What to do after priming

I have just primed my IOM hull and I thought that I had sanded and faired it good, but after the primer went on there were little pin holes and small wrinkles? What next? what do I fill with? do I need to sand back to epoxy and fill with thickened epoxy? I would assume I can not uses spackel of drywall filler?

Will take the first stab at this one …

  1. Pin holes = dirt, oil, fingerprints, or missing epoxy from initial/subsequent coatings.

  2. Wrinkles = paint runs, secondary primer coat applied before first coat was dry, too heavy single coat.

Let’s do #2 first. If using sanding primer ( fast build, thick and very soft matte finish) you can simply sandpaper/block sand out the wrinkles until smooth. Be sure to sand out far enough to allow a "feather edge. Wait for at least a week for primer to dry. If sandpaper loads up, keep changing so you are using sharp grains.

Sand back, then sand entire hull, then re-spray primer in very light coats - almost as a mist. Most of the mist will be dry as it reaches the hull, but only one coat and let dry. Continue this “Misting” build up to about 3 coats, then sand back down ending with a very fine wet/dry paper.

  1. Wipe down with acetone/alcohol to be sure any fingerprints or dirt have been removed. Use a tack rag dampened with same cleaner on clean white cotton cloth. Don’t use polyester T-shirts or similar as they probably have finishes on them left over from production, regardless of their age. Again - sanding down as noted in #2 above will present the pin holes. Using a dark red or gray primer with bulb inside hull, you can see and mark the pin holes.

If they are big get green or red “Spot Putty” which is polyester based. It looks like very thin “Bondo” and drys very quickly. A small dab on finger quickly applied to hull will catch most of the pin holes and the stuff sands very easily as it has a high talc powder volume. Once you have them filled, go back to the primer and do several light coats. The “spot putty” can be found in most auto areas of Wal-Mart, etc. - or directly from a good auto parts store that caters to local auto painters. It’s a tube about twice the size of toothpaste and be sure to keep capped. Knead tube before using, otherwise you’ll only get a red or green liquid without the filler.

You can use joint compound for deep fillets or hollows, but then need to coat to keep from water. Personally, I only use that stuff for plugs - or for foam hulls that will get coated in glass and epoxy. Not sure I would take a chance using on the exterior of a hull.

Just remember to keep it clean and apply very light coats - whether primer or paint.

Depending on the severity of the job at hand you could always use West System epoxy and some fairing compound (a light brown fine powder) you mix with your epoxy. This can be found at most boat stores but is expensive and overkill if it is a smaller job. Dick sounded like he had the right idea to me. Although I have always use West System. Good Luck.

Thank you Dick and Millrtme,

I thought about the bondo filler, but I used epoxy on to build the hull, would that work with the epoxy. I thinking of somthing with the high talc base to do as you said rub on with my finger, I use to be a finishing carpenter and we used all different fillers to rub into the nail holes. Would an exterior wood filler work seeing it will be covered in paint and does not sit in the water all day? The pin holes do not go right throught the hull, it looks like it is just the texture of the fibre glass. I do not know if epoxy with micro balloons will stick to the primer. Thank you Dick for telling me to wait a week before sanding primer, I somtimes rush things.
The hull was rubbed down with acetone so no finger prints.


Another thing that has been mentioned before by Nigel. You can use Rust-oleum (Trem clad)clear coat. Spray a bunch in a cup and use a toothpick to apply enough to fill in the hole. NIgel uses clear as a primer so he might be able to shed any light of interaction problems between primer and clear.

Dick has described the whole process quite well. Follow his instructions for a good result. I do take issue about having the primer rest for a week. Not necessary if you use the right stuff. Water based paint will indeed need a week or ten days to fully cure. Laquer/solvent based paint needs no such time interval.

Go to the auto paint store, buy a laquer based primer. You will need some laquer thinner to go with this stuff. Do not buy “etching primer”, it has phosphoric acid in it that is designed for bare metal application. Plain old gray primer will be ready to sand in an hour or so. We use this stuff on a product we manufacture, it is followed by a two part urethane (Automotive) paint that yields beautiful results. When possible we leave the primer, for a few hours after sanding, before we apply finish coat. Been doing this for 20 years, no problems.

One stunt that you can do to fill pin holes is as follows: When a can of laquer type primer has been sitting for a week or so, much of the filler will precipitate to the bottom of the can. Dunk a paint stick into the bottom of the can and pick up a glob of precipitate. Dab it into the faulty area, or pinholes. with a limber spatula or even your finger. Dip the spatula, or heaven forbid, your finger, in thinner to smooth the patch. The heavy deposit will need extra time to harden, but not more than a few hours. Sand as needed, repeat as needed.

Automotive two part urethanes, for finish coats, are very durable and can be polished to a fare thee well. These finishes do indeed need extended cure time. We do not process our product for at least 48 hours after applying the finish coat. I do not put my boats in the water for at least that long after finish painting. If you want to get an absolutely spectacular finish job that is as smooth as a baby’s butt, try this…Let the urethane cure for a week or ten days. Get some 3M brand Finesse-it at the auto paint store. Finesse-it is a super fine buffing compound that yields a satin finish unrivalled by anything else I have used. This is a concours winning finish. Best of all the ultra smooth finish on the underwater part of the boat cannot help but add to boat performance. :zbeer: