We're going to have acid stained concrete floors with radiant heat in our new house.  They (slab in basement and suspended for main living floor) get poured on Friday (8/21).  Does anyone have any do's or don't's for the pour/finishing?  And then for protecting the floor for 6 weeks or so while it cures?  We were thinking of putting down plywood of some sort or plastic.  Is that a problem with condensation forming underneath?  Any other thoughts?  Thanks in advance. Cathy

Acid staining is a good look (whole foods in walnut creek ca).  Are you going to stain the thin 1 1/2" overpour upstairs also?   Or just the standard 3 1/2" slab in basement.....
Basement should be no problem but I wonder about acid staining the thin qypcrete product?  Acutally I would like to do that as well.  Condensation will go away eventually and you will get a stronger floor with slow cure.

You MUST talk to a concrete finisher in your area to determine what you should do - do not rely on us unless you want more cracks than you anticipate. At a minimum, you should keep the slab wet (preferably covered with burlap) for at least 2 or 3 weeks, but there are so many variables in curing concrete (thickness, foundation at the edge? Temperature and humidity, underlayer - sand or not, vapor barrier) that professional help is a must if you want a professional finish.

It sounds like you have someone to do the acid staining, so what does that person say?

Jeff

Forget acid stain on Gyp crete, different product all together.
We have stained 2 inch concrete on platforms. expect cracking, use control joints on all corners, still expect cracking.
4 inch slab nice look. keep slab wet after cure for a week or so, that will help with cure. Acid wash has to go in a dry concrete. Plan on having you heat on or holding of until building is framed and roofed and slab is dry. (months)
Acid is messy and you will need proper protection, respirator, glasses,gloves, mud boots. If it can be done before sheet rock and mechanical systems you do not have to protect walls and can be messy concerning the clean up. lots of water, gallons and gallons.
After sealed, surface protection from the trades can be done with role out heavy butcher paper/thin card board type on role.
A nice effect on a slab is concrete saw 1/4 deep cuts on 2x2 or 4x4 foot patterns.
good luck,
Dan

I believe we have 3 1/2 inch concrete going in for both the basement and main living floor.  Basement is on sand, main living floor is OSB (I think) then both the basement and OSB are topped with.....drat....terminology has evaporated from my brain.... roughly 2 inch styrofoam insulation....white, not blue or pink.... then the pex is stapled on to that then 6 inch square mesh on top of pex.  No gypcrete.  We have lots of steel and trusses to carry the load for the main living floor.  My husband will be cutting the expansion joints the day after the pour.  

At this point, we have no interior walls so my assumption is that we can eventually do the acid stain before any interior walls go up.  We are doing the staining ourselves with some input from a friend who has done a lot of stamped concrete work and has done a modest amount of stained worked.

We are learning that the "experts" locally all have different takes on how to do a project (and more and more we're finding out some of the "experts" are not so expert....a whole other discussion!!) so it is always interesting to get some feed back from the folks in the trenches who follow this forum. 

So the question specifically, was how to best project the concrete from any "stuff" that could impede the uptake of the acid stain since we can't do the stainfor 6 weeks or so.  Should we cover it (after the initial cure) with plywood?  Plastic?  We've been told not to have the concrete company (who will actually be putting in the floors) burnish the wet concrete too much because it will close up the pores and lessen the acid stain uptake.  Any other thoughts?

Thanks so much, especially for the comments about how much water the neutralizing and cleaning will take....good point about doing it before the walls go up! Cathy

Dan: If we go larger than 4X4 foot squares, does that increase the chances of cracks?  If we keep the concrete nice and wet for a week or so, will that help lessen the cracking issue?  Thanks.  Cathy

Cathy,
I am not an expert on acid stain, or concrete. I have place considerable amounts of concrete, and done several thousand square feet of acid.
As to cracks, this is mostly a function of support under the slab, foam is fine (best r value) but what supports that. Platform same thing, how solid. The tighter your cuts 2x2 foot for instance the less likely the crack will run across the room, it will usually stop on the joint baring a weakness further down, soil shift, platform shift.
Acid wash I have had good luck with the brown shades, the green is tricky, get a pro for that.
Plastic is a ok choice to protect the floors, I prefer heavy paper.
Dan

Small, sometimes inslightly plastic (or shrinkage, I believe) cracks form in concrete as it cures because different "parts" of the slab cure at different rates. Small plastic cracks can form at the top of the slab as the "top layer" of concrete dries and cures faster than the "next lower" layer. Often, I think, these cracks come with a dusty-ish top layer, and while the dustiness can be fixed or managed, the cracks cannot.

