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Old 11-08-2009, 06:43 PM
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Default Obligatory first-time-mortar-concerns post

I mortared my first bricks last night (pairs together, for later transport to the hearth) and then the first courses today. I used Lars' 6:4:2:1 recipe with about 4 to 4.5 parts water.

I have four questions: behavior over time, recipe, sand, watered consistency.

First, after twelve hours, and again this evening (about twenty-four hours) -- admittedly not very long yet -- the mortar seems very tacky and small globs break off easily (not chipping like old concrete, but like dried glue. Despite extremely ginger care when transporting brick-pairs to the hearth, admittedly a few were abused and easily fell apart...which I then bar-clamped together and left to sit, although I'm not sure if a break after twelve hours can simply be pushed back together or if it is too late at that point.

Question one: is this behavior from the mortar acceptable? I thought it should act like concrete and be impressively hard the next day. Admittedly, numerous posts on FB confirm that this might be okay, so I'm trying not to worry about it, but it seems a little odd to me that is stays soft for so long.

Question two: There seem to be almost as many recipes as oven-builders. I am NOT asking which recipe people blindly recommend, FB already has no shortage of such posts. What I would greatly appreciate, however, is an understanding of what effect variations of the recipes should have. For example, Lars' increased the fireclay and decreased the lime relative the James'. Many other recipes do something similar. What does each change do? What does increasing the fireclay do? What does decreasing the lime do? Many recipes increase the sand. Some completely dismiss lime entirely. How should these changes affect mortar? I could experiment, except that I wholly admit I don't even know what to look for, which makes "playing around" rather unproductive. Experimenting is only useful if you know what you're shooting or.

Question three: I bought the white silicate sand available at Home Depot (100 Lb. #30 Silica Sand - 362201999 at The Home Depot), image attached (the image shows "settled" sand, the smallest grains after shaking it level. There are slightly larger grains below the surface I'm afraid.). My mortar has a gritty consistency, as one would expect from such sand. I find this at odds with the numerous "peanut-butter" recommendations, although I admit that that is w.r.t. water, not sand. Is everyone's mortar gritty?

Question four: Water. I know the peanut-butter mantra, but I'm not sure I "get" it. The mortar is very unlike peanut-butter due to the sand, so any advice on this topic would be appreciated. What I used today was 6:4:2:1:4-1/2 (sand, fireclay, portland, lime, water). I felt that 4 parts water was too dry and 5 parts was pushing runny...but I just don't know what to shoot for...sigh.

If you read this far, thank you.

Cheers!
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  #2  
Old 11-08-2009, 08:11 PM
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Default Re: Obligatory first-time-mortar-concerns post

hey keb..

What type of portland are you using ? n, s, ?

The peanut butter thing, I didnt use the home brew, Used the Heat Stop. It may not be the same for the home brew...

Part of your problem could be the hand mixing, you may not be getting a good consistency that way...

sorry im not answering your questions directly as i dont have the answers, just trying to get some more thought on it and Im not being critical of you just trying to help..

also dont forget you are moving the bricks, In a dome situation they are under constant pressure holding them in place and keeping pressure until your bond forms and cures,

dmun pre joined his cut bricks for his dome, but he also used Heat stop 50,, Maybe the home brew just cant acclomplish a joint properly this way...

Hope my thoughts arent making you more nuts

Cheers
Mark

are you keeping your joints moist after they start to dry...
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Old 11-08-2009, 08:42 PM
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Default Re: Obligatory first-time-mortar-concerns post

Quote:
Originally Posted by ThisOldGarageNJ View Post
hey keb..
What type of portland are you using ? n, s, ?
I got the standard stuff from HD, labled type 1 and 2.: 94 Lb. Lafarge Portland Cement - 352903999. I don't know if it's N or S. The lime is type S however.

Quote:
Originally Posted by ThisOldGarageNJ View Post
hey keb..
Part of your problem could be the hand mixing, you may not be getting a good consistency that way...
I'll buy a drill mixer from HD tomorrow. It's $13 instead of $4 (from HF), but I don't want to drive to HF.

Quote:
Originally Posted by ThisOldGarageNJ View Post
hey keb..
sorry im not answering your questions directly as i dont have the answers, just trying to get some more thought on it and Im not being critical of you just trying to help..
No no. I appreciate the feedback. Thanks.

