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boccu 01-04-2007 05:32 PM

underfloor mortar - wet or dry?
Should the sand / clay mix under the floor bricks be wet or dry? I understand that the main reason for this mix is to ensure as smooth a surface as possible, but the FB instructions are a bit unclear on this point:

Do not mortar the floor in place, but rather spread a thin layer of sand and fire clay to provide a slip plan between the oven and hearth. That will allow them to expand thermally at different rates.

The underfloor is paste, the texture of a sticky mortar, comprised of 1 part fine sand and 1 part fireclay

Any thoughts?

fdn1 01-05-2007 06:27 AM

Re: underfloor mortar - wet or dry?
The use of the adjective "paste" is misleading. Laying the mixture dry provides you, amongst other things, the opportunity to level the firebricks. One way of doing this is to gently tap the top of say a piece of "flat" lumber that spans several rows or columns of bricks to eliminate any difference in sapce betweeen the bottom of the wood and the top of the bricks.

A dry mixture also makes it easier to remove any damaged bricks in the future should that be necessary.

pjones 01-05-2007 07:47 AM

Re: underfloor mortar - wet or dry?
I am laying down my floor today or tomorrow and I was also thinking it was a paste with water added. I am glad this came up for discussion.

DrakeRemoray 01-05-2007 08:35 AM

Re: underfloor mortar - wet or dry?
Well....I used a paste of fireclay and sand mixed with water. I troweled it with a 1/4" tile setting trowel before laying the bricks on. It worked well for me.


boccu 01-05-2007 09:49 AM

Re: underfloor mortar - wet or dry?
since writing my query yesterday, I was thinking that perhaps the difference is in the use of the word 'mortar', which is probably what misled me. I now think that perhaps the important thing is not to add any cement to the mix (which is what would make it 'mortar'??). Whether it is wet or dry then becomes a personal choice on what works best to level out the bricks.


james 01-06-2007 07:42 AM

Re: underfloor mortar - wet or dry?
I think the "personal choice" comment is a good one, as there are a number of methods that will work. Though I think the paste method is the best. For a brick cooking floor, you can use either:

1. A fireclay and sand paste, mixed with water -- you use a knotched trowel to spread it so you can tap the bricks level. The process is like setting tile, but you don't use a cement-based mortar.

2. A dry fireclay and sand mix. You can still set the bricks level that way, through it might be a little more difficult to set the floor.

3. Sand by itself. It you want to keep it simple, or not have to shop for fireclay, sand will do it. Again, it might be a little more difficult to get the cook floor set as level as possible.

I have re-written the cooking floor page of the Pompeii oven plans, which I think are now more clear. Take a look:

Comments are always appreciated.


boccu 01-06-2007 12:33 PM

Re: underfloor mortar - wet or dry?
ta james - much clearer that way in my opinion.

Pannabecker 07-25-2007 06:28 AM

Re: underfloor mortar - wet or dry?
I used the fireclay, sand paste yesterday and today some of the bricks are still loose. It's also been rained on and I'm concerned my floor is too loose. Nothing has moved but I'm concerned about moving on to building the dome.

Unofornaio 07-25-2007 10:36 PM

Re: underfloor mortar - wet or dry?
Don't be, fire clay will stay soft for a very, very long time its final set (hardening) is with heat, depending on weather and thickness it can stay soft for days. This mixture for the floor is really only there to enable setting the bricks level. I would purchase a tarp, your gonna need to keep the rest of the build from this point on out of the rain.

Good luck

Pannabecker 07-26-2007 02:40 AM

Re: underfloor mortar - wet or dry?
I'll do that. I ended up taking the whole floor up anyway because I looked at my bag of "fireclay" yesterday and saw they store delivered me one bag of ground clay, not fireclay. Wouldn't you know, that's the one I chose to open and use. I cleaned it all up and used the right stuff and I got it layed tighter and smoother anyway. I feel better. Today I begin the dome. I'm excited.

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