Should You Put Chinking Over Cement?

Published on | Log Home Chinking |Josh Horner

A question that often gets asked from log-home owners is: “Is it OK to put chinking over cement?” and the answer is “Yes”, but that ‘yes’ answer is assuming the old cement is in good shape and isn’t showing signs of crumbling. Due to the heaviness of cement, this medium typically cracks which, unfortunately, will permit water to travel under thin edges. Older cement-based chinking materials have relatively low bond-strength and no elasticity.

Chinking Over Cement

When one chinks over cement, it’s best to use a synthetic chinking instead of mortar chinking due to the synthetic’s adhesion and flexibility advantages. Synthetic materials have superior elasticity and fully prevent weather and insect infiltration. First off, you will need to remove any loose pieces of old chinking and fill in any gaps with a backing rod, so the surface of the backing rod is level with the original chinking. There is a myth that chinking does not require a backing rod; and that is, indeed, a myth. A correctly designed backing rod provides a non-adhering surface which results in the chinking adhering only to the logs above and below the chinking point in two thin lines. This is termed “two-point adhesion”; and this condition permits the chinking to shift with the logs. Additionally, backing rods offer substantial joint insulation, which minimizes the amount of necessary chinking. This is important since you don’t want chinking to travel into the joint where it will experience movement beyond its elasticity boundaries. It should be noted that if a joint isn’t deep enough for a backing rod, caulk can be used, instead.

Next, you will cover the joint with bond-breaker tape; and is has been reported that high-quality clear packing tape or water-proof masking tape can be effectively used.

Finally, a full-thickness application of the new chinking material will be applied. The new chinking should extend 1/8 to 3/8 inch beyond both edges of the tape and cement on clean wood.   By ‘clean’, I’m referring to the wood being free of any waxes or silicone which will compromise the adhesion. Any number of stains and sealers contain waxes and silicone, so keep that in mind.

A Side-Note About Cement

As a side note, it should be mentioned that regular cement that might be used as chinking material has an inherent drawback in log homes. Once dried, it possesses a density issue which minimizes uniform breathability; and this can cause logs to become water-saturated since the water can’t be released in a timely manner.   Concrete, without an added modern concrete water-proofer, will absorb water and pass it through from the outside to the interior walls.  Damp logs, of course, present rot and mildew issues. In the past, when cement-based materials were used for chinking, one had to live with chinking that provided absolutely no elasticity. With that being said, there are chinking materials that use special additives with cement-based products that, reportedly, work well.

Easily Apply Chinking Over Cement

Applying modern synthetic chinking materials over cement is quite easy; and can be applied right out of its container. A drywall pan, a trowel, a grout bag (which resembles a cake-decorating bag) will make your chinking application quite effortless! Today’s advanced chinking materials over archaic cement-based chinking will allow for much tighter adhesion; and its unsurpassed flexibility will prevent cracks as the logs expand and contract.