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Old 05-09-2012, 10:52 AM   #1
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Concrete block grouting - what product and how much


I am new to this forum and may not have the correct construction terminology, so here goes..
Busy building an outdoor barbecue with concrete block and will make a counter top from concrete. I have already built the 4 walls (rectangular). The corner blocks and block midway along each wall have rebar. Now I have to grout the voids.
1. What is the best concrete mix to use? (I used Sakrete Maximizer to do my floor slab)
2. Do I need to grout all the blocks or will grouting just the blocks with rebar in them be enough?
3. What concrete mix should I use to make the concrete top (plan to tile over it).

Thanks

Gary

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Old 05-09-2012, 12:17 PM   #2
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Concrete block grouting - what product and how much


Just grout the cores with rebar in them.

Use a very wet (soupy) grout, allow it to consolidate a while (hour or so) and top it off. You really should not use either concrete or mortar for a good job even though people can get away with it in the short term.

Even big boxes usually sell bags of grout.

Dick

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Old 05-10-2012, 10:41 AM   #3
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Concrete block grouting - what product and how much


[quote=concretemasonry;917876]Just grout the cores with rebar in them.

Use a very wet (soupy) grout, allow it to consolidate a while (hour or so) and top it off. You really should not use either concrete or mortar for a good job even though people can get away with it in the short term.

Even big boxes usually sell bags of grout.

Dick[/quote


What Dick said with one exception,don't make the grout too soupy,the lower the slump the stronger the mix.

For your counter tops i'd use a mix with 3/8" max coarse aggregate.
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Old 05-10-2012, 11:53 AM   #4
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Concrete block grouting - what product and how much


Unfortunately, the terminology and use of cement based products is highly variable because they can take many forms and have different desired properties.

For grouting the cores of block, you want a very wet mix (8" to 11" slump per ACI/NCMA specifications) to insure maximum filling and coverage. The strength is not important and high strength grout is discouraged is block construction because the grout carries little load except to bond the block to the rebar. Some engineers limit the maximum strength of the grout to 2500 or 3000 psi to make it work in the structure. Grouting block is not a competition and lower strengths can be beneficial. I have seen some serious projects (20 story loadbearing buildings) where the biggest problem was grout slump that was less than 8", which is the opposite for poured concrete and bothe the engineer and contractor waned it wetter.

For grouting tile or similar applications different properties are desired, so the consistency to use it properly is the critical point.

If you are grouting column base plates, you want a special very dry grout that can be packed into the space between the plate and foundation and allowed to expand.

The problem with cement based products is the different uses, ways of using them and procedures used to reflect the properties. - That is why there are codes to protect people/individuals from themselves.

As an example, I have made block prisms (2 hollow ungrouted block laid with face shell bedding using 2500 psi Type M mortar) and the prism tested at 4800 psi. We made prisms of the same block using Type S 1800 psi mortar and the strength of those prisms was about 4600 psi. That points out that mortar strength is not important and continues the debate whether the mortar holds block together of keeps them apart.

When you build with cement based products, you are building structural walls and not just nailing different materials together. As an example, the specifications for mortar (ASTM 270) contain a note that suggests using the lowest strength possible to carry the structural loads, because high strength mortars do not possess many other more important properties (workability, bond, adhesion, etc.). Few people, outside of professionals do not bother to read or understand the reasons.

I am not a counter top expert and the methods of forming and placing can vary widely. They are not structural, so just use what local materials work since some areas have rounded aggregate and some only have crushed angular aggregate that poses different finishing problems.

Dick
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Old 05-10-2012, 01:14 PM   #5
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Concrete block grouting - what product and how much


Thanks for all the info.... I am on a mega learning curve here.... this is good.
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Old 05-10-2012, 01:50 PM   #6
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Concrete block grouting - what product and how much


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Originally Posted by howzitmybro View Post
Thanks for all the info.... I am on a mega learning curve here.... this is good.


" high strength grout is discouraged is block construction because the grout carries little load except to bond the block to the rebar."

And this is why your grouting in the first place
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Old 05-10-2012, 02:16 PM   #7
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Concrete block grouting - what product and how much


I have to agree with Dick on this one, and I believe it's fairly clear through-out the industry. You want wet grout that fills every every crevice and to ensure the grout makes it to the bottom of the cells. You do not want grout that is stronger than the CMU which can generally vary between 3-4000 psi. In this scenario, the grout is nothing more than a "cheap filler"........

If you want to keep it simple, you could buy the cheapest quikcrete (usually 4000 psi) and mix it with about 30-40% additional sand, along with making it wet.........
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Old 05-10-2012, 03:35 PM   #8
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Concrete block grouting - what product and how much


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Originally Posted by jomama45 View Post
I have to agree with Dick on this one, and I believe it's fairly clear through-out the industry. You want wet grout that fills every every crevice and to ensure the grout makes it to the bottom of the cells. You do not want grout that is stronger than the CMU which can generally vary between 3-4000 psi. In this scenario, the grout is nothing more than a "cheap filler"........

If you want to keep it simple, you could buy the cheapest quikcrete (usually 4000 psi) and mix it with about 30-40% additional sand, along with making it wet.........


Right,it's only a barbecue

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