Scratch coat for veneer

[paponte]

I didn't want to hijack Adam's thread, but I have got to ask. I see almost every one of you guys doing a scratch coat over newly installed block. Why is this? I can't for the life of me understand why you would waste such a great amount of time and material doing that?

Also , I've never seen anyone use any brick ties Not starting any fights here, just wanted to hear the reasoning behind this and your point of views. I have always just blocked and used brick ties, then just veneered directly over the block, utilizing the staggered ties in my joints. :noidea:

[MuirView Design]

Paul, I do a scratch coat with cultured stone and brick ties for natural stone veneer. I think the scratch coat is cheaper and faster. I also like to be able to lay the block a little quicker and not have to worry about all the joints being perfectly sealed, as the scratch coat will plug any holes.

Lick and stick adheres well to a scratch coat. Just a personal method...I'm always open to change though.

[joeymaze]

Paul,
I Apply a scratch coat to block for a couple of reasons. First the grooves(scratches) in the mortar make a better surface for bonding the veneer. Second, A scratch coat puts a barrier between the block and the stone. This way the porous block doesn't suck the water out of the mortor too quick when applying the veneer potentially weakening the bond. Especially important if not pointing the joints( dry stack, ledgestone) Of course you could probably get away without a scratch coat but why tempt fate your name is on the job. Heck, I have even seen were guys will scratch coat and apply stone in the same day.:scared:

[paponte]

I think the scratch coat is cheaper and faster.

Adam could you elaborate on that a little? It's extra time and material, Thanks.


the grooves(scratches) in the mortar make a better surface for bonding the veneer.

I can see it bonding to the scratch coat better, but the scratch coat is still bonded to the cmu the same way as if it were directly applied. So if the scratch coat gives, essentially the veneer would pop regardless.

I think the thing that bothers me is that a scratch is such a thin coat. I feel much better using a good backer and letting it all squeeze into my joints utilizing the brick ties.

I also don't like to tempt fate, and it literally is my name on the line. I believe in building bigger and better, hence the reasons for my questions. I don't like doing something because that's how someone said to do it. I like to understand the science behind it and to be able to explain why we as a company do it. I've never had a problem with any of our veneer installs, but if I am in fact doing it the wrong way I would like it explained. If not, then I could save someone alot of time and material. :thumb:

[joeymaze]

Adam could you elaborate on that a little? It's extra time and material, Thanks.

I also don't like to tempt fate, and it literally is my name on the line. I believe in building bigger and better, hence the reasons for my questions. I don't like doing something because that's how someone said to do it. I like to understand the science behind it and to be able to explain why we as a company do it. I've never had a problem with any of our veneer installs, but if I am in fact doing it the wrong way I would like it explained. If not, then I could save someone alot of time and material. :thumb:

Sorry dude didn't mean to offend, I was just using a figure of speech not refering to yours or any other company.

Your scratch coat and slurry mix will have bonding adhesive mixed in that will greatly add to the cohesiveness. Also seals the moisture out of the block.

[CaptainsLS]

Paul, it’s actually pretty straightforward. You have 2 types of veneer. Full-dimensional (5-7”) and thin stone (1-2”). (these are actually determined by weight but I forget the spec’s)

Thin stone does not require ties to the block.

Full thickness veneer requires ties and a shelf.

In regard to the scratch coat over CMU for natural thin stone, it’s not necessary. A bonding agent however is necessary. Over other back-up’s a scratch coat may be needed. I personally do apply one. It allows for a nice bond and we like to parge all of our block work, plus it addresses any imperfections in the block work.

[CaptainsLS]

This way the porous block doesn't suck the water out of the mortor too quick when applying the veneer potentially weakening the bond.

It is more cost effective to just dampen the block than apply the scratch coat.



Heck, I have even seen were guys will scratch coat and apply stone in the same day.

This is a non-issue, there is nothing wrong with parging CMU's as you work as long as you are applying natural thin stone.

[paponte]

Sorry dude didn't mean to offend, I was just using a figure of speech not refering to yours or any other company.

No reason to apologize dude, there was nothing offensive said. Simply just a conversation, and as I stated not meant to offend anyone in any way. Were all professionals on here and there are many different techniques and we were probably all taught differently as well. I'm just looking for the technical aspect of the "belief" of the need for a scratch coat.


It is more cost effective to just dampen the block than apply the scratch coat.

Ditto

As far as the ties go, you are correct. We will not use ties in thin stone on a small installation. However on a larger application we will. sort of cheap insurance for us. As far as a bonding agent I've seen guys both milk the cmu as well as add it into the mortar. Do I fully believe in it? Not sure, I think an experienced mason would be able to adjust the workability of his mortar to fit the specific jobsite conditions.

