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-   -   Repair vs. Replacement of Concrete Stoop (http://www.houserepairtalk.com/f17/repair-vs-replacement-concrete-stoop-11902/)

LindaB 08-07-2011 09:19 PM

Repair vs. Replacement of Concrete Stoop
 
5 Attachment(s)
Hello,

I confess I am not a DIY-er when it comes to concrete, but would very much appreciate some advice so I can hire the right contractor. I have an 8-step concrete stoop. The sides are falling away and the cinder blocks inside are deteriorating.

Iíve had 2 estimates so far. The contractor that does only concrete wants to demolish the stoop and build a new one. The 2nd contractor is a mason and wants to replace the bad cinder blocks, repair the side, install field stone on side and risers, and flagstone on steps. The price is about the same as replacing the porch, but would be more attractive.

Iím just concerned that repair vs replacement might not be structurally sound. How can I tell? The porch is about 58 yrs old and seems solid but does have a crack between the top riser and step, and someone evidently tried to repair a corner of it before. Photos are attached. Thanks for any advice!

Linda

RocLok 08-07-2011 10:13 PM

I can not tell from that photo if that post (that had the base cracking out) is the railing or if it is a support for the roofing above. That would change my thoughts slightly.

So the next question is which look you prefer. The completely new concrete porch may crack in a year regardless if there is not a perfect mix of water to cement, enough rebar, not enough compaction etc… Concrete loves to crack, that is just the way it is. The block wall you have now seems to be holding, the mortar may be failing and mostly it is the skim coat over the block that is cracking. Again concrete cracks so no surprise that it is cracking. Having the fieldstone and pavers installed over the current system would look good, and the cracks would be around the inserted stone so it could look good for a potentially longer time. On the other hand if the concrete is prepped and installed perfectly it can last over 100 years without cracking.

It looks like your system now is block wall, filled in with rock or dirt then there is a slab poured on the top, the corner of that slab has failed near that post. If you repair the system you have now you may want to have that corner cut out and cut back farther, the base material compacted further then a new corner slab poured, wait a week or two then have the overlay done. Concrete cures a lot over the first few weeks then the final cure happens over the next 30 years. As it cures it looses hydration and it shrinks, if it does not have proper joints it will pull itself apart and cause cracks.

Either way you go you will have a new system that could fail later (sorry) but will be better than you have now. If the cost is the same it just depends on which look you would prefer. Both systems can work well and last a long time, solid concrete walls can last longer as long as they are supported well.

Sorry for not telling you to go one way or the other, but hopefully I helped frame your decision a little. Please post back with more questions or which way you want to go.

Good Luck,

-Ryan

inspectorD 08-08-2011 05:07 AM

Well
 
I would go with replacement. Those blocks are what we call cinder blocks, which are basically junk over time.
I would remove it all, and replace it with a wood porch if that is possible.
Good luck, and get another contractor out there...2 is never enough.:D

LindaB 08-09-2011 09:08 PM

Thanks to both of you for your suggestions! I'll let you know which way I end up going. And fortunately that post IS the railing -- not a roof support.

LindaB

BridgeMan 08-10-2011 08:36 PM

Something that hasn't been pointed out before--the corner failure of your stoop's top slab is likely a result of corrosion of the embedded steel pipe sleeve for the railing post. When steel corrodes (rusts), it expands and greatly increases its volume. With moderate corrosion, the concrete surrounding the sleeve has been put in tension, resulting in the cracks. Concrete is very weak in tension, but quite strong in compression. There may be other, contributing factors as well, but you will continue to have corner cracking problems unless the railing sleeves are replaced with a corrosion-resistant material.

If it were my house, I'd go with rebuilding what's already there and dressing up the sides with fieldstone and maybe using tile on the steps and top. But I also consider it a run project, and would do it myself, instead of paying someone serious money. It's not a particularly difficult job.

Here are a few questions you can ask any/all contractors who are giving you quotes--"Tell me the process you plan to use to properly cure the concrete (or repair mortar)." "How many sacks of cement per cubic yard of mix will you be using?" "Could you give me names/addresses of similar projects you have done in the last 5 years?"

LindaB 08-13-2011 09:28 PM

Thanks, Bridgeman - and some questions
 
Thanks for your advice. I'm leaning toward repair at this point, and field stone and flagstone.

But as long as that cracked corner has been holding for years (which it has), is there anything wrong with just putting flagstone over the top slab (including that corner) and not touching the pipe sleeves?

And if I ask the contractors those 1st 2 questions you recommended (the process they'll use to cure concrete or repair mortar, and how many sacks cement per cubic yd of mix -- what are the correct answers I should look for?!).

BridgeMan 08-13-2011 11:10 PM

Eventually, the forces being exerted on the broken slab corner could become strong enough to visibly move it. Just a small amount at first, but then moreso over time, especially when enough moisture has penetrated the crack and begins the ever-present freeze-thaw behavior. When the corner moves enough to break the bond with your flagstone topping, then the real problems begin. It may take years, or even decades, so you can gamble and try to live with it "as is." You can be sure whoever you hire to do the work will try to wash his hands of any problems that might develop, saying he's not responsible for things that may have been caused by flawed conditions present before he started his work. As an aside, have you checked the existing slab for delaminations? Easily done by taking a steel-handled hammer and dragging the head across the slab. If you hear a hollow, dull sound instead of a higher-pitched "zing." it means the slab has delaminations (horizontal separations) in it and shouldn't be used as a base for any additional topping material without removal of all of the delaminations first.

If a prospective contractor tells you he doesn't bother with any kind of cure on his work, move on to the next bidder. He obviously doesn't know enough about concrete performance to understand hydration (Portland cement particles locking onto water molecules), strength gain and durability properties to be trusted with your investment. Good answers would be "water cure," "sprayed on curing compound," or even "covering with plastic" (clear in summer, black in cool/cold weather). Doing nothing, and allowing the concrete surface to dry out before adequate hydration has taken place, is a recipe for disaster.

I have never met a residential concrete contractor who knew the cement content (sacks per yard) of the mud he orders. It's a trick question, meant to show him that you didn't just fall off the turnip truck. Most contractors will trust their concrete supplier to deliver a quality product that performs well, and that usually means at least a 3000 psi mix (5.5 to 6 sacks per yard). Your successful bidder should at least know the strength of concrete he is installing on your stoop. Also, if you live in an area with extreme cold and freezing conditions, you will want him to specify AE in the mix (air entraining)--it's usually just a few more dollars per yard, and does a great job of enabling the concrete to resist freeze-thaw conditions without cracking, by means of an additive that puts tiny air bubbles in the mix before it hardens. The bubbles enable any trapped water in the concrete to freeze and expand (inside the bubbles) without damaging the concrete.


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