Water Repellent, Low VOC Coatings and Sealant Additives

Michem Wood Coating 75 is a low VOC water-resistant topical wood treatment for wood composites and exterior wood that was developed for providing good water beading and wood swell resistance even if diluted to 10% solids. One of the key features of Michem Wood Coating 75 is improved recoatability. The less volatile water-based formulated product can be used as an additive in sealants or as a ready-to-use coating requiring few additional ingredients.

Figure 1. Swellometer device

Standards

ASTM D-4446 – Description of Test Method for Water Repellency (Swellometer)

Southern yellow pine specimens are dipped in the formulation of 3 minutes. Excess coating is removed and the sample is dried and cured for 72 h. Untreated and treated samples are placed in a swellometer and submerged for 30 minutes. The dimensional increase is determined for treated as well as untreated specimens using a micrometer to determine the effectiveness percentage of water repellency.

D-5401 – Summary of Test Method for Absorption (Weight gain)

Ponderosa pine specimens are treated with the clear water repellent under test and drying is done for seven days. Untreated specimens act as controls. The untreated and treated specimens are each weighed and made to float in water for 30 minutes. The specimens are removed, excess water is wiped and each is weighed again. The water repellent effectiveness is calculated and reported as a percentage.

Development Phase and Swell Resistance

As per the ASTM D-4446 test method, the conventional wax emulsions do not clear the swell resistance requirements. Michem Wood Coating 75, even at a solids content as low as 10%, cleared ASTM D-4446 in laboratory tests. This popularly accepted test method is developed for evaluating the effectiveness of water- repellent compositions for retarding dimensional changes in coated wood submerged in water. It can also be used for measuring the differential swelling of untreated wood when exposed to liquid water environments. Table 1 shows results of the swell resistance test carried out on a straight-grained, knot-free, flat-sawn Southern Yellow Pine. Furthermore, Michem Wood Coating 75 also performs well based on the ASTM D-5401 test method, which evaluates the effectiveness of clear water repellent coatings on wood before or after exterior exposure.

Applications Phase and Water Beading

Recently, outdoor exposure of waterborne stains was begun at Michelman’s site in Aubange, Belgium (mainland Europe Coordinates 49.5833°N, 5.8000°E). Water beading performance of a number of Michelman additives was tested as per the following parameters:

• The initial substrates were autoclaved pine and itauba
• Michelman additives were tested in a standard formulated stain recipe
• It is a low build system with 15% non-volatiles
• A styrenated acrylic with a small particle size is used as the binder. An alternative binder is a urethane modified co-solvent free short oil alkyd resin emulsion (32% oil). This is a second series for which results have not been reported yet.
• One set is tinted with yellow iron oxide (UV protection). A future experiment will include a clear coating. The formulation is a highly simple recipe without any wetting agents or other additives. A future experiment will include a clear coat
• The formulation is a highly simple recipe without any wetting agents or other additives.
• 5% Michem Wood Coating 75 is added to the formulation.
• The stain was applied by brush to a thickness of three coats

Figure 2. South 45° exposure rack; Aubange, Belgium

Table 1. Swell resistance performance of Michem Wood Coating 75

Table 2. Performance of various wax emulsions with regard to water beading on Autoclaved Pine

Results

Three questions were answered with respect to product performance that includes the following:

1. How is the water beading performance of Michem Wood Coating 75 related to outdoor durability in comparison to conventional wax blend emulsions?
2. Is the water beading still effective after weathering?
3. Is durability related to wax nature and hardness?

After three and a half months weathering, samples with Michem wood coating 75 did not show any visible damage or changes except slight darkening. Analyzing the differences for water beading before and after 3.5 months weathering was performed and some results and pictures are presented.

Studying the three questions addressed, when compared to standard water repellent wax emulsions the Michem Wood Coating 75 offers better water beading initially with no perceivable loss in performance under short term weathering conditions. While standard wax emulsions definitely help water beading in a number of water-based systems, the Michem wood coating 75 can exceed their beading performance and also offer resistance to swelling when water is present which brings down cracking. Based on market evaluation, it offers higher recoatability than most water repellent wax emulsions as well as other products in the Michem Wood Coating line.

Addressing question three, the performance of different wax types; experience normally favors synthetic or paraffin emulsions and paraffin emulsions that can enhance water beading in specifically selected polymer systems. While observing weathering of the coating, synthetic or paraffin blends can maintain acceptable long term water beading. In this study, softer wax performs better than completely refined paraffins and harder paraffin/synthetic blend emulsions. With softer wax emulsions, durability and dirt pickuo can be potential issues.

Figure 3. Unweathered Michem Wood Coating 75

Figure 4. Weathered Michem Wood Coating 75

The enhanced performance of the Michem Wood Coating 75 is probably attributed to the good penetration of the product into the substrate as well as the proprietary chemistry. This certainly contributes to the swell resistance properties of the product and durability of the water beading.

Benefits of Michem Wood Coating 75

Certain major benefits of using Michem wood coating 75 shown in this study are:

• Excellent water resistance
• Excellent water beading
• Enhanced resistance to swelling, cracking and warping
• Deeper wood penetration
• Long lasting effect

Other known properties derived from market feedback and testing include retarded tannin staining and recoatability.

Conclusion

Michem Wood Coating 75 can be added to sealants or used alone. With VOC levels below 100gms/lit, it has more to offer when compared to previous wax emulsions since it has been exclusively formulated to add more durability to the coating by holding out water and reducing cracking and swelling. The outer exposure portion of this study is still in process. Coated boards including Southern Yellow Pine will be added in the next phase.

This information has been sourced, reviewed and adapted from materials provided by Michelman.

For more information on this source, please visit Michelman.