After doing a comparison of skinning options, I was leaning towards PMF for the following reasons:
1.- Ease of application compared to fiberglass.
And
2.- cost.
I am not afraid of fiberglass, but living in the Pacific Northwest and building a teardrop in a garage could prove problematic. Temperature fluctuations, humidity and dew points are things to watch out for when working with fiberglass/epoxy.
This teardrop will be parked outside with a tarp cover. It rains almost all the time here. Cars are always wet from rain or dew. Moisture is inevitable.
I figured I would do an experiment with PMF to find out how well it would keep moisture out. And to prove it to myself that it would be an adequate skinning option for my climate.
So, I prepared a block of OSB. If moisture gets in it will show up in this material. I followed the PMF instructions: applied Titebond II to the OSB surface, then applied the canvas. Waited for it to dry and applied diluted primer followed by full strength primer. Then applied 3 coast of exterior latex house paint to saturate the weave. For each coat of primer or paint I waited at least 12 hrs for it to dry and recoat.
After applying the last coat I waited 48 hrs for the paint to cure and drilled a hole. I placed a bolt through the wood and added weather stripping caulking. Then waited 72 hrs for the caulking and paint to dry.
Next, I placed my block into a bucket and placed a weight to hold it down under water. I added some red food coloring to see if it would migrate from the exterior into the OSB substrate.
Waited 8 days and rinsed off the block and dried it with a towel.
Initial inspection showed no signs of dye intrusion through the PMF membrane. So far so good.
I removed the bolt and no water/red dye had made it past the caulking. That was good.
Then I cut the block using my jig saw. The wood appeared moist but not wet. I did not see any dye where I made the cut.
Then proceeded to check the PMF adhesion to the OSB. It peeled easily with just little force. Moisture had migrated into the membrane and compromised the adhesion. There was a noticeable amount of red dye that had made it past the membrane into the glue/primer.
In conclusion at least for my teardrop, I will be using fiberglass. Maybe in dryer climates PMF will be perfectly adequate. But for the Pacific Northwest mushroom patch where I live it does not seem like a good choice. The moisture intrusion would just cause the cotton fibers to mold and rot. Same for the wood. Perhaps I used the wrong glue or the wrong paint. I know 8 days under water is a long time and it may not be a fair test for PMF. However, It is wet for weeks at a time where I live.
Comments welcome.
Wood block preparation:
Inspection after 8 days in water:
