Frequently Asked Questions – Masonry & Mortar

Common Masonry & Mortar Questions

  • We don’t recommend painting brick with conventional paints since they will act as a water barrier and trap moisture in the wall. It’s tempting to think that the paint will protect the masonry and keep water out of the wall system, but in reality there is always going to be water making its way in and it’s vitally important that moisture have a way to migrate out of the wall system. An impermeable coating over the brick and the mortar will trap moisture, leading to bubbling and peeling paint, dampness, and the eventual deterioration of the brick and mortar itself.
  • However, there are breathable masonry coatings that are appropriate for brick, stone, and concrete. We recommend KEIM Silicate Paints and Stains, which are well-suited for historic structures and feature a vapor permeability rating of 75+ perms depending on the product. (By contrast this Modac product has a perm rating of 3.43.) Silicate paints are breathable, have no VOCs and even act as mild consolidants to help maintain the integrity of the masonry. They provide a natural looking matte finish and can be custom color matched to the existing masonry or you can select a color from KEIM’s extensive color palette.
  • Silicate paints have numerous advantages and we’re impressed by both their aesthetic and functional advantages. Silicate coatings work by penetrating the masonry and chemically bonding with the substrate. This means that when applied to a properly prepared surface in proper conditions it will last for many years and that there is no flaking and peeling; instead the coating will very slow fade away. While we generally consider that an advantage, it also means silicate coatings can’t be stripped, so once it’s on it can’t be removed. Always do a mockup!!!
  • Finally, if your brick has already been painted take heart—you can still use silicate paints. KEIM Soldalit Exterior All-Purpose Mineral Silicate Finish is designed to penetrate sound existing latex/acrylic finishes
  • Limewash is a traditional coating made from slaked lime, and it can be pigmented to achieve a wide range of colors. Like silicate paints and stains it is vapor permeable, has no VOCs, and has a beautiful natural matte finish. While part of its appeal is the way it fades and develops an aged look, that also means that it needs regular reapplication and realistically its lifecycle is relatively short in our harsh Midwestern climate.  It would be reasonable to expect to have to reapply every 3-5 years and reapplication would have to be part of a regular maintenance cycle. It can be used for interior applications but is only recommended for those areas that are low traffic and don’t require regular cleaning. For more information about lime paints we recommend KEIM’s limewash information pages.

Here are the basic guidelines for selecting a proper repointing mortar:

  • Use a pointing mortar that is weaker than the original mortar.
  • Use a pointing mortar that is weaker than the surrounding masonry units (i.e. brick, stone etc.).
  • Use a pointing mortar that is more vapor permeable than the original mortar.
  • Use a pointing mortar that is more vapor permeable than the surrounding masonry units.
  • Use a sand that is well graded with some fine, lots of medium and some course grains.
  • The largest grains of sand should have a diameter roughly 1/3 the width of the mortar joint.

We rely on two kinds of mortar for most of our historic restoration work: natural hydraulic lime and pozzolain hydraulic lime. Both are hydraulic limes which are limes that impurities, called pozzolains, that allow the mortar to set in two stages: the first set is when water is added, and the second occurs as the mortar is exposed to the atmosphere. The first set is important, since it allows the mortar to attain strength more quickly and to cure in wet conditions.

