Fireside • Materials Guide
Type S vs Type N vs Refractory Mortar: Which to Use
The difference between the two everyday mortars, where each one goes, and the one place neither belongs: anywhere the fire touches.
Type S mortar is the stronger one, rated at 1,800 psi, and it's the pick for block stands, foundations, patios and stone veneer. Type N is softer, at 750 psi, and more flexible, which makes it the usual choice for above-ground brick walls, brick veneer and repointing. Neither one belongs where fire touches. Fire brick needs non-water-soluble refractory mortar.
Most backyard builds use all three. A BrickWood oven sits on a block stand laid in ordinary mortar, wears a veneer set in ordinary mortar, and hides a fire brick barrel or dome laid in high-heat mortar. Pick the wrong one in the wrong spot and you get a stand that cracks or joints that crumble out of the oven. This guide shows which is which, and exactly where each one goes.
Type S vs Type N vs Refractory: Quick Answers
- Type S: 1,800 psi. Block stands, foundations, retaining walls, patios and stone veneer.
- Type N: 750 psi. Softer and more flexible. Above-ground brick walls, brick veneer, chimneys and repointing.
- Stronger isn't always better. Mortar should be weaker than the brick it holds, so cracks run through the joints, not the bricks.
- Neither handles fire. Portland cement mortar starts losing strength above about 570°F and crumbles with repeated firing.
- Refractory mortar goes in the fire zones: the barrel or dome, the back wall, the vent and fire brick liners.
- Outdoors, it has to be non-water-soluble. Premixed wet refractory mortar washes out in the rain.
Type S, Type N and Refractory Mortar at a Glance
| Type N | Type S | Refractory mortar | |
|---|---|---|---|
| Minimum strength | 750 psi | 1,800 psi | Rated by heat, not strength |
| Typical mix | 1 Portland : 1 lime : about 6 sand | 1 Portland : ½ lime : about 4½ sand | Factory blend, or our 3:1:1:1 recipe with fire clay |
| Personality | Softer, more flexible, easy to work | Stronger, stiffer, better bond | Holds up to repeated high heat |
| Best for | Above-ground brick walls, brick veneer, chimneys, repointing | Block stands, foundations, retaining walls, patios, stone veneer | Fire brick in ovens, fire pits and fireboxes |
| Below ground | No | Yes | Not the job it's made for |
| Near fire | No. Breaks down above about 570°F | No. Breaks down above about 570°F | Yes. Medium-duty grades are tested at 2,550°F |
| On a pizza oven | Hearth border, veneer, stucco coat | Block stand, hearth border, veneer, stucco shell | Barrel or dome, back wall, vent, outer arch |
Type S vs Type N Mortar: What's the Difference?
Both are ordinary masonry mortars made from Portland cement, hydrated lime and sand. The difference is the recipe. Type S has more Portland cement and less lime, so it cures harder and bonds more strongly. Type N has more lime, so it's softer, stays a little more flexible, and spreads more easily off the trowel.
- Strength: Type S has to reach at least 1,800 psi. Type N only has to reach 750 psi.
- Flexibility: the extra lime in Type N lets a wall move a little with heat, cold and settling without cracking the brick.
- Weather and ground contact: Type S holds up better at grade and below grade, where soil, water and freezing push on the masonry.
- Workability: masons often find Type N easier to spread and tool, especially for long runs of veneer.
Stronger isn't always better
It's tempting to grab Type S for everything because the number is bigger. The Brick Industry Association says the opposite: pick the weakest mortar that will do the job. Mortar should be softer than the brick it holds. When a wall moves, you want the crack to run through a mortar joint, which is easy to repoint, instead of splitting the brick. That's why Type N is the standard choice for above-ground brick veneer, and why old, soft brick gets repointed with a soft mortar.
Which one should you buy?
- Building a block stand, foundation, retaining wall or patio? Type S.
- Setting stone veneer? Type S is the most common choice. Type N is also allowed by stone veneer installation guides.
- Laying an above-ground brick wall or brick veneer? Type N, or Type S if you prefer.
- Repointing old brick? Type N, or something even softer for very old brick.
- Laying fire brick? Neither. Keep reading.
What Is Type S Mortar Used For?
