surface peeling

[ifinish]

Alrite i have read through some of the other posts that were on here about peeling but i have a different situation. I work in a shop pouring concrete wall panels. We do 2.5" inch on the bottom 4" of foam and then another 2.5" on top of the foam. We pour about 30 of these panels a day. So first off, we pour at 8 1/4" slump, we use type 30 concrete. Once these panels are poured we have no bleed water coming to the surface. I wait till i can wait no longer to do my first pass with a pan. i do 2 hits with a pan and then to blades after that. I wait to blade till i can walk on the panel withouot barely leaving a footprint. i continue this till polished. Now this is where its tricky, i finish 30 panels all the same, but every now and again i get 1 or 2 out of 30 that start to peel. sometimes so bad all i have to do is rub my finger on the polished concrete and the finish will peel off on my fingers. I take it that its not my fault as i get 27 to 28 good panels and only 2 bad panels. Ive been told i maybe over working it, but in my experience if im hitting all 30 in a row one after the other shouldnt they all be over worked and all be peeling then? i am officialy stumped with this situation. I have never had this problem before in the 6 years ive done this. Any suggestions or explanations? thank you and sorry for my book ive written just want everyone to get the low down before making any assumptions. Thx again

 

[Ron]

Keep in mind that each time you batch concrete, you can have a difference sufficient to create a different finish. Your problem does sound like overworking. That can be a timing issue. Overworking might be tolerable at one stage of bleedwater rise, but not at another.

 

[msucog]

i have seen this with mechanical screeds that seem to run at pretty high frequency (that's my interpretation from years of performing concrete work as a contractor) and perhaps overworks the surface. this particular time i saw the issue, it was for a 2' thick slab and it was likely more an issue of too little consolidation initially with a fair amount of bleed water then overworking the surface. either way, as the mechanical screed would go across the top, you could actually see bleed water push out of blisters a foot or so behind the screed. and the end product had significant areas that roughly 1/8 to 1/4 of the surface would peel off. you could almost identify the areas before they broke with a broom stick tapping the top or dragging a chain.