Concrete Laitance and Epoxy paint

[saiello]

Hi,
We had a concrete floor ( 70sqm ) laid in our commercial premises about 1 month ago. Unfortunately the contractors had used too much water and hence we have a very friable surface ( they also never laid a DPC down which was specified and I only discovered this after the job was complete ). They came back and ground the surface to a small extent to improve the overall surface flatness but dusting still occurs. I have tried scrubbing the surface of the concrete with a wire brush and although it improves becoming less dusty and revealing a rougher surface texture as the grains are exposed, the surface still dusts. We have at our disposal some water based epoxy 2 pac paint. I cannot lay this down on the concrete as it is as it will surely lift. I have tried to source a readily available concrete sealer from the big DIY stores such as Ronseal's concrete sealer but am unsure if they will be suitable for a water based epoxy paint to adhere to as they all seem to be solvent based. I was told by the seller of our paint that the only solution is to grind the surface down to a stable layer and they were unwilling to offer any other advice. Grinding is not an option for us as we have a very short time to lay the paint down plus the fact that we have entry/exits that need to be level with the floor and lastly, grinding may not solve the problem anyway. There are water based epoxy dustproofers available but again, I am not sure if they will be suitable for our paint as I cannot determine if these are over paintable. One last bit of information, the paint we are using allows for the dilution by 10% using water for the first coat. Does this mean that the first coat will act more like a penetrator/dustproofer in the same way that a normal water based epoxy sealer would work? Is that the manufacturers intention? I need a solution pretty fast, any help much appreciated.

Thanks.

 

[HMCFlooring]

The paint will soak in when diluted 10 to 1, but i'm not sure to what extent. Maybe try a little area with the paint scheme you have in mind then attack it with a pen knife to see how well bonded the paint is to the slab. This should give you a good idea and is a test that paint company chemists would carry out.

Other option is to prime the concrete slab then use a self leveling screed over it this will give you a perfect surface to paint onto.

 

[mac391]

Firstly and most important,,,

Was it a concrete screed or a anhydrite screed ??

Concrete is usually supplied ready mixed or mixed on site with 20mm stone in the mix.

Anhydrite is applied by pump and has no stone in the mix.

Either way, Laitance almost always occurs with either screed and must be removed. Absolutely nothing will stick wether it is epoxy resin, solvent or water based.

I install both types of screed regularly and can tell you that Laitence (the dusty layer on top) can occur the day after screeding or several weeks later depending on conditions. The fact that you have no DPM is a big worry even when applying fast track DPM.
I use a large grinder a bit like a hover mower with a grinding disc the size of a bin lid, it's actually quite quick to use but produces a fair bit of dust. After which i often apply epoxy resin dpm ready for the final floor finish. I assume your paint meets these requirements as it's a water based epoxy.

Without a DPM under the screed you will have a constant moisture flow depending on what the screed was laid onto. If this is the case not much will work and your contractors should be taken to account.

If you havn't much time try these people,,, http://www.f-ball.co.uk/

They just might have a solution, They will want to know exactly what paint you want to put down, what screed you have down and when it was laid to give you the right info.
Go to the website then contat numbers and ask for (technical)

 

[saiello]

Thanks for the replies. The concrete was delivered by those cement mixing lorries, no idea whether it was normal concrete or this anhydrous stuff as I was off site most of the time although I do remember that it did look fairly lumpy as I saw the last of it going in. As far as I know about 5 inches of hardcore was laid down and then around 5 inches of concrete with a steel mesh embedded. One of the guys doing the job said that the last batch of concrete delivered was too dry, the lorry driver had added water but too much which resulted in a very wet top layer. After brushing the surface with a stiff broom I appear to be getting down to a layer where sharp sand is beginning to be exposed I'd say around 25%-30% sand to pure cement, but the surface still comes up when I rub a finger over it. I need to do some further investigation, I will contact the contractors to find out what company they used for the concrete and hence what type was laid down. Having no DPM does worry me but it's too late to do anything about that now. f-ball seem to have lots of good info, I'll contact them to see what advice they have to offer...