Dry stack block

[azgreg]

I was reading (again) JackRabbit's build thread and I see that he used dry stack blocks for his crawl space foundation. Here's his build thread: http://countryplans.com/smf/index.php?topic=13714.msg179148#msg179148

What are the pros and cons of this method?

[low277]

I am interested in this as well.  Does anyone here have any experience shallow frost protected foundation walls as they would be used in a crawl space?  I have read about it but the information is a little vague in regards to a crawl space.

[Don_P]

Better in shear and out of plane but since they are not bedded worse compressive strength. When this was first brought out they were going to introduce precision block to be used with this method. They never did, so some shimming may be needed to keep things true. Surface bonding cement is a good bit more expensive than morter and is no joy to work with. That said when I lay block I usually grout it full because I'm not a good mason.

low277 have you read the codebook section of FPSF? Chapter 4 I think.

[NathanS]

I'll throw my 2 cents in after laying a block foundation the old fashioned way, having never done any masonry work prior.

The hard part is moving the blocks. They are heavy.

Mixing mortar (I did about 100 bags by hand), laying a bed of mortar, and buttering the ends of the blocks is probably less work than actually having to move all the blocks around. I found it to be good honest hard work, but did not feel back breaking to me, but maybe I do have a little coal miners blood running through my veins. I could see how guys that have done it for the past 20-30 years are broke down.

I actually really loved doing the masonry, and am looking forward to doing more in the future. I really want to try my hand at stone masonry.

Here's the thing with 8x8x16 blocks, they are actually 3/8 small in every direction. So if you want a 20 foot wall, you are going to have to use a diamond blade to get there.

Another thing, none of the blocks are perfectly square and they all have minor defects. When I was squaring my foundation before laying the block, I stacked 3 blocks perfectly plumb in each corner to take my measurements and make adjustments. Even at three blocks high, I had shims sticking out every which way to get plumb. Another decent example would be to go into the lumber yard and stack 6 blocks (4 ft - 3/8" * 6) and just eyeball how out of plumb it is.

I think mortar is the way to go for truing everything up, and you are basically making minute adjustments with every single block you lay.

Once your corners are built and correct, you then stretch lines of string and 'lay the block to the line' for each course. The tension of that line would pull a dry stacked block out of plumb, so you would need to rig something up to prevent that.

I'm guessing those precision blocks were never introduced because they are impossible to make. The same thing is true with brick, they are warped and all slightly different sizes.

Finally, masons have been using mortar for thousands of years.. might be something to that. The worst thing about mortar is that it is caustic... I have a scar on my knuckle that is all built up like 1/8 of an inch scar tissue, because the mortar kept getting on it and tearing it up. Felt like acid.

All that said I am not saying that the dry stacked foundation is any weaker or worse than the traditional, I just think it's got to be more work.

[low277]

Don_P thanks for the lead to the code reference. It's a lot to absorb but I'm used to reading code although it's mainly NFPA 70!  I do have some time to read and review before the snow melts!   😀