Chemicals in concrete

[alexwright]

I have run into some jobs that have chemicals in them. Cure and seals, calcium chloride and who knows what else. My understanding is that when calcium chloride is used, anything you put down will eventually come up, sometimes as soon as you get a couple of feet away. Cure and seals can be removed but some jobs are hard to tell. Some concrete looks as if the chemical is all the way through it. Some will take the acid stains but the fear is in the sealer. What I have offered on these jobs are cuts like tile. Anyone else running into this? Out here in San Diego accelerators and retardants are used quite a bit and I am seeing this more and more. Any thoughts? One job I ran into this and sealer turned white, well I don't think it was the sealer but a reaction or something under. I had cleaned it and it went away but as I applied the sealer and advanced a little the white spots started to reappear. So for everyones sake I have just done cuts and my customers are thrilled. We both wish to have stained but both not willing to risk and get something ugly.

[Lindy]

If calcium cloride has been used as a curing accelerator, acid staining causes very dark spots and is not recommended; moddled appearance is also very unpredictable, sometimes over time going to almost to a moddled black (some colors being worse than others).

Do you make it a practice to test the PH of the concete to determine that alkalinity rate? ie: using a PH tester (if you don't have one go to www.vaportest.com to read up and acquire). Basically you clean the concrete, allow it to dry, wet with distilled water (just wet/not puddled water), mark with tester, then use the color guide to determine the PH of the concrete. If it is too high you can etch with 10% muratic solution, neutralize wiht 1 cup ammonia to 1 gallon of water, rinse thoroughly, allow to dry, retest for PH. Once you get the concrete to have a neutral reading (5-7 PH), you could use a concrete dye, there are some very good ones on the market that can be used on exterior or interior surfaces, that will provide a moddled color (instead of a reactive acid stain) then seal. Might want to consider this.

Lindy A.