Last week we talked about pier footings, today we need to look at the top of the footings, the cap blocks, spacers and shims.
The job of the pier cap is to take the all the weight from the I-Beam and spread it out over the entire surface of the Concrete Masonry Unit (that is fancy talk for concrete block). So, we are taking between 5,500 and 6,900 lbs. concentrated in the 3″ flange of the chassis beam, and spreading it out over the top of an 8″ x 16″ block.
Keep in mind, while a concrete block is very strong, it is also very fragile. But I think you would agree that it is very rare to see a concrete block fail if it was properly loaded and supported. While the footing provides the support, the cap blocks handle the loading! If the pier is made of single stack blocks, the cap must be 8″ x 16″, if double stack blocks, the cap must be 16″ x 16″.
Also, if capping double block piers, with two 8″ x 16″ caps, the joint in the cap blocks must be at a right angle to the joint of the blocks being capped. AND, the joint in the cap blocks must be at a right angle to the chassis beam.
Generally, the cap block must be 4″ solid, pre-cast concrete or 2″ x 8″ x 16″ pressure treated lumber. Most installation instructions also allow ½” steel to be used as a cap, but I have never seen this in the field (if you use steel, could you send me a picture?).
Shims are needed between the I-beam and the cap block. While a few manufacturers might suggest that shims are optional, I think they are very important and I highly recommend that you always install shims in your installations. Shims need to be used in pairs and should only take up 1″ of space between the cap block and I-beam. Most shims are hardwood (usually made from locust or oak) 4″ x 6″, however ABS shims are also available. One thing about the ABS shims is that them have grooves that lock them together so they can’t slip apart.
Spacers are needed if you have more than 1″ of space between the cap block and I-beam. Manufacturers differ somewhat on what you can use as a spacer. Some say a maximum 2″ thick hardwood lumber, or a 2″ or 4″ solid block (I assume that this manufacturer allows 1″ hardwood as a spacer as they don’t indicate a minimum). Yet a another manufacturer allows the use of two layers of 2″ lumber. Most manufacturers simply say 2″ lumber or 2″ to 4″ solid concrete.
For me, the take away is that the use of 1″ concrete is not permitted, and most installation instruction do not permit 1″ lumber. Sorry!
Just remember, you want to spread out the load to as large of an area as possible. So be sure your cap blocks are the same size as the pier. Be cautious when selecting spacers and shims.
As always, verify your installation practices to the manufacturers installation instructions that come with the home!
Ok, next week we will take a closer look at the pier itself!