Masonry guide / Before you estimate
Mortar vs Grout for Masonry: What’s the Difference?
Mortar bonds bricks or blocks together at the joints. Masonry grout fills hollow spaces inside the wall, such as block cores. Your project plans show which spaces need filling. A block wall may need both materials, so estimate them separately.
Check the information you need before ordering01 / Start with the location
Two materials, two places in the wall
Masonry means building with bricks, blocks or stone. The joints are the gaps between these pieces. The hollow spaces inside a concrete block are called its cores.
Wall face / Simplified sketch
Mortar joints
A mason spreads mortar between bricks or blocks to join them together. It needs to be easy to spread while the pieces are put in place.
View from above / Simplified sketch
Filled cores or spaces
Grout fills the spaces shown in the project plans. Where steel reinforcing bars are used to strengthen the wall, grout helps connect the steel to the surrounding masonry.
Why they behave differently
Mortar needs to spread easily while a mason positions the bricks or blocks. It also needs to stay in the joints as the pieces are laid. The Concrete Masonry & Hardscapes Association, or CMHA, explains this working consistency in its guide to masonry mortar.
Masonry grout needs to flow into the spaces being filled, including around steel bars and other obstructions. CMHA’s guide to masonry grout explains this flowable consistency and how grout connects reinforcing steel to the masonry. Those different jobs help explain why the products are not automatic substitutes.
| Check | Masonry mortar | Masonry grout |
|---|---|---|
| Where it goes | Horizontal and vertical joints between bricks or blocks. | The hollow spaces that the project plans say to fill. |
| What it does | Bonds the bricks or blocks together. | Fills the required spaces, including around steel bars where present. |
| How it needs to behave | Spreads under a trowel and stays in the joints as bricks or blocks are laid. | Flows through the required spaces and around obstructions. |
| What to check | The required mortar type and product. | The required grout product and whether it suits the space being filled. |
| What to estimate | The mortar needed for the joints. | The grout needed inside the wall. Keep this separate from mortar. |
02 / Read past the product name
Not every grout is made for the same job
Masonry grout can be fine or coarse. These names refer to the size of the aggregate, meaning the sand and small stones in the mix. Fine grout uses fine aggregate. Coarse grout also includes larger pieces.
CMHA explains that the space available and how the grout will be placed matter when choosing between them. The words “fine” and “coarse” do not tell you which product is better for your wall. Use the type required by the project.
Grout for tile joints and grout for machinery bases are made for other jobs. A bag labelled “grout” may not be the product required inside your block wall. Read the manufacturer’s product data sheet and compare its listed uses with your project requirements.
03 / Estimate each material separately
What to confirm before ordering
- Keep the materials separate. Estimate joint mortar and core-fill grout on different lines.
- Check the product and the plans. Confirm the required material, the exact block’s hollow-core volume and which spaces need filling.
- Check mixed yield. This is the volume of usable material a bag makes after mixing. Use the selected product’s data sheet.
The Concrete Block Calculator estimates blocks in the finished wall and joint mortar. Use the installed block count for core fill; spare blocks bought for cuts or breakage do not automatically add grout.
04 / Check how much a bag makes
Check the bag’s yield, not just its weight
For example, the QUIKRETE Core-Fill Grout Fine 1585-08 data sheet, revised November 2024, says an 80 lb bag makes about 19 L of mixed grout. This figure applies to that product. Another bag of the same weight may make a different volume.
For one example, use 160 installed blocks with 5 L of hollow-core space per block. Assume the specified spaces to fill add up to 25% of the total core volume. This is a quantity assumption, not an instruction to fill each core one-quarter high. The plans determine which spaces need grout and how it is placed.
Add a chosen 8% allowance for waste and use 19 L per bag. The block volume, fill percentage and allowance are illustrative, not values to use for every wall.
| Quantity | Worked example |
|---|---|
| Grout in the wall, before waste | 160 × 5 L × 0.25 = 200 L |
| Chosen 8% allowance | 16 L |
| Volume to order, including waste allowance | 216 L |
| Whole 19 L bags | 216 ÷ 19, rounded up = 12 |
Twelve bags at 19 L each make about 228 L. Whole-bag rounding adds 12 L beyond the 216 L order volume; the wall still needs 200 L. Joint mortar and labour are separate.
Ready to estimate the grout?
Use your block count, core volume, specified fill percentage and product yield to calculate the wall quantity, allowance and whole bags.
Calculate concrete block core fillCheck the plans before choosing materials
This guide helps you understand the materials and estimate quantities. It does not design the wall or tell you which mix to use. The CMHA guides explain the basics and refer to older building standards. Follow the current project requirements and the manufacturer’s instructions before buying or using a product.