Lime Mortar Recipe for old masonary

[HB2]

It's kind of a tricky proposition with these old stone houses. What I've found is that the stones generally are locked into place and can't move too much, even if there's pointing missing. The old stone masons generally didn't allow the header of the windows and doors carry much weight either since they knew the wood headers weren't going to support all that weight for long without serious deflection. In a lot of areas you'll find that the stones over a door or window are wedge shaped and laid in such a way that they are forced together by the pull of gravity. It's usually not a full blown arch with a keystone, but if you look carefully you'll see a pattern.

That being said, I'm chicken and I would first repoint the area to give it some additional strength.

Here's my repointing recipe that seems to work.

Type "S" dry hydrated lime - (White powder)
Playbox sand, or any relatively fine sand with sharp edges. (Not river sand)

Mix the lime with water until you have a consistency something between cream cheese and sour cream. I use a drill (GOOD STRONG DRILL)with a paddle attachment and do the mixing in a 5 gallon pail. Just add a little of each into the bucket as you go. WEAR GOGGLES AND GLOVES. It's bad for your eyes and it'll give you the worst dishpan hands ever if you have too much skin contact with the lime.

I would make up about half a bucket to start. Once you've reached the right consistency, smooth out the putty in the bucket to make it level and then pour just a little water over it to cover it. (1/2 to 1/4 inch)

Put a lid on the bucket and let it sit for at least a week.

After the lime putty has aged for a week, you can mix it with sand to prepare your pointing mixture.

First pour off the water from the bucket of putty into a spray bottle. You'll nees this to wet the surface you're pointing. The lime in this water helps the mortar stick to the stone.

The recipe that I use is 2.5 parts sand to 1 part Putty (by volume) I use a coffee can and spatula to measure the stuff out.

Dumpe that stuf into a mortar pan or dishpan or something like that and then mix it up using a garden hoe. It should wind up the consistency of cookie dough. It's hard work and it will seem like your not getting anywhere for a while and then suddenly things will look a whole lot better.

The key thing is that the more you work it, the better it will be. It's one of the strange properties of a lime putty based mortar.

Now, vacuum out any loose stuff from the gaps that you're pointing, and physically knock out all mortar to a depth of about 1 inch from the face of the stone. Then spray the areea thouroughly with your lime water and start packing the mortar in place using a tool or your fingers, whatever. Try not to make layers more than one inch thick cause it will take a long time to dry. Make sure you pack it as deeply into the crevices betweeen the stones as possible.

When you're done, any leftover mortar and putty that you ahve mixed up can be stored indefinitely as long as you keep it from exposure to air. I seal mine up in a five gallon pail with a wet rag laying on the putty or mortar and the lid sealed on the bucket.

Keep in mind that the color of the mortar will depend on the sand you use. You can probably also get some tinting colors at the masonary supply store.

It's been my experience that Lowes or Home depot have nice 5 gallon pails, but that neither in my area carry the lime. Look in the yellow pages under masonary supplies for a supplier.

Good Luck - post back with any questions.

HB - lime geek in his spare time.

[Wackyshack]

thank you HB (lime geek)..... it was a few years ago you helped me and I got 2/3 of the cellar done....I need to finish the rest....

[HB2]

Great to hear - how's the mortar holding up? Any issues?

HB

[hartwood (WavyGlass)]

I will add my thanks, as well. I'm saving this recipe to use when it comes time to start to repoint the walls of our basement.

[Texas_Ranger]

Actually, lime putty is nice but not strictly necessary I think. Dry-mixing lime and sand (usually 1:3 for exterior applications) and adding water works fine, as long as you really work the mortar while you mix it. This makes the mortar nice and sticky and easy to use. If you use too much lime, the mortar will get so awfully sticky you can't get it off the trowel any more.

I've watched an old-timer mason mix lime plaster in huge quantities (enough to plaster the interior of an entire house) and he didn't bother with lime putty. He had a concrete mixer, a huge pile of sand and a few bags of lime. First he mixed sand and lime by the shovel (throwing both into the running mixer) and then he added water from the garden hose. When the mix was done, he emptied the mixer into a wheelbarrow.

Side note: for basement walls I'd recommend parging rather than pointing as it seems much easier. Just apply a very thin coat of plaster and smooth it out with a large wet brush. If there are larger holes and wide cracks I'd recommend getting a hawk trowel for applying the plaster. Load it with a small amount of plaster/mortar and with a flick from your wrist throw the slurry into the hole/crack. If anything threatens to fall back out, push it in with the edge of the trowel. Ideally, you'd clean up or cover the floor before you start, then you can pick up any droppings and use them.

Lime plaster takes days to cure, so if the mix gets a bit stiff after a few hours, add some more water and stir again.

The basics of plastering and masonry repair aren't exactly black magic, the real trick is getting it all straight and even.

[HB2]

I've read about the dry mix method, but all the information i had suggested that creating the putty first, (and letting it age a while) ends up in a stronger final product - at least that's wha the theory is.

I don't know that there's any empirical evidence to support it though. I would say that an actual mason that does this for a living that has success with the dry mix method is pretty good proof that it's a viable alternative.

I would also say that there's a big difference between mixing by hand and using a mortar mixer - That powered mixer adds a lot more energy to the mix, and probably results in a more plastic final product (stickier and more workable, better bonding, etc.)

Thanks for mentioning it.

HB

HB

[Texas_Ranger]

Actually I'm not sure the motor mixer makes much of a difference, as there are only two tiny "paddles" inside the drum. It is definitely not recommended to mix adobe in a normal cement mixer as it won't work the sticky mud thoroughly enough (read that on the German timberframe forums). The main downside to mixing large quantities by hand is the physical exertion - it's back-breaking labour! About 10 years ago we replastered the bottom part of our kitchen after we removed the old tile and mortar bed and I can't remember how many tubs of plaster we had to mix.

If there is a difference in durabilty between using lime putty and dry mix I'd say it likely only matters in outdoor applications. I definitely know that lime putty is essential for whitewashing, using powdered lime for that will cause the whitewash to rub off easily and is only recommended for outbuildings.

[lupinfarm2012 (WavyGlass)]

Is this the same mix used for "Old Brick" houses?

[Texas_Ranger]

Probably yes. There are a few different types of lime I think, but the mix itself is usually the same. For walls that are not exposed to the weather (interior or stuccoed) you can probably reduce the lime content even further, but why? Lime isn't that expensive.

[Sow's Ear Mal]

Hello, I'm new to this forum but it looks great! Re Lime mortar: I'm in Ontario, and I'll be repointing my stone house this summer, 1 white portland, 1 type S lime, 6 sharp sand. I've been researching this, and I noticed there's no mention here of hanging wet burlap over lime mortar to keep it from drying too fast (that, or frequent misting with water) Can anyone comment on this, whether it is a necessity? Thanks, Mal