High-Temperature Mortar Ingredient
Portland Cement for High-Temperature Mortar
Portland cement is the binder that sets your firebrick mortar. It's also the easiest ingredient to buy wrong, because the shelf next to it is full of look-alike mortar and concrete mixes.
Quick Answers
- Portland cement gives high-temperature mortar its first set, so each course of brick holds while you keep building.
- It's 1 part of 6 in the recipe: 3 sand, 1 lime, 1 fire clay, 1 Portland cement, by volume.
- Buy plain Portland cement (Type I, II or I/II). Not mortar mix, masonry cement or concrete mix.
- Every home improvement store and lumber yard carries it.
What Is Portland Cement?
Portland cement is a fine gray powder that hardens when it reacts with water. It's an ingredient, not a finished product. Mix it with sand and gravel and you get concrete. Mix it with sand and lime and you get mortar. Mix it with sand, lime and fire clay and you get high-temperature mortar.
In the U.S. it's usually labeled Portland Cement Type I/II and sold in large bags (commonly 94 lb) at every home improvement store and lumber yard.
Why Portland Cement Is in High-Temperature Mortar
Portland cement provides the early strength. It sets the mortar firmly within hours, so the bricks stay put while you lay the next course, and the joints are solid by the time you're ready to remove the form and start your curing fires.
Portland cement on its own is not a high-heat material. Ordinary cement paste starts to lose strength once it gets much past about 570°F (300°C), and a wood-fired pizza oven runs far hotter than that. That's why it is never used alone inside an oven. In this recipe, the fire clay and lime carry the heat-resistant load, and the Portland cement handles the job it's best at: the first set.
How Portland Cement Is Used in High-Temperature Mortar
Portland cement is 1 part of every 6 in the mix. It gives the mortar its first set, so each course of firebrick holds while you keep building.
The 3 : 1 : 1 : 1 Mix (by volume)
Measure by volume, not weight. Lime is fluffy and weighs far less per scoop than sand, so weighing the ingredients throws the recipe off.
The short version: dry-mix all four ingredients by volume until the color is even, then add water a little at a time until the mortar is firm and buttery, like thick peanut butter. Dampen your firebrick, lay thin, full joints, and let the mortar cure for about a week before your first small curing fire.
Our full guide covers every step, the tools you need, where to use the mortar (and where not to), and how it compares to factory-made refractory mortar.
Which Bag Should I Buy?
| Product | What it is | Use it? |
|---|---|---|
| Portland cement Type I, II or I/II | Plain cement powder, nothing added | ✓ Yes |
| Type S or Type N mortar mix | Finished mortar that already has sand and lime | ✗ No |
| Masonry cement | Portland cement with lime or other ingredients already blended in | ✗ No |
| Portland-lime cement | Pre-blended cement and lime in the wrong ratio for this recipe | ✗ No |
| Concrete mix | Cement, sand and gravel | ✗ No |
| Fast-setting or rapid-set cement | Sets in minutes, leaving no working time | ✗ No |
Read the label
The bag should say "Portland Cement" and nothing else in the product name. If the label lists sand, lime or gravel, put it back.
Other places Portland cement shows up in an oven build
You'll use Portland cement elsewhere too: in the concrete hearth slab, in perlite or vermiculite insulating concrete, and in the Type S mortar or stucco for the outer shell. Only the firebrick joints get the high-temperature recipe.
Store bags off the ground and keep them dry. Portland cement that has absorbed moisture turns lumpy and hard. If you can't crumble the lumps between your fingers, don't use it.
Find These Materials in Your Area
Need it today? Check a store near you.
We ship every bag FREE to the contiguous United States. If you would rather pick it up today, all four ingredients are stocked at stores near you, so check these places first.
Call ahead and ask for each item by the names on this page. Counter staff sometimes suggest a premixed substitute that doesn't belong in a wood-fired oven.
Portland Cement FAQ
Can Portland cement handle high heat?
Not on its own. Ordinary Portland cement paste starts losing strength above roughly 570°F (300°C). In high-temperature mortar it's combined with fire clay and lime, which carry the heat-resistant load, while the Portland cement provides the first set.
Which type of Portland cement should I use?
Plain Portland cement, Type I, II or I/II. These are the standard gray bags at any home improvement store.
Can I use Type S mortar mix instead of Portland cement?
No. Type S mortar mix already contains sand and lime, so adding it throws the 3:1:1:1 recipe off. Type S mortar is great for the oven's outer shell, but not for the firebrick joints.
Can I use masonry cement?
No. Masonry cement is Portland cement with lime or other ingredients already blended in, in a ratio that doesn't match this recipe. Use plain Portland cement and add the lime yourself.
How much Portland cement do I need?
One part out of six, by volume. Your oven's materials list gives the total amount of high-temperature mortar to plan for.
Where can I buy Portland cement?
Every big-box home improvement store, most hardware stores and lumber yards, and all landscape & masonry supply stores.
Please Order Carefully: Refractory Materials Are Non-Refundable Once Shipped
Refractory materials are heavy, costly to ship and can't be resold once they leave our warehouse. For that reason, refractory products can't be cancelled, returned or refunded once your order has shipped.
We're happy to help you get it right the first time. If you're not sure which product or how much you need, contact us before you order and we'll walk you through it.
Shipping
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Keep Building
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Store availability and prices vary by region. Always follow the safety information printed on each bag.
