i skim coated my mom’s porch with quickcrete. i don’t have too much experience with concrete so i had a friend (who is a concrete inspector) check in on me as i worked. he gave me the thumbs up as i worked and said it was a pretty crackerjack job.
the problem is that the next day there were several portions of the 1/2 inch slab that DID NOT bond at all to the porch. as the concrete cured more and more of it lifted off and you can feel it cave as you walk over it. now i have to smash a 500 lb slab and repour.
i figure using some sort of bonding agent would be a good idea, but does anyone know why the porch apparently actively repelled the concrete?
Remember when War was just a card game?
Replies
Was the porch ever sealed withe a concrete sealer? Grease/oil stains? Did years of shuffling feet burnish the concrete until it was glass-smooth?
It sounds like you had supervision so that you had a good mix.
Did you wet the porch before applying the veneer so the dry porch didn't suck the moisutre out of your mix, causing it to cure too quickly?
Did you mist the veneer to keep it moist for a good, slow, cure?
Did you tarp it to keep direct sunshine off it during the cure?
Ah...I dunno. Could of just been bad luck.
Edit: One last thing...for a job like this, I'd rather mix my own instead of using a bagged mix.
And...you had a nice, stiff mix and trowelled it on? Or did you "pour" it on.
Edited 8/10/2002 3:00:01 AM ET by Mongo
thanks for all the advise.
as for the listed problems, this was on a porch with an awning that gets sun for about an hour and the concrete was applied after the sun was gone, so i don't think a tarp would've helped. i did mist the patch several times. the mix was good (apparently except for the fact that it was quickcrete). i had a very stiff mix that i spent several hours trowelling on. the old surface was actually (gulp) painted red many moons ago. however, years of traffic merely broke up the paint and exposed a rough surface beneath.
next time i think i'll go with the bonding agent. as my knowledge of concrete is slim to none, can anyone suggest a good pre-mix or a happy ratio for me to use for mixing my own (preferably suggest a good commercial ready mix as i'm currently working 11 hour days six days a week)? should i do something with the paint? is that a stupid question? i really don't relish the thought of being out there for a few more hours scraping paint of a 100 sqft porch.
again, thanks to all.Remember when War was just a card game?
Ardex is a brand name that makes leveling compounds. Another is Swift Set; manufactured by Amstone. Top-N-Bond is another product that should work. Abocrete is the name of a latex bonding agent; though I'm sure there are plenty more brands out there.
So it's your mom's porch, and you only want to go up 1/2". Instead of a layer of concrete, why not tile? It's a much better looking surface, and it'll get you to the level you want. You do have to get rid of the paint completely first, though.
-- J.S.
heh heh, my mom's a pain in the ####. wondering why someone with no concrete experience is doing the job? no one else would work for her. can't be thicker than 1/2 inch because that's what she wants, no tile because she wants concrete. anyone else want to do it? be my guest.Remember when War was just a card game?
Amazing how we try to doi the impossible for those we love when it is better and easier to do otherwise. I liked the tile idea. that's one of the beauties of Breaktime. Somebody always has a different point of view!Excellence is its own reward!
oh, no, i like the tile idea too, but not to be.Remember when War was just a card game?
Mongo points out a lot of the variables and possibilities. Quikrete is one of the poorest products you could use - they scimp on Portland so it isn't very 'sticky'. You need more fines for a thin patch. Too much water will make a mix shrink.
BTW, not to cast blame on the inspector friend but some inspectors don't know didly and it wasn't his nickle.
Piffin
"you need more fines for a thin patch"
Ive heard that term before, what do you mean "fines"
Doug
A concrete mix is a combination of various sized aggregates. In large job like a damn, You might have lots of quite large stone. The finer and finer sizes of aggregate fill the spaces between the larger ones. In a pour only two inches thick, the largest aggregate should be no mmore than 3/8" and probably best to be all sand.
Notice that masons sand is still pretty grainy though. Filling the spaces between the grains of sand creates a stronger patch. Leveling compound for floors, thinset, hydropatch, etc all have more fines than quikrete.
I'd want to mix my own and use an admixture for a bonding agent and in the mix itself.Excellence is its own reward!
Hey Piffin, is there any mix that will work at a half inch as he said he was doing?
You'll need to get the paint all the way off, etch with muratic acid and use keyways I suspect. All in addition to a thicker pour. Is this correct?Old Pro, not quite old, not quite pro, but closer every day on both...
someone correct me if I'm wrong but I've always thought that concrete alone doesn't have -any- 'stickiness' to it. it only bonds to old concrete as far as it can key into it.
anyway, we always use bonding agent (water based) and/or rebar keys for placing new conc. against old.
GO
I mis-sread the 1/2" to say 2" somehow.
