Don’t Know Much About Concrete Block…
I am building a 10×12 pump house on a thickened edge slab. It’s in the woods and there’s a slight incline in the terrain in back so I thought I’d put a row of concrete block all the way around to get the siding up off the ground and two, maybe three rows in the back. The soil is very sandy, so it drains beautifully, and hydrostatic pressure against the wall won’t be a problem.
I have just about enough 4x8x16″ block left over from the chimney to do the entire job, but I’ve never used block for a foundation like this, and I’m wondering if I should go buy 8″ block instead. I’d like to use what I have on hand, but I don’t want to build something substandard.
Any opinions? I know some of you folks use block all the time. What do you think? Thanks – Jim
Replies
I'm not a mason, but I want to add an idea to yours to see what the experienced people would say.
As a compromise, how about making an 8" thick wall, but using many of the 4" blocks back to back just to use them up and save some money. I would think the entire top course should be 8" block, as well as the corners and door opening. But I'd think you could use doubled 4" block elsewhere on such a light building.
What do you guys think?
If I were you, since you're only going 2 courses high I'd pick up some extra long anchor bolts and go continuous from the footing right up through the sill. You'll have to lay out the locations carefully so they fall within the cores of the block. Those cores should be filled with concrete.
Jim,
I did this about 20 years ago on a property that I still own ( now rental ) I think this is what they call "partition block" The wall I built was neither structural nor load bearing - it was under a post-and-beam carport roof. I ran three courses of the 4" block then framed the wall conventionally.
I chose the 4" block because space was at an absolute premium, and it worked out very well for a 22 foot wall. Sounds like your application would be just as good. It's not a terribly large structure, won't be occupied, and, structurally, the smaller block would support the roof structure and wall framing just fine. Hopefully it's hollow block, and you can fill the cores.
Greg.
Edited 10/1/2003 1:45:22 PM ET by Greg Gibson
Jim, I know this isn't fine homebuilding (and we have no seismic considerations here), but back in the days of yore when I started building, most single storey houses over crawl spaces simply sat on "curtain walls." Just bricks on a footing. 2x4 PT mudsill fastened on top of the bricks with cut nails.
30 years later, and those places are still there. Now this really is a pump house, right? 'Cause if'n it were a still, you might want to make some provisions for accidental lift off<G> EliphIno!
As has been suggested for what you're doing, the 4" block is probably fine. I'd probably hammerdrill in some 1/2 holes in the slab (make sure of your block layout) and drive in some short #4 rebar stubs. Fill the cores with sakrete and Tamoseal the exterior to keep the H20 out.
Jim , You will be fine with the 4" block . Buy your self some 3/4 longs for your corners (4x12x8 ) or some half highs (4x16x4) cut them in half (4x8x4) to make the 4" block into an 8" Or even better ,if your block supplier has 4" return blocks get them and save some agrivation.
I rebuilt my dads pump house foundation two years ago , top three courses . They suffered damage from the snow plow and a leaky roof .
It has held up for over 50 years with 4" block 5'x5'x 6.5' deep
Geez, this is encouraging. Thanks you guys.
I stabbed several verticals of #4 bar into the edge of the slab when I poured it, leaving the space for the 6' sliding door clear, so I'm not worried about shear. I was mainly concerned with "tipping".
Heck of it is, today I asked at the lumber yard and 8x8x16" block is only about a buck and a half/block. I only need about 40. But that is almost exactly the number of 4" block I have left over and I like the idea of using what I already have instead of letting it sit around ten more years until I get around to building that smoke house...wait a second...now THERE'S an idear!
3/4 block, huh? I like the sounds of that.
Depending on how you wire that pump you could make it a a twofer, pump house and smoke house.
...maybe a black light...
If I understand you correctly, you are concerned of overturning or bending of the starter courses of block due to soil pressure? So what you basically have is a short retaining wall? If it's less than a couple of feet tall, I wouldn't worry about it, although an 8-inch wall would make me feel much more comfortable. Just make sure you grout the vertical cells with reinforcing in them, and it wouldn't hurt to have a bond beam top and bottom with horizontal reinforcing in the grouted cells. (You'd need bond beam units, though.) The horizontal reinforcing will tie everything together. You mention that the soil is sand and drains which is fine, but water makes up about 1/3 of the total lateral pressure exerted on a retaining wall in an undrained (where you don't have weepholes though the wall or a french drain) situation. The soil pressure, makes up the other 2/3.
I don't remember the right term, but suggest u consider "ladders" between the rows.
these ome in configurations that look like ladders and one where the interiors are zig-zag.
these help ties the units together
if the slab isn't there yyet considere putting in a key way where the blocks will go and fill with cement when done, along with cores.
not a mason, my experience is in building a 100' retaining wall w/12" blockbobl Volo, non valeo
Around here the ladders are called durawall.
Hi Jim.
Seems like everyone is giving you the "thumbs up" on this one, so I hate to be negative, but how about you return those 4 inch left-over block and buy the 8 inch stuff? A $1.50 per 8 inch block is pretty much the norm. If your supplier lets you return the 4inch stuff, the total cost difference would amount to you paying something like $20 - $25 for the 8 inch block.
I'd go with the 8 inch block.
And, before opting for the 4 inch, I'd rather opt for no block at all ( use PT sill plates, bolted to the slab with 3/8 or 1/2 inch wedge anchors) Cover the bottom 16 inches or so of your plywood sheathing with felt paper and metal lath, and then parge this with B-Bond ( cement with chopped fiberglass spread on about 1/4 inch thick) The B-bond is waterproof when cured. IMHO the bolted wood plates would withstand racking far better than if they were perched on a 4 inch block.
As for "curtain walls that was earlier mentioned...I've seen that practice firsthand...that's how my original garage structure was built....it was racked so bad that I took a chainsaw to the structure and built a new garage...using a thickend slab and 2 course high, 8 inch block...with my framing on top of that. The block cells were filled, and I used 1/2 inch all thread rod every 4 feet embedded through the block cells and into the slab itself. The all thread bolted down my sill plates. The block were never mortared in place, they had a coat of B-Bond on both face sides and the bottoms were glued with construction adhesive ( I'm not too good with mortaring block) That was 7 years ago...building is single story, 24 X 36...it hasn't moved; period. No cracks, no racks, no nothing.
For less than $65 ( if your supplier doesn't give you credit on the 4's) why fool around? Unless this building is for your personal use only and you feel like experimenting.....then, what the heck...its your dollar.
Davo