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lee12 07-07-2010 07:08 AM

block fill grout
Hi everyone,

Building foundation walls with standard 8" hollow blocks and vertical rebar through the cores spaced every 4'. The spaces that have rebar need to be filled with grout. 'Grout' used in this context is new to me - my understanding is that is has very low slump so that it is easy to pour into holes without forming voids. The extra moisture apparently also allows for the high absorption into the block (again, this is my limited understanding).

My question is - how would I mix this on site? Is it simply watered down concrete? What size aggregate? I would assume that this could be specified to a concrete company and delivered as ready-mix but I'd like to avoid the delivery and small-load charges - and will also need to fill as I go in some places rather than doing it all at once when the walls are built. I see quikrete has a 'block-filling grout' mix on their website but I've never seen it in stores.

If anyone has done this on site or has a better understanding of the whole concept I'd appreciate any info you could offer.


concretemasonry 07-07-2010 08:16 AM

Grout is a high slump material. Concrete is 3"-4" slump and grout specifications require an 8"-1" slump, so it is much wetter and the maximum aggregate size is less.

The materials in grout are sand and small rock, usually about 3/8" (depending on whether it is fine or coarse grout). Larger rock has a negative effect of the grots ability to fill since the rock (or dry grout) could cause "bridging" and incomplete filling.

You will use grout much faster than mortar, so mixing it fast enough could be a problem.

Resist the urge to fill a grout cell from top to bottom. Go up about 2' - 4' and consolidate with a rebar to get out any voids. Move on to another cell.Within a 1/2 to 1 hour add some more grout, consolidate and and move on to the next cells. Finally, top off the grout and consolidate, making sure the rebar used for consolidating going into two different layers of grout. After an hour or so, go back to the wall and you should find some grout settlement due to the absorption of the excess water. Top it off again and let it work.

You can mix it yourself and tote 5 gallon buckets.

On a commercial job it would be pumped and probably come from a ready-mix truck, but there can be charges for excess truck unloading time, but that is not a barrier when compared to mixing the grout on site.

My instructions are not absolutely correct for high spec grouting, but adequate if the principals are followed on a basement. The grout itself does not appreciably increase the load carrying strength of a block wall, but the use of the grout and rbar increase the lateral strength. The steel is the flexural reinforcement and the grout just transfers the load due to soil pressure from the block to the rebar. Since you have the typical 4' spacing, the steel may be required for a prescriptive code purpose and not alway for engineering purposes unless you have high walls or wet, or heavy soil and not sand.


lee12 07-07-2010 08:43 AM

Dick - thank you for the information, very helpful. My mistake about the slump - high slump was what I had in mind but got it backwards.

You are correct about the vertical rebar - this is to satisfy a code requirement, not specifically engineered. The wall are only 10 courses high as well. This is for an addition, total size 20' x 17'.

I will fill as I go like you said every few feet and then consolidate with rebar. Thanks for the tip about making sure I consolidate into two layers of grout. And the suggestion to mix right in the bucket.

What is typically the reason to choose coarse or fine grout? Could you give me a 'recipe' with proportions?

Again - thanks. Always nice to get someone who's willing to help.

jomama45 07-07-2010 10:19 AM

I agree with all of Dick's advise.

As for grout proportions, we typically use about 25-30 round, heaped shovels of torpedo sand per 94# bag of portland.

Couple more notes:

- Check with your local codes on placement of the rod inside of the block cavity. You will want to favor the inside wall of the block, but your code may very well have parameters on the limits of placement that need ot be followed.
- Pour a quart or so of water inside the cells first ot help the grout flow. Dry block (especially 8") can aid in jambing up the care fairly fast.
- Using straight portland is the best practice, although some still see some need for a little lime in the grout for some reason. Avoid the lime.
- We mix our own grout on most smaller to mid size jobs right in our mortar mixer, which is why we use torpedo. Not enough clearance for stone. On larger jobs where we can pour all the pilasters at once, we will call a redi-mix truck and use small stone (pea gravel sived) 3000 psi for block fill. But, this is typically when were pouring 5+ yards of grout.

lee12 07-07-2010 11:16 AM

Thanks jomama, more good tips!

Footer is already poured with rebar in place. I did put each one at least 1" off center in the direction of the inside wall.

For the grout - seems that if I use 1:3 portland cement/torpedo sand with a slump of 8-10", and use the recommended suggestions I should be in good shape. Thanks for the help.

For anyone who might come across this thread in the future, I just found a good article on grout.

Thanks again

stadry 07-07-2010 06:58 PM

' torpedo ' sand ? ? ? wtf's that OR are you guys just showin' off ? ? ? :laughing:

jomama45 07-07-2010 07:12 PM

I would think you would have heard of torpedo sand before, you've been around sooooooooooooooooooooooo many years....... :laughing:

Google it, same thing as "concrete" sand or "sharp" sand.

NJ Brickie 07-07-2010 07:16 PM

Like Jo suggested fine grout may be better for you. If you will be laying block it sounds like you will have a mortar mixer on site. Fine grout will be able to be mixed in a mortar mixer, coarse grout (with stone) has to be mixed in a concrete mixer (spinning drum style). 1 part portland cement to a maximum 3 parts sand is a good ratio. Also pouring some water down the cells is a good idea. Be sure to pour it along the inside edges of the block.

kwikfishron 07-07-2010 07:47 PM

199 Attachment(s)
You mud guyís crack me up :laughing: Sometimes itís comedy at itís best. :thumbsup:
At least until that is I find myself chiseling on a stem wall or dealing with a HD bolt a mile off :furious: not that anyone here would ever put a framer through that. :jester:

stadry 07-08-2010 04:53 AM

certainly happy we can provide some humor for the fish :laughing: never heard the term either in upstate ny, the city, nj, or down here... thx, yomama, for the post,,, fish, you're welcome :thumbup:

we do grout but its all retro for the most part - bowed & crack'd masonary walls,,, normally we'll use 10 to 12,000 spec mtl & 3 #4 bars then patch the cell holes w/hydro

concretemasonry 07-08-2010 07:30 AM

Beware of grout that is too strong.

On new construction the intent is to have the grout strength equal to or slightly greater than the block strength. Some engineers put a lid on the maximum (15-20% max over block strength).


stadry 07-08-2010 09:29 AM

true, indeed, conc,,, usually our method choce's limited due to budgets,,, intent is to create strengthen'd pilaster/columns,,, have used this method over 35yrs & no complaints,,, we'll often submit pe stamp'd dwgs, too !

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