I used Portland cement with lime mixed in

Hi, I did not read any of this before I started my oven. When making my high temp mortar I used Portland cement with lime added. I have seen everything now telling me this was a bad move. I have only placed 5 rows on one side of the oven and 4 rows on the other side. Do I need to rip all that out and start the dome over?

Hello Bradlee,
Welcome to the forum. I’m sure either @bikerbudmatt and/or @BrickWood will chime in but I’m pretty sure you should hit the redo button on the arch. The high temp mortar has Portland cement, lime AND silica sand and fireclay. Without the last two ingredients I’m afraid your mortar will just crack and fall apart due to the thermal cycling in the oven.

Thank you, I did not mention it was not just Portland cement I put that up with. I used the other ingredients you suggested, ( silica sand, fire clay) I just did not get a separate bag of hydrated lime. I used the Portland/lime mix.

Thanks for the clarification. Do you have the info on the Portland cement/lime mixture? I could see it working if it was a 1:1 mixture of Portland cement and type S hydrated lime. Not enough lime or the wrong type of lime and it can cause trouble. If you don’t know then assume the worse. See the attached link:

This is what I used. It does not have a ratio on the bag. Thanks again

That’s funny. This is manufactured about 20 miles from me and I didn’t know they existed until your post :slight_smile:

Here’s the spec sheet:

It does have the right type of lime. The bad news is that the ratio is 2:1 Portland cement to hydrated lime (type S mortar) and you want a 1:1 ratio so it is different than the highly recommended high temp mortar.


Your awesome kgondoly, I appreciate all your help. With that being said would you start over? If I absolutely have to I will. My kids and I have put HOURS into this already and dont want something that’s going to fall apart.

I’m split on this… but if it were me, I’d keep on building, but use a different Portland (one w/out lime). And that’s ONLY if you just built as far as shown in your pic.

If you built the entire oven, I’d be a bit concerned, but it looks like you only built a few rows on the sides. And the sides rarely get direct fire contact or retain the same intense amount of heat as the top / ceiling or back of the oven.

The mortar w/ the lime may start flaking (which is not good in food), but that won’t happen for a year or so. And IF that does happen (not saying that it will), you will need to occasionally pick / inspect those joints to remove any loose mortar. Keep in mind, the joints are 4.5" thick, so you won’t need to replace any mortar if you do loose a little here and there.

If you completed the oven, then yes, @kgondoly is 100% correct - you would want to consider rebuilding. But if it’s just a few rows… I’d keep on going. Keep in mind, these things are extra heavy duty, so “Uh-Ohhhhs” like this are usually okay.

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Hi Brad, and welcome to the BrickWood forum!

Along with @BrickWood I’m split. The extra lime is going to have a mixed effect: it will be strong, but it will retain water longer and need longer to cure.

I agree that you’re okay for the part you’ve built so far. But this is a time to pause and let it cure for a couple of extra days. Lime pulls in carbon dioxide from the atmosphere as part of its chemical curing, but you also need to protect it from rain. So I’d suggest a loose tarp, and let the arch base cure for 5 days to ensure that the mortar has set up properly. And as @kgondoly Ken says, use that time to get the two separate materials so you are ready to go when you resume building.

Follow @BrickWood’s recommendations, above, just to be sure that you’re not seeing any shedding of the mortar. My guess is that it won’t, but you just need to be a little mindful when you do your annual inspection.

Good luck with your build, @Bradlee Brad, and don’t let this worry you. With a whole family helping you out, your final oven is going to be extra-awesome.

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I really appreciate you. I will hold off with the build for now and go get the correct materials


3 posts were split to a new topic: Do I Need High-Temp Mortar For The Stucco Layers?