varnishing ribs

[ken nougaret]

hello all,
i'm aware that the ribs should be varnished with 3 coats of the poly. should the top and bottom of the rib capstrips also be varnished or should they be left bare for the glue during covering?
thanks, ken

[HansLab]

Hi, i did my varnishing all over the ribs, including capstrips: it should be 'sucked into the vaines' of the wood to prevend rotting. The PolyBrush you put on before covering is too rubbery and thinck to accomplish that.

[dholly]

Ken-

The answer depends on what covering process you intend to use. I believe the rule-of-thumb is:

If using a polyurethane varnish with the Poly-fiber covering process, mask the top and bottom capstrip fabric glue surfaces with blue painter's tape. Do NOT finish the capstrip glue surfaces with polyurethane varnish as it is incompatible with MEK and Poly-tac and the fabric will not bond correctly. If using Poly-fiber epoxy varnish with the Poly-fiber covering process, DO seal the capstrips as this (any?) epoxy varnish is un-affected by the solvents used in the Poly-fiber covering process. Obviously this is not applicable for the water based glue products and care should be taken to follow their instructions when using their products.

On a related note, my KF-III builders manual also says:

1.) Lightly sand ribs w/ 220grit, including top and bottom capstrips, before varnishing (never wipe dust off, it will push dust into the pores of the wood which can impede fabric cement adhesion, use compressed air to blow it off instead)

2.) When using Poly-fiber covering system, mix Poly-brush and Reducer 50/50 and apply two coats to the capstrips (appears to be applicable for both un-finished capstrips when using polyurethane varnish, or epoxy varnish finished capstrips). The coats of Poly-brush applied prior to covering will soften from the solvents in the Poly-tac creating a good bond in the fabric.

3.) When using Poly-fiber covering system you can; a.) apply Poly-tac directly to the capstrips then fold the fabric over and rub it into the wet cement, or b.) apply Poly-tac through the fabric, rubbing it in thoroughly to cement the fabric to the capstrip. It specifically says Do Not use process 3b.) on the bottom of the wing, only the top (although that is for the older, under-cambered rib profile wing and may be less of a concern with the newer flat bottom wings).

Clear as mud?!