[MuirView Design]

Adam could you elaborate on that a little? It's extra time and material, Thanks.



I think we can parge coat a wall in 5 -10 minutes with less than a few dollars in mortar and sand. I don't know that it is a significant time or money savings to use ties. To each his own....as long as you can get good suction and do a thorough job pointing, the veneer will hold. I've seen veneer applied straight to block with no ties or scratch coat and hold up.

I like the idea of unifying the wall with a waterproofing coat. That's the main reason moreso than the veneer.

[paponte]

I like the idea of unifying the wall with a waterproofing coat.

Good point, can definitely agree with reasoning behind that.

[joeymaze]

I think an experienced mason would be able to adjust the workability of his mortar to fit the specific jobsite conditions.

Masons do that anyway to adjust for different Temperatures.(time of year etc.) It really doesn't have anything to do with adding bonding adhesive or not.

[CaptainsLS]

No one has suggested any method that is considered “incorrect or improper” – I just wanted to clarify that…..

There are however masonry construction standard guidelines set. Applying a scratch coat to CMU is only adding a step, not in anyway inhibiting the proper method.

[GreenMonster]

Can you guys explain in a little more depth how your are using brick ties in a stone veneer application?

[MuirView Design]

Mark, they go in the same way as for a brick application...just between the joints of the CMU to give the veneer something grab and bind it to the wall with....just as a brick laid against CMU would.

[CaptainsLS]

(I don’t want to sound like an arse, but if we could all use the correct terminology it would allow our conversations to be more fluent IMHO. I find myself rereading posts trying to identify what type of masonry is being talked about.)

Tying to the backup with cultured stone and natural thin veneer is not recommended. Full dimensional veneers that are structural –require- to be tied to the backup.

[MuirView Design]

I hear ya Captain. Out here the 7" veneer is not very common so most thin veneer is simply called veneer and the full size is called structural veneer or stone facing. In hardscaping, I think veneer is 99.9% of the time going to be referring to thin stone. I like the masonry section idea though. There is a lot of terminology I'd like to learn.

[GreenMonster]

Mark, they go in the same way as for a brick application...just between the joints of the CMU to give the veneer something grab and bind it to the wall with....just as a brick laid against CMU would.

OK. forgive me if I sound foolish, but in a brick application, they are placed to be bent into the mortar joint of the brick, correct? In a stone application, where your veneer is random, or mosaic, how are the ties used to further secure the stone? won't you end up with several ties installed that won't actually meet up in a joint where they can be of benefit?

[CaptainsLS]

Mark, picture a 6” thick stone veneer wall built in front of CMU construction. The brick ties span from the mortar joint in the block, through the air space, and into the mortar joint of the veneer. They tie the veneer fascia to its backup.

[GreenMonster]

Ok, I get it, in theory. but, don't you end up with a lot of ties that aren't placed such that they can actually enter the mortar joint of the stone?

[Mark]

Yes when you can't make them work you simply abandon them


Ok, I get it, in theory. but, don't you end up with a lot of ties that aren't placed such that they can actually enter the mortar joint of the stone?

[CaptainsLS]

The best way I can explain it is;

A (natural thin stone or cultured stone) is an -adhered- veneer thus relying on the bond between the unit and the backup from mortar/thinset. This system doesn’t benefit from brick ties since they are designed to hold 2 wydths together.

You could use ties to span adjacent courses (wydths) or to span running units. In a full dimensional veneer application, ties are needed to connect the wall to it’s back up since the system doesn’t rely on bonding to the backup.

[custom patios]

Paul, it’s actually pretty straightforward. You have 2 types of veneer. Full-dimensional (5-7”) and thin stone (1-2”). (these are actually determined by weight but I forget the spec’s)

Thin stone does not require ties to the block.

Full thickness veneer requires ties and a shelf.

In regard to the scratch coat over CMU for natural thin stone, it’s not necessary. A bonding agent however is necessary. Over other back-up’s a scratch coat may be needed. I personally do apply one. It allows for a nice bond and we like to parge all of our block work, plus it addresses any imperfections in the block work.

Captn I believe the THIN stone veneer should not exceed 8 lbs. per sq ft.

[paponte]

In the case where a tie does not line up with a joint, we simply just hook them so they will catch behind the stone. Alot of great questions and answers here young grasshoppers. :nerd:

[custom patios]

Captn I believe the THIN stone veneer should not exceed 8 lbs. per sq ft.

ah correction, the max weight is 15 lbs.
anything greater requires ties.

In case you guys need resources... look in the UBC uniform building code