Hello!

We recently purchased an ICF home which was started but not completed. All ICF work completed, it is a one-story 2800 square foot home with a full basement. ICF construction was used on both the basement and main floor.

The drywall is up in most, but not all of the house. Along the back wall is a large window (actually 4 windows side-by-side) which were placed within a single vinyl buck. The total width of these 4 windows is slightly less than 12 feet. The bottom sill of the buck is about 2 feet off of the floor.

During an inspection of the house today, I discovered that there is a void under this set of windows. The builder of the house did not cut holes into the bottom surfaces of any of the vinyl bucks in the home. Concrete seems to have flowed completely under the bucks in the other windows of the home, which I determined by probing the areas under them. But apparently due to the large area under the 4-window set, the concrete did not completely fill it.

The area lacking concrete is approximately the middle 6' of the 12' wide window area, and about 2' in height (from the underside of the buck down to the top level of the basement level.

What is the best course of action? Can I cut an opening in the bottom surface of the buck, and then fill the void with some ready-mix concrete? Also, should I apply some type of adhesive to the surface of the existing concrete to give better adhesion to the new concrete?

Any ideas greatly appreciated!

It sounds like you have already answered your own question. Yes, cut out the bottom buck and top it up with more concrete. If you have access to a concrete drill you could drill in a few holes into the concrete and epoxy in some short pieces of rebar, but it shouldn't really be necessary.
Paul Stevens

I would consider filling the voids with something like non-shrink grout mixed to a flowable/fluid consistency unless the void area is extremely large (from the description above, this may be the case - the grout costs significantly more than sack-crete). See the following link as an example:

http://www.quikrete.com/ProductLines/NonShrinkPrecisionGrout.asp

Thanks for the responses!

Paul, I can see from a cutout in the foam block that there is some horizontal rebar in the void, which apparently is already running through the exisitng concrete, so I guess that is a plus.

arkie6, thanks for the suggestion about the grout. I checked the link out. Would the grout have the advantage of better adhesion to the existing concrete, compared to pre-mix concrete in sacks?

Also, I realize that a void under the center of a window is not the ideal situation, but is it the kind of thing from which I can expect future problems, even after I fill it with additional concrete?

Thanks again.

If you already have rebar that is partially exposed you should be fine just mixing up some sack crete and filling it up. The big concern would be having a void over the window!!
Paul Stevens

Thanks again, Paul!

I can see where a void over a window would be a problem. Fortunately, I think I'm OK there.

Apparently, the guy who did the ICF work on the house just poured the entire main level of the house, allowing concrete to flow under the windows rather than cutting holes in the bucks. In spite of the fact that he did it that way, it appears that the other windows are solid below (they are all narrower than the one in question).

There is another window which appears to have solid concrete underneath, but the bottom surface of the vinyl buck seems slightly hollow. Is it necessary to have concrete all the way up to the underside of the buck, or is a space of an inch or two OK?

Also, on the subject of probing for voids, will probing compromise the insulating qualities of the foam? If a person wanted to be thorough, and probe each block one time (using a narrow instrument), would it make much difference?

The problem of the space between concrete and the buck on the bottom of the window wouldn't do any structural harm but now you have a way for cold air to creep into your home. An easy fix would be to fill up the void (if not a big one) with spray foam.
If you have the time and patience then by all means probe away, but I truly believe it would be a waste of time. It seems like the ICF installer bid a decent job, by your own comments, having the one void under the big window isn't a huge deal. If you feel comfortable that the rest is OK I would leave it at that.
Paul Stevens

DABA78,

I think the ICF contractor and/or builder should be told about the missing concrete under the window.  Without feedback, the ICF contractor may never know and never change his ways.

Bonding agent probably is not necessary and access might be a problem, but if you want you can aid the bonding by: Make sure your concrete is warm (I am in Minnesota) wet the existing concrete under the window, no puddles, brush on a slurry of portland and place your concrete.

Paul -- Thanks for the idea about using the spray foam to fill any smaller voids I may find under any of the other vinyl bucks. I could probably drill a few access holes in the bucks to get the nozzle in. And thanks for the reassurance regarding the fact that the installer did a good job. He was building the house for himself, and appeared to have used high-quality materials in the remainder of the house. Before buying it, I checked it over pretty thoroughly, even running a metal detector along the walls to verify the presence of rebar. This void under the window eluded me at first, though.

