Concrete Block Foundation Walls

1. Concrete Block Foundation Walls Unit 26

2. Sizes • 7-5/8” high • 15-5/8” long • Common depths – 8”, 10”,12” • 3/8” mortar joints • Walls usually stand 7’-4”

3. Block Walls • Series of blocks one layer over another is called a course • Concrete blocks do not use forms • Concrete block may be reinforced by pilasters • Stack bond pattern is when one block is laid directly over another to produce a continuous vertical joint • Stack bond requires reinforcement

4. Mortar • Freezing weather affects mortar • Low adhesion • Less strength • Failure in joints • Coat of asphalt over mortar will ensure a dry basement • Applying roofing felt over first coat will provide extra water-proofing

5. Mortar (continued) • Mortar strength depends upon • The rate which block absorbs moisture from mortar • Plasticity or workability of mortar • How much water the mortar retains • Quality of workmanship by the mason • Mortar will be usable for 2-1/2 hours at 80 degrees or higher • Do not water down block before adding mortar • Position the first blocks before applying mortar

6. Construction of concrete block walls • Alignment of the first course is the most critical • Lay the smaller holes of the block up to provide a larger mortar bed • Check the blocks with a level or a straight edge • Use a story pole to check if one course is 8” above the next • Final gap in the wall is filled with a closure block • “Thumbprint” hard will not leave an indentation and the mortar should be tooled • Tooling should be done when the mortar has set

7. Control Joint • Controls cracking due to stress • Permits slight movement in a wall • Gives the wall longer life • Built vertically into a wall • Should be plumb • Should be caulked if it shows

8. Finishing • Remove excess mortar from walls after it has dried • Intersecting walls must be anchored • Tops of windows and doors require lintels • Total mixing time of fiberglass reinforced mortar should not exceed 5 minutes • Use a joint guide when fiberglass mortar application is interrupted for more than 1 hour

9. Finishing (continued) • Wet the wall prior to fiberglass mortar application • Slope the finish grade away from the foundation for good surface drainage • Backfill material should be expected to settle

10. Foundation information • The same block is needed for reinforced mortar as is conventional mortar • Split face block has one rough face that looks like stone • There are many specialty blocks for specific purposes