We have a cottage in northern Michigan built in 1913. It is frame construction faced with natural stone. The stone is smooth lake rock which is seen on a lot of older homes up here. The dimensions range from probably 3 to 5 inches in diameter Since Lake Michigan is still full of it, I imagine is was a popular and inexpensive building material.
The mortar around the stone has recessed significantly in the past 95 years, and I need to re-point it. I am looking for advice on the type of mortar to use. I have searched the archives but haven’t found anything that addresses repointing stone. Usually in a 95 year home the issue is using soft mortar to prevent damage to soft brick. I imagine I won’t have this worry because the rock is as hard as, well, a rock.
I am also interested in tips on packing and tooling the mortar joints. Some areas will need to be filled nearly two inches. The chimney was re-pointed before we bought the place, and it appears that some of the “tooling” was done by hand, probably by someone wearing a heavy glove.
I am not concerned about matching the color or tone of the original mortar. The whole house needs to be done, so there will be no original to match. This will be a long term project, and I will just do sections until I get done.
Any advice will be appreciated.
Replies
The mortar on your cottage is probably a portland cement/lime mortar. Portland cement was first manufactured in the US in the 1870s. Lime has been with us since biblical times; the remains of a lime kiln in Mesopotamia are dated to about 2450, B.C. Mortars made from a mixture of portland cement, lime and sand were very common in 1913.
In the late 1920s, a competitor to portland cement/lime mortars was developed: namely, masonry cement. Like portland cement/lime mortar, masonry cement has, as its primary bonding ingredient, portland cement. But, instead of lime, it uses proprietary ingredients (pulverized clays, latex, ground limestone, etc.). Both lime and the proprietary ingredients ingredients in masonry cement are used for three main reasons: 1.)they make the mortar easier to work with; 2.) they help retain moisture in the mix (which lengthens the board life of the mixed mortar and enhances hydration); 3.) and they make the finished wall more water repellant.
In your case, I would use Type S portland cement/lime mortar. In some locations, you can get the ingredients pre-blended. If not, you can make it by mixing:
9 parts sand
2 parts portland cement
1 part lime
To get these proportions use a small container, such as a coffee can and count off the parts. Figure out what size batch you'll use in 1-2 hrs and change the change the size of the container to fit the batch size you need.
If you can't find mason's lime or pre-blended portland cement/lime mortar or you want to simplify matters, use Type S masonry cement, which is available at HD or Lowes. I think the pc/lime mortar is better but the masonry cement is completely adequate to the task.
I would not wet the wall prior to repointing. The stones you have do not absorb water as old bricks do, so this is not necessary and could be counter-productive. Use either a tuck pointer or simply your hand, with a rubber glove on, to push mortar into the joints. As the mortar begins to dry, carefully clean the faces of the stones with dry burlap or synthetic steel wool (i.e., the green scratchy pads sold in the paint department of the big boxes). The next day go over the area again with the scratchy pad drenched in water.
Thanks for the advice. Sounds like your screen name says it all! I have seen type S mortar pre-mixed, and I have seen portland cement and sand, but no lime in bags. I will shop around and use one of your suggested products.
thanks for the history and primer, Mudslinger -
D
"there's enough for everyone"
Could you explain why you advised using type S portland cement/lime mortar in this case. Is the ultimate "hardness" of the mortar the key issue here? How does type S differ from type O and type N?
Is it accurate to say that S, O and N differ by the ratio of cement to lime? Type N has equal parts lime and cement? Type O has double the lime as cement?
Of the three types, is type S in the middle as far as "hardness" and the ability to "give a little"?
Thanks for your teaching here.
Rick
http://www.taunton.com/finehomebuilding/how-to/articles/mortar-what-type-need.aspxSamT
Thanks Sam.
Rick
Could you explain why you advised using type S portland cement/lime mortar in this case. Is the ultimate "hardness" of the mortar the key issue here? How does type S differ from type O and type N?
I advised using Type S portland cement/lime mortar mainly because it has very high bond strength; in terms of flexural bond strength it often tests higher than portland cement/sand mortar (i.e., no lime or proprietary ingredients). The owner described the stone as round, smooth and very hard and I believe that this mortar offers the best chance of adhering tenaciously to those smooth, non-porous units.
I recommended pc/lime mortar because it I'm convinced that it performs better in terms of water infiltration and flexural strength than masonry cement. I would not get too hung up on whether it's pc/lime or masonry cement in this application, however; either one will work fine.
The Types of mortar are based on the percentage of portland cement to lime or, in masonry cement, pc to proprietary ingredients. Type M has the highest percentage of portland cement, followed by S, N and O, which has the lowest percent of pc. The letters in the Types come form the word MaSONry. Before 1954, mortar types were designated as A-1, A-2, B, C and D. Because masons got the impression that these designations meant that first was the best and the last the worst, they were dropped in favor of the present system. The truth is no single mortar type is suited to every application. And the trick is to find the one best suited to the job at hand. Gentlemen, that's all I've got tonight; it's past my bedtime.
Thanks Mudslinger.
Rick
This book has just about everything you need to know about masonry mortar:
http://www.wocbookstore.com/w-mht03.html
And this book has just about everything you need to know about masonry design and details:
http://www.amazon.com/Masonry-Design-Detailing-Christine-Beall/dp/0071377344/ref=sr_1_1/002-8100923-1929649?ie=UTF8&s=books&qid=1183061050&sr=1-1
I would add one more ingredient to mudslingers list. Concrete glue. You'll find it at most yards and it makes the mortar much harder, more durable, and water resistant.
Feel free to respond back mudslinger. I just think that if you are going to re-point the house ( a lot of labor) a little glue won't break the bank.
