Mortar or thin-set mortar for filling brick joints in hearth pad?

Kfm

New Member
Jul 16, 2020
5
Juneau
Question for anyone with brick hearth pad building experience: what should our joints be filled with? Mortar or thin set? We used thin set for adhering the brick to the Durock with a 1/4” notched trowel - spritzed with water first - which worked great and the bricks are very firmly adhered. Due to the required dimensions of our hearth pad and brick size/spacing, we have a little over 1/2” gap between all of our bricks. We are worried the thin set won’t dry when it’s applied so thick and that it won’t provide enough strength to keep the bricks in place over the years as people stand on the hearth pad. We found Rapid Set Mortar Mix at HD and are wondering if that would be better? Or another type of standard mortar? We are wary of using mortar because of another thread on here where a guy said his S type mortar didn’t adhere his bricks... that being said our bricks are already adhered, we just need to fill the joints. Seems like thin set is best for it’s fine sand/adhesive properties whereas mortar is best for filling larger gaps and structural strength? Is that right? For reference, here’s a pic of the hearth pad currently and the thin set we used. We have a 300 lb Supreme Vision that will go on top of it. Bricks are at least 100 years old - from the fireplace we removed, hence the rustic look - not sure if that makes a difference in joint-filling. Thanks for the help!
image.jpg image.jpg
 

RetsooR

New Member
Nov 21, 2019
39
41224
Quikreet makes a grout for this. Sold in 50lb bag. It can be thinned and poured in those joints if you like. You can also mix it thicker and tuck point . If you mix thin just pour in and use some sponges and a bucket of water to remove excess after it has set little.
 

RetsooR

New Member
Nov 21, 2019
39
41224
Just to clarify. The problem you don't want is having whatever you put in there shrink and leave cracks between the brick and grout. It's usually recommended to wet cure for a certain amount of time after application. Many products will work for you . The problem is hardly anyone wants to keep there project wet for 3 or 4 weeks after they complete it.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,568
central pa
It is just brick so use regular mortar don't try to treat it like grout those old brick are so porous it will be a complete mess. And no need to wet cure at all.
 

Kfm

New Member
Jul 16, 2020
5
Juneau
Just to clarify. The problem you don't want is having whatever you put in there shrink and leave cracks between the brick and grout. It's usually recommended to wet cure for a certain amount of time after application. Many products will work for you . The problem is hardly anyone wants to keep there project wet for 3 or 4 weeks after they complete it.
Ah ok thanks for clarifying! That makes sense. It doesn’t look like this stuff needs to wet cure: https://www.homedepot.com/p/Quikrete-50-lb-Non-Shrink-Precision-Grout-158500/100318529
 

Kfm

New Member
Jul 16, 2020
5
Juneau
It is just brick so use regular mortar don't try to treat it like grout those old brick are so porous it will be a complete mess. And no need to wet cure at all.
Hm ok. I wonder if spraying them with water first is what helped the thin-set mortar work so well since they had already been saturated with water when they came in contact with the thin set. We could spray them again before applying the Quickrete product. Or try regular mortar. Just concerned it won’t adhere as well as something more grout-like. But you’re right - they’re definitely porous.
 

RetsooR

New Member
Nov 21, 2019
39
41224
You can use the quickreet just like regular mortar.. just don't add as mutch water.. You application is exactly what that stuff is made for. I'm sure it has more lime in it. Most likely some polymer. I'm also sure it should be wet cured. Anything you use should be wet cured. Regular mortar only needs about 36 hours though. Just read the directions on whatever you use.. and don't use the thinset. You will definitely have a sticky mess. Oh yea if you can read some more on it I think the grout will have a water reducer in it..just means you can make it workable with less water.. less water equals stronger.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,568
central pa
Yes with old brick like that I always dampen them first. They are so porous they suck the water out very quickly making the bond weak.

As far as wet curing goes it is completely unnessecary. I have been doing masonry a long time and have never wet cured brick and have never had issues. And none of the courses I took on masonry called for it.

With old soft brick I would recommend a weak mortar. Type n or even type o would be appropriate. Your mortar should always be a little softer than your masonry units. Although it doesn't matter as much because it is interior only.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,568
central pa
If the weather is over 75 degrees we do wrap the chimney with plastic though to slow the drying process. But in a house for this application I don't see any reason to worry about any of that.
 

Kfm

New Member
Jul 16, 2020
5
Juneau
Thanks guys!! We used rapid set mortar mix from Home Depot. We sprayed the bricks down with lots of water prior to application and it took a lot of elbow grease with a wet sponge to get the bricks clean - we kind of dumped the mortar on top and spread into the joints bc we were afraid of it setting to rapidly. We found we actually had plenty of time to work but maybe that’s because of our 55F Juneau summers. We then sprayed water over the next 30-60 mins if it looked dry but it was pretty wet from all the sponge work. We also covered in plastic to create a greenhouse effect but probably wasn’t necessary. Anyway thanks for all the input, we’re really happy with the result. Still need to sand and stain the wrap but that’s about it.
 

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begreen

Mooderator
Staff member
Nov 18, 2005
82,969
South Puget Sound, WA
Looks nice though maybe a little shy on the sides? What does the manual say? If you want to remove some more of the mortar haze, wipe down with muriatic acid.
 

Kfm

New Member
Jul 16, 2020
5
Juneau
Looks nice though maybe a little shy on the sides? What does the manual say? If you want to remove some more of the mortar haze, wipe down with muriatic acid.
Thanks! We'll try the acid. The manual requires 16" in front of each door, and 44" wide, which we have. Might get around to adding a little mortar crack repair once we no longer have a hole in our roof :D
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,568
central pa
I would not recommend acid on old soft brick
 

begreen

Mooderator
Staff member
Nov 18, 2005
82,969
South Puget Sound, WA
I would not recommend acid on old soft brick
I did it on our entryway, made from old soft brick. 15 yrs. later it is fine. You wash if off thoroughly. If concerned one could follow with a baking soda treatment, but we didn't do this.
 

begreen

Mooderator
Staff member
Nov 18, 2005
82,969
South Puget Sound, WA
Thanks! We'll try the acid. The manual requires 16" in front of each door, and 44" wide, which we have. Might get around to adding a little mortar crack repair once we no longer have a hole in our roof :D
OK, it didn't look 44" wide in the pic, that was why I asked. Camera shots can be deceptive.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
21,568
central pa
I did it on our entryway, made from old soft brick. 15 yrs. later it is fine. You wash if off thoroughly. If concerned one could follow with a baking soda treatment, but we didn't do this.
I have seen it eat allot of the brick we have here. I guess it really depends upon the type of clay used for the brick. Ours usually have fairly high lime content
 

begreen

Mooderator
Staff member
Nov 18, 2005
82,969
South Puget Sound, WA
Could be. I suspect our bricks were made from local clay. They are from our fireplace removal and outdoors. I made our entryway step out of them. I think following up with a baking soda bath will neutralize any residual acid.
 

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