Concrete over existing porch to raise porch height

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Old 06-23-12, 01:07 PM
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Concrete over existing porch to raise porch height

Hi, I have a early 60's brick house with a driveway/carport along the side and a 4' x 22' concrete porch across the front of the house. It's pretty standard for the houses in my neighbor hood. The problem is the porch sits about 5" lower than the carport it is adjacent to and is at ground level and constantly fills with leaves, dirt, etc. and rain water when it pours. The porch butts up to the bricks and doesn't appear to be part of the slab. An easy fix it seems would be to just add to the top of the porch with concrete slightly sloped away from the house. This would still leave a 3"-4" step up into the house. Does anybody have any suggestions to make this a long lasting solution to my problem. My idea was to put some rebar through the existing porch and used fiber reinforced concrete. Is there any prep to do to the existing concrete. Any type of buffers between the new concrete and the house bricks and carport concrete. Also want to tackle this job in sections, maybe in quarters to make it easier. Thanks for any input.
 
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Old 06-23-12, 04:11 PM
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Surface prep should consist of either pressure washing or even sand blasting, to remove any/all dirt and debris that could inhibit a good bond between new and old concrete. Roughening the surface with a bush hammer would be better yet. You'll probably be batching in a rental mixer, being such a small quantity-placements. Use a neat Portland cement slurry bonding agent applied to the moistened existing concrete and broomed in, vigorously. You're wasting your $$$ adding fiber reinforcement to the concrete. Use joint filler at abutting brick or concrete surfaces.
 
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Old 06-24-12, 11:48 AM
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Thanks for the info Bridgeman. I don't know very much about concrete so this all new to me. So there is no need for rebar to help anchor each section to keep it from shifting. Also no need for mesh at only 5" thick correct? Thanks.
 
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Old 06-25-12, 02:58 PM
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If you properly bond the new concrete to the old, as I described earlier, there will be no need for any kind of steel anchorage. If it will make you sleep better at night, then by all means go ahead and do it. Structurally speaking, totally not necessary. The above bonding process has been used by state DOTs for more than 35 years to bond thousands of thin concrete overlays to bridge decks all around the country if not world, where they have to resist the forces exerted by 80,000-lb. trucks moving at 70 mph. If your porch loads exceed that, then yes, you should do some additional anchoring. Regarding the internal mesh question--the relatively small dimensions of your individual placements, along with the solid, non-yielding base below it, will act to minimize internal cracking. Properly mixed (6-sack +/-), placed and cured concrete at 5" thick, shouldn't require any mesh or other internal reinforcement. You may wish to add grooved control joints directly over any joints (contraction, construction, or expansion) in the existing base concrete, because those locations are likely to show reflective cracking coming up through the new overlay.
 
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Old 06-25-12, 05:10 PM
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Thanks again Bridgeman for the info. Gathered some info on tools and stuff from your first post and now after your second I feel pretty good about the project. Can't wait to get started. Thanks again.
 
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Old 06-25-12, 11:56 PM
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Glad I could help. A few more hints:

1. Make sure to vigorously spade the mix everywhere, especially up against the sides and forms. Doing so will minimize the chance of entrapped air pockets.

2. Don't batch your mix too wet--you want it somewhat stiff, as opposed to so wet that it flows everywhere. Scooping up a shovel-full should result in a small mound, standing up.

3. Biggest mistake most newbies make is over-working the mix. After you strike it off with a 2 x 4, hit it with a wood float or darby, then let it sit until the bleed water evaporates off. Since you're pouring on a dampened, concrete surface, that may take a while. Be Patient!

4. With surface bleed water gone, you're ready for the serious finishing. Use a mag hand trowel (a rental bull float would be even better), use broad, sweeping strokes to work the surface imperfections down into the mix. Fill any low spots with a few dabs of fresh concrete, and work those in. Hit the edge at your separation form with a nice edger (I prefer 3/8" min.), bearing down hard to compress the mud and get a nice, smooth corner. Then knock down the ridge that develops next to the edger with the mag float. I wouldn't edge at the expansion felt along the sides, it's just more work that doesn't accomplish much--just finish up flush to the tops of the joint filler.

5. If you really want a durable surface, hit everything next with a steel trowel to bring up the last of the fines and create a hard, smooth and tight surface. You want the trowel to actually sing to you, giving out a "hissing" sound as you make broad, sweeping passes with it. As in any hand-floating, lift the leading edge while bearing down with the trailing edge of the trowel.

6. To keep the surface from being too slick when wet, you should give it a textured finish. I prefer a pass with a stiff broom, bearing down hard to make some definite impressions (as by now, the concrete surface will be getting a bit firm). A stiff rubber hand float can also be used for this, working in repetitive "wavy" patterns across the porch.

7. Cure can be accomplished by using a fog spray of water every few hours, or better yet, spraying some Kure-N-Seal with a garden sprayer in counter-directional passes (2 coats, at right angles to each other). Doing the latter will result in the best-performing finished product, because moisture required for proper cement hydration (and strength) is sealed in and can't evaporate.

Good luck!
 

Last edited by BridgeMan45; 06-26-12 at 01:38 AM.
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Old 07-12-12, 04:41 PM
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Hey, thanks again for all of the info. So many details. Just to clarify...mix up bonding agent/cement mixture, apply to dampend concrete, brush it in with a stiff brush, and pour new cement over it while its still wet. Correct? Of course after conditioning the existing concrete with a bush hammer and cleaning it thoroughly. Also noticed I have a crack running from outer edge to wall, probably caused by a tree root. I'm going to dig down and cut the root in front of the porch to keep it form getting any worse. Should I cut out a section of the porch in way of the root and replace that first before adding the new part on top. Thanks again.
 
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Old 07-12-12, 08:05 PM
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If the tree root crack is no longer "working" (with your cutting it off, essentially killing it), I'm not sure you need to do anything to it. Doing a full-depth removal/replacement would be double insurance, I guess. If it is straight and perpendicular to the house wall, you could just form a segment joint over it, or even groove a control joint over it should its location not be conducive for an end form.
 
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