Penta Wood Treatment and Log Homes

by: Matthew Edmunds
Edmunds and Company Log Home Restorations, LLC.

Edmunds and Company Log Home Restorations

Penta is a chemical that was used as a wood preservative from the 1950’s up until the 1980’s. Penta (pentachlorphenal and creosote) was outlawed in the 1980’s for public use because of its toxicity. Many log homes here in the Midwest have had this chemical applied to the exterior over the years. Now, many of these same log homes are turning black and the preservative effect of the chemical is wearing out. Penta wood treatment tended to preserve the outer 1-2″ of the wood and if it did develop rot, the rot would take hold deeper into the log where the Penta had not penetrated.

building that had Penta applied to it

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Here is an example of a building that had Penta applied to it. Notice all the black discoloration on many of the logs.

Unfortunately, on most log homes, Penta is no longer an effective preservative because it leaves the logs vulnerable to the elements. Modern exterior stains act in a different way to control rot than Penta did. While the chemical reactions in the Penta prevented the rot from taking hold, today’s modern stains actually control moisture, which ultimately prevents decay.

Surface preparation is very important in order to control the surface moisture on the logs.

On log homes that have been treated with a Penta preservative, it is necessary to remove the old preservative first. This prepares the outer surface of the logs to “accept” a new application of stain, which will better protect the logs from the elements. In cases like these, we recommend sand, glass or cob blasting to remove the old finish. ( This process takes off a layer of the wood and cleans up the logs, making them ready for staining.

To learn more about why logs rot, click here

After blasting and before staining, we apply a preservative that contains borates – a natural preservative as opposed to Penta. The borate treatment raises the PH level in the logs to the point where they need a few higher percentage points of moisture before rot can get started. The final step in the process is the application of a high quality exterior stain. There are many options to choose from but protection, UV inhibitors, and breathability are all important factors to look for when selecting a stain.

After the building is protected with borates and stain.

Log Home

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If you need help restoring your log home please feel free to contact us:

Matthew Edmunds – Edmunds and Company Log Home Restorations, LLC
76050 McKinley Road Washburn, Wisconsin 54891
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