  • Both are sold as dry bagged products. NHL mortar is produced using limestone that contains naturally occurring impurities (pozzolains) such as clay and other minerals which enable it to cure when water is present. The mortar is categorized by the level of naturally occurring impurities: Feebly Hydraulic (NHL 2.0), Moderately Hydraulic (NHL 3.5) and Eminently Hydraulic (NHL 5.0). The most popular NHL mortar in our climate for exterior work is NHL 3.5, whereas NHL 2.0 is generally used for interior plaster.
  • PHL also has hydraulic characteristics but it is a manufactured lime product and pozzollans are added in a controlled factory environment. PHL is available as either a Moderately Hydraulic (PHL 3.5) or Eminently Hydraulic (PHL 5.0). The most popular PHL for our Midwestern climate is PHL 5.0.
  • Both NHL and PHL mortars are flexible and breathable enough for historic restoration, and they are durable enough for the extreme conditions.
  • The other type of lime mortar is nonhydraulic lime, which is sold as lime putty. In the past, masons would create non-hydraulic limes by slaking (adding water to) quicklime, or lump lime, to create a putty that would then be mixed with sand. This putty was often aged before it was used, and the resulting lime putty mortar is soft and very permeable, but it cures very slowly and doesn’t withstand extreme weather or significant exposure. It is well suited for interior  lime plaster. NOTE:“Lime putty” is often used as a generic term for lime mortar, but this is a misnomer; lime putty is in fact a specific kind of nonhydraulic lime.
  • While the term “tuckpointing” is widely used to describe the process of replacing old mortar with new it’s actually a misuse of the term. True tuckpointing refers to the process by which coarse brick or stone are laid with a mortar that is designed to match the masonry units, and then a fine, even mortar in a contrasting color is applied over the joints to create the illusion of high quality straight jointwork. While it’s now a rare survivor and something that’s always exciting to find, it was historically a way of concealing rough masonry.
  • Having said that, we typically use the term “repointing” but we know that “tuckpointing” is widely used so we accept it, albeit reluctantly.
  • Anyway, the question was how to do it properly. Here are the basic steps to properly repoint/tuckpoint a wall with lime mortar:
  • Grind or chisel out mortar joints to a depth of 2-2.5 times the width of the joint or deeper until sound original mortar is located.
  • The minimum depth of thin joints is 3/4″.
  • Remove all mortar fins left by the grinder from the top and bottom bricks so pointing mortar obtains a direct bond to the brick.
  • Remove all dust and debris from joints to ensure sound bonding.
  • Perform the above steps without damaging the masonry units or building. (If you haven’t done this kind of work practice on inconspicuous area or your neighbor’s house. Just kidding about the neighbor’s house!)
  • Pre-wet the wall with copious amounts of water. Setting up a lawn sprinkler on the masonry and letting it run for an hour or so is usually a very good way to ensure the wall is thoroughly wet. Simply misting the wall with a hand sprayer or Hudson sprayer is NOT sufficient.
  • Lime mortar is an extremely dry mix so you want to keep the walls from absorbing what little water is in the mix. If your walls are not thoroughly pre-wetted your mortar will fail and/or the color will shift.
  • Protect the walls from high winds, direct sunlight and/or heat by tenting the area with dampened burlap attached at the wall on the top and draped over the scaffold. A good rule of thumb is that if the workers are comfortable and happy working then the lime mortar they are installing will be comfortable and happy.
  • Lime mortar does not require water to grow crystals, cure and get hard like cement based mortars. Limes get hard by absorbing carbon dioxide from the atmosphere.  As such, you must add only just enough water to make the mortar workable.
  • Mortar can be mixed by hand or in a modern cement mixer.  Mix the mortar for 5 minutes, allow to rest for three minutes and re-mix for another three minutes.  USE A TIMER.
  • Add water slowly as the mixer is running to help control the amount added. It is very easy to add too much water.
  • The final consistency of the mortar should be that of brown sugar. To test for proper consistency you can do either of the following:
      • Grab a handful of mixed mortar and form it into a ball.  Toss the ball into the air and let it land in your palm several times.  The ball of mortar should just barely hold together without breaking apart but it should not leave very much (if any) residue on your skin.
      • Take a handful of mixed mortar and squeeze it in your palm.  If the mortar readily oozes between your fingers you have mixed with too much water.  If the mortar just starts to push between your fingers you have a good workable consistency.
