A quick and inconclusive ‘heads up’ about a recent experience we had painting Boral TruExterior® composite trim. We have been sharing in our Facebook Spray Group the progress on a large pre-finishing project, with about 6000 lf of 1×12 pine shiplap siding for a new barn build by a local custom builder. The siding stain is Sherwin Williams Woodscapes custom mixed to a dark brown color from Benjamin Moore.
A Different Sort of Substrate
We painted the trim package last…a mix of 1×8 fascia stock and custom moldings – in a variety of building materials. The 1×8 is Boral TruExterior® trim which is a fairly new synthetic/composite product made of “poly-ash”…a mix of bio polymers and fly ash.
Fly ash is a by product of coal combustion that is filtered out and collected. Not an easy hazardous waste to dispose of legally, it has become a (we guess) “green building alternative”. A recycling, ‘keep it out of the landfills’ concept if you will. Fly ash is also commonly used in concrete construction.
What Happened when we started Painting Boral?
We approached the trim package with the same sprayer set up as the siding: Graco 395 Finish Pro II air assisted airless with fine finish low pressure tips. We changed product…moving to Benjamin Moore Regal Select High Build soft gloss for the trim package, in the same color as the siding batch. Regal Select is a good product that is compatible with most everything.
Boral is shipped from the manufacturer with a “factory applied primer” that seems to be well done and good product. We were spraying the paint on the faces and edges, and that is when we saw micro bubbles forming.
There are many variables that can cause micro bubbles, so we quickly experimented with our sprayer air and fluid pressure settings and double checked the Boral for cleanliness, etc. And took a look at our shop climate. No red flags in the variables…and our finish had bubbles that we couldn’t stop.
We had six 16′ boards wet and all showing the same problem. So, we tried back rolling with velour minis and back brushing, but the bubbles would only flatten out and then resurface.
The Boral seemed to stay wet forever on the drying racks. Some of the bubbles laid down and left dimples in their wake as the paint tacked up. We proceeded, knowing the worst case scenario would be buffing out bubbles later. The rest of the package was synthetic PVC type of trim items, which took the paint fine. As did the pine moldings.
This may just be what happens when you paint a porous substrate that your product can’t penetrate. Odd circumstance.
What About the Bubbles?
Bubbles that did not lay down could be wiped off the surface by hand the next day. The paint was well adhered and intact. Any subtle depressions from the bursted bubbles are mostly lost in the fake wood grain of the Boral and the color of the paint.
The micro-bubbling was unique to the Boral. It took paint differently than the thousands of feet of pine siding, the PVC trim items and the pine molding details.
According to the Boral website FAQ’s, the product “absorbs virtually no moisture”. We suspect that this (and the unknown primer coating that the product ships with), caused the sprayed paint coat to sit wet for longer than usual with no absorption at the substrate.
That is fine from a paint performance standpoint. Latex paints don’t need to penetrate, they need to adhere. Performance will be normal, but the application made for an awkward few moments in the spray shop.
Just something to be aware of if you are painting boral…you may see bubbles in the finish during a sprayed application. We’d be curious to know if rollers and brushes cause it too.
A final tip for painting Boral is that the product is quite heavy and also flimsy like PVC. It doesn’t lay flat like solid wood, so handling the product definitely requires two people.
Do you have any experiences to share about painting Boral?