One word of caution. You have to be more careful with the glue in the mix. If it dries where it's not supposed to be it is really hard to get off. But if you are careful it will make the pointing very strong.
I would add one more ingredient to mudslingers list. Concrete glue. You'll find it at most yards and it makes the mortar much harder, more durable, and water resistant.
On what testing is that conclusion based? Concerning mortar admixtures, here's what Christine Beall wrote in Masonry Design and Detailing For Architects, Engineers, and Contractors:
Although admixtures are often used with some success in concrete construction, they can have adverse effects on the properties and performance of masonry mortar and grout. ASTM standards do not incorporate, nor in fact even recognize, admixtures of any kind.
A variety of proprietary materials are available which are reported by their manufacturers to increase workability or water retentivity, lower the freezing point, and accelerate or retard the set. Although they may produce some effects, they can also reduce compressive strength, impair bond, contribute to efflorescence, increase shrinkage, or corrode metal accessories and reinforcing steel. As a rule, if admixtures are used to produce or enhance some special property in the mortar, the specifications should require that laboratory tests establish the effects on strength, bond, volume change, durability and density.
I would not agree with you concerning concrete glue. It's effects are unknown, save some anecdotal opinions and the manufacturer's claims. The mortar that is presently on the wall, on the other hand, is almost 100 years old. It has no concrete glue in it and it has performed extremely well. Why add anything to it?
I would add a couple things to mudslinger's excellent primer:
Don't let the mortar dry out too fast- on a warm day in the direct sun, you'll need to lightly spray down the mortar, to keep the edges from drying before the rest of the mortar. It should take a couple days to dry, and it should set long before it looks truly dry. A garden sprayer works ok, wet moving blankets or burlap work great too.
Second, try a cake decorator/grout bag. I know some people don't like them, but I find them a great way to get mortar into narrow joints. You'll need to mix the mortar a bit wetter for using in the bag. One of the big advantages is how cleanly you can apply the mortar- less scrubbing of the rock later.
zak
"When we build, let us think that we build forever. Let it not be for present delight nor for present use alone." --John Ruskin
"so it goes"
Thanks for the tips, Zak. I have heard of the grout bag and it sounds like it's worth a try. I will keep the mortar damp and start plugging away at the job.
Don't let the mortar dry out too fast- on a warm day in the direct sun, you'll need to lightly spray down the mortar, to keep the edges from drying before the rest of the mortar. It should take a couple days to dry, and it should set long before it looks truly dry. A garden sprayer works ok, wet moving blankets or burlap work great too.
I agree but would add a word of caution. It's easy to start this process too early, which can make a mess. In the summer, the best thing to do is work away from the sun; work on one side in the morning and the other in the afternoon. On the part you do in the morning, you might use a tarp to keep the sun from baking the mortar in the afternoon. If you keep the work out of direct sunlight for the first 12 hours, you should be fine. Even work that gets baked in the sun can be hydrated up to three days after the fact with a hose.
I agree with mudslinger,use type "S" mortar and one more thing besure and tool the joints this gives you a better job buy compacting the mud ,thus making the joint more weather resistent. I personly use a quickpoint mortar gun for repointing its the best money I have ever spent for that type of work saves your forearms and knuckles/wrists from a lot of wear and tear, a little pricey but well worth it.plus you don't have to water down the mud thus weakening it when you put in the wall.with a helper I can repoint about 600sq. ft. in a day using the gun with out it about 300sq.ft. If you order the gun also get a bottle of plastisizer additive with it ,half oz. to about 5 gal. of water makes the mud super creamey and a pleasure to work with it also is a weather proofer.
<I personally use a Quickpoint mortar gun >
Cool! Had to look that up. Looks interesting to use.
Forrest
Bigger and Cheaper than the OriginalIt's not often that a company upgrades a best-selling tool to make it bigger and better, yet less expensive, but that's exactly what Quickpoint Inc. of Concord, Mass., did with its Quickpoint mortar gun.
View Image"It's basically the tool of the industry," said Joel Aronie, company vice president. "Would you go back to nailing by hand? That's the same as going back to pointing without this tool."
Quickpoint is up to five times faster than conventional pointing methods, he said, adding that over the last 16 years, the company sold 30,000 of the old units.
"We just upgraded it to make it better," Aronie said. "We've made it a nice tool at a better price."
Improvements to the tool include a plastic hopper that holds three quarts of mortar (rather than two), changing the color from orange to blue, and dropping the price from $469 to $325. Like its predecessor, the newly designed Quickpoint offers four steel nozzle sizes and a vibrator auger
thanks for posting that, but...
Improvements to the tool include...changing the color from orange to blue,...
pretty weak....
"there's enough for everyone"
The way we set up tp use the gun is to make a full batch of mud of regular consistency, then load the gun up " which I have a gallon attachment for mine" and also load up a grout bag ,me and a helper then proceed to lay grout into the wall using both the gun and the bag until we have about 100 sq.ft ahead of wet untooled mortar then I take a break "my helper hasn't caught on to this part yet"as he his still putting grout intp the wall while I make another batch of mud, he continually grouts with the gun while I start back at the beginning tooling the joints and cleaning the wall and mixing new batches of mud, we keep this up until approx. 1.5 hours until quitting time or the job is finished or a good stopping point such as a corner or under a deck .
This way by waiting until the end, and doing all the grouting at the end of the repointing job or in a lot of cases the grouting phase of a imatation rock job, you have more control of the color variations of the mortar due to mixing time, mortar wetness,and material ratios.
For lime, I buy 50-pound bags of hydrated lime from a local agricultural supply store. About $6 a bag last time.
Allen