Redwood peel up problems

[John Yarnell]

I have had problems on my last 2 redwood sand blasted signs. When I pull my mask some of the grain will pull up with the mask. These are the steps I have been using If you can point out a problem area please let me know. I'm starting out with dry redwood sanding it smooth priming it with Sign Life and painting with One Shot. Next I applied my mask and cut out the artwork. I went by all the drying times recommended by primer and paint companies before I applied my mask and cut. Sand blast mask is Anchor #111 low tac. I blasted next usually a 1/4 to 3/8 in deep. Next I apply my paint to the blasted areas and let dry. Last I pull my mask and get wood peeling up in places. If anyone has any ideas on the reason for the failure of the grain in various places please pass on the wisdom. Thanks to anyone with advice.

[Mike Jackson]

John,
That is the reason I never liked and trusted the "finish first" method of blasting. You are now farther behind than if you did it the other way.

Culprits:
a: the wood is horizontal grain instead of horizontal grain
b: an aggressive batch of sandblast stencil
c: a mis-labeled roll of sandblast stencil
d: old stencil?
e: stencil stayed on too long (weeks or months)
f: stencil got too hot while sandblasting
g: lousy wood
h: too coarse sand causing the top layer to get pulverized
i: rushing the job, not allowing previous steps to cure to a hard state

Those are the ones that come to mind for me right off this morning.

We always "finished last".

Call Sign Life. I am sure they have had to deal with this problem since they sell a product designed to work with this method.

Mike

[John Yarnell]

Well out of all the things you described the one thing that could have gone wrong is the grit of the sand. The place I sandblast at had half a pot of course sand still to use. I started blasting with it until it ran out then I finished with the finer sand I always bring. Thanks for the time and advice Mike.

[John Arnott]

John, I make a lot of sandblasted signs. That method of finishing before your finished making the sign has never worked. It fails where the edge of the prefinished edge and the background meet. If it did, it took way too long for everything to dry. I also belive that if you remove the sandblast tape and putty and sand everything. Then completly paint (seal) the entire sign with the background material, that gives you the best "sealed" sign. Then simply roll the paint on the raised areas. Completely sealed and durable. John

[Kent Smith]

I agree with John basically. West Jenkins who used to be with Continental once explained to me that what often happens is that during the blasting process, the heat creates a curing of the paints much like oven baking. During that curing, the adhesive of the masking permantly bonds to the paint in areas and is better bonded than the paint is to the wood. Much of the new growth wood is soft enough between the grain that it will easily pull up. Try a scrap of wood, put mask on it and or duct tape and hit it with a heat gun. When you pull it up. the grain will pull up too. I have been using waterborne acrylic primers with better success, mask, blast then finish. Saves a lot of time.

[Mike Jackson]

For 95% or more of our sandblasted signs, we simply bought a gallon of laquer sanding sealer at our local lumber yard and applied it with a cheap brush...slopped it on quickly. It is cheaper than some commercial sealers (First Step) and it dries fast and hard. (Also, we did not have to pay shipping and hazard fees on the First Step product.) The stencil sticks to it fine once you knock off the high spots caused by any raised grain or garbage in the brush or laquer. Once we were through blasting, we removed all the stencil and ran a coarse belt sander over it to quickly remove the laquer, followed by a fine sand paper belt sanding. We owned two different industrial Milwaukee belt sanders—one with each grit of sandpaper. I also bought one of the sandpaper cleaning blocks to help prolong the life of the sandpaper since there would often be some gummy residue on the surface. We used Anchor's more aggressive stencil made for wood, even though we were applying it to a laquered surface.

After the sanding, we painted or stained away as normal. I am not a fan of the finish first process.

Mike Jackson

[Rick Sacks]

I've never found sucess with the finish first method either, but every few years I try it again hoping it might work.

Mike, why the sanding sealer? I use Anchor #155 on bare wood and find very little pull up. If I had a way to regulate the pressure down, I could really dial in on it. I'm using a fine sand and throwing it out of a worn out 1/4" nozzle at around 150 or more pounds pressure. I just stand back farther....usually around 30" from tip to board.

[Mike Jackson]

Rick,
I like to err on the safe side and coat the board with the sealer. That assures a good grip for the stencil, especially after lightly sanding the high spots. On raw wood, it is easy to miss a little fine sawdust and get a weak bond.

I found it was easier to sand off the laquer than it was to use Bondo and putties to fill or repair blow-outs.

It is not necessarily the RIGHT way, just my way!

Mike Jackson

[Mike Jackson]

Here are a couple of groups of signs prior to blasting. The group above might have been a larger group than usual and the one below was probably more in the normal size. Sometimes the panels were larger.
You can see where we had sealed the wood with sanding sealer, then covered with stencil, and peeled the sandblast areas.



Mike

[Jimmy Goines]

What a great looking pile of signs, Mike....

I also switched to laquer sanding sealer after First Step VOC/UPS charges got so high in cost. Most of the time, I do 2 coats. I use anchor 155 stencil that is high tack, unpunched, and will cut on my plotter. Due to the high tack of the 155, I can weed before application to the redwood panel. I use 2 layers of application masking, usually R-tape high tack. From my experience that method is faster that weeding after stencil is applied to the panel. This method works for hand cut stencil also, the anchor 155 stencil has a heavy mylar backing that will hold the lettering during weeding.

Our compressor is diesel 185cfm, air varies from continuous 90lbs to 110lbs. We have available medium grit silica sand that is mined locally. I like to get very aggressive with the blasting act to get it over sooner. Many times I use extra spray adhesive before stencil application and especially with smaller lettering. I always go 3/8 to 1/2 inch deep, depending on design and single/double faced. The heat from aggressive blasting softens the adhesive, so Most Importantly, I remove the stencil very soon after blasting while it's still warm. Most of the time, I have very little redwood peeling. I use homemade grain frames to induce grain of panel areas that blast flat (without raised grain) and most always end up with entire backgrounds that are lovely grained. I usually only have to sand the lettering with a pad sander and 100 grit paper. If perhaps I do get blowouts, (not that often) bondo works well for me to fix splinters or rebuild lost letter edges.

Most of my work is finished with oil enamel primer, finish oil base, and one shot or chromatics for lettering and pictorials. I hand brush the primer and first background finish coat. I usually spray on a second background finish coat, that leaves the lettering surfaces very smooth for the final lettering paint.