# New hearth pad on top of existing pad? R value questions

Posted By shelster0805, Nov 12, 2017 at 4:08 PM

1. #1

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
So we are installing a Quadrafire Explorer III. We have an existing built-in hearth pad. It is flush with a wood floor and measures 44" wide and 36" deep, the bricks are a red, smooth brick that is 5/8" thick (which is flush with the floor). There is a crawl space under this flooring. We need to have an R Value of 1.06 for this stove and the Quadrafire manual says hearth should be 35 3/8" wide and 39 3/8" deep.

Our question is... how does this existing pad calculate into our new pad we are building. We have already purchased 1/2" Hardibacker 500, 1/2" Durock, and we have slate tiles to go over the top. We are planning to build the pad 60" wide and 58" deep.

Thank you for advise and input!

2. #2

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
It sounds like the pad you are building is going to be larger then the pad made out of bricks??

If that is the case then I would treat the existing pad as 0 r value since part of what you are building is going to be built directly on the wood.

Hardibacker 500 R value .20
Slate R value .10

Total of .69 R value so you need to add some more.

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3. #3

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
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4. #4

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
We are very confused with figuring out the R Value, we thought it was a certain formula with K value and C value??? Are you just adding these? If that is the case, it looks like we would need one more sheet of Durock to get to 1.06 but thinking we should add 2 layers for good measure.

Yes, we are going bigger. The stove will fit exactly on top of where existing pad is but we are adding out for the clearances out.

5. #5

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
Yes add them together. Thin set will add a little r value as well.

The brick you have is just a bonus. The entire pad needs to be at or above the r value required.

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6. #6

### edyit Minister of Fire 2. ```NULL ```

Nov 30, 2014
665
218
Loc:
Wilmington NY

https://www.chimneysweeponline.com/horvalue.htm

the entire hearth you are building is going to need the R value of 1.06, so anything that is going to built not on the existing bricks is going to need to be that as well, not just where the stove is sitting.

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7. #7

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
Thank you all for your information! When researching online the websites make the r value calculating seem very confusing! The chimney sweep website link you list is awesome! Answers a lot of questions. Thanks again

8. #8

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
And please read that link I shared closely unless of course your durock says next gen on it. There is still some of the low r value durock out there for sale and it makes a big difference how much you need.

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9. #9

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
Well, we have been to both Home Depot and Lowes a couple times in the last few weeks (this has been the never ending project haha). We really didn't notice this or think about until we read your link. But both places advertise that they carry the Next Gen and that is what their labels say... but the ones at Lowes do not actually say Next Gen on the cement board like what they advertise online but Home Depot does. We are going to go 4 layers thick to be on the safe side. Plus, I feel like it would be less likely to stub toes maybe if it is higher off the ground?? maybe This will also give us the room to do a nice trim of slate around the bottom instead of a wood trim.

10. #10

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
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11. #11

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
Thank you for sharing your post and pictures! You did a great job and love the look! I was worried we had the wrong durock but all these posts have been a huge help! We for sure have the right stuff. I am going to work on laying out the slate today and hopefully just mix up one batch of the thin set tomorrow. When I go back to Home Depot, I need to check about sealing the slate tiles we bought. I am also going to get with a manager about some information/advise one of their senior employees was giving us. He told us that we should just use 1 sheet of wonderboard and we would be good... I would hate for him to tell that to someone else that is not researching and then have a fire. Nice guy but needs to get updated on info!

12. #12

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
Some stoves only require ember protection. I'm guessing he assumed that was the case with your stove. Bad assumption.

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13. #13

### Vigil Igne Member 2. ```NULL ```

Apr 26, 2014
57
6
Loc:
Northern Wisconsin
Just throwing this in because I needed the same R-value after buying the same stove. After research, I used the following with R-value of 1.04 and then put Hardibacker on top for my slate. Bought it from an online source (I believe efireplacestore).

Micore-300 Mineral Fiber Board

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14. #14

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
When researching building a hearth pad, I thought I read that slate needed to be sealed. When I was at home depot, this same employee, told me it didn't and I did not see any sealer for sale by it. I am not feeling quite confident in his answer and need to research more on it. We bought slate tiles. They do flake but no one is going to be walking on it. Been a busy couple days away from the house. Need to sit down and do some reading today.

15. #15

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
The Micore 300 is very hard to find. We would of liked to have found that local... not even the fire store had it. How are you liking your stove? How many square feet are you heating?

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16. #16

### Doc C Minister of Fire 2. ```NULL ```

Jul 26, 2017
625
140
Loc:
Bonner County Idaho
My suspicion from your post is that you bought the 99 cent per square foot slate from home depot that comes in multiple colors.

Nothing wrong with them really. I have used countless square foot of those tiles and I also have used some of them in my entry way at my own home.

Some key points when working with those.

1. Be very rough with each one. I'm talking try to flex them, shake them, bend them, do everything you can to get them to break before you lay them. You will probably break about alot of them. Home depot will exchange all the broken ones. If you thin set them down and they are weak you will have a mess on your hands. Even not being walked on I would still do this.

2. Break off all loose flakes of slate before you install or seal them.

3. Use a good trowel. Around a 3/8" NOTCH not the V groove ones. Those tiles are not the same thickness as each other. And you will want the thickness of thinset to be able to make them flat.
Also try to avoid laying in straight lines. With the different size tiles it becomes obvious in lines.

4. 1/4" spacer or even a little larger if you don't mind bigger gaps. Those tiles are not rectified so you will have slightly different size tiles.

5. Large format thin set is what I have found best for slate even in the 12"x12" size. I don't use the added latex stuff they tell you to use. Unless my tiles are huge.

As far as sealing the tile because it's a hearth??? I can't think of any reason that you would HAVE too. Maybe some other folks have some logic to share here but I don't see a need.

With that being said. I would seal it. With a few caveats.

The sealer you get from home depot is mostly a water based surface type sealer. I have tried most of their sealers over the years and have been less them impressed with all of them. The problem is I can't find a sealer I really like for indoor use.

I still use the home depot sealer because it's just as bad as everything else and it's cheap.

The kind I use is the Tile Lab natural stone sealer.

If you put it on to thick it turns white, ruins your slate, and you have to take a stripper to remove it.

The only way I found to apply it safely is pour a little into a paint roller tray insert, use a large smooth sponge, and put on so little at a time that I have to do about 4 coats. I wipe it with the sponge until it's almost clear and then I let it sit until it dries and then repeat.

Just know that the nice shine you have when your done will disappear in a hurry with any traffic at all.

Also read the reviews on home depot and make sure you understand the problems with ANY of these sealers.

Any other questions let us know.

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17. #17

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
Thanks for all your advise! We took it and survived this project still married LOL! We are pretty impressed with ourselves. Once this burn season is over, we are going to do the back wall in the slate they sell for walls. We finally got the wood stove in on Thanksgiving Day when we had family over for help.

18. #18

### shelster0805 New Member 2. ```NULL ```

Dec 26, 2016
18
2
Loc:
Missouri
If I can figure out how to get on here with my phone, I will upload some pics