Different Methods of Historic Preservation
Mark Nelson of Nelson Restoration was recently working on a job up in Grand Teton National Park. Mark needed specific information to share with key decision makers that compared preservation of log structures using older methods of mortar and linseed oil with modern products. Sashco was honored to partner with Mark provide a report outlining the pros and cons of historic preservation. Below is that report. Mark was able to clearly communicate the value of using a specialized log restoration contractor who uses modern products and won some future business as a result.
In any historical preservation, the goals are simple:
- Honor and preserve the historic aesthetic of the log structure
- Preserve the actual logs on the structure itself and prevent future wood rot/decay
- Decrease the time and money spent on maintenance of the structure in the future
While the goals are straight forward, how that’s done means sorting through a variety of methods. So, what must the products themselves contain to accomplish those goals?
The products used to protect the underlying wood need to be able to move with the logs as they breathe, taking on and giving up moisture with changes in temperature, humidity, weather patterns, etc.
- The chinking must remain elastic, while also adhering tenaciously to the underlying wood.
- The stain must be able to move freely with the logs, while maintaining a continuous coating to prevent moisture and insect infiltration.
Any stain applied needs to contain high-quality transparent oxide pigments to protect against UV damage. UV damage is the gateway to the other big three: air, moisture, and insects.
A semi-transparent stain is best. Anything solid will hide developing problems until it’s too late. Major repair or log replacement becomes necessary, which is costly, both in time and money.
#3 Proper Prep
At first application, getting the wood back down to bare, clean wood is absolutely necessary to ensure long-term performance of the products put back on the wood. On any log refinishing or staining project, this is where most of the cost comes from. Products only account for 8-10% of the job costs.
#4 Routine Maintenance
When routine maintenance is delayed, the probability that major prep (and, therefore, major expense) will happen. Keeping up on the recommended maintenance reduces costs significantly over time.
What is acceptable as “historically accurate” has changed over the years. Roads have been paved. Electricity and plumbing have been installed. Old thatch roofs have been replaced with metal roofs. On log structures, chinking went from mud and straw to mortar because mortar was better; now, acrylic chinking is the norm. Wood surfaces went from unstained, to oiled, then painted with oil-based stains and paints and now acrylic stains and paints have become commonplace. Protecting large logs and timbers is always a challenge. Thankfully, product technology today can deliver a result that honors the past aesthetically while still protecting the structure well into the future.
Following is the breakdown of the performance between two competing methods of accomplishing historic preservation, as well as a review of what the routine maintenance requirements would be with both methods.
|Linseed Oil and Mortar Chinking||Sashco’s Capture® and Cascade® log stain system with Log Jam® elastomeric Chinking|
|Stain Aesthetic||Delivers authentic look; allows underlying aged wood to show through.||Can be tinted to create the old-log look.|
|Overall Stain Durability||Nominal. Broken down by UV and weather within two years; must be removed and re-applied every two years to renew protection.||Superior. See the Capture Competitive Stain Report. High-performance stain lasts much longer with routine maintenance.|
|Protection Against UV Damage||None. Clear coating allows wood underneath to age with exposure to UV, darkening it over time.||See the Capture Competitive Stain Report. Highest quality pigments protect against UV damage while delivering a historically accurate look.|
|Elasticity*||Flexible, but not elastic. Will withstand some movement over time, but will crack within 12-18 months.||Ultra-elastic. Moves with the logs as they expand and contract with temperature swings and moisture cycles.|
|Algae, Insect, and Mildew Protection**||No algae protection, as post-add algaecides are not available. Linseed oil can be applied over top of a borate-based wood preservative treatment for protection against mildew, rot, and insects. Would need to be re-applied to bare wood when stain maintenance is done (every 2 years).||Algaecide included in Capture® and Cascade®. No borate in stain. Stain can be applied over top of the borate-based wood preservative treatment for protection against mildew, rot, and insects. Would not need to be re-applied until taken back down to bare wood (10+ years, depending on maintenance).|
|Stain Maintenance||Fairly frequent. Requires full re-application every two years. Will likely require major prep like power washing or sanding every 2-4 years.||Infrequent and easy. Minor touch-ups in highly exposed areas. Power wash the surface and apply more Cascade® clear coat where needed, when needed. No stain removal necessary for several years (a minimum of 10 years with routine maintenance…some homes have gone over 20 years now!)|
|Stain Odor||Solvent odor that takes 1-2 weeks to subside.||Paint-like odor that subsides within 24-48 hours (or sooner in warm, dry conditions).|
|Chinking Aesthetic||Delivers authentic look.||Delivers authentic look. Can be customized by applying more texture to the surface to get a rougher look, if desired.|
|Chinking Sealing Performance||Mortar does not adhere well to wood. Loses adhesion to edges of joints within a few weeks of application, allowing in bugs, moisture, and outside air.||Elastic with excellent adhesion to wood. Moves with the wood to seal against the elements and insects.|
|Chinking Maintenance||Must be replaced when it loses adhesion and/or crumbles out of the joint.||Once and done. If/when small tears happen, simply apply more over top. Maintenance rarely required.|
|Rot Prevention||See photos below. Linseed oil cracks over time, allowing in moisture. Mortar holds on to moisture right next to the wood. The combination results in areas of high moisture content, prime location for rot to grow.||Stain moves with the logs, preventing moisture infiltration. Synthetic chinking keeps moisture out of chink joints. Probability of rot very low. Borate treatments generally prevent most any rot.|
*Note: Most commercially available stains/coatings are not elastic.
**Note: Borate-based pre-treatments are effective against insect wood ingesting insects like termites, carpenter ants, and beetles. They leech out of the wood with moisture exposure, so must be covered by a coating.
|Maintenance||Linseed Oil and Mortar Chinking||Sashco’s Capture® and Cascade® system with Log Jam® Elastomeric Chinking|
|Every 2-4 years||
Photos of Problems Associated with Mortar Chinking
Above, some mice and birds have built nests in the wood behind the chinking.
Fruiting bodies, including the mushrooms shown above, find a haven in the areas behind mortar chinking. Since mortar absorbs and retains moisture, a virtual greenhouse is created in these spaces.
Decayed wood behind mortar chinking, as shown above, requires log replacement, which is costly. In some cases,
there is no guarantee that the building can be preserved.