Remember Me?

 Straight Dope Message Board Remember Me?

 Thread Tools Display Modes
#1
09-10-2019, 12:30 AM
 Guest Join Date: Nov 2011 Location: Medford, OR Posts: 48

## Geometry and concrete blocks

I am thinking of getting concrete retaining wall blocks that are angled on both ends, I was wondering if I laid them side to side how big would the circle be. Any ideas on a formula so I don't have to do to the store and lay them out?
#2
09-10-2019, 12:42 AM
 Guest Join Date: Jan 2013 Posts: 4,212
I’m not an expert but I’m pretty sure the angle is to allow several different radii. In other words, I don’t think it’s necessary to place the angled ends flush.
#3
09-10-2019, 12:42 AM
 Guest Join Date: Dec 2010 Posts: 7,888
You haven't said how the angles are specified, but let's say that it's a number of degrees off perpendicular. For example, say that each side is 3 degrees short of the 90 degrees you'd get for a straight-cut block.

Take 180 and divide by this angle to get the number of blocks around. For 3 degrees, that's 60 blocks.

Divide by 3.14 to get the number of blocks across. That comes to 19 in this example.

Then, multiply by the length of the block. If they're 1 foot long, then the circle is 19 feet in diameter.
#4
09-10-2019, 06:58 AM
 Guest Join Date: Mar 2012 Posts: 1,749
Quote:
 Originally Posted by ric62 I was wondering if I laid them side to side how big would the circle be. Any ideas on a formula so I don't have to do to the store and lay them out?
I think the blocks are not designed to be laid side to side. You fill the gap up with pebble stones or the like to get good drainage. If you stick them side to side, my guess is you will get something like a 6-8 ft circle but I wouldn’t advise doing that.
#5
09-10-2019, 07:35 AM
 Charter Member Join Date: Jun 1999 Location: Milwaukee, WI Posts: 29,100
Quote:
 Originally Posted by ric62 I am thinking of getting concrete retaining wall blocks that are angled on both ends, I was wondering if I laid them side to side how big would the circle be. Any ideas on a formula so I don't have to do to the store and lay them out?
Find out what brand they have and check out their website or check the website of the store you're going to. It's going to be different from brand to brand (I assume), but I've seen plenty of displays (online and IRL) that show you exactly how big of a circle the angled blocks will make if you butt them up against each other.
But even ignoring that, you can cut them to change the angle to whatever you want it to be. A good masonry angle grinder blade can be had for about \$10 and will cut a block in 30 seconds or so.
#6
09-10-2019, 07:37 AM
 Charter Member Join Date: Jun 1999 Location: Milwaukee, WI Posts: 29,100
Quote:
 Originally Posted by am77494 If you stick them side to side, my guess is you will get something like a 6-8 ft circle but I wouldn’t advise doing that.
Maybe the OP is making a fire pit or is just trying to figure out how big of a corner they're going to end up with on a retaining wall if they don't cut any of them.
#7
09-10-2019, 08:00 AM
 Guest Join Date: Mar 2012 Posts: 1,749
Quote:
 Originally Posted by Joey P Maybe the OP is making a fire pit or is just trying to figure out how big of a corner they're going to end up with on a retaining wall if they don't cut any of them.
You are right. If that’s the case, then go to the manufacturer’s website and they will have a Chart like this one : https://www.allanblock.com/retaining...ius-chart.aspx

(The curve radius is dependent on the wall height since subsequent layers “lock” on to the lower layer)
#8
09-10-2019, 11:31 AM
 Charter Member Join Date: Jun 1999 Location: Milwaukee, WI Posts: 29,100
Quote:
 Originally Posted by am77494 (The curve radius is dependent on the wall height since subsequent layers “lock” on to the lower layer)
Not that it really applies here, but a chisel and hammer will knock that 'lock' off pretty quickly. I just put up some like this. In this picture, some of the bricks are upside down and you can see a lip opposite the curved side. That's what sets each course a little behind the one below it. When I go around bend, I'll chip that off, otherwise the brick is set too far back.
#9
09-10-2019, 11:55 PM
 Guest Join Date: Nov 2011 Location: Medford, OR Posts: 48
I am trying to make a circle. I think I can figure out the radius or diameter, if not I'll ask the people at the outdoor department.
#10
09-11-2019, 10:45 AM
 Guest Join Date: Feb 2009 Posts: 14,975
The angle that each end is off 90 degrees creates, essentially, a piece of a triangle with the sides pointing to the center of the circle. you need to know the angle. take two straight edges or boards, push them flat against the angled ends, and see where the two boards meet. That's the center of the circle, no math required (unless the radius is more than about 8 feet, too long for a plank - unlikely. )

 Bookmarks

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is Off HTML code is Off Forum Rules
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Main     About This Message Board     Comments on Cecil's Columns/Staff Reports     General Questions     Great Debates     Elections     Cafe Society     The Game Room     Thread Games     In My Humble Opinion (IMHO)     Mundane Pointless Stuff I Must Share (MPSIMS)     Marketplace     The BBQ Pit

All times are GMT -5. The time now is 11:19 PM.

 -- Straight Dope v3.7.3 -- Sultantheme's Responsive vB3-blue Contact Us - Straight Dope Homepage - Archive - Top
Copyright ©2000 - 2019, vBulletin Solutions, Inc.

Send questions for Cecil Adams to: cecil@straightdope.com