Quote:
Originally Posted by ThisOldGarageNJ View Post
hey keb..
also dont forget you are moving the bricks, In a dome situation they are under constant pressure holding them in place and keeping pressure until your bond forms and cures,

dmun pre joined his cut bricks for his dome, but he also used Heat stop 50,, Maybe the home brew just cant acclomplish a joint properly this way...
An excellent point, worthy of consideration. That part's pretty much done anyway. I was only doing that for the first three flat courses. I had considering making my inner arch separately and transporting it in one piece, but now, maybe not.

Quote:
Originally Posted by ThisOldGarageNJ View Post
hey keb..
are you keeping your joints moist after they start to dry...
Hmmm, I can easily mist it on occasion, as I did with the concrete at earlier stages. Thanks for the tip.

Cheers!
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  #4  
Old 11-08-2009, 08:45 PM
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Default Re: Obligatory first-time-mortar-concerns post

Quote:
Originally Posted by ThisOldGarageNJ View Post
What type of portland are you using ? n, s, ?
The HD website says it's pressure rating is "N/Apsi". Is that what you mean?
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Old 11-09-2009, 04:43 AM
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Default Re: Obligatory first-time-mortar-concerns post

Mortar Cements

Type N Cement
For Exterior, Above-Grade Walls.
Type N is a medium compressive-strength cement. Type N is recommended for most exterior, above-grade walls exposed to severe weather, including chimneys.

Type S Cement
High Strength Non-Shrink Grout.
Type S is sometimes specified for masonry at or below grade, but offers another quality. S has high compressive strength, but adds high tensile bond strength.



Portland Cement Association
Type 1 - Normal portland cement. Type 1 is a general use cement.

Type 2 - Is used for structures in water or soil containing moderate amounts of sulfate, or when heat build-up is a concern.

Type 3 - High early strength. Used when high strength are desired at very early periods.

Type 4 - Low heat portland cement. Used where the amount and rate of heat generation must be kept to a minimum.

Type 5 - Sulfate resistant portland cement. Used where the water or soil is high in alkali.

Types IA, IIA and IIIA are cements used to make air-entrained concrete. They have the same properties as types I, II, and III, except that they have small quantities of air-entrained materials combined with them.



Water to Cement Ratio: The #1 Issue Affecting Concrete Quality
A low water to cement ratio is the number one issue effecting concrete quality.

The ratio is calculated by dividing the water in one cubic yard of the mix ( in pounds) by the cement in the in the mix (in pounds). So if one cubic yard of the mix has 235 pounds of water and 470 pounds of cement- the mix is a .50 water to cement ratio.

If the mix lists the water in gallons, multiply the gallons by 8.33 to find how many pounds there are in the mix.

Low water cement ratio impacts all the desired properties of hardened concrete listed in desired properties of concrete.
Use a maximum .50 water to cement ratio when concrete is exposed to freezing and thawing in a moist condition or to deicing chemicals per the 1997 Uniform Building Code. (Table 19-A-2)

Use a maximum .45 water to cement ratio for concrete with severe or very severe sulfate conditions per the 1997 Uniform Building Code (Table 19-A-4)

Water permeability increases exponentially when concrete has a water cement ratio greater than .50.

Durability increases the less permeable the concrete mix is.

Strength improves with lower water cement ratios. A .45 water cement ratio most likely will hit 4500 psi (pounds per square inch) or greater. A .50 water cement ratio will likely reach 4000 psi or greater.
Cement Types
************************************************** ********
Hydrated lime is used as a component in building products such as mortars, plasters, whitewash and stuccos. For building lime products, two different types of hydrated lime products are defined in ASTM standards:


Type N or Normal hydrated lime products are only partially hydrated and/or have poor workability. Additional additives and/or long soak periods are required for these products to perform effectively in building applications. At least a 24 hour soak period is required before Type N dolomitic hydrated lime can be used acceptably for masonry or plaster applications. High calcium hydrated lime products normally are classified as Type N hydrates due to their poor water retention. ASTM C270 (Mortar for Unit Masonry) states that if a portland cement/lime blend contains Type N hydrated lime, the blender must show through performance or testing that the Type N product is not detrimental to the soundness of the mortar.


Type S or Special hydrated lime products are a combination of calcium and magnesium hydroxides. Type S hydrated lime products are characterized by their chemical purity, high level of hydration and water retention. In building applications, Type S hydrated lime products have high hydration levels and controlled plasticity (water retention). This allows for minimal soak periods prior to application. Though there are some high calcium Type S hydrated lime products, most building lime applications utilize Type S dolomitic hydrated lime.

we all love Home depot, But sometimes thier lack of knowledge on certains things really sucks,, I would consider after reaading all this,, you can either call or stop by your local masonry supply, explain your situation and often these guys will be filled with good knowlege...

