BY POPULAR MECHANICS

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When restoring an old foundation, a standard mortar starting mix for restoration work is one part Portland cement, two to four parts lime and eight to 12 parts sand. You may have to do some experimenting with the different kinds of sand available locally before you choose what’s best.

It’s OK to mix different kinds of sand to try to get the consistency of the mortar as close to the original as possible. Keep the mix relatively dry – it’s easier to work with and you’ll get less splattering. Try to be as neat as possible, because this will reduce the time spent on cleaning the surface when you are done.

When it comes to tinting agents, iron oxides are the best way to go. These oxides are available at masonry supply outlets. The tint is anywhere from one-half percent to 2 percent of the volume of the mix. Start with about one-eighth teaspoon as a base, and work your way up from there.

Make four samples and let them sit four or five days (the mortar will lighten up considerably over time) and see which one comes closest to the original color.

Then, try going a little above and a little below this mix, to give you two more shades to choose from. Out of the three, one should be close enough so that your repainting blends in with the rest of the wall.

The basics of repainting hold true for any foundation work. First, the joint must be cleaned out to a depth about three times the width of the joint. So, if you’re working on a one-half-inch-wide joint, cut it back to one-and-one-half inches.

Various sized cold chisels and stiff wire brushes are good cleaning tools. Be sure to brush away all the mortar before adding your new mortar.

Keep the joint moist and layer in the new material – don’t try to fill it all at once. On interior walls or any areas below grade, it’s OK to fill the joint flush with the wall surface. On exposed areas, shaping the mortar in a V-joint to expose the edges of the brick looks nice.

The unevenness of the joints in a rubble or stone wall makes this repainting project a bit harder. A general rule of thumb is to show as much of the building material (in this case the stone) as you can.

Keep the mix as dry as possible, drier than you would for brick. You’ll need a variety of different size pointing tools on hand to fill the different size joints, and will find yourself switching constantly between them.

These are commonly available at masonry supply houses.

The final step in this job is aging and cleaning the results of all your hard labor. This must be done a day or two after your reprinting is complete. Don’t wait any longer since you must do this while the mortar is still soft and hasn’t completely cured.

First, wet the wall down thoroughly – really saturate it. Then apply a weak solution of muriatic acid to the new spots you’ve pointed. Generally, you’ll end up with a solution that is 4-, 5- or 6 parts water to one part muriatic acid. (The acid is sold in a solution form to make it safer to use. Therefore, the solution you create for cleaning your masonry work is dependent on the strength of the acid solution you buy.)

There’s an easy way to arrive at the right mix. Add a little acid to a bucket of water and drop in a piece of the new mortar. If it doesn’t foam, add a little more acid. The minute the mortar foams, you’ve attained a chemical reaction between the lime and the acid, and the mix is ready.

Just brush it on the wall with a soft or natural bristle brush. Don’t leave it on for more than a minute or two. Follow this with a thorough rinsing with a hose. Only tackle patches of 10- to 15 square feet at a time.

No matter how good you are, you’re bound to slop a bit of the mortar on the face of the brick or stone.

If you kept the mortar mix dry, it shouldn’t require lots of elbow grease or a strong acid solution to remove the mortar stains.