, and when our site rep is back in town, I'll show him a couple of existing finished and take photographs to give him an approximate range and see if this can be done just using a power float.

Dik

 

[Ron]

dik...sorry, I thought vertical. For slab work, I would specify trowel then light broom finish as you noted. That should give the texture you want.

As you have also noted, be careful of the slipperiness of silanes/siloxanes, even with a roughened surface.

What is the purpose of the surface protection? Also, a light acid etch should not result in residual acid in the area, so the electrical equipment should not be affected.

 

[dik]

To protect against the ingress of chlorides... The client requires 3" concrete cover, even for slabs and walls... have done a dozen parkades with 1-3/4" cover... and still standing.

Dik

 

[Teguci]

ICRI Surface preparations

http://ppc1989.com/index.php?option...ration-standards&catid=1:ppc-primers&Itemid=9