need to coat some poured in place concrete walls with 2 part epoxy paint.
A comment from the concrete people was to make sure I wait 28 days for a complete cure prior to coating or I would get a incomplete cure.
Does this make sense to anybody?
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yes
Many epoxies are sensitive to moisture and won't cure properly when applied to recently placed concrete. Also, alkali can rise to the surface of concrete during the curing process, and the alkali interferes with the bond between epoxy and concrete. 28 days is an arbitrary figure, it depends on how much moisture is remaining in the concrete when the epoxy is applied.
I don't know if the converse is true, that is, that the epoxy can harm the curing of the concrete. Brownbagg, is that what you meant?
epoxy will not hurt the concrete, it just stick to wet concrete.
For most epoxy paints you have to acid-etch the concrete. If you know what a lousy job this is, you'll put it off at least a month anyway.
Jeff
comment about wet cure, concrete generates heat as it hydrates. Once place the top layer will cool quicker than the internal concrete as in footing and bottom area. the different in temp or drying is what cause the cracks. so by wet cure you are controlling the temp rate.
The crete will cure anyplace as long as it is not well below freezing temnperatures. In a plastic bag, under water, behind epoxy paint.
But the paint might not cure nor stick very well. Thaat would be a big waste of time and money.
Have you read the label on the paint cans?
I'll bet it says thirty days or something like that
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crete will cure anyplace as long as
Dang it, now you've got me thinking (and you know that's not my strong suit <g>)
I'm trying to remember the physics of both cures. Or, I guess, the chemistry of it, them.
I know epoxy cures as soon as the harderner is added, that's a straight chemical reaction. But, I'm not remembering if the water+portland cement reaction is purely chemical or not.
Now, since curing concrete does try to "sweat" water out of it's own mix (that's why we wet it during curing), so, and pores in the concrete, to which the polymers in the epoxy might bind would be filled, instead, with water. That is not likely to improve the bonding.Occupational hazard of my occupation not being around (sorry Bubba)
Also, with both reactions being exothermic, that slice of moisture between the two just has to do some boiling off....
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being exothermic, that slice of moisture between the two just has to do some boiling off
Or transpiration, if we are carting out the six-bit words <g>
What mere memory will not divulge is if the water-cement reaction yields anything other than the heat (not that I'd know one molarity from another--other than to napalm the holes <g>).
I want to remember that wetting a curing slab will "drive" any temperature transpired water vapor away from the ponded water, while keeps water molecules available for the curing process where we want it most.Occupational hazard of my occupation not being around (sorry Bubba)
I don't know it the wetting 'drives' water one way or another. My understanding has always been just that it slows the transpiration to keep the mixed water where it needs to be for curing. - more important down in the hot south. Not something we often need to worry about up here except those three hot summer days we get each year.and we knock off the play baseball then.
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Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together. The water causes the hardening of concrete through a process called hydration. Hydration is a chemical reaction in which the major compounds in cement form chemical bonds with water molecules and become hydrates or hydration products. Details of the hydration process are explored in the next section. The water needs to be pure in order to prevent side reactions from occurring which may weaken the concrete or otherwise interfere with the hydration process. The role of water is important because the water to cement ratio is the most critical factor in the production of "perfect" concrete. Too much water reduces concrete strength, while too little will make the concrete unworkable. Concrete needs to be workable so that it may be consolidated and shaped into different forms (i.e.. walls, domes, etc.). Because concrete must be both strong and workable, a careful balance of the cement to water ratio is required when making concrete
Does that help with the old memory?
Dave
http://www.epoxyproducts.com/chemistry.html#part1
More than you ever wanted to know about epoxy. Brings back nightmares of organic reaction chemistry for me.
Think I'll go balance my check book, that is easier.
Dave
Thanks guys. I can see it harming the epoxy cure, but these guys were pretty pointed about the concrete cure. IMHO they got it backward.
Not epoxy but I can attest that paint will flake off if the concrete hasn't cured all the way. A client had a large patio area poured in her backyard and had a guy paint it this blue-green color about two weeks after it was poured. A few months later large splotches of paint were wearing off, leaving a whitish blue-green stain. It actually looked pretty cool though. The concrete was fine.Handyman, painter, wood floor refinisher, property maintenance in Tulsa, OK