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Thread: OT: 3/4" top coat of concrete
03-26-2007, 03:57 AM #1
Is there a way to put a 3/4" top coat onto an existing concrete slab, and have it actually bond to the existing slab?
We put in a patio & walk that we had intended to tile, then found that the tile is no longer available (trying to match existing adjacent tile). So we are considering other options. Is there a technique that would provide good adhesion between new concrete and old (3 months), so that we could add a 3/4" top color coat with a stamped finish?
03-26-2007, 09:48 AM #2
There is a product called Surface Bonding Cement from Bonsal that should work. I've used it to parge coat some blocks but don't know how well it stamps.
03-26-2007, 10:32 AM #3
They have stains for concrete one is an acid stain.
You can lay out a pattern or design than use a 4" hand grinder and grind (1/8" deep)on the line to make a trough or boarder line. After that's done pick your color and start staining.
I looked it up on Google after my brother-in-law told me about it.
If you can't find anything about it let know.
03-26-2007, 01:49 PM #4
I don't think you will have much success with a 3/4 layer of concrete over concrete. Also, if you stamp it you would introduce the stress cracks and weak lines that would cause the topcoat to eventually fail.
There are a number of epoxy resin based systems that are designed to resurface driveways, pool areas etc. They include aggregate mixed with the epoxy so are at least a half inch or more thick and can be colored to match an existing area.
Look in your local yellow pages for driveway resurfacing. Of course the internet probably has a wealth of information too.
03-26-2007, 02:33 PM #5
If you HAVE to go the concrete-over-concrete route, then make sure the base is clean, free of loose pieces, and make sure the base is wet for a while (no standing water).
Dry contrete will pull the moisture out of the new mix and it will dry out before setting up with a good bond.
This is no promise, just insurance that you do everything you can to get it to work.
03-26-2007, 03:01 PM #6
03-26-2007, 03:30 PM #7
3/4" topping is tough. We do alot of jobs pouring a leveling course over existing. As said above there are bonding agents available to help with the cold joint you will experience. A pea gravel or similar smaller aggregate is used. Fiber mesh can help a bit as reinforcement because you won't get any mesh is something that thin although it is NOT a substitute for steel. I think the minimum thickness is a ratio of largest aggregate size. 5x sticks out in my mind.
In the olden days 30's 40's, a lot of concrete was poured with a separate topping of say 1". Some sidewalks and slabs poured this way. A smaller agg. was used in this topping to aid in finishing or if a color was desired. There is a tennis court across the street from my house poured this way, built in 1946, still in respectable shape. They key here is that the topping was placed on the base course while the latter was still "green" or not cured completely.
Hope this helps.
03-26-2007, 08:23 PM #8
Thanks for the ideas. My readi-mix provider (Granite Rock) only uses one cement, standard portland cement, but they will add additives and modify the mix as required. Their applications engineer suggested a sand slurry with Eclipse (a surface agent that reduces surface tension) and fibers (they have 1" and 2.5" fibers available); However, the engineer also said that adhesion is a problem because of the contraction that occurs as the concrete hardens. And in general he was pretty negative about the risk of surface cracking.
John M, the polymer overlay looked interesting, but all the applications looked very thin.
LD, epoxy does sound like an option, but expense is driving this, so I need to investigate the cost for 1.5 cu. yds installed (600 sq. ft), also the durability. Epoxy breaks down in UV, and this is an outdoor patio.
So, I'm still considering options. Tile may be the best solution.
03-26-2007, 10:35 PM #9
There are guys that make a living analysing failed concrete coatings.
Think about that before you try it.
03-27-2007, 01:51 AM #10
Dave, I think tile is the best solution fwiw, but the polymer overlays can be done just as you were considering...a colored stamped overlay up to 3/4" thick.
If it were my home I would do tile in an exterior application regardless, and I would consider a fully adhered anti fracture membrane underneath it as well before the modified thin set & tile installation. I've researched and applied these membranes alot under 3/8" exterior tile applications...sometimes they can be worth the trouble.
Best of luck,
03-27-2007, 02:00 AM #11
Tile Pros add cementicious coatings to old concrete regularly.
They do not do it casually. Be very careful about asking anything of such around big box stores.
These days, It is done by adding water to a special prepared mix available at serious tile distributors. even available at big box stores IF you already know what you want.
Also they use a better inter-layer adhesive than simple neat-portland.
Among other things, you must seriously avoid using too much water, and equally seriously pay attention to the various phases as the portland hydrates.
Go to a URL called the John Bridge Forum and ask in the "pro-hangout"
03-27-2007, 02:00 AM #12
Hydraulic cement, the type that cures to a semi-shiny dark grey color. (poly based?) Not cheap, and an 'odd' color compared to normal cement, but it's tough.
made to bond to cured cement. If the surface is clean, you won't easily knock it loose with a hammer.
just spent HOURS trying to bust some 30+ year old splats off the front porch to put handrails in, finally had to get the grinder, the hammer and chisel wasn't working.
03-27-2007, 02:10 AM #13
I've done this several times. Used pure portland and sand, 2 to 15 ratio I think, mixed DRY (like molding sand), tamped and screeded into place over concrete wetted with latex admix (milky stuff you mix with tile thinset in the days before it was latex modified in the dry state), then wet cured it with plastic over it for about a month.
I think a couple hundred square feet cost me about $50, but was A LOT of work.
03-27-2007, 11:34 PM #14
I'll go with tile. Tile's a lot of work as is, but the result is a known quantity. I'll avoid the size problem with a border or a change in pattern.
Thanks for all the suggestions and info that helped make the decision.
03-29-2007, 08:59 PM #15
There are company's out there that do exactly what it is you are looking for. They do it for pools mostly and there are other products out there that you can use such as "cooldeck" tp name a few. I'd contact a couple of pool contractors in your area to get info from them on who they use.
They also do stamping which is just 3/4' thick.
03-29-2007, 09:27 PM #16
By the way, what I described is essentially a thick set mortar bed, which was the norm in tiling YEARS ago. The mortar mix is known as deck mud frequently. Might contact some high end custom tile setters for some help.