I think that larger plastic cracks occur as the slab cures differently across the slab, from left to right. This is why an integral foundation at the edge of the slab that cures "slowly" can cause cracking as the 18 inch deep concrete cures differntly than the 4 inch thick slab. Control joints can generally force many plastic or shrinkage cracks to either disappear, by relieving the pressure at the joint, or to appear near the joint.

Plastic cracks appear in the first months, and are generally not a result of anything underneath the concrete. Keeping the concrete generally wet controls the curing rate, and therefore controls (to some extent) plastic cracks. The warmer your climate, the more important this is.

Cracks that are caused by support failures are different entirely, as they are caused by stress on the concrete from the weight of the concrete, and are not a function of drying. This is where compacted - or non compacted - can come into play. BTW, I do not believe that cracked foam is that important, as foam does not compress, but cracked foam on top of uncompacted or non-level soil or gravel is a problem. All problems start at the ground.

You could also get cracked concrete on an upper floor if the floor joists were not designed with an appropriate amount of stiffness, or the concrete isn't thick enough, or any one of a number of other reasons. For this, you trust your engineer.

Jeff

Cathy,
As much as we try not to, concrete cracks. Expansion and control joints are a great way to minimize them as well as keeping the concrete damp for a week or so. As for the Acid stain, I have done this in several projects and here are some general rules to guide you. Protect you floor from damage during construction. I use one layer of rosin paper not taped to the concrete and then perpendicular to this I cover it with tar paper. Do not use plywood if there is a potential of it getting wet (rain) the plywood will leave stains on the concrete. Seems kind of like a lot of work but if you don'd do this the pasters and painters will surely make your prep work for the stain much harder. I suggest doing the staining near the end of the project just before installing you baseboards and door trim. I would hate to see a newely finished floor ruined by damage during construction. One post mentioned acid wash, some acid stains will not work if you use a product like muriatic acid to prep the surface. Most just require a clean surface that has been cured for a minimum of 28 days. Don't wait for the control joints to be put in place, these should have be done within 4-12 hours after the initial floor is finished. As for location of the control joints? place them in the finished floor pattern. If you want a 2'x2' or 4'x4' pattern use some of these as you control joints. The rule for placing control joints 2-3 times the floor thickness in inches by Ft. So a 4" slab should have controls joints placed at 8-12' spacing. Control joints should be a minimum of 1/4 the thickness of the slab or in this case 1" deep. here are some pictures of the acid stained floor, including the cracks. http://picasaweb.google.com/TomPittsley/PassiveSolarHomeMiddleboroMA#
If you absolutely don't or can't live with cracks there are different methods of dealing with this, like thin set overlays if the concrete cracks and you don;t like it. When the floor we poured cracked I had a fit, the homeower thought it added character. Good luck with your project.

Tom Pittsley
[email protected]
www.eebt.org

Tom,

That is a beautiful job on the floor.  Can you tell me what product and colors you used on that? Also, are the joints grouted? If so doesn't the grout cause any issues with the stain?

We are in the process of building and would really like to duplicate that look on our concrete floors.

Thanks,

JohnR

JohnR,
The stain was from an online source I believe it was this site http://www.directcolors.com/
Believe it or not that floor was a black acid stain although it came out more like brown. It took two applications of the product to achieve that color. We did several test patchs in closets and under cabinets to get the color right. The grout lines aren't really grout lines, just thin saw cuts into the concrete about 1/8" to give it the look. No grout was used and it was done prior to staining the floor. If you haven't seen the process don't panick while doing it, the end result will look nothing like the finish during the process. Three coats of sealer and several coats of wax were used after staining to give it a shiny surface. People can't believe it's concrete, I had one guy argue with me that there was no way that was concrete and though it was some kind of imported tile. It is a lot of work, cleaning, preping, applying, nutueralizing, cleaning and sealing the floor but well worth the effort.

Tom Pittsley
[email protected]
www.eebt.org