Does grout interlock blocks like mortar? 3

[rothbard]

Howdy, I am a dumbass DIY stem wall builder with a question regarding the function of grout in a stem wall. The stem wall is 4 courses high of 6 inch cmu (32" high, max 16" of unbalanced backfill).

I used a spec type S mortar mix on my stem wall but it seems to have poor adhesion to the block. If I rip a block out and stomp on the mortar from above anything small than 1-2 square inches are crushed by my weight. I'm guessing this means it is weaker than it should be.

Ideally I'd like to just core fill the whole wall with grout and interlock the blocks that way. The question is would this effectively act as a double mortaring in case the mortar fails? Or is there really no other option than to just knock the wall over and completely start from scratch.

 

[phamENG]

If you can rip a block out by hand, then you probably made a mistake on your mortar mixture.

For a stem wall, you should be grouting it anyway. But no, that's not what grout does. Properly proportioned and placed mortar is necessary. There are other alternatives, but they are not suitable for DIY.

 

[rothbard]

Thanks phamENG for your comment.

I have a really dumb question. Lets say a wall was built, core filled in all cores, and then all the mortar was chipped out. Would you expect the core fill hold the blocks in place?

 

[phamENG]

"Hold the blocks in place" isn't the right question. Lots of things 'stay in place'...until they don't. There's a continuum there that ranges more or less from a house of cards to the tower in Miami that collapsed a few years ago.

The better question would be: "will it reliably resist the loading it may plausibly experience during its service life?" I don't know enough about your project to answer that definitively, but chances are the answer is no, it would not.

Now, I should inform you that your post violates forum rules. This site is intended for engineering professionals to communicate about technical and professional topics, solve problems, etc. DIYers, contractors, etc. are not supposed to post here. If you need engineering services, you should hire an engineer.

Good luck.

 

[phamENG]

rothbard,

One nice thing about the antiquated nature of this site..."delete" really doesn't mean delete. All I have to do is click on "Post Deleted" and I, or anyone else, can see exactly what you posted.

As it turns out, the world isn't out to get you and me providing some insight/opinion followed by notifying you, a brand new member of this forum, of a rule you were violating, was not an attack. Now, if you consider somebody cautioning you about doing something that could get your post deleted or even your account in some extreme cases, thereby preventing you from posting here again to discuss interesting topics a personal affront, so be it. You do you.

 

[rothbard]

phamENG,

You're right. I apologize. I just felt frustrated. Thanks again for your help.

 

[phamENG]

No worries. What is this stemwall for? At 6" block I imagine not much...a shed? I've seen a few houses done with 6" block, but not many.

 

[rothbard]

IT is a 600 sq ft house small one story house. I looked up IRC 2021 and it said I could use solid 6" block (since it will have full lateral support floor platform at 32" with wood frame above). They don't sell solid block here so I bought hollow 6" CMU with the plan to grout the entire structure, but discovering the mortar adhesion was questionable is making me put a halt and refigure how to proceed. We don't have a lot of money for the house so we're doing it all ourselves, and basically with one man doing the footing mixing one bag of concrete at a time the best I could do was a footing and finish for 6" block.

 

[phamENG]

For a house, I would recommend redoing it with better care for the mortar mixture. You may want to do a few tests to get the hang of it - mix up a little bit to get a good feel for the consistency and then just bond two blocks together. Once you're comfortable, build the foundation.

If you had 10" or even 8" block, what you're suggesting may be defensible (especially if you switched to dry stack masonry with a surface bonded coating). But 6" block has a very small cavity and is too narrow for the proven dry stack techniques I'm aware of. The grouted course would be too small to depend on for what you want.

 

[rothbard]

Roger that makes sense. I will practice mortaring! At least mortar and blocks are cheap and good exercise.

 

[XR250]

Edited 11 Mar 24 16:13
I'm an ABET accredited engineer asking theoretical questions about how grouted blocks may function without mortar. I think it's an interesting question. Maybe you don't, that's fine, you're free to smugly fuck off somewhere else, you're under no obligation to say anything.
Original Post: Posted 11 Mar 24 16:12
I'm an ABET accredited engineer asking theoretical questions about how grouted blocks may function without mortar. I think it's an interesting question. Maybe you don't, that's fine, you're free to fuck off somewhere else, you're under no obligation to say anything."




Oh, wow. You are very gracious, Pham.