  • Dry lime mixes are good for the integrity of the mortar itself and great for the contractor. The drier the mix the fewer mortar smears you will get on the building during the pointing process.  Most lime mortar pointing projects can be completed with little or no washing afterwards which saves the contractor significant time and money.
  • Compact mortar into joints using back fillers. Never use grout bags or pointing guns which require too wet of a mix and segregate the paste from the aggregate.
  • Apply mortar in one lift.
  • Remember the more your compact the mortar the denser the joint will be thus reducing vapor permeability. Ultimately, do not over compact mortar joints; allow them to transmit water vapor and “breath”.
  • Have fun with different joint profiles. Historic mortar joints were rarely struck in a concave pattern.  Lime joints look great in a “V” struck, weather struck or raked joint profile.
  • Remember lime mortar does not “cure” but rather carbonates over a long period of time. The longer you can damp “cure” lime mortar the more resilient your joints will be.  Humidity and frequent misting deposit CO2 into the masonry that lime requires to get hard.
  • If at all possible protect your pointed walls with dampened burlap raised 1-2 inches away from the wall for a period of at least 3-5 days.
  • Keep the burlap damp by misting it with water periodically. Dampened burlap shades the wall keeping it cool and provides for a humid environment that lime mortar loves as it gains initial strength.
  • If you cannot drape burlap then gently mist the wall frequently to keep the wall damp.
  • We never recommend washing lime mortar joints with any type of acidic product.
  • If you need to remove mortar smears from masonry simply use a green scouring sponge and water. Most smears are easily removed with the method within 24-48 hours after pointing.
  • If you absolutely must clean lime pointing work with an acid use Vanatrol at a dilution of at least 12:1 with a dwell time of only a few seconds. This chemical should only be applied to a thoroughly pre-wetted wall.
  • If it’s a white powdery buildup it’s most likely efflorescence. Efflorescence occurs when masonry is saturated with water and the soluble salts in the masonry units dissolve and are brought to the surface by water. Efflorescence can cause the surface of the masonry unit to spall so it is a condition you need to address but it is also a symptom of a bigger issue.
  • While many building owners are concerned because they don’t like the way efflorescence looks they should first focus on the water infiltration that’s causing it. And that’s number one: figure out the source of the water that’s soaking your masonry and deal with it. Common causes are overflowing gutters and clogged downspouts, improper flashing, sprinklers, and a lack of drainage around the building. Using hard, impermeable mortars, sealers, and repair materials can also trap moisture in the wall system and if moisture can only escape through the brick or stone it will bring efflorescence to the surface. (This is illustrated in the photo above where the modern mortar is applied over the original, softer mortar and is forcing water out through the relatively soft masonry units.)  If you have inappropriate repairs in place these need to be removed and replaced with more sympathetic materials.
  • Efflorescence will usually diminish and eventually disappear once the problem is addressed but if it doesn’t Ef-fortless by Eaco chem will remove remaining deposits. As always, carefully follow instructions and always do a mockup in an inconspicuous area.
  • Remove all loose concrete and stone with a chisel.
  • Roughen the substrate with a toothed chisel. The rougher the surface the stronger the bond.
  • Patching material shall not be applied at feather edge thickness but at a minimum thickness of 1/4“-1/2” deep.
  • Cut or Chisel the patch area to obtain regular geometry with straight edges and near right angles (no curves or sharp angles).
  • Remove all dust and debris from area to ensure sound bonding of patchwork.
  • Pre-wet the substrate and surrounding existing concrete until the point of complete saturation and allow only the surface of the substrate to dry just prior to patching (SSD = Saturated Surface Dry).
  • Follow all mixing and placement directions as specified by your selected product (refer to the product’s data sheet).
  • If directed to scrub a slurry coat into the substrate prior to patching BE SURE to install the patch before the slurry “scrub coat” dries.
  • Typically patches thicker than 2” shall contain a 3/8” rounded pea gravel rock.
  • Always slow cure your repairs by trapping in the moisture with plastic or continuously dampened burlap for at least 3-5 days.
cracking concrete