Alton, I haven't met the fellow who built the house, but if I do have the opportunity to, I will let him know, and suggest that, in the future, he cut holes in the bucks and pour concrete directly in!

ICF Construction, I will be able to access the area pretty well, because I intend to cut an opening in the vinyl buck, the entire width of the void. It's probably a little warmer here (southern Illinois) than where you are, but to ensure that the concrete is warm, I'll probably wait until spring to undertake this.  I've heard of the expression "slurry," and if I understand correctly, it is a rather thin mixture, correct? So I will brush on the straight Portland slurry, then fill the void with concrete made from sack mix. Should the mixed concrete be of a medium consistency, or more on the runny side?

Spray foam is a good idea but make sure pressure is applied to the buck in order to maintain the same win. opening area(people tend to forget that it expands).Just a precaution.
cheers!

Fogot! Regarding the larger void looking into non-shrink grout would't be a bad idea.
Do it once do it wright.

arkie6 also suggested using non-shrink grout to fill the void.

What are the main differences between grout and sacks of concrete mix?

For starters, grout has no coarse aggregate like sack-crete and it has lots more portland cement.  As a result, grout has a much higher compressive strength than sack-crete.  Non-shrink grout that is mixed to a fluid consistency will still be ~twice the compressive strength of sack-crete.  This fluid consistency will allow it to flow into nooks and crannys better.  The grout will also provide a better water barrier than sack-crete.  The downside is that it costs considerably more than sack-crete.

I do like the idea that the grout can be mixed to a fluid consistency, so that it will flow better into any voids.

So, even at such a thin consistency, the grout will still be plenty strong when it cures?...the Website for Quikrete grout states that at 28 days, the compressive strength of the fluid version is 8,000 psi...

fill under large areas requires use of a concrete vibrator. over vibrating can cause the rocks to settle to the bottom. some people use a sawsall with no blade to vibrate small projects. comparing the total cost of your house the extra cost of non shrink grout is not much. 

I checked and found that the local Home Depot sells 50 lb. sacks of the Quikrete non shrink grout for $11.23. This is more than regular concrete mix ($2.66 for a 60 lb. sack), but I really don't need all that much...I figure that the width of the void is 6 feet, the height is about 2 feet, and the thickness 6 inches. I'll have to do a little calculating to determine the volume of grout per 50 lb. sack, so I'll know how much to purchase.


EDIT: According to product specifications, one 50 lb. sack of grout covers 0.45 cubic feet. I figured that my void is 6' x 2' x .5', which is 6 cubic feet. So, it looks like I'll need 13.33333 sacks.

If you can drill access holes you can mix gravel with your non shrink grout.  rocks won't shrink.  In commercial projects with steel columns with 4 or 6 anchor bolts the footings with the bolts are poured 2 or 3 inches below finish location.  nuts then washers are installed then you drop the column into position, loose install the top washers and nuts and adjust  all the nuts to final position and plumb.  We install a 2 x 4 frame around the column base leaving an access hole to pour in the grout.  If it's a big hole we usually added some gravel.  the mix is about the consistancy of pancake mix.  ( for pancake mix add 2 cups of mix, 2 eggs and enough milk to make it the same as non shrink grout)

I can drill access holes to fill the area under the window buck, no problem. In fact, I was going to cut a hole in the buck the entire width of the void in order to fill the area.

I will have to slightly recalculate the amount needed to fill the area, since I realized that 8" rather than 6" Amvic forms were used.

If I were to add gravel to the grout, at approximately what ratio? Also, what size gravel would be best to use?

Grout works great under columns and for small patches. For the area you are talking about and your approach to open the whole bottom of the buck up I would buy regular concrete mix and use it. Using grout is not going to benefit you in any way for what you are trying to accomplish and it is going to cost you a small fortune

Why are you doing this repair for someone else? Have the builder/installer come back and fix it, they are not going to learn from their mistake without going through the school of hard knocks.