Varnish prep: cleaning dust from pinholes

[ae6rt]

Having finished sanding my Pygmy Artic Tern, the next step is cleaning epoxy dust from the pinholes. I fabricated a garden hose fitting to act as a high pressure scrub device to clean epoxy dust out of those pinholes.

The local hardware store sold me this for under $2. It's a garden variety brass cap that fits on the end of a garden hose:

http://www.doityourself.com/invt/u775528

My drill bit kit, which has a typical do-it-yourself selection of bits, provided me with a very small bit, probably a 1/32" diameter. I drilled a hole in the brass cap, attached to the garden hose, and proceeded to clean the surface of the entire boat. A quarter turn of the faucet provided plenty of pressure delivered in a set of jets of various cross sections. The cross section variety resulted from a near circular hole, with brass burrs still in place. This is actually, good, as I used the various jets in the aggregate stream to probe into small pinholes.

I followed up when the boat dried and probed the pinholes with a straight pin: no additional dust came out, even where it sort of looked like dust remained.

Holding the jet about 3-5" from the surface seemed about the optimum distance. The pressure was great enough where holding a finger in front of the jet proved rather uncomfortable after a few seconds. At about 9-12" from the cap, the stream was diffuse enough that it could safely be called just a directed mist.

 

[mick_allen]

the method that i use is to take a small abandoned fridge compressor, jam on a cheap air hose with a syringe needle electrician taped on.

then no water spray at all and can blow out very very tiny and awkward pinhole situations.

also use a thin ss wire 'toothbrush' to assist. you can buy them in sets of 3- nylon, brass and ss bristles- for a few bucks.

 

[Astoriadave]

Let's hope those pin holes do not penetrate to wood. If they do, then it is likely the varnish will not bridge them. It would be a good idea to get some epoxy in them and then re-sand to a fair surface before varnishing.

The pinholes likely resulted from outgassing of the wood during epoxy curing.

 

[mick_allen]

The pinholes likely resulted from outgassing of the wood during epoxy curing.

the pinholes that i get mainly come from vertically stippling the epoxy and glass with a brush to try to force it to conform to complex surface changes. the epoxy becomes air entrained with hundreds of tiny miniscule bubbles that get partially exposed upon sanding and filled with the nice white epoxy dust. in my case i fill them w/ more epoxy 1st before final sanding and varnishing.


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[Astoriadave]

the pinholes that i get mainly come from vertically stippling the epoxy and glass with a brush to try to force it to conform to complex surface changes. the epoxy becomes air entrained with hundreds of tiny miniscule bubbles that get partially exposed upon sanding and filled with the nice white epoxy dust. in my case i fill them w/ more epoxy 1st before final sanding and varnishing.

Man, I hate those. They are the bane of working in a cool environment, I suspect. Somebody told me if I switched to a lower viscosity resin (like System Three's Clear Coat) I would not get them. I'm too stingy to do that. :roll:

 

[Dan_Millsip]

the method that i use is to take a small abandoned fridge compressor, jam on a cheap air hose with a syringe needle electrician taped on.

Yup, I've been using that method as well (except with the luxury of an air compressor) and it works quite well. I'll try to remember to take a photo of the setup.

also use a thin ss wire 'toothbrush' to assist. you can buy them in sets of 3- nylon, brass and ss bristles- for a few bucks.

Sometimes stubborn dust just needs a little coaxing.

Interesting as to why you used the stainless brush -- I would have thought that it would be a bit too aggressive. I've been using the nylon (similtanously with air) with good results but maybe I should pull out the serious metal artillery for those stubborn spots.

*****

 

[mick_allen]

I've been using that method as well (except with the luxury of an air compressor)

i always carry a cut down 4" crescent wrench on my keychain and whenever i saw an abandoned fridge i took the compressor home (the tubes seem to be always cut).

voila - free small air compressor or vaccum pump!

( i remember i used the black 1/4" tubing and fittings that you can get from home depot for underground sprinkler drip lines.)

Interesting as to why you used the stainless brush -- I would have thought that it would be a bit too aggressive.

the wire bristles are so fine (which is perfect for the tiny holes) that they do not apparently scratch or abrade the resin even a tiny bit that i can see.


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