There is no such thing as an “all-in-one” concrete repair mortar.  Good quality repair mortars are designed specifically for unique applications.

Concrete Re-surfacing

  •     Concrete Renew – Mapei

Repairing Surface Spalled Concrete

  •     Thin Patch – Euclid Chemical

Partial Depth Horizontal/Vertical Repairs

  •     Red Line – Euclid Chemical
  •     Jahn M90 – Cathedral Stone Products (tintable)

Full Depth Horizontal Repairs

  •     Sikaquick 1000 – Sika Corp.
  •     Master Emaco T1061 – BASF Master Builders

Partial Depth Vertical/Overhead Lightweight Patching

  •     Sikaquick VOH – Sika Corp.
  •     Master Emaco 424 – BASF Master Builders

Partial or Full Depth Horizontal/Vertical Form & Pour Repairs

  •     Sikacrete 211 – Sika Corp.
  •     Master Emaco S440 – BASF Master Builders

Non-Shrink Grouting Under Load Bearing Members

  •     Sikagrout 212 – Sika Corp.
  •     Masterflow 100 – BASF Master Builders
  • Most concrete is simply stained by general atmospheric dirt. Use a mild masonry detergent (Prosoco’s 2010 All Surface Cleaner) mixed with warm water and aggressive scrubbing to remove general soiling.
  • Dark blotchy stains are typically due to biological lichen growth.  Use a proper masonry grade biological cleaner only (Prosoco Revive).
  • Use the weakest effective cleaning solution on your concrete. STRONGER IS NOT BETTER!
  • Create test panels on every type of substrate to ensure product(s) will not stain or damage concrete.
  • Never apply paints, sealers or any other film forming coating to concrete. Only deep penetrating water repellants shall be applied (Prosoco’s Saltguard).
  • Dig out sub-grade soil to a depth that will accommodate the thickness of the aggregate bases and the concrete slab.
  • Thoroughly pack down the soil sub-grade using a gas powered plate tamper.
  • On top of the packed soil lay down several inches of ¾” crushed limestone as a sub base and pack down thoroughly with a gas powered plate tamper.  The thicker the stone sub base the more load the concrete slab will be able to handle.
  • Install a base layer of course torpedo sand over the stone sub base. Spread the sand evenly so that the concrete slab thickness will be consistent throughout.  Pack the sand base thoroughly using a gas powered plate tamper.
  • Total combined thickness of aggregate bases should be at least 4”.
  • Install steel reinforcing rebar or wire mesh in concrete slabs that will carry moving (dynamic) loads such as driveways, garage slabs, aprons, etc.
  • Pour a 4” thick concrete slab for surfaces that will accept only foot traffic and a 5-6” thick slab for surfaces accommodating vehicular traffic.
  • Use a 5 bag mix (3,000 psi) for sidewalks and basement floors. A 6 bag mix (4,000psi) is typically used for city walkways, driveways and garage slabs.  A 7 bag mix (5,000 psi) is used for structural concrete for foundations, columns retaining walls etc.
  • All exterior concrete should be ordered with air entraining admixtures added to help with freeze/thaw durability.
  • Always screed the surface of freshly placed concrete using a long straightedge (2×4 stud works great), sawing it over the surface in a back and forth motion to work course aggregate down from the surface. Probing fresh concrete with an electric vibrator is the most effective and least strenuous method of consolidating concrete.
  • Trowel the fresh concrete after surface bleed water has subsided. Never trowel bleed water back into the concrete surface as this can lead to surface delamination and spalling.  Refrain from misting fresh concrete with additional water prior to troweling.
  • Magnesium trowels should be used to finish exterior air-entrained concrete. Steel trowels shall only be used on interior non-air entrained concrete for a very smooth dense surface.
  • Exterior concrete should be broomed to provide for a slip resistant walking surface.
  • Always allow concrete to cure slowly by keeping it damp for at least 3-7 days. Covering the fresh concrete with plastic, continuously dampened burlap or liquid applied curing agents are all acceptable curing methods.
new concrete placement

Don’t use caulk as a substitute for mortar. It’s only for moving joints, namely the places where different materials come together, like the junction of wood window moldings and brickwork or where concrete meets a brick. The materials have different rates of expansion and contraction so the caulk is flexible and will accommodate movement and prevent cracking.

Here are some tips for successful application:

  • Use polyurethane caulking material.
  • Caulk should only be bonded on two sides.
  • Use backer rod to de-bond bottom side of caulk joint and to set the proper depth of caulk joint.
  • Depth of caulk joint must be ½ the width at the center.
  • Caulk joint must have convex tooling so as to provide hourglass shape in section.
  • Always use caulking primer.
  • Never caulk on wet surfaces.
proper caulking installation

Here are a few things to ask:

  • Can they provide addresses to jobs they performed 10+ years ago?
  • Can they provide addresses to jobs they performed in the last year?
  • Can they provide you with a copy of their insurance certificate showing workman’s compensation coverage?
  • Are they willing to create sample mockups on your building (grinding, cleaning, pointing)? You should expect to pay for this service, but it is a solid investment to establish the contractor’s competence before they do any substantial work.
  • Ask what materials they plan to use on your project and ask them to provide product data sheets.
  • Ask how they plan to prepare your masonry for cleaning, pointing, etc.
  • One major warning sign is any contractor who tells you that you need to repoint your old building with “good strong mortar.” WRONG. The mortar in historic buildings is sacrificial and should absorb the wear and tear and protect the masonry units and it should be softer than the masonry units. Also, if a contractor proposes sandblasting don’t let them anywhere near your building. Sandblasting is an abrasive cleaning method that will permanently and irreversibly damage your masonry.