Thread: Laitance on a new slab - how to approach removal/repair?

Hi

Blasting or Acid Wash will remove the laitance and fines, leaving probably too rough a surface for a shed floor. You would need to screed after. Blasting is very messy too.

Looked at a self leveling or other compounds they may help too? Ardit.,BASF, Parchem, Xypex. There's more than one way to skin a cat, tech reps will usually help.

Maybe grinding is the only alternative, but will be slow. How bad is it?

If is not too bad you may be best trying soemthing else, is it going to effect the functional use of the slab? You may have trouble mounting a successful argument as this is a natural process of concrete.

Of all the components in concrete sand, aggregate, cement and water, the latter is the lightest and always rise to the top. Excess working exacerbates this, but all the same his always happens to a least some extent, you can only really argue on the amount. Hard to proove this.

I suppose I'm getting to the point, there is no point entering into an argument withholding money etc unless realistically you can prove its bad.

Usually you would grind and seal the slab from the start if this was key performance characteristic of the end product. There is nothing to stop you/them doing this now

I would suggest you negotiate an outcome, withholding money can quickly descend into an expensive building dispute which may not result in a higher grade of slab.

Don't take this the wrong way, what I saying is this if they reject your assertion if put undiplomatically even if its right, you may be expend a lot of money they could be used provide the grade slab you really need and/orwant.



Clive

If its dusting badly that is not normal. Whilst I am NOT a concreter, I am in construction, have done my own concreting and been around it enough. How many sheds and garages have we been in with a simple concrete floor that is not dusty/ing

I have a fair idea of what you are describing, and it is most common because of rain. Most concreters don't over finish for many reasons. I have NEVER heard of someone coming back the next day to finish

Who supplied the concrete? i.e. what brand (boreal, hammercrete, etc) I would speak to them and see what they think.

I can not comment on how your outcome is going to work out.

One large tilt up shed I was working on had one of its showroom floors hit with rain during poor. They did the best they could and had the same outcome as you. The builder got commercial finishers in to grind and epoxy the floor.

Had a simular problem with a slab I done and coated it with bondcrete, a sealing/water proofing agent I am led to believe. Fixed my problem
cheers
blaze

Have seen this happen too. Outcome was to grind it then seal it. Turned out good in the end.

Slate Sealer is a good product to use when concrete is dusting and also makes spills like oil etc easier to clean up, but on the down side it can make the surface very slippery.

Good luck!
Cheers, Mick.

Sorry to hear about your problems. There are many shonky concrete layers that do not have any idea about concrete.

What you are going to end up with is in effect a pebblecrete finish ie aggregate exposed. Many unprofessional concreters think that concrete is a water soluble process - it is actually a chemical reaction that requires water to complete. therefore by playing around with it after it has started to started the chemical reaction (as soon as the cement component comes in contact with air and water) destroys the concrete resulting in a powder. The only cost effective solution will be epoxy paint - about $3000 for a slab that size.

It will keep on powdering down until you end up with a very rough pebble finish the way it is.

Originally Posted by Scouse

Anyone here a concrete expert?

I've just had my shed slab done & the finish is very powdery - rub it and it comes off.


A bit of internet research tells me that it's laitance & is caused by excessive water on the surface and/or overworking the surface; both of which the concreter did.


It was poured last Monday (6 days ago) on a slightly drizzly morning & the rain had set in by lunchtime. The concreters did use a helicopter trowel that day but the finish was no good with the rain. They hung around until 5pm & then left saying there was enough moisture in the concrete for them to come back on Tuesday morning to finish the job.


Tuesday morning, they rock up, brush the excess water off the slab & get the trowel going again. I don't know exactly how many times they went over it but they were going for quite a few hours all up.


In the end it looks OK but not exactly how I have seen helicopter trowelled surfaces look in the past. He says once it dries out it will be fine.
He also said he didn't want to do a slab like this again.......


So now, 6 days later, I have a powdery (laitance) slab which is not what I want.


I have read that the surface can be blasted, acid washed or ground to remove the laitance but does anyone have any experience with any of these methods?


I haven't approached the concreter yet. I'm concerned he will fob me off & may even delay the building of the shed itself (family run shed business) if he thinks I might cause an issue.


I'm thinking I will contact the concreter about the problem once the shed is just about finished & I have a bit of leverage with $$.






BTW, size is 225sqm, 100mm 25MPa.

Was a concretor nearly all my working life and your problem is common, where ideal weather conditions are not perfect.
I too have/had dusting on my paths around home, so it can happen to all of us.
Please don't be too hard on the fellow as he is working with a controlled product in an uncontrolled environment, the weather.
I would pressure blast the slab and leave it at that as I have done. Of course you will expose the aggregate, but this will not affect the application it was intended for.
It will continue to dust up for a while, but the more use it gets the better and it is a shed floor after all.
If you apply sealers, you will have to re-apply and re-apply year after year as they wear, so the blasting method is just as effective and will keep the floor clean.

Why not try a a wearing layer like this from Parchem after stripping the laitenance away

http://www.parchem.com.au/public/pdf...top-XD-TDS.pdf

This seems like the right product, providing you do this before you get grease on it.

You could go a step further and put an epoxy coat on providing a very tough, impermeable slab, but they are slippery.

Clive