Scratch Coat

bline22

Hello,
I am trying my hand at applying a cultered stone to a fireplace. I have the lathe up and am getting ready to apply the mortar. This brings me to my question. What type of mortar do i use for the scratch coat?

The stone that is going to get put up is either an elderado stone or an owins corning profit. On there site they say to use a "Type N" mortar, but I believe that is the type to use when applying the stone to the scratch coat?
Thanks for the help.

tkle

I use the same mud for both.

NJ Brickie

Type N would work fine.

jciotti7

I use type-s, more portland, sticks better.

bline22

Thanks for all of the responses. I went to Menards and Lowes yesterday in hopes of finding a type n but nobody had ever even heard of it. Everyone that works at our stores are a bunch of teenage kids though so it was the response I would have guessed i would get. Have any of you bought your type n or s mortar there?

Tscarborough

Type N is a strength designation, not a type of mortar. Pre-bagged mortar at the big boxes is usually formulated to the Type S specification just to cover their ass because it is usually so crappy. For your application, it is fine, however.

If you want to mix it yourself, the proportion specification for Type N mortar is: 1part portland, 1part Type S lime to 2-1/4-3 parts washed masonry sand, by volume. Or you can mix 1part Type N masonry Cement to 2-1/4-3 parts washed masonry sand, by volume.

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gallerytungsten

Try a masonry supply house.

NJ Brickie

All of the Lowes around me sell "mason mix" made by quikrete. Mason mix is a type S mortar. Type S is a bit stronger then N. You might be better off with this because it will be a bit stickier also. Not to mention stronger. I do not do alot of cultured stone work but i have use type M or N always because it was speced in the prints.

Tscarborough

Adhered stone manufacturers specify Type N mortar because it has better adhesion characteristics than type S mortar, as a rule. When doing segmental and adhered masonry, the Golden Rule is: Use the weakest (compressive strength) mortar possible for the application.

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NJ Brickie

What makes the adhesion value higher in lower strength mortar? Higher lime to cement ratio?

Winchester

I tried SikaBond construction adhesive for the first time and didn't like it.

The stones are being held on with screws while the crap cures and I'm going back on friday to grout with the premix mortar. I was reading the Owens Corning installation manual and noticed the construction adhesive was an option for interior installations... I should've just stuck with the normal way of doing it :P

I have no lathe on the plywood that the stones are glued to, and worried about the mortar grout now... Has anyone ever done this? Stupid instruction manuals giving me ideas. I'm too impulsive sometimes

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Ryan

loneframer

My mason bypassed the scratch coat and set the stone in the stucco wire with the colored mortar. 9 years later it still looks great. Owens Corning Carolina Ledge in Chardonney

Tscarborough

Construction adhesive has a final bond strength much greater than is needed. The problem, as you have found, is that it has no immediate bond strength like mortar does.

Adhesive bond in mortar is developed by the substrate and the stone/faux stone absorbing moisture from the mortar quickly. Construction adhesive is applicable to very few applications. Profit by Cultured Stone and Stacked stone by Eldorado stone are exceptions, although it is not the best solution in any case.

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Tscarborough

Loneframer, that is an acceptable method of application, if not the best for interior work.

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loneframer

It was actually exterior, but in any case they're still on the wall.

Tscarborough

The only problem with doing it on exterior is the possibility of moisture intrusion through gaps. On exterior it is better to have a solid coat first then wet set the stone.

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tkle

Specmix

bline22

OK i got some specmix and I got the scratch coat done i think. Here is a picture of it:

ww.flickr.com/photos/25179547@N03/3320211952/

This was just applied a few hours ago, but there are small chunks that I am wondering if, when it dries completely, do i need to knock off? I want to make sure the stone will adhere to this as best I can. Does this look correct as best you can tell from a picture??

The chunks were a result of using the trowel and letting the applied mortar sit until it had dried to some degree.

6stringmason

Couldnt see any pictures

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rbsremodeling

Hold up I can't believe I let this thread get this far out of hand



























are you licensed?

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