Polished concrete floors

[mtldesigns]

To my concrete Chiefers...

 

I have a descent sized house that the clients wants a polished concrete slab throughout.  Any special notes or requirements that I need to call out?  Google gives you a thousand different answers, so I am looking for more of a direction by asking you pros.  I typically use a 4" monoslab, I know because of the grinding and polishing I will need to go thicker. 

 

So far this is what I have called out, please tell me if I am going in the wrong direction.

Min. 4 1/2" thk slab/slump

min. compression of 4000#. 

What about joints?  

Special aggregate?

[GeneDavis]

Here is a good article about it.  https://aicoat.com/polished-concrete-the-complete-guide/

 

I did the plans for a wood-framed house that got this floor finish on its basement slab and the main (wood framed) floor.  Built in cold snow country, with radiant heat pex tubing in both slab on grade and the topping slabs, the polishing work took away only about 1/8" of the top, so I had no concern about specifying more thickness than "normal."

 

It is up to your client, the owner, to view samples and specify the level of cut to achieve the desired look, and the polish (800 grit, 2000 grit, or whatever).  The article describes the different looks achieved by depth of cut, and also the level of polish determined by the pad grit.  That info is the only thing I would put on plans.  

 

The plans included the layout for the sawcut scoring, 24" centers both ways.  This happens right away after initial cure, and the cuts are vacuumed clean of dust and debris and immediately filled with an expandible sealant, color matched to the 'crete.  This, prior to the grinding and polishing.  I left it to the builder to work with his concrete sub for placement and polishing to specify the mix, colorants, aggregate, and any screeding and troweling techniques.  For the wood-framed main floor, the pour depth was 3 inches, all the exterior walls, got bottom triple-plated with 2x pressure treated lumber before the pour, the unbuilt interior wall plates (bottom two only) functioning as screeds.  

 

What material did you use for your floor texture in the Chief model you show?

[mtldesigns]

 

2 hours ago, GeneDavis said:

Here is a good article about it

Great web site Gene.  Full of information esp. the process.  Thanks.  

 

Why did you have to do saw cuts 24" on centers?  Did your plan showed that or the contractors plan?  I didn't really see where they mentioned new construction, but I would assume they don't grind and polish until the house is dried in.  So your house was on a wooden frame, that's why the 3 plates..  Now that I've had a cup of coffee, I had to read that again.  

 

I used Cloudy Stained Concrete via Chiefs core catalog.  I set a thickness on top of my concrete slab (4 1/2") as 1/32".    I didn't realize there were so many color and style options.  I will pass this onto my clients for them to review as well.  This is a Jacksonville company, I wonder if they'll come west to Tally, a 2.5 hour drive on I-10..  There reviews were all great.

[GeneDavis]

The 24 x 24 grid was requested by the builder and I did a plan view just for that, using CAD for the grid and dimensioning.

 

Whether that tight or something else, you're going to do sawcuts to control the eventual cracking.

 

The placing contractor and the polisher contractor work hand in hand, and for this job, drove 2.5 hours to get to the site.  No other options.  You'll want to talk to whoever is going to do it.  It's not much different than terrazzo work, and where I am in SW FL all that is done inside, fully weathered in.  They can  those big twin-pad units close to walls and corners, and they finish with hand units.  It's a great look, far better than stained 'crete.

[rgardner]

9 hours ago, GeneDavis said:

Whether that tight or something else, you're going to do sawcuts to control the eventual cracking.

This is highly debatable and most of the true pro concrete guys will tell you not to score an interior slab if monopoured with the footings as it is unnecessary and can even weaken the overall foundation slab.

[JKEdmo]

On 8/4/2023 at 8:39 PM, mtldesigns said:

Any special notes or requirements that I need to call out?

If you go to Construction Specifier online magazine and search keyword "polished", there are a number of articles on the topic.

 

Jim

 

 

[ValleyGuy]

Hey Michael,

I ran my own concrete company for many years before I started drawing plans. Approximately the last 12-15 was doing pretty much all decorative concrete - both inside and outside, horizontal and vertical. Here are a few things I learned through 'trowel' and error that you may want to consider.

- Grinding and polishing like you are describing will not diminish the concrete thickness significantly. The paste (actual concrete) is what you want to become your finished product as opposed to the aggregate (stone and sand). Concrete paste accepts colour and reacts with acid stain, rocks don't. Should you grind down to the aggregates, you will have the colours of the stones showing and have more of a Terrazzo finish, and that is a whole other kettle of fish. Concrete should have aggregates within the top 2mm to retain its strength and durability when used outside. Inside, because there are no violent climate changes, paste toppings only are used quite often and sometimes work fine, especially in light traffic areas like residential settings.

