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So here we are finally at the compression article.  As we all know, compression is the key to delivering a well performing project.  In fact, if you don’t compress… the process is not complete and you will have failure.  Properly compressed walls perform well, are easy to repair and will last.  Before I start, I want to just say one thing, a properly compressed wall does not dust or chalk.

Compression can happen at any time after your final coat (notice I did not say second coat) has evaporated most of it’s water.  Another way to say this is any time after the final coat hits that “leather hard” or “in love” state of moisture content.  Compressing American Clay is about moisture content only!  You cannot sand it to a sheen, or leave a wall uncompressed.
I find it advantageous to do a smoothing pass with a trowel or utensil of your choice (pre compression) at the leather hard point in the process.  Often we use water to work out trowel marks and other imperfections and trowel the wall quickly at leather hard.  Then return once it is completely dry to compress it that final time.  Practicing this allows you to put the finish in the wall without having to completely re-hydrate the clay and work your arms until they fall off.  This of course is optional whereas the final compression is necessary, try it on your next project and I’ll bet you like it.

When doing the final compression, you need to get the wall too wet in order to get it wet enough (read that again if you need to).  Basically wet the wall  until you see a sheen of water build up on the surface, then let that evaporate for about 20 seconds.  When working a wall, I like to wet about a 2 foot by 2 foot area then pass my trowel over that  area to spread any water that might drip.  Then move on to the adjacent 2 foot by 2 foot area repeating the steps, then go back and compress both sections.  If it is too wet, the trowel will be sticky and there won’t be a “sing” in the trowel.  Just wait for 10 or so seconds and repeat.  If it is too dry, then you will be scratching the wall and there will definitely not be a “sing” in the trowel.  You can also check with your fingers, if the clay grabs at your skin then it’s a little too wet, if the entire surface is not evenly damp then it is not wet enough.  Also, if you are ever seeing “fat” or “cream” moving on the surface, then it is definitely too wet.

Once you master the “feel” of the correct moisture content of the clay for compression, you can start playing with other things.  You can compress at leather hard without water and have a compressed surface.  Be careful when doing this because if you ever have to come back to do repairs the color won’t match.  You have to re-wet and re-work the walls after they are dry to have repairs match in color.  Porcelina often dries fast enough that you can compress it as you spread it.  Be careful with this too, because unless you are smoking fast, it can get away from you and you’ll have to use water anyway.

Another trick is to add 15-20% penetrating sealer to the water you use for compression.  I like this especially for Porcelina (you know the softest product we have and the one I don’t particularly like but it is beautiful!) to keep my arms from falling off and to eliminate any dusting.  This is also great for walls with texture where your utensil does not make contact with the clay and subsequently never gets compressed.

Sponges, floats and so many other tools are not used as widely as they should in my opinion.  Wetting a wall with a sponge is a great way to control the moisture content then follow it with a trowel  This also helps remove trowel marks and imperfections.  Compressing with a sponge is a lot of work, but it can be quite beautiful.  I like to use a damp sponge and have a dry sponge on hand in case I over wet an area.  A dry sponge is great for pulling excess moisture out of the clay (good trick for repairs too).  Be careful here too because you can burnish with a sponge and get shiny spots.

The biggest thing with compression is practice and consistency.  Once you get the feel, use the same techniques as you work a project and you’ll get a more perfect finish.  Having your crews using similar methods helps also.

As always, please let us know if you have any questions.