Grouting for masonry repair

[samdamon]

I need to strengthen an unreinforced existing 8" cmu wall for bending. The wall spans vertically. Would like to cut open a set of vertical block cells from the interior face, insert and tie in vertical reinforcing bars, and then grout the bars in place with a hand applied grout mix or patching mortar.

Is there a grout mix or patching mortar out there that can be used for this type of repair, and be applied with a trowel and not need forming? Using a traditional 8"+- slump grout will require forming the inside face of the repair area, and grouting in lifts. Or, other option is to pump the grout in from low to high, but I need to keep this particular repair low tech if possible.

Any help appreciated.

 

[jheidt2543]

Using an interior or exterior pilaster is out of the question?

 

[samdamon]

JHeidt-

A pilaster is another potential fix but its not preferred for architectural reasons. Would like to keep the interior face of wall a single plane.

 

[amokhta]

You may want to consider reinforcing the wall externally by applying carbon fiber strips or even steel bars/plates to the face of the wall without cutting the cells open and without need for grouting.

 

[samdamon]

Amohkta-

Not familiar with either method you suggest but my gut is that using carbon fibers or adhered plates would be pretty expensive and high-tech. If adhering steel plates, how would they be attached? Regards.

 

[amokhta]

You can bolt narrow steel plates (say 1/2" thick and 6" wide) to one or both faces of the CMU wall (depending on the loading condition). If steel is attached to both faces, through bolts are the best way of attaching them, else use masonry epoxy anchors. Anchorage shall be done in CMU units with filled core cells.

 

[samdamon]

Amohkta- Catch 22, the cores are typically hollow at present. If I have to grout some cells to attach the plates, might as well put bars in and be done.

What I'm really looking for is a trowel-applied patching mortar or grout that will not need forming.

Thanks for your post.

 

[Wrightguy]

How about using some heavy gage metal studs spaced as needed (8",12" or 16" o.c.) along one or both sides. You could fasten them to a
8" channel along the top and fasten them into slab on grade.??? I'm not sure of your top of wall condition?Through bolting could work for the channel too....(Of course this would have to acceptable to the Architecture??)

Just throwing that idea out there. Maybe someone could expand on it.

Not knowing the particulars is the real stumbling block around here..but the ideas that your collegues will come up proves that this web site is great!!!

 

[Ingenuity]

SamDamon,

Re trowel-appplied patching mortars there are many available and the characteristics you require would be similar to a reinforced concrete repair in a vertical application. Check out Master Builders or SIKA web site for actual products.

BUT...I think this will be a big challenge to do this - opening up cells in vertical runs x 1-cell width at a spacing as required, then install rebar (central to cell?) then trowel apply and get good coverage around the bar circumference and length (especially the back of the rebar in a small cell width) will be a bit more than "low tech" in my opinion.

If you open up "columns" of vertical cells from one face, install the rebar, I would use a low-velocity spraying technique (not shotcrete as such) with a pre-bagged cementitious mortar to adequately embed the rebar - then "knock down/trowel" the finish to achieve the desired face finish. This technique will probably NOT be cost effective if the project is very small, but if more than say 100 linear feet of rebar embedding I would think it would start to become economic.

There is a exterior applied cement-based plastering system that uses fiberglass reinforcing to strengthneing walls for in and out-of-plane loads...POLYPLAST STRENGTHENING SYSTEM. Do a GOOGLE search and it should direct you to the site. There is also a Design Manual in PDf form available. The system was developed in New Zealand (for E/Q retrofits) and has had extensive testing. We have specified it before in a very remote area in the Pacific with a labor force that previously had no experience so it is easy to apply by masons. I know it is not what you asked for, but may be worth considering. It is certainly less destructive than opening up CMU cells.

HTH

 

[samdamon]

Hth-

Will look into it. Thank you all for your comments.

 

[PEinc]

SamDamon,

Amohkta and Ingenuity had good suggestions about external carbon fiber or fiberglass reinforcement.

Go to

http://www.thereinforcer.com

for additional information.

 

[scofie]

Not sure what the height of your wall is, but here is an idea. Since 1998, the ACI 530 Code for masonry has included a chapter on prestressed masonry. I know because I wrote the chapter. You could open up two top CMU and two bottom CMU faces, thread down a prestressing bar the full wall height, grout solid the CMU above the bottom and below the top of the prestressing bar (use a sleeve for the bar through your grouted block), then when grout is hard, post-tension the rod per ACI 530 requirements. Hence, you eliminate full height grouting, you are much safer because you have not cut a continuous vertical swath of CMU face shells (which I am concerned about per your stated plan), and I bet this will prove the cheapest option that maintains the CMU wall face. Dur-o-wal sells the necessary prestressing hardware you will need.

I believe that the overall cheapest option is likely cement plastering a reinforcing mesh on both faces, or composite carbon fiber-epoxy mesh sheets adhered to the face of the wall is also a cheap option, but you mentioned these are not the desired options aesthetically.

 

[tamu]

If masonary wall is situated in a coastal or corrosive enviromental area any attempt of reinforcing by steel or prestressing wire will create problem in future so take care before you decide any method.