Home Repair Guide

February 2008

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In This Issue...

Concrete and Mortar Defined
Painting Masonry
Repairing Cracks in Masonry
Problems with Masonry
Concrete Coatings

Concrete and Mortar Defined

Chances are when doing repairs around the house you will have to deal with masonry materials like concrete and mortar. Concrete can be found in walkways, floors and poured foundation walls. Mortar is used to bond masonry building materials like brick and cinder block.

Both concrete and mortar are made using portland cement, a powder produced by super heating limestone and clay. When portland cement is mixed with water it becomes a thick paste that will set rock hard in a few hours. Mortar is made by mixing fine sand and water with the portland cement. Concrete is made by adding coarser sand, gravel and sand.

The usual proportions for a concrete mixture are: 1:3:4, where one part is portland cement, 3 parts sand and 4 parts gravel. Mortar mixture ratios should be 1 part cement to 3 parts sand. You can buy both mortar and concrete pre–mixed in 60 and 80 pound bags in your local home store. These work well for most masonry projects but for repairs of cracks and repointing brick joints it's best to mix your own mortar using a finer sand than the pre–mixed products use.

Painting Masonry

Let new masonry cure for at least 6 months before coating it with any sealers or paint. This will give the excess alkali salts time to leach from the portland cement. If not allowed to escape these salts will prevent paint from bonding to the surface.

Prep the surface to be painted by removing all loose material using a stiff brush like a nylon–bristled scrub brush to go over the surface. Hose the masonry down if possible. If you're inside and can't do that, use a shop vac to go over the surface to pickup any dust.

If the masonry has been painted before, scrape off any loose or peeling paint with a putty knife. Brush the peeling areas with a stiff brush and dust off the surface. Prime the spots with a coat or two of latex or masonry primer and let it dry completely before applying the new paint.

Painting any masonry material is difficult when trying to get good coverage with the paint coat. Bare masonry is the toughest because it's so porous it sucks up every bit of moisture that comes in contact almost instantly and it will keep absorbing moisture until it is saturated. This can mean that a full roller of paint will not go very far and it requires many coats just to cover a few feet.

To make painting masonry easier try a few tricks. First be sure you have a very thick roller. A nap of at least an inch will be needed to spread the paint into all the little pits and crevices in the masonry surface. When using latex paint, mist the masonry with water just before applying the paint to make it easier to spread. Plan to do two coats on bare masonry to catch all the missed spots rather than trying to cover every inch with the first coat. To improve coverage, a third coat will probably be necessary and essential to get a smooth, consistent coat.

Problems with Masonry

Masonry is primarily susceptible to two problems, cracking and efflorecence. Efflorescence is the term used to describe the white powdery substance that forms on masonry walls. It's caused when moisture penetrates a masonry surface causing the alkali salts in the portland cement to leaches out and deposit on the surface.

To repair cracks use the process included in this newsletter. To remove alkali efflorescence from masonry use a weak solution of muriatic acid and water. Be very careful with the acid, it is very corrosive and will burn everything including skin. Even a minor splash of the acid solution can do damage so wear long sleeves, gloves and eye protection. Use a nylon bristled brush to scrub very gently to minimize splashing.

Rinse the acid from the surface using lots of clean water. Watch the run–off; soak it up with absorbent rags and wipe all surfaces down well to prevent the acid from damaging things like floors. Let the treated area dry well if you're using anything other than a latex based coating. Latex can go over a damp surface and in fact the masonry should be a little damp to make painting easier.

Most of the time this acid treatment will cure the efflorescence problem but if necessary you may have to repeat the process a second time. If moisture is a constant problem, that issue will have to be addressed before using this process to curing an efflorescence problem.

If you're going to deal with efflorescence on an interior surfaces where you don't want to use a dangerous acid, try using a strong vinegar solution in place of the muriatic acid. Boil a cup of vinegar down to a half cup. This will double the normal acid in the vinegar which may be effective on many minor efflorescence problems.

Repairing Cracks in Masonry

To repair cracks in foundations, walls, slabs and walkways first be sure the movement that caused the crack has been stabilized. If the movement causing the crack is minimal, it may be possible to fill it with masonry caulk that will move with the crack for a permanent seal. If the movement is more severe it may be necessary to reinforce the footer or foundation to stop movement. Multiple cracks, like those pictured, are an indication of major problems with the stability of the structure.

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Prepare the crack for repairs using a putty knife or screwdriver to scrape out all loose material. Hose out the crack if possible, if not, use a shop vac or compressed air to remove all debris. Soak the crack completely using a spray bottle when working inside and a hose on exterior cracked surfaces. Saturate the masonry well just before applying the mortar patch. If a crack dries out before the mortar is applied, soak it again. You can't get it too wet but if it becomes too dry the new patch will not bond well.

Mix a batch of repair mortar using one part portland cement and three parts very fine sand. Use the finest sand you can get from your local home store to make your patch mortar bond well with the old masonry. Mix the cement and sand well and then add water to make a thick mud that holds its shape.

Use a putty knife to press the mortar into the crack starting a one end. Press mortar into the crack until it starts to ooze back out. Do this along the entire length of the crack and then go back to scrape off the excess. Finish the repair by applying a smooth coat of mortar to level the masonry surface along the crack. As you work keep the masonry surface around the crack damp with a spray bottle of water if necessary. After the repair is completed use a spray bottle to keep the patch damp for about 3 days until it cures.

Masonry Coatings

There are a number of coating products made for masonry surfaces. These include alkali–resistant primers, masonry sealers, waterproofers and floor paints. In addition to these specially made coatings, common latex paint is a suitable coating for masonry including brick, cinder block and concrete walls.

Alkali–resistant primers are made using chlorinated rubber and are primarily used on surfaces that have a chronic problem with leaching alkali salts known as efflorescence. Masonry sealers are normally clear and are used to prevent staining, stop sanding debris and to make cleaning the surface easier. The use of clear sealers is particularly helpful for interior exposed brick walls where the look of the natural surface is enhanced while making the wall smooth and debris free.

Waterproofers are made by mixing portland cement with a latex paint base to create a thick coating that will block moisture from escaping. These coatings are used mostly on basement and exterior walls. When properly applied these waterproofers will bond with a masonry surface preventing future blistering and peeling. These coatings should not be applied over previously painted surfaces. Use two coats on bare masonry and keep the coating moist with a light spray of water for 2 days as it cures.

Masonry floor paints are available in epoxies, urethanes, latexes, alkyds and rubber–based enamels. Of these, the epoxies are the most durable and resistant to abrasion and sub–surface moisture. Urethanes and alkyd based floor paints work well in garages and workshops that see a lot of traffic. For interior basement floors in living areas, latex floor paint will work fine.

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