Vertical Concrete Repair

[Stress02]

I need to present method and materials to repair on the vertical surface of a chipped corner at the top of an exterior concrete foundation wall.

Previously, the exterior brick veneer had a 1" overhang outside of the face of the foundation wall, but due to mechanical damage, the foundation corner was chipped such that the brick now overhangs 2" to 2 1/2". The damage tapers down to normal about 8" down vertically from the top of the wall and about 12" horizontally from the corner of the foundation.

The brick and backup blockwork at the corner is damaged and will be removed and rebuilt as part of the process.

The issue that troublems me about just trowelling on a thin patch is that the patch needs to bear weight along the vertical shear surface, and the patch is so thin there is no way to get reinforcing/dowels into the detail.

We might also need to deal with marginally cold weather as the repair may take place in late March in New England.

We can impliment any amount of concrete removal to make this a more dependable repair, so I am tempted to just chop the entire top of the wall down some significant amount and pour a cap, but lesser approach advise would be welcomed.

 

[SperlingPE]

Look at SIKA's vertical surface concrete repair product. It can go fairly thin but it needs a clean, rough surface. If you opt to go the concrete removal route, SIKA has products for bonding the new to the old. If their is a concrete restoration contractor in your area, you might want to contact them to see what can actually be done in the field. The use of some of the repair products looks simple in the brochures but in pratice can be challenging.

 

[JAE]

For a lot of concrete repairs, where you have a spalled condition, or a condition where the damage tapers off to nothing, creating a feather-edge condition in your patching material, you can usually use a proprietary patch such as a modified polymer to feather edge.

Prefereably, though, I would recommend chipping back the concrete to a minimum thickness, perhaps 1" to 1 1/2", and then patching. Even better, a lot of patch details require removal of concrete back to expose the reinforcing steel. This would be taken back to allow about a 3/4" gap between the bar and the back side of the patch such that the new material would completely surround the exposed rebar. You can also add small 9 gage stainless steel pins, epoxied into the base concrete to further tie the patch to the wall. These pins can be easily fabricated into little "L" shapes where you end up with a small hook in the patch. Plain or epoxy coated WWF can also be laid out in the patch to further help hold it together.

All these are options as to how far you want to go with the "beefing up" of the patch.

 

[Stress02]

JAE,
This is merely a frost wall, so I don't anticipate significant reinforcing steel; maybe a couple horizontal bars top and bottom of the wall, so they are not going to be of much help.

I didn't expect to feather the repair and expected to increase the missing condition.

As far as "pinning", being such a thin slice, even is cut back to 2" thick, that doesn't leave much concrete cover for corrosion protection. I am sure they spread salt on the immediately adjacent driveway. And I we couldn't count on them not salting at the building anymore than we could expect the truck to not smash through the corner of the building in the first place.

The fact that the brick overhangs the foundation means there will be significant bearing/prying on the piecr that we place there.

Thanks for your imput.

 

[samdamon]

I agree with above posts that chipping back to increase thickness of the patch is a good idea, even if manufacturers say that their repair mortars can be feather edged. I prefer to have at least 3/16" to 1/4" of thickness at a minimum. Chipping will also provide a fresh, clean substrate for you to bond to. Getting the material to bond properly is key. Make sure the people doing the work follow the manufacturer's directions on how to get good bond- usually it involves first placing a bonding agent with a limited open time or scrubbing in a slurry before placing the patch mortar. The patch also has to be cured properly to give the best chance of success, again the mfgr's directions need to be followed closely. If temperaturea are low in your area that needs to be considered. Most patch materials set and gain strength much quicker than normal concrete, which may help.

If your repair is on an outside wall and only partial depth, the cured patch material should have a coeff of thermal exp similar to the substrate, and should not form a vapor barrier. Bond strengths also vary, everybody reports them differently. Read the mfgrs data carefully. Good luck.

 

[samdamon]

Stress- Minor detail, but also forgot to say that if your repair is exposed, note that a trowel applied mortar is not going to look as smooth as formed concrete. Color will not match either, most likely. You can also "form and pump" a patch but this is usually done for deeper and thicker repairs, and is more expensive due to the addtnl labor involved.

 

[JAE]

Yes..as SamDamon says - color will be different - the modified polymers are usually a dark green when dried.

 

[Stress02]

Yes, it is slightly exposed to view.....outside face of the foundation wall with about 8" of exposure. It's in the back of the building, will be seen regularly by the crew working there, but I don't consider it to be anywhere that architectural aesthetics govern. It might be good to have it show just to remind the fellow who caused it.
Patch will be in the weather for its lifespan.
What are some material names to consider?

 

[Ron]

I agree that chipping to reasonable depth is necessary. I prefer at least a 3/4" thickness. Pin it to existing surface with screws or nails. TapCons work fine for this type of pinning. Put lots of them in there since they are easy to install. Leave about 1/2" with head exposed. Size doesn't matter much.

Agree that Sika materials are good for this application. Not only consider the Sika specific products but look at SikaDur Hi-Mod Epoxy with dry aggregate thrown in. Works well for small, vertical repairs. Consider a layer of carbon fiber overlay after all done to provide some surface protection and overlay.

 

[DaveFlax]

As long as there is good surface preparation any structural CEMENTITIOUS repair material is good. I have found that CementAll from Rapid Set is among the best. While Sika does have products that will work well in this application, I would not recommend their epoxy or anyone else's epoxy. Epoxy will create three problems in this application. First: You are looking for the patch to carry some load, but the epoxy will not carry its share because of its low modulus of elasticity. The modulus is raised with the addition of sand, but unless enough sand is added that there is actually sand to sand contact throughout, the mismatch of modulus can cause problems. Second: The thermal expansion of epoxy is much higher than cement based products and that can cause excessive stresses on the bond line and cause failure. Third: Epoxy patches look different from cemetitious repairs, so epoxy is a bad choice if aesthetics are a concern.

 

[Stress02]

DaveFlax,
Some reps suggest an epoxy bonding adhesive followed by a polymer modified cementitious mortar.
Think the epoxy bonding agent is not good?

I would sure like to make a one layer repair, but the material thickness might be up to 2 1/2" at one end and the trowel materials recommend to build it up, and as I see it, that makes for more joints to fail. We can form and pour, but that clouds which material is appropriate.

 

[DaveFlax]

Since epoxy bonding agents are so thin, the diferences in modulus and thermal characteristics do not normally cause any problems.

Polymer modified cementitious products are fine as long as the modulus approximately matches concrete.

You are right, placing 2 1/2" vertically is a challenge in one layer, but done correctly placing multiple layers is fine.

 

[Stress02]

Do the layers need to set or cure between applications?
If so, is there bonding agent between each?

 

[DaveFlax]

The most common way is to leave the first layer with a rough surface and let it set up only to the point that it will support the next layer without sagging. In some cases the first layer is allowed to harden for a day before the second layer, in which case a scrub coat of the material itself is used to enhance the bond.

Many people also use the scrub coat of the material to bond the repair material to the base concrete instead of epoxy. It that case the base concrete must be SSD (saturated, surface dry).

 

[Stress02]

Looks like SIKA is the way to go.
The company that bought MasterBuilders wouldn't give me the time of day.
Thanks all.