Type S mortar is used anywhere masonry carries weight or sits in the ground: block foundations and stands, retaining walls, patios, walkways, steps and below-grade work. It's also the go-to mortar for adhered stone veneer, and most bagged veneer mortars are Type S.
On a pizza oven build, Type S is the workhorse. It lays the concrete block stand, sets the brick or stone veneer, and works for the stucco shell over the insulated oven. If you only buy one bag of ordinary mortar for your oven, make it Type S.
Type S mortar for stone veneer
Stone veneer goes on in two steps: a scratch coat of mortar on the wall, then mortar buttered on the back of each stone. Both are typically about ½ inch thick. Type S is the industry favorite because of its strong bond, and most stone veneer mortars sold in bags are Type S. On a pizza oven, the veneer goes over the insulated oven, so the heat never reaches it. Ordinary Type S is all it needs.
Is Mortar Heat Resistant?
Ordinary mortar won't burn, but it isn't heat resistant either. Type S and Type N are both held together by Portland cement, and heat slowly takes that cement apart.
- Above about 570°F, cement paste starts losing strength faster as the water locked inside it is driven out.
- Around 900°F to 1,000°F, one of the main compounds holding the paste together breaks down. Concrete research puts the strength loss at roughly half by about 930°F.
- Then it cools. What's left soaks up moisture from the air and swells, which cracks the joint from the inside. Every firing repeats the cycle.
A pizza oven's firebrick cooking surface runs about 650°F to 800°F, and it gets much hotter right under the flames. So ordinary mortar in the oven's walls doesn't fail on the first fire. It fails over a season or two, as the joints crack, sand out and let the brick shift.
The "Type N is good for high heat" myth
You'll see this on some popular how-to pages. The extra lime makes Type N more flexible, and that helps a brick wall ride out temperature swings from sun and frost. It does nothing for a joint that faces a 900°F fire. Type N and Type S are both Portland cement mortars, and both break down in a fire zone.
Where Refractory Mortar Takes Over
Refractory mortar is made to hold fire brick together through hundreds of firings. It's what code requires in a fireplace firebox, and it's what belongs between the fire brick of a pizza oven, a fire pit liner or an outdoor fireplace. For an outdoor build, it has to be the right kind.
Dry, non-water-soluble mortar for outdoor builds
Outdoor ovens and fire pits get rained on, so the mortar has to stay put once it sets. That means a dry mix you add water to that cures hard and doesn't dissolve, like BrickWood Refractory Mortar. You can also make your own with our 3:1:1:1 high-temperature mortar recipe of sand, lime, fire clay and plain Portland cement.
Premixed wet mortar is for indoor fireboxes
Ready-to-use refractory mortar from a tub or caulk tube is made for thin, neat joints in indoor fireplaces and stoves. Most of it stays water-soluble until it has been fired, and rain can wash it right out of an outdoor oven. It's also meant for joints about 1/16 to 1/8 inch wide, far thinner than a pizza oven's joints. Our premixed air-set mortar is made for exactly that indoor job.
One exception on our own ovens: the poured Cortile Barile and 28" Mattone Cupola use a very small amount of premixed high-heat mortar as a gasket. On the Cortile it seals the seams as the five castable pieces go together, and on both ovens it seals the oven to the firebrick cooking surface underneath. It's a thin seal, not a structural joint, and it ends up covered by the oven's insulation and finish.
Why you can't just add fire clay to Type S
Bagged Type S mix already has its cement, lime and sand proportioned for regular masonry. Stirring fire clay into it doesn't give you a high-temperature mortar. If you want to make your own, start from separate ingredients and follow a tested recipe with plain Portland cement.
Mortar on a Pizza Oven, Zone by Zone
A pizza oven uses ordinary mortar and refractory mortar side by side. The rule is the same one we use for brick: if fire touches it, it gets high-heat mortar. If not, ordinary mortar is the better choice. It's cheaper, easier to work and made for weather. Here's every part of a BrickWood build.
