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Powdery Substance On Sealed Concrete
So been talking to this new guy in town that had a concrete stain company come in and grind and seal his slab with a penetrating sealer that is supposedly penetrate down one inch,.
Problem is a powdery substance coming through the surface. I've seen lots of concrete problems but this one is a dozy. The owner had a company come in a grind the concrete and seal but without stain as in a typical acid stain job.
Finally got in there and did a couple Rapid Rh tests. Dang thing is dry as a bone. Numbers came in at 57 initially and 67-8 ish after an hour later.
Course I kinda new that since he had installed a floated thin solid stranded tiger bamboo solid over a closed cell foam in a couple bedrooms that has not had any moisture issues at all since. And thats been awhile now, like weeks maybe over a month.
The most unexpected thing was the ph test on top of the sealer with the powdery gritty substance. I was expecting something hot, but danged if it came out neutral, the unsealed concrete is 9...perfect???
Is next to a golf course and some people thought it might be from all the watering but no the golf course is not effecting the slab and neither is all the rain we have been getting.
I only had two Rapid Rh tests on me person and time was of the essence so we just did two in areas not to disturb the main floor. I wanted to do one in the middle but hey, not my call.
I don't think a cacl test is warranted in this case but I did want to run some and one on top of the sealer. It's all about the ph and what's down below.
What do you think it is?
Problem is a powdery substance coming through the surface. I've seen lots of concrete problems but this one is a dozy. The owner had a company come in a grind the concrete and seal but without stain as in a typical acid stain job.
Finally got in there and did a couple Rapid Rh tests. Dang thing is dry as a bone. Numbers came in at 57 initially and 67-8 ish after an hour later.
Course I kinda new that since he had installed a floated thin solid stranded tiger bamboo solid over a closed cell foam in a couple bedrooms that has not had any moisture issues at all since. And thats been awhile now, like weeks maybe over a month.
The most unexpected thing was the ph test on top of the sealer with the powdery gritty substance. I was expecting something hot, but danged if it came out neutral, the unsealed concrete is 9...perfect???
Is next to a golf course and some people thought it might be from all the watering but no the golf course is not effecting the slab and neither is all the rain we have been getting.
I only had two Rapid Rh tests on me person and time was of the essence so we just did two in areas not to disturb the main floor. I wanted to do one in the middle but hey, not my call.
I don't think a cacl test is warranted in this case but I did want to run some and one on top of the sealer. It's all about the ph and what's down below.
What do you think it is?
Tags: concrete, effloressence, problem, sealed
Replies to This Discussion
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Permalink Reply by Bob Higgins on -
This sounds like a form of carbonate (i.e. trona), which can be found in contaminated aggregate, or may be native to the soil and has migrated up from the bottom of the slab (if the concrete is several years old).
The pH would be approximately the same as neutralized concrete (9.0-9.5).
Garages usually do NOT have any form of under-slab vapor retarder/barrier and therefore can allow contaminants from the soil into the concrete, which usually doesn't create a problem, until some form of surface modification is attempted.
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Permalink Reply by Stephen on -
Bob, thanks for checking in. I got some pictures of inside the house. I am absolutely certain the slabs in these upperscale townhomes have no barrier under the slabs. Built about ten 12 years ago next to the golf course.
I was under theimpression this just may be just bad concrete. The guy that did the work came in a ground down the surface as you can see in the photos to the aggregate in most spots, pretty uneven. Being of a gritty nature I felt the grit could be from the surface as well.
The powdering keeps coming through or off the surface not sure about that since the ph was 6 on top of the sealer. They used a densifier and some Duro-Polish, then he stripped off the polish with some strong stripper. Tried using some paste wax which stopped it initially but then is reoccuring. But man has this concrete been through the wringer!
I also have a funny feeling the guy may have used some old sealer and chemicals on it. You know what happens when things get slow, stuff sits around and expires.
I'm going back in this week to check the Rapid Rh probes and grind down a few spots to see just how far this sealer penetrated. It was sprayed on and I hear old penetrating sealers don't penetrate so well. An inch is what they claim, What do you think?
Maybe I should try some home made ph paper too eh? I found a few holes where the tackstrip was pulled and the ph was still a 9ish in the hole probably a half inch down.
The owner wanted to gluedown a wood floor. I told him that is titally out of the question.
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Permalink Reply by Bob Higgins on
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This sounds very much like another project I was made aware of (about 25 years ago if I'm not mistaken) where the concrete pathways around the golf course had a mysterious efflorescent material, that only showed up in the spring and fall...one expert went out and announced it was a certain type of efflorescence without doing so much as a single test...
Come to find out, there exists a certain carbonate in the soil that is active ONLY within a certain temperature range..a carbonate WILL have a pH in the range of 9-9.5, so that sounds very much as a likely candidate for what you are seeing
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Permalink Reply by Stephen on
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Great Bob so whats the fix? See that big stack O long wood planks on the front pages slide show? Well, we floated it over the slab. Problem solved, 5 grand buried under wood. I thought it didn't look that great anyway
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Permalink Reply by Bob Higgins on
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perfect solution, because it truly isn't a "moisture problem" unless that accompanies it..but the powdery substance from the photos and the facts around the project lead me to believe you had a similar problem..isolating the slab is the best idea..good job!
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