For that thin it definitely needs to be a patchcrete floor leveling typ compound that is mostly fines and dsigned to have non-shrinking properties. It sounds like he is attempting to do this like stucco on a vertical surface. Keeping it moist with damp burlap or a plastic sheet as has been mentioned will help. Keying will too. But it can be done with leveling mix and bonding additive. Clean etched surface is essential if no keys are cut and helpful if they are. The keys provide a mechanical bond while the additive provides something close to a chemical bond.
In my understanding, the action of cement particles is like this;
Under a microscope, you see the cement particles as miniature suction cups because they are tiny marine skeletons broken up. Picture how many larger shellfish have cup-shaped skeletons. Clams, oysters, mussels, snails.
So by adding water, you activate the suction cup properties of all these millions of particles.
Adding more portland to a mix makes it 'stickier'
Adding too much makes it more brittle tho'
I don't know how scientific this description is but it helps me understand it.Excellence is its own reward!
The two concrete subs that I have worked around have different approaches for overlays.
One insists that the slab be mechanically "keyed" to make sure the patch bonds. Kerfs cut with a concrete saw or side grinder and sandblasting are his favorites. Where dust is an issue he uses acid to etch the slab. To this prep he trowels over a stiff custom mix of what looks like concrete without much aggregate or mortar mix. This he floats smooth and then covers with wet burlap and a tarp.
The other is a firm believer in bonding agents, latex primarily but I thought I saw him using an acrylic version once. After cleaning, sweeping and wire brushing or chipping any glazed spots he applies the bonding agent mixed with water. This he allows to dry. When he is ready to apply the patch he applies a second coat of bonding agent with water and fortifies the concrete he uses substituting the bonding agent for much of the water. Toweled smooth he covers the patch with plastic.
Both ways seem to work and neither show any signs of parting with the original slab. One seemed pretty messy but more of a sure thing. The second looked better to me for small jobs. I can't say I might not have missed a step or two but from what I saw done this is a fair outline of two methods that saw work.
I agree with piffin about quickcrete. It's good when used for very small, rough concrete work like fence posts, a slab for an AC condenser, or something along those lines, but not very good for what you want to do.
None are of your quetions are stupid either, if you don't know it's worse to keep trying without asking for help. Everyone here seems to be giving you good information that you can run with.
For your prep work I also agree with JS that you will need to remove as much of the old paint as possible. You should not have to remove every last spec of it, but getting the majority of it will improve the chances of a good bond with your new coating.
What you use the next time around will depend on how much money you are willing to spend combined with how much time you have, and it doesn't sound like you have much time to spare. The somewhat expensive, but time efficient way to go would be to use an epoxy self leveling coating. There are serveral on the market and after doing a search on Yahoo I found 64 links to websites for self leveling flooring. If you don't feel comfortable using an epoxy product (or don't have the stomach for the awful smell put out by the resin, that stuff can be very potent) you can always stick with a mortar mix
As was mentioned by someone else you will want to rough up the surface with something prior to putting down your new coating. The easiest and least labor intensive way is to use muriatic acid broadcast from a sprayer. If you do this make sure that if there is any plant material in the immediate area (grass shrubs or flowers) that you wet the ground down heavily before starting. Mix the acid 4 parts water to 1 part acid (someone correct me if this sounds too weak.) Read the label on the acid container it will probably give you a mix ratio for various tasks, light, heavy, etc. Spray the acid on the concrete evenly in one coat, like you would spray paint something. Let the acid sit on the concrete until it starts to dry (roughly ten minutes). Then hose it down heavily with water. Let your hose just pour out water steadily and don't start spraying it off until after the water has sheeted over the surface for several minutes. If you have ever killed grass with gas or chlorine the muriatic acid will do the same thing so also make sure to hose down the ground area around the porch heavily after. You don't have to make mud puddles, just make sure the ground is saturated before and after you apply it.
You may want to try the acid etch on the old paint surface then after you wash it down and nuetralize the acid you can wire brush it to remove the majority of what is left.
If you decide to go with another mortar mix talk to a material supplier in your area. Don't go to Home Depot or Lowes or some place like that. People educated in various trades working at those type places are few and far between. Go to a material supplier that sells concrete, stucco mix, block and other concrete products. They can answer any other questions you may still have.
If you use a mortar mix I would also recommend the two applications of bonding agent before the coating goes down, and I would also recommend substituting the bonding agent for some water in the concrete mix. The label on the bonding agent should provide you with the right amounts for substituting it for water in the concrete mix. You can use either latex or acrylic bonding agent, they will both work fine. The acrylic mixes tend to make the mix harder when it cures and some companies even add additional hardener to the dry mix.
Good luck, and let us know how it goes.
jesus, what did i get myself into? maybe i should just stick to guitar.
thanks for all the input folks. i'll keep you updated if i ever get around to doing this before it gets cold again.Remember when War was just a card game?