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Author Topic: Log Cabin Restoration - Chinking Questions  (Read 551 times)

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Online Suebrook Farm

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Log Cabin Restoration - Chinking Questions
« on: August 02, 2017, 07:32:42 pm »
I'm about to begin chinking an 1860's log cabin restoration.  I'm using cement / sand blend.  Most recipes I found call for lime, but one does not.  I've decided not to use synthetic chinking.

1.  What is the purpose of the lime?  The guy who did not add lime said his worked great.
2.  I've seen referenced "lime", "hydrated lime" and "masonry lime".  Are these all the same product?
3.  Do you have any recipes you've tried and recommend?

Here are some recipes I've come across (there are as many variations as homemade vanilla ice cream recipes) ...

1 part portland cement
3 parts sand
part masonry lime

2 parts portland cement
9 parts sand
1 part lime

2 parts cement
7 parts sand
1 part lime

1 part white cement
4 parts sand
1 part hydrated lime

1 bag portland cement
17 shovels sand

Thanks,
Steve

Offline Don P

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Re: Log Cabin Restoration - Chinking Questions
« Reply #1 on: August 02, 2017, 09:36:33 pm »
Masonry lime is hydrated lime, that is, quicklime (burnt limestone) that has had water added back to it. They are saying don't use ag lime which is simply ground up limestone (unburnt). There are specific types of hydrated lime for specific types of masonry and hydrated lime is also used agriculturally... so like everything you can get as picky or confusing as needed.

Hydrated lime absorbs carbon dioxide from the air and tries to return to being stone where ground up limestone is, ground up limestone. Limestone is calcium carbonate. When burnt it becomes calcium oxide, very reactive (it can burn you, blind you or destroy your lungs, this is thirsty stuff, hydrated lime is not to be taken lightly for that matter). When quenched in water it become calcium hydroxide... hydrated or slaked or "slack" lime. Over time it reabsorbs carbon dioxide and becomes calcium carbonate, limestone.

Dad remembers the plasterers digging a pit in the back yard early during construction, filling it with water and adding quicklime to begin slaking it. The longer that process aged the better the lime putty was for plastering the interior.

Lime helps make the mix stickier and less likely to crack. There are lime renders that contain no Portland and some folks say logs didn't rot as bad until we started adding Portland to the chinking. They have a good point but I have no experience there. I've removed that type of chinking and mortar here locally, Portland was pretty late arriving in these poor mountain counties. There is still the remains of an old lime kiln nearby, that was a local product where Portland cost money. I've removed 100+ year old "soft" mortar that had served well.

The recipe I've used is 1 part white Portland, 1/2- 1 part hydrated lime, 4 parts white sand. I did that as a 2 coat over expanded wire lath. Applying the first coat and scratching it well then working back around after that has cured and cracked applying the second coat and sponge finishing it with a well wrung out sponge to give a nice sand texture. Make sure you tuck the upper part of the chinking well under the log, you don't want to create a water trapping gutter, it has to shed water.

Offline logman

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Re: Log Cabin Restoration - Chinking Questions
« Reply #2 on: August 02, 2017, 10:51:12 pm »
I used Charles McRaven's recipe when I did this little log cabin.  I don't have his book handy to see what it was and can't remember.  It was a portland cement, lime and sand recipe.  It seems to have held up pretty well .  I built it back in 2000 and this picture was from a year or so ago.

  

 
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Offline Don P

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Re: Log Cabin Restoration - Chinking Questions
« Reply #3 on: August 03, 2017, 07:45:57 am »
McRaven's stone mortar recipe is 1/3 part lime, 2/3 parts Portland, 3 parts sand. I don't have Mac's chink recipe.

Portland is the compressive strength, type S mortar is 2200 psi mortar at 1 Portland, 1/2 lime, 4-1/2 sand
Type N is 750 psi at 1:1:6
Type O is 350psi at 1 Portland, 2 lime, 9 sand

In masonry terms the mortar should be the weak link, it is better to repoint than to replace broken bricks. That is why modern hard mortars destroy old handmade bricks where the old lime mortars are preferred for restoration work there. Stronger is not neccesarily the goal in all cases. Portland is what shrinks and cracks where the aggregate is stable, the sand doesn't shrink. Wood has a compressive strength around 350 psi. Not trying to direct just stuff to ponder.

Online Suebrook Farm

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Re: Log Cabin Restoration - Chinking Questions
« Reply #4 on: August 03, 2017, 08:40:26 am »
Thanks to both of you!  This is exactly what I was looking for and unable to find outside your forum.  I really appreciate the science behind it as well so I understand the "why".

Don two questions regarding your replies ...

1.  When you say "scratch" the first coat what exactly do you mean?
2.  Is there a reason you don't just do it all in one coat?

Thanks,
Steve

Offline logman

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Re: Log Cabin Restoration - Chinking Questions
« Reply #5 on: August 03, 2017, 08:54:29 am »
I also put on a scratch coat and then a final coat and used hardware cloth between the logs.
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Offline Don P

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Re: Log Cabin Restoration - Chinking Questions
« Reply #6 on: August 03, 2017, 08:08:55 pm »
Logman, we need to meet for lunch sometime. I used to be in Fleetwood every week but you know how life works, haven't been over there in a couple of years. I'm in Elk Creek between Independence and Wytheville.

The reason for a 2 or even 3 coat system (read up on stucco) is the scratch coat builds and gives a base but almost invariably cracks as it cures (read up on the difference between curing and drying mortar, you really want to cure this rather than having it dry out and turn to weak powder). I take a scrap of the lath and use it to rough up the surface of the trowelled scratch coat when it is thumbprint hard. This gives the finish coat something to mechanically bond to. The finish coat is about 1/4-3/8" thick. You can also add some of the bonding latex additives to improve the bond and flexibility, never tried it. If this fails there are modern brush over synthetic flexible chinks that can go over the mortar chink to reseal it. Mainly keep an eye on the upper log to chink lateral joint, you don't want to admit water. A real purist will take a grinder and cut a shallow drip groove on the underside of the upper log to create a drip ledge to help drop any water flowing down the face of the logs before it gets to that chink joint.

Offline logman

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Re: Log Cabin Restoration - Chinking Questions
« Reply #7 on: August 10, 2017, 09:53:05 am »
Logman, we need to meet for lunch sometime. I used to be in Fleetwood every week but you know how life works, haven't been over there in a couple of years. I'm in Elk Creek between Independence and Wytheville.
 

That is pretty land up there, we go that way sometimes to get to the interstate. 
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Online Suebrook Farm

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Re: Log Cabin Restoration - Chinking Questions
« Reply #8 on: Today at 08:35:16 am »
Thank you for the great advice!

Online Suebrook Farm

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Re: Log Cabin Restoration - Chinking Questions
« Reply #9 on: Today at 08:48:08 am »
I have another question about treating the logs ... I think I'll do it in another post.