cracks in cement over brick fireplace

Old 11-09-02, 04:34 AM
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cracks in cement over brick fireplace

Our contractor hired a mason, who covered over our painted brick fireplace with cement to give us a modern, clean look. Needless to say, it cracked. So he put up another coat of cement. Needless to say, that cracked too. We were told by a friend of a relative that we needed a more elastic finish to cover over the cement, but we don't know what this is or where to buy it. We are pretty disgusted with our contractor, who doesn't return phone calls any more, and with the mason, who says all cement fireplaces crack (so why build them???). HELP!! Can anyone tell us what to apply over this cement, so that this beautiful looking fireplace looks good up close!!
Old 11-18-02, 06:04 AM
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Applying stucco

Stucco is made from portland cement, sand, lime, and water. On a stable surface like brick, wire mesh is typically not needed. It is very important that it be applied in 2-3 coats, giving each coat given proper drying time. The first coat is called the scratch coat and is usually a thin coat of about 3/8" thick. The surface is scratched before it hardens, so that the next coat will have a textured surface to which to adhere. This coat is allowed to dry, but must be dampened before the next coat is applied. If second coat is being delayed, it must be kept misted with water.

The second coat is called the brown coat and is also about 3/8" thick. This coat is smooth. If a third coat is not being applied the first 2 coats should be about 7/8" thick. If a third coat is being applied, the second coat is kept misted until it dries for a couple of days or so.

The third coat is called the finish coat and is very thin about 1/8". It can be very smooth or designs applied with trowel.

Applying Stucco. Retrieved 18 November 2002.

In adequate drying, misting between coats, applying too thick layers of stucco, and excess moisture in the mix could result in cracked stucco. A professional plaster or stucco mason is preferred for this type of work. Applying new stucco over cracked stucco without addressing the cracks will not resolve the problems with the cracks.

Cracking overview with general repair guidelines:

The SMA and member plastering contractors are constantly striving to improve stucco. From time to time, even stucco manufactured and installed correctly will crack.

Certain fine or smooth textures accentuate cracks in stucco, while heavier textures tend to hide stucco cracks. Although not all cracks are objectionable, cracks in stucco acceptable to one person might be unacceptable to another person. Cracks can occur in stucco regardless of texture.

Cracks that appear within the first 30 days after installation and are larger than 1/16" (the thickness of a penny) can be filled or repaired with the same color coat material. Cracks that are patched and re-appear could indicate a structural or substrate movement problem, necessitating the use of an elastometric coating. If a crack is visible from more than 10' away or is a source of leaking, it should be patched. Patching small hairline cracks (smaller than 1/16") is not recommended. Small cracks will not accept material, and the resulting patch will detract from the natural beauty of the stucco and will serve no useful purpose. If these hairline cracks must be repaired, they could be fog coated.

Color coat stucco is not structural; it is a decorative finish. Plaster cracks form when a stronger force exceeds the restraint capacity of the stucco system. Cracks are "stress-related energy." The UBC and ASTM do not call for a required hardness (PSI) for Portland Cement Plaster. Minor cracking at the corners of doors and windows and other stress points is reasonable and should be anticipated.

There are two primary reasons for stucco to crack:

Shrinkage cracks may develop as the excess water evaporates from the drying cement mix. Shrinkage cracks can occur very early on and cannot be seen after the finish color coat is applied. Hairline or egg shell cracking or "checking" in the finish color coat is also the result of a rapid dry out and most commonly occurs on hot, windy days.

Structural cracks can occur in stucco when stress is transferred to the plaster membrane from various external sources.

Cracking overview with general repair guidelines. Cracking Overview. Stucco Manufacturers Association. Retrieved 18 November 2002.

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