Replies

1. 
   rez | Sep 01, 2002 12:03am | #1

   Good Lord, that's called a workin' man!

   Half of good living is staying out of bad situations.

2. 
   69firebird | Sep 01, 2002 12:11am | #2

   Dampen the blocks..........

1. 
   joeh | Sep 01, 2002 12:23am | #3

   I thought of wetting the blocks, but how wet? Water evaporates quickly, think I'd need an umbrella for shade and switch the grunt to the hose instead of the mixer. Why do they call these things "Lightweight blocks"? Too old Joe H (Getting rapidly older too)

1. 
   coonass | Sep 01, 2002 01:04am | #4

   JoeH,

   I wish it was that cool down here. Wet your blocks. Set up a mister. An old blower out of H&A with a piece of pvc connected to hose sitting in airflow. Drill some 1/16 holes in pvc. Blocks happy, Joe happy.

   KK

1. 
   joeh | Sep 01, 2002 01:42am | #5

   KK, If wet blocks are happy blocks I'll be happier. This is the wrong time of year for this crap. Form boards turned from nice straight KD lumber to propeller stock, water level was boiling I think. Rebar hasn't melted yet though. Press on, Winter is coming. Feeling better, Joe H

1. 
   Piffin | Sep 01, 2002 01:52am | #6

   You should almost always prewet the block. Light weight plus hot dry weather jusy make it three times as necessary.Excellence is its own reward!

2. 
   Mongo | Sep 01, 2002 09:03am | #7

   Joe,

   I used to live in Tucson.

   When the temp was high and I had to work outdoors, I rigged up misting heads on sections of 8' pvc pipe. I had four of these. An 8' pipe with a head threaded on one end, a cobbled "X" on the bottom for stability. They were rigged so they could stand straight up, I'd space them about 15'-20' or so apart. They were connected by lengths of garden hose that fit onto male/female fittongs on the bottom of each 8' pipe. Total cost was only about $45 or so for all four and the hose.

   It'd cool the work area by about 20 degrees.

3. 
   IronHelix | Sep 01, 2002 02:03pm | #8

   Most premix is a little weak in the cement department........ditch it  or add your own extra masonary cement to achieve a "more buttery" mortar to work with on the christened blocks.

   Some brands of premix use whatever grade of sand is least expensive or most available..................and that means the mix is not necessarily of the correct consistency to be good to set block with.

   Locally the masons mix from scratch and are selective of the source and type of sand that they use.

   ..............................Iron Helix

4. 
   BKCBUILDER | Sep 01, 2002 07:13pm | #9

    All good advice, richen it up a bit and wet the block, but don't be too depressed when you come back a few days later and some of the heads are cracked. It will shrink back more in heat/dry climates. Maybe too obvious, but throw double head joints, it will be less likely to crack, and will fill the heads much better.

1. 
   joeh | Sep 01, 2002 07:56pm | #10

   Thanks for the advices. I had ordered masonry cement, premix was delivered. Got plenty of sand to mix in with it though.............what were they thinking I wanted all that sand for? Since the (and all) supplier was closed Saturday by the time I figured out what I had, I tried to use it. Easier ain't better though.

   Making a couple misters sounds like plan one, get rid of the premix or add to it and see what happens.

   And hope it's cooler next time I can get back there later this month. Thanks, Joe H

1. 
   JCarroll38 | Sep 02, 2002 11:13pm | #11

   Joe,

   Before you go to the trouble of buying and rigging up misters, consider this from "Masonry Design & Detailing" (p.101):

   "A high initial rate of water absorbtion, or suction, adversely affects the bond between mortar and (concrete masonry) unit just as it does in clay masonry (bricks). Unlike brick, however, concrete products may not be pre-wetted at the job site to control suction because of the moisture shrinkage inherent to concrete. Prewetting concrete masonry units could cause excessive shrinkage cracking in the wall. Suction can be controlled only through proper product specification by ASTM standards, and through the use of highly water retentive mortars to ensure the integrity of the bond." (I added the emphasis and the words in parentheses.)

   Although very porous and dry bricks can be moistened, they should be dry on the surface when laid. Concrete blocks should never be moistened and, indeed, they should be protected from moisture at the job site.

   I think your problem is mainly caused by the preblended mortar you're using. As a mason, I never use those because I find them to be hard to work with. I would suggest Type N portland cement/lime mortar. PC/lime mortars are more water-retentive than masonry cement mortars. You usually have to go to a masonry supply house to get mason's lime (also called hydrated lime). If you can't get lime, the more easily obtained Type N masonry cement will suffice. Also, try to keep your blocks in the shade, try to work in the cool hours of the day, and consider rigging up a tent or canopy to protect the wall you're building from the sun.

   Here's a link to the National Lime Association for more information on lime mortars: http://www.lime.org/ 

   -John Carroll

1. 
   eborg2 | Sep 03, 2002 05:16am | #12

   John,

   After reading the posts preceding yours I hoped someone would log in with some empirical data.  Thankfully you did.

   If anyone is interested in something more than seat-of-the-pants advice on this subject there is a lot of useful information located at the Brick Institute of America website http://www.bia.org , Technical notes or http://www.masonryonline.com , Forums.

   Quality masonry isn't amateur territory.  If your're building a fence or a barbeque that's one thing but structural masonry should be performed by professionally trained masons.

   That's my two-cents; take it for what it's worth.

   Eric

2. 
   Mongo | Sep 03, 2002 08:23am | #13

   John,

   Just to let you know, the misting system that I described was not intended to wet the block...it's designed to disperse fine water droplets into the air. The droplets evaporate before settling on any surface, thus cooling the work area.

   Works quite well in arid areas.

1. 
   JCarroll38 | Sep 03, 2002 07:42pm | #14

   Eric,

   Thank you for your response. In posting my remarks I expected something of a row because just about all the preceding posts recommended exactly the oppostite course of action that I suggested. To reinforce what I said in my prior post, here's what the Portland Cement Association wrote in its "Guide to Building with Concrete, Brick, and Stone" (published in 1988):

   "The suction rates of concrete masonry units are low enough that they never require wetting prior to laying of mortar. Some clay bricks units have such high suction rates that poor bond will result unless the bricks are wetted; surfaces of the wetted bricks should be dry before applying mortar."

   Mongo,

   Your point is well-taken. I would caution, however, that if you use misters to cool the air, make sure that moisture does not collect on the surfaces of the block. Bond requires suction and suction does not occur on a wet surface. Also, keep in mind that there is a one-time shrinkage of blocks, just as there is in all concrete products. This occurs as the water used in hydrating the cement and in curing it is gradually given up. In the desert, where the blocks will eventially be bone dry, this one-time shrinkage can be assumed to be large and it would seem that laying them as dry as possible would be best. After this one-time shrinkage, expansion and contraction in the presence of moisture is much smaller but it still occurs.

   Unlike blocks, which emerge from the manufacturing process bloated with water, bricks come out of kilns bone dry. When they absorb water from the air and from rainwater, they go through a one-time expansion. The fact that CMUs are shrinking and bricks expanding is one reason (not the only one) that designers like to use a cavity to separate them.

   --John

2. 
   joeh | Sep 03, 2002 10:06pm | #15

   John and Eric, thanks for the help. I know blocks are supposed to be kept dry, but I was thinking too dry was part of the problem. It didn't occur to me that they weren't actually going to soak up any water from the mortar.

   The mortar I was stuck with, all local suppliers closed on Saturday. The closest lime was at a HD 50 miles away. I think the temp will be cooler by the time I can get back, and I'll get some masonry cement or go the cement & lime route.  Thanks again, Joe H