- Usually hardeners are used in the process when polishing (to fill in the porous surface) so the strength doesn't need to get too crazy. You've maybe seen concrete counter top guys filling all the little air pockets and blemishes before they polish - same idea on the floor.

- A very important caution point..... vapour barrier under the slab means that all moisture must come out the top surface! Any topical coating will have a bare minimum moisture content that the concrete will need to be before applying. I strongly suggest using a proper desiccant moisture test beforehand so that you don't get any moisture trapped under the top and ruin the job. Removing moisture is easy.... just give the concrete a long enough time to cure. The tough part is not putting anything on the surface that will damage  the concrete or cause it to cure differently - customers don't like their project on hold for months waiting to get the proper moisture reading. Protecting the surface with cardboard, house wrap, blankets, etc only changes the moisture release rates of the surface causing inconsistent curing (blotchiness). I've seen different coloured stripes on floors where the Tuck Tape held the overlapping house wrap at 9' intervals. If left uncovered and construction continues, contaminants such as oils (potato chips...) and adhesives (Tuck Tape,  glue...) are the worst and sometimes never come out of the concrete surface. These, and physical damages, will often show up in the final product adding a bit more character.

- Cracking.  Concrete, like most everything else, will shrink when the moisture is removed and thus pulls at the concrete. Shrinkage cracks often happen most frequently between two shortest points like inside corners to pipes, narrow areas like small rooms off of larger ones. Control joints are used to help guide the concrete in it's cracking. Creativity is key here in trying to control how the slab will look. Saw cuts are risky with in-floor heating, and are 1/8" wide. You may suggest that your client discuss alternatives with the concrete contractor like concealing control joints under walls and cabinets, or using wet-set plastic strips instead of cutting, changing your house design may also be an option. Leaving hairline cracks over short distances are often less noticeable (under doors or in halls). Sometimes a nice big room will not crack at all. Concrete has a life of it's own and your client will need to assume some risks as this isn't made in a factory setting. 

- Scoring the surface for a pattern like tile, boarders or jumbo diamond shapes is for aesthetics only. They only penetrate enough to leave a shallow groove to change the texture (unpolished) and colour - control joints need to be 1/4 the depth of the concrete to be effective. Note: leave a boarder at the walls should they want a pattern - it's very hard and time consuming to extend scoring lines (made with a circular blade) out to wall edges.

 

Bottom line, I wouldn't put too much direction on the plans. This is a subject that has tremendous technical and logistical requirements that are often not followed through on after the customer has gained a good understanding. Usually the expense vs risk with project timelines and customer expectations involved often abandon these types of floors - you may be better off to let the customer and the concrete contractor make up the specs with the builder, much the same way a kitchen supplier handles the kitchen. 

 

 

[rlackore]

You may want to consider a polishable overlay. Shayne makes excellent points, especially about the moisture content of the concrete. When I'm specifying a polished finish, this is my starting point:

 

033543 Polished Concrete Finishing

General

Includes ground and polished concrete floor slabs, including stained and polished concrete.

Products

Coordinate colorants, aggregates, and castings with the Owner.

Concrete: Use normal weight concrete only, no air entrainment. Do not use volcanic aggregate for areas to receive an exposed aggregate finish. Admixtures may be used, except for calcium chloride accelerators.

Densifier: Duraamen Hermetix Densifier, www.duraamen.com.

Sealer: Duraamen Hermetix Protector, www.duraamen.com.

Execution

Comply with the General Requirements.

Curing: Water curing is best to minimize edge and joint curling. Do not use topical curing agents that will act as a barrier to densifier penetration.

Densification: Allow concrete to cure a minimum of 28 days before application of the densifier. Apply densifier ten days prior to installation of equipment and substantial completion to provide a complete, uninhibited concrete slab for application.

Placement: Pour and work concrete to achieve a minimum Floor Flatness rating of 40 and minimum Floor Levelness rating of 40, where possible.

Polishing: Perform the entire polishing process prior to erecting non-load bearing partition studs. Achieve the following finish: Coordinate the finish with the Owner:

•              Level 1 – matte finish (150 grit final polish).

•              Level 2 – satin finish (400 grit final polish).

•              Level 3 –medium sheen finish (800 grit final polish).

•              Level 4 – mirror finish (1800 grit final polish).

•              Class A – cream (no exposed aggregate)

•              Class B – salt and pepper (1/16” exposed sand, small aggregate).

•              Class C – medium aggregate (1/8”-1/4” exposed aggregate).

•              Class D – heavy aggregate (1/4”-1/2” exposed aggregate).

Protection: Protect the concrete slab from damage both before and after polishing. All hydraulic powered equipment must be diapered to avoid staining of the concrete. No trade will park vehicles on the slab unless necessary; always use drop cloths beneath the vehicles. Do not stack or store construction materials or chemicals on the slab.