The BrickWood High Heat Mortar Guide
High Heat Mortar, Premixed: Medium Duty Fire Brick Mortar for Indoor Fireplaces
What a premixed medium duty mortar is, where it works, how much to order and how to use it. Please read the section on where this mortar is not for before you order.
BrickWood High Heat Mortar is a wet, air-setting, medium duty refractory mortar rated to 2,700°F. It comes ready to use in the pail, trowels on smooth and lays fire brick with thin, clean joints. It's made for professional masons and for indoor work: fireplaces, fireboxes, wood stoves and other masonry heaters that stay out of the weather.
High Heat Mortar: Quick Answers
- What it is: a ready-mixed, air-setting, medium duty refractory mortar.
- Rating: 2,700°F maximum service temperature.
- Where to use it: indoors only. It's water soluble, so it isn't for outdoor or DIY pizza ovens.
- Joints: 1/16 to 1/8 inch. Never thicker than 1/4 inch.
- Coverage: 35 to 40 lb lays 100 standard fire bricks.
- Set time: typically 48 to 72 hours.
- Sizes: 50 lb pail or a 4-pack of 15 lb pails. Minimum order of 2.
- Shipping: FREE to the contiguous United States. Non-refundable once shipped.
Inside this guide
Where This Mortar Works (and Where It Doesn't)
Premixed medium duty mortar is the go-to for masons laying medium duty fire brick in indoor fireplaces, fireboxes and wood stoves. It's smooth, ready to use and accepted by the International Code Council, the International Residential Code and the NFPA.
Not for outdoor or DIY pizza ovens
- This mortar is water soluble. Rain or snowmelt will slowly wash it out of the joints.
- Don't use it to fill voids or gaps. It shrinks and cracks if applied thicker than 1/4 inch.
- Building a pizza oven, fire pit or outdoor fireplace? Use our outdoor-safe, non-water soluble Refractory Mortar instead.
High Heat Mortar Specifications
| Type | Wet (ready-mixed), air-setting, medium duty refractory mortar |
| Maximum service temperature | 2,700°F |
| Pyrometric cone equivalent (PCE) | 29 (melts at about 3,018°F) |
| Bonding strength (ASTM C-198) | 207 psi after 230°F; 584 psi after 2,730°F |
| Pier test at 2,730°F (ASTM C-199) | No flow from joints, no cracks or shrinkage |
| Water soluble | Yes. Indoor use only. |
| Recommended joint | 1/16 to 1/8 inch. Not thicker than 1/4 inch. |
| Coverage | 35 to 40 lb lays 100 standard 9 x 4.5 x 2.5 inch fire bricks |
| Set time | Typically 48 to 72 hours |
| Shelf life | 6 to 12 months |
| Loss on ignition | 4.73% |
| Chemistry | Silica 92.14%, alumina 4.41%, sodium oxide 2.48%, titanium dioxide 0.42%, potassium oxide 0.22%, iron oxide 0.21% |
| Building codes | Accepted by the International Code Council, International Residential Code and NFPA |
| Sizes | 50 lb pail or a 4-pack of 15 lb pails |
Values are typical results from standard ASTM testing and can vary slightly from batch to batch.
How Much High Heat Mortar Do I Need?
Count your standard 9 x 4.5 x 2.5 inch fire bricks and use the table below. The minimum order is 2 pails or 2 four-packs.
| What you buy | Total mortar | Lays about |
|---|---|---|
| 2 pails (50 lb each) | 100 lb | 250 to 285 fire bricks |
| 4 pails (50 lb each) | 200 lb | 500 to 570 fire bricks |
| 2 four-packs (15 lb pails) | 120 lb | 300 to 340 fire bricks |
How to Use Premixed High Heat Mortar
- Open and stir. If there's liquid on the surface, stir it back in or pour it off to get the consistency you want.
- Use dry brick. Damp fire brick slows the set.
- Butter and set. Lay each brick with a 1/16 to 1/8 inch joint. Never go thicker than 1/4 inch.
- Cap it right away. Close the pail tightly as soon as you're done. The mortar starts setting once it's exposed to air.
- If it freezes, let the pail thaw at room temperature before use.
Set Time and Storage
Typical set time is 48 to 72 hours. In cool, humid conditions it can take as long as a few weeks: the surface may harden while the mortar inside the joint stays workable. Once all the moisture has evaporated, it finishes setting. Shelf life is 6 to 12 months. Store sealed pails indoors. If the mortar gets too stiff, add a little water and mix. If it has dried in the pail, throw it out.