Hope some of this if not helping, explains it more for you..
Im also wondering if your sand is too grainy...

When I mixed my Vermicrete, I measured everything with coffee cans and scraped the extra off the top.. How are you measuring ??

Cheers
Mark
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Old 11-09-2009, 05:08 AM
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Default Re: Obligatory first-time-mortar-concerns post

some more info:
Soft sand (or Builders sand): a smooth sand, non-gritty, loamy and with cohesive properties, can be used for:

Bricklaying mortar
For bedding paving slabs
For rendering walls


Sharp sand: this has a gritty feel and is similar to that used to condition soils and potting composts, can be used for:

Concrete
For rendering floors and walls
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Old 11-09-2009, 05:15 AM
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Default Re: Obligatory first-time-mortar-concerns post

one more thought before I leave for work,, Lime, can act as an accelerator in the mortar, making it set too fast before it binds.. try a small batch without it.. Im thinking you could almost go without it...

Good Luck... The drill mixer should help a lot too...
Looking forward to hearing your progress later
Mark
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Old 11-09-2009, 10:03 AM
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Default Re: Obligatory first-time-mortar-concerns post

Wow, thanks for all the great info. You commented on HD. Just to be clear, I got my fireclay and lime from a masonry supply, my Portland cement and silica sand from HD, so my current ingredients are:
Your comment above suggests that smooth sand is good for certain mortars. I had read that you always want sharp-edged sand so the lime (and other powders?) grip and coat the sand securely. Thoughts?

I also found this disturbing comment and then again about the fireclay on two different sites. I wonder what that means.

I found a reference that describes the Lincoln fireclay as:
  • SiO2 52.29%
  • Al2 O3 32.55
  • Fe2O3 2.19
  • MgO 0.55
  • CaO 0.19
  • K2O 0.76
  • Na2O 0.33
  • L.O.I. 11.14
  • P.C.E. 30 31.5

Gladding McBean, the distributor of Lincoln Fireclay 60 has an official tech sheet which doesn't differ too much from the numbers shown above.

So, what do you think? Are those approximately the right ingredients? Should I replace any of it in my future mixes, perhaps the sand and/or fireclay?!! I think the Portland and lime are probably right, right? I posted a photo of the sand earlier in this same thread to show scale and texture.

Thanks, as always.
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Old 11-09-2009, 05:13 PM
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Default Re: Obligatory first-time-mortar-concerns post

Hey Keb..
Quote:
silica sand
It's kinda odd, as your finding out the more you read the more contradictions you get.. As far as sand, the best I can determine is silica sand, washed 1-3 mm in size,,, smooth in texture for mortar use....
Quote:
Home Depot LaFarge Type I & II Portland cement
Type I Portland Cement
Type I Portland cement is general purpose cement with no particularly special attributes. It is suitable for use in general applications, however it should not be used in applications where the cement will be in contact with the ground, or with ground water, as these substances tend to contain sulphates which can attack the cement and make it expand and distort out of shape.

Type II Portland Cement
Type II Portland cement has some sulphate resistance, and releases less heat during setting and hardening than Type I Portland cement. Type II cement is therefore suitable for construction projects which involve exposure of the cement to ground water, such as pavements and drainage systems. Type II cement can also be used for large scale work such as retaining walls and other such masses.

Im assuming this description is the same for Type 1 & 2 (combined) so so far I think your okay....

It sounds like you pretty much have it good..

My comments as follows

Mix a small batch and measure precisely,, level cups etc...
Use the drill and premix your dry ingredients
add the water and use the drill till thoroughly mixed..
you might want to lighten up on the lime to slow the setting some,
dip your bricks in water for a few before mortaring
butter the brick and use the trowel handle to tap it in place, will help it set in

if i think of anything else I will let you know...

Good Luck and keep me posted, Hope I helped
Mark
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  #10  
Old 11-09-2009, 06:34 PM
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Default Re: Obligatory first-time-mortar-concerns post

A couple of things. Lime is a plasticizer, not an accelerant. It does not increase the set time, it decreases it. Portland is used in lime plasters to gauge them, i.e. give them a faster set FYI. The purpose of the lime is to improve workability, board life, and plastic cracking (it improves the water tightness of the mortar as well).

ThisOldGarageNJ, the information you posted about water is for CONCRETE not mortar and does not apply. For mortar you can mix it wetter and even add more water and re temper it. That is a big no-no for concrete. Since you are laying very non-absorbent firebrick, you will want the mortar to be drier than if you were laying your CMU, but it is not nearly as critical as it is with concrete.
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