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Thread: Does a concrete driveway need to be sealed?

  1. #1
    Join Date
    Dec 2004
    Location
    St. Louis
    Posts
    3,287

    Does a concrete driveway need to be sealed?

    Had a new concrete driveway put in last year. My wife remembered that they talked about sealing it this Fall. After pricing sealers at HD (I'll need almost 2000 sq ft worth), I'm hoping that it isn't really necessary. Is it? Will it significantly increase the life of the concrete? By helping avoid cracking, spalling etc? Hopefully it isn't something that needs to be done regularly.

    Any guidance appreciated.

  2. #2
    Yes, the driveway definately will need to be sealed. I found out the hard way after pressure washing my drive and not sealing it. The sealer closes up holes in the driveway and prevents water from freezing and cracking in the driveway.


    Highly recommended.


    Wallace

  3. #3
    Gary, I could stand corrected, but I think the only real benefit from sealing a concrete slab is to help prevent stains and such. Sealer manufacturers will also tell you it protects from road salts and acids and a host of other evil and vile things (some of which are probably true), but as far as preventing spalling and other actual concrete failures, I don't think it adds any benefit to what you already get from a good curing compound (applied to the freshly-finished concrete).

    Of course, this is assuming the concrete was properly finished and cured in the first place. If the mix was too wet, or the finishers got a bit lazy and souped up the finish, it's a case of spalling waiting to happen, especially in a freezing climate. Sealer might help delay the problem, but I don't know if it'd completely eliminate it. In cases like Wallace mentioned, it sounds like the finish might have been a bit punky on the surface (usually from too much finishing water) and the pressure washer exacerbated the problem. Sealer very well might have helped prevent the problem, or at least slowed it down.

    I've inspected over half a million square feet of concrete slab used for aircraft parking aprons (before, during and after the pour), and unless they did it years after I left the job, that slab has not been sealed to this day. (The joints, yes, but not the slab.) It's in a freezing climate, and it's held up well, but it is stained. It was also placed and finished by a commercial crew building to pretty stiff slump and PSI specs. Homebuilders might not take as much care (or have a guy like me getting paid to watch them. )

    I guess the main criteria (besides the expense) is how important the stain resistance of this slab is to you. If you intend to use a pressure washer on it, sealer might buy a bit of protection.

    Hope this helps -

    - Vaughn

  4. #4
    YES!

    Every winter, I think about doing it, but get lazy. I've lived in freezing/snow climates, and this is what happens.

    Cold, frozen slab... Park car in driveway... Engine heat melts snow... Concrete absorbes melted snow... Refreezes... Frozen slab crumbles... Result = pitted concrete...

    This is what it will look like in two years of a frost climate...
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    Go Big, or Go Home... He who has the gold, makes the rules

  5. #5
    Join Date
    Apr 2004
    Location
    New Haven, CT
    Posts
    1,395
    YUP! It is a good idea to get a couple of coats of nasty, solvent based sealant. It should last 2-5 years. I currently have 2 coats on mine and it is still shiny from the coating.

    Dan
    A flute without holes, is not a flute. A donut without a hole, is a Danish.

  6. #6
    Quote Originally Posted by Scott Parks
    ... Concrete absorbes melted snow...
    This is what it will look like in two years of a frost climate...
    Scott, you're right about melted snow infiltrating the concrete surface, freezing, then causing the spalling you showed in your picture. But...the fact that the moisture is getting absorbed into the surface is the result of how the concrete was finished and/or the concrete mix design used. Not all concrete has such a porous surface. As I mentioned earlier, I've been involved in the placement of lots of unsealed slabs, all of which have been exposed to freezing weather (and much heavier wheel loads than your typical driveway) and these slabshave not spalled over the past 15+ years. (And they have an intentionally rough surface, which you'd think would make them more prone to absorbing water.)

    Spalling is the result of a bad finish (technique) or concrete mix (materials), and no sealer that I know of will fix these problems. I was discussing this yesterday with my dad (a P.E. Civil Materials Engineer who's been designing concrete mixes and writing concrete specs for about 50 years) and I mentioned Wallace's experience with the pressure washer. In his opinion, a sealer would not have been enough to prevent the washer from washing away the punky surface layer of the slab. To put it in a woodworking perspective, of you put a coat of hard polyurethane over balsa wood, it only makes the wood minimally more resistant to dents. A bit, perhaps, but not much.

    - Vaughn

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