Safety and Handling
Like all refractory products, this mortar contains crystalline silica. Dust from dried mortar can damage your lungs over time.
- Wear gloves and safety glasses. Wet mortar can irritate skin and eyes.
- Wear a NIOSH-approved dust mask when cleaning up or cutting dried mortar.
- Work in a well-ventilated area, and don't eat, drink or smoke while you work.
- If mortar gets in your eyes, rinse with water. Wash skin with soap and water.
WARNING: This product can expose you to chemicals including crystalline silica, which is known to the State of California to cause cancer. For more information go to www.P65Warnings.ca.gov.
High heat mortar mistakes to avoid
- Using it outdoors. It's water soluble. Use Refractory Mortar for anything exposed to weather.
- Filling voids or thick joints. It shrinks and cracks thicker than 1/4 inch.
- Laying damp brick. It slows the set.
- Leaving the pail open. It starts setting as soon as air gets to it.
Which Refractory Mortar Do I Need?
We sell four refractory mortars. Only one is made for outdoor and DIY pizza ovens. The other three are for professional and industrial work. Since refractory products are non-refundable once shipped, please check this table before you order.
| Mortar | Comes as | How it sets | Rated to | Water soluble? | Outdoor / DIY ovens? | Made for |
|---|---|---|---|---|---|---|
| Refractory Mortar | Dry mix, add water. 50 lb bag or 4-pack of 10 lb pails | Hydraulic (chemical set) | 2,700°F | No, once set | Yes | Outdoor pizza ovens, fire pits, outdoor fireplaces and chimneys |
| Super Duty Mortar, Dry Heat-Set | Dry mix, add water. 55 lb bag | Heat-set (needs kiln-level heat) | 2,900°F | Until fired | No, industrial | Kilns, furnaces, forges and industrial equipment |
| Super Duty Mortar, Premixed | Ready to use. 50 lb pail or 4-pack of 15 lb pails | Air-set | 3,000°F | Until fired | No, industrial | Kilns, furnaces, boilers and indoor high-heat equipment |
| High Heat Mortar, Premixed (Medium Duty) | Ready to use. 50 lb pail or 4-pack of 15 lb pails | Air-set | 2,700°F | Yes | No, indoor only | Indoor fireplaces, fireboxes and wood stoves |
Building a pizza oven, fire pit or anything that will see rain or snow? Choose Refractory Mortar. It's the only one of the four that stays put outdoors.
High Heat Mortar: Frequently Asked Questions
Can I use this mortar for my outdoor pizza oven?
No. It's water soluble and will wash out of the joints when exposed to rain or snow. For pizza ovens, fire pits and outdoor fireplaces, use our outdoor-safe Refractory Mortar.
What is it best for?
Laying medium duty fire brick in indoor fireplaces, fireboxes and wood stoves.
How hot can it get?
It's rated to 2,700°F and passes the ASTM pier test at 2,730°F with no flow from the joints and no cracks or shrinkage.
How thick should the joints be?
1/16 to 1/8 inch. Don't apply it thicker than 1/4 inch or use it to fill voids. It will shrink and crack.
How many bricks does one pail lay?
About 125 to 140 standard fire bricks per 50 lb pail, and about 150 to 170 per 4-pack of 15 lb pails.
How long does it take to set?
Typically 48 to 72 hours. In cool, humid weather it can take up to a few weeks.
Is there a minimum order?
Yes, the minimum order is 2, either two 50 lb pails or two 4-packs of 15 lb pails.
Can I return it?
Refractory materials are non-refundable once your order has shipped. If you're not sure which mortar you need, contact us before you order.
How fast does it ship?
It ships within 1 to 2 days, with FREE shipping to the contiguous United States.
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
FREE shipping on every refractory product to all locations in the contiguous United States (the lower 48 states). Orders ship by ground carrier or commercial freight, depending on size, and freight carriers will call to schedule delivery. Please leave a phone number we can reach you at in the order notes.
Shop Refractory Materials
Every refractory product ships FREE to the contiguous United States.
Ready-to-use mortar for indoor fire brick
Choose a 50 lb pail or a 4-pack of 15 lb pails at the top of the page. Minimum order of 2, and shipping is FREE.
Not sure this is the right mortar for your project? Contact us before you order and we'll help you choose.
Specifications are typical values from standard ASTM testing and can vary slightly from batch to batch.
