# how to fill in voids/gaps after removing forms from concrete pour



## jogr (Jul 24, 2007)

Use mortar and a trowel. Next time vibrate the concrete to avoid the void.


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## concretemasonry (Oct 10, 2006)

It is good that you formed a groove (or appears to be) for use as a drip line on part of the cap.

It is tough to vibrate a concrete cap sitting on to of a wood frame box. A wetter mix for the concrete would be better, but there wll always be some leakage downward.

Dick


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## Mort (Nov 26, 2008)

Go to your favorite home store and get a sack of stuff called "parge." It's used to fill in rock pockets on formed concrete placements, such as walls. 

I've never used it, but I imagine applying it with a trowel would be the ticket. 

Next time, as was mentioned, pour it wetter, and smack the forms with a hammer. That'll eliminate most of those rock pockets.


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## de-nagorg (Feb 23, 2014)

A rubber hammer. And not aggressively either, you risk knocking it apart before it sets well.


ED


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## hardmat (Aug 8, 2014)

Thanks Mort for replying to the question. I appreciate your recommendation of the product 'Parge' and will look for it at my big box store.

Do you or anyone else have any advice regarding how soon I can begin the repair using the Parge product. This concrete I will be working on is only 1 week old. does it need to cure completely before I add additionally product to it or is it ok for me to add the Parge product right now? If anyone knows for sure, let me. know. 

The directions on the product say it can be sanded - what tool is used for this and if its just a block and sandpaper setup, is there a special sand paper to use on concrete and if yes where do I purchase it.

I'm still looking for an answer regarding the use of a grinder on a sharp concrete edge. Is the concrete grinder disc used like a regular metal cutting disk where the outside perimeter of the disk is the cutting edge and not the sides of the disk, using it as a sanding type of application?

thanks
Tim


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## Canarywood1 (May 5, 2012)

The forms should have been stripped the next day and grout applied, now you should use a bonding agent or mix cement with water to form a slurry, and paint on before applying the grout or parge in this case.

As to the grinding of the edge, use the flat side of the disc for grinding.


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## stadry (Jun 20, 2009)

woody, for grinding, why not the carborundum rubbing stone ?


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## Canarywood1 (May 5, 2012)

stadry said:


> woody, for grinding, why not the carborundum rubbing stone ?


 
OP said he wanted to use a grinder with a disc.


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## hardmat (Aug 8, 2014)

I am not partial to grinding, I just don't know anything about sanding as mentioned previously. Is a carborundum stone preferably for smoothing surfaces...more controllable, finer final surface? Where can I get one?

Fill me in on the pros and cons guys...I don't know thats why I am asking.

I applied a Quickrete product call Fastcrete to the voids today. It was recommended due to low slump characteristics and ability to be used on overhead surfaces. It went on pretty well but just a base coat...finish coat to follow tomorrow. It specifically said not to use a bonding agent so I just used water in the mix. I did not clean the surfaces because they were clean already (had saran wrap between them and the forms) and the forms just dropped off when I unscrewed them.


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## hardmat (Aug 8, 2014)

I see home depot has a 20 grit silicone carbide rub brick - 6" x 3" with handle for $12.00 Is this essentially the same thing as the carborundum stone?


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## stadry (Jun 20, 2009)

that's it :thumbsup: $ 9.87 @ lowe's, tho ( jk :laughing: )


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## hardmat (Aug 8, 2014)

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I did a rough job of filling/smoothing out the aggregate voids. This picture gives you an idea of it but the the sun was too bright for much detail.

I used Quickrete Fast Set Mortar. It worked pretty well. I choose it due to low sag for the overhead work and having to build out (sculpt) some corners and edges. It was a hot day, about 90 degrees, the limit for the conditions suggested to use the product. I mixed it in very small batches. It was hard to put it on thin and it seemed a bit crumbly probably due to the quick set up time and air temperature. It did harden however and stuck well to the concrete already in place without use of bonders. I used a grinder wheel and the Rub Brick to smooth things out later. Both of those worked well too. I am tempted to go back and do some more smoothing work on the rough areas but that will have to wait for now. 

Can anyone recommend a sealant for the concrete and mortar after it has all cured? Is it generally applied by brush or pad or sprayed on (aerosol can)? 

I plan to use a razor knife to cut at the concrete level on the top of the chimney cap, the pink foam insulation that will act an expansion joint. After I cut out the pink foam, what kind of caulking do I use to cover it along with the edge of the clay chimney on one side and the concrete on the other side of the foam layer.

Any advice would be appreciated. thanks - Tim


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## stonecutter (May 23, 2014)

Make a paste with acrylic admix and Portland....slurry in multiple coats.


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## ovexi (Aug 13, 2014)

please disregard this post. thx


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## hardmat (Aug 8, 2014)

Stonecutter - the slurry of admix and portland you recommend, is this for sealing all the surfaces of the chimney cap or for covering the foam material between the concrete and the clay chimney?

If for sealing all the concrete surfaces, do you brush it on once the slurry is made?

What caulking product, that can expand and contract, would you recommend to keep water out of the joint created by the pink foam between the concrete cap and the clay chimney?


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## stonecutter (May 23, 2014)

It's to fill all the holes you have in the casting. Mix some Portland with the acrylic to a thick clay like consistency and push it in by hand( with rubber gloves on ) and once all the voids are flushed out, you can shape the coating with whatever you are comfortable with...tape knife, mud trowel, mortar trowel...etc,etc.


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## stonecutter (May 23, 2014)

Use any high temp silicon that is exterior rated for the expansion joint.


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## hardmat (Aug 8, 2014)

thanks stonecutter for the additional info and instructions !

One more question - after everything has cured, should I be sealing all this concrete before the winter weather or is it good to go just like it is now?
If sealing is recommended - what product would you use and how do you apply it?


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