Priming HDU – Tips From The Experts

Want to know how the experts prime their signs for an ultra smooth finish? Check out some tips on priming your sign using FSC-88WB Primer/Filler!

First of all, FSC-88WB Primer/Filler is a water-based, high build primer designed for use on Precision Board Plus HDU. It also works well on wood, metal and concrete. Typical primers do not have the amount of solids required to fill the cells of HDU without many coats – a problem we addressed by creating FSC-88WB.

In order to give your sign the smoothest coat possible, be sure to keep these tips in mind:

When Spraying FSC-88WB:

  • Thin only as necessary, usually about 40% +/-, to desired spraying consistency using water. Final thinning will depend on type of spray equipment and operator. Spray at about 40 psi with max size tip available. Adjust thinning for maximum hide and smoothest surface application.
  • First coat should be a little lighter than subsequent coats. Allow to dry, usually about 10 minutes. Do not sand between coats. When tack free, apply next coat a little heavier than first coat. If surface has to reached the smoothness desired, wait until tack free and apply next coat. When spraying, multiple thin coats are recommended over fewer, thicker coats.
  • Be sure to use a large tip, such as a 2.7mm or 3mm tip for your HVLP spray gun.
  • FSC-88WB also works well when used in a “cup gun.”
  • Unlike traditional primers, FSC-88WB reduces viscosity by compression, which causes it to atomize. Other primers reduce viscosity only by thinning.
When Brushing or Rolling FSC-88WB:
  • Reduce the FSC-88WB about 15% with water to reduce roller drag and extend drying time.
  • Always use a short-knap cloth roller – 1/4″ or 3/8″. A heavy knap roller will leave too much texture.
  • Be sure to roll/paint in several different directions to ensure full wet out of the Precision Board Plus cells.
  • Do not use a foam roller! Foam rollers will pick up just as much primer as they put on, leaving no primer build.
Drying/Sanding Precision Board Plus HDU:
  • Allowing the primer to dry is very important. Because Precision Board Plus does not absorb water, all water must be forced out via the surface. If any water is still in the primer when it comes time to paint, blistering will occur.
  • You will know when it is dry when it does not ball up on the sandpaper while sanding it. The FSC-88WB should powder when it is being sanded.
  • Start out using a 120 grit sandpaper, and work your way up to 220 or 320.
  • After sanding, and before painting, place the sign under a shop fan for at least an hour. This will prevent moisture reabsorption, which can occur even if the primer has been applied days or weeks earlier.
Painting Over FSC-88WB:
  • Once  FSC-88WB is completely dry, it is compatible with all types of paints and finishes, including most lacquers, automotive paints, and even gold leafing.
  • All sides of the sign must be painted. This is due to Paint Tension Balance – because Precision Board Plus has no beam strength like wood, it can be pulled in the direction of the drying paint. This is eliminated by painting both front and back of the sign.
General Tips:
  • FSC-88WB can also be used as a filler. Simply place on something absorbent such as cardboard, and give it a few minutes to body up. It can then be used to fill cracks and seams.
  • One of the reasons FSC-88WB works so well is because it is so high in solids. High solids fill the cells of HDU much more efficiently than typical primer which has low solids.
  • Be careful not to apply the primer too thick, or place the shop fan too close as this can cause mud cracking.
  • Because of the high solids in FSC-88WB, for wood or plywood priming it must be reduced by about 50% in order for it to be absorbed.
  • FSC-88WB works very well on wood but it must be reduced with water to make it a “wood primer”:
    Simply pour half  of a gallon of full strength 88 into a clean, gallon sized paint bucket. Take this unmarked, 1/2 full bucket and add water to within about 1″ of the top. Thoroughly mix the water into the 88 to a very smooth consistency. Mark on this container WOOD PRIMER ONLY. You now have  a half gallon of FSC-88WB and almost a full gallon of Wood Primer – All for the price of 1 gallon of 88WB. For maximum wood sealing be sure to use at least 2 coats of “88 Wood Primer.” The first coat will be absorbed deep into the top surface.
Many of these tips can also be seen demonstrated on video in our video library.
Interested in trying FSC-88WB? Request a free sample here.
All priming was done by Insiginia, a full service sign shop located in Anaheim, CA.