| Part of the oven | Mortar | Why |
|---|---|---|
| Block stand | Type S (Type N also works) | Carries the weight of the oven. No heat reaches it |
| Hearth slab | None. It's reinforced concrete | Holds up the oven and the insulation under it |
| Hearth border | Ordinary Type N or Type S | Warm at the edge, but outside the fire |
| Firebrick cooking surface | No mortar at all | Dry-laid on sand so it can move with the heat, and no mortar ends up in your food |
| Barrel or dome, back wall | Non-water-soluble refractory mortar | Takes direct flame on every firing |
| Vent and chimney brick | Non-water-soluble refractory mortar | Flame and hot smoke pass right through it |
| Outer arch | High-heat mortar | Right next to the opening, even when the brick is regular clay brick |
| Stucco shell | Stucco mix, or Type S or Type N mortar mix | Sits outside the insulation. Don't use refractory mortar here |
| Brick or stone veneer | Type S (Type N for brick also works) | Stays cool once the oven is insulated |
Two spots surprise first-time builders. The firebrick cooking surface gets no mortar at all, ever. And the stucco shell over the insulation is ordinary mortar or stucco mix, not refractory mortar. Factory refractory mortar never fully cures out there, because the shell never gets hot enough, and it can end up looking like the back of an alligator.
Not sure which kind of brick goes where? Our guide to using regular brick on a pizza oven or fire pit walks through the same zones for brick.
Mortar for Fire Pits and Outdoor Fireplaces
- Dry-stacked block fire pits don't need mortar at all. Our Fire Pit Grill Kit is built this way, from dry-stacked cinder block capped with pavers.
- Brick or stone fire pits can use Type S for the outer wall. If you line the inside with fire brick, set the liner in non-water-soluble refractory mortar and leave small gaps at the bottom so rain can drain out.
- Outdoor fireplaces follow the oven rule: refractory mortar for the fire brick firebox, Type S or Type N for the brick or stone around it.
- Indoor fireplaces are covered by building code. The firebox lining has to be laid in medium-duty refractory mortar, with joints no wider than ¼ inch. Check with your local building department.
Mortar Mistakes Builders Make
These come straight from questions on our BrickWood Builders Forum.
- Using premixed tub mortar in an outdoor oven. It's meant for thin indoor joints, stays soft until it's fired, and can squeeze out of a wide joint like ketchup.
- Using bagged Type S mix in a high-temperature recipe. Homemade high-temp mortar needs plain Portland cement, not a mortar mix that's already proportioned.
- Using Portland-limestone cement by mistake. It's sold right next to plain Portland cement. Read the bag.
- Letting mortar freeze before it cures. One builder's joints froze overnight and turned crumbly. Don't lay mortar when a hard freeze is coming. If it happens, dry it out slowly before you fire the oven.
- Panicking over Type N. Builders who used Type N instead of Type S on the hearth border or as a stucco coat asked if they had to tear it out. They didn't. Both are fine outside the fire zone.
Frequently Asked Questions
Is Type S mortar stronger than Type N?
Yes. Type S has to reach at least 1,800 psi, and Type N only 750 psi. Stronger isn't always better, though. For above-ground brick walls and veneer, the softer, more flexible Type N is often the better match.
Can I use Type S mortar in a pizza oven?
Yes, outside the fire. Type S is right for the block stand, the hearth border, the stucco shell and the veneer. It's the wrong choice for the fire brick joints in the barrel, dome, back wall or vent, which need non-water-soluble refractory mortar.
Can I use Type N mortar for a fire pit?
For the outer wall, yes. Don't use it on the fire brick or block that faces the fire. Like Type S, it breaks down with repeated high heat.
Which mortar should I use below ground?
Type S. It's made for foundations, retaining walls and other masonry in contact with soil. Type N is for above-ground work.
Is mortar fireproof?
Ordinary mortar won't burn, but it isn't made for fire. Portland cement mortar starts losing strength above about 570°F and cracks and crumbles with repeated firing. Fire zones need refractory mortar.
Can I use premixed refractory mortar outdoors?
Usually not. Most premixed wet refractory mortar stays water-soluble until it's fired and is made for thin indoor joints. For an outdoor oven or fire pit, use a dry, non-water-soluble refractory mortar.
Which mortar is best for repointing brick?
Usually Type N. Repointing mortar should be no stronger than the original mortar, so very old, soft brick often needs an even softer mix.
What's the difference between mortar mix and masonry cement?
Mortar mix comes with the cement, lime and sand already blended, so you just add water. Masonry cement is a cement blend you mix with your own sand. Both come in Type N and Type S versions.
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