Filling inside & outside corner gaps in trim with caulk. - Help needed!


I've just done a bunch of inside beaded corner round and outside corner trimming for my basement reno. Mainly 90 corners around whiteboarded-in utilities, built in cabinet, furnace cleanouts, closets... Its spruce shellacked, primed and twice painted with semi-gloss oil.
Naturally I will I will be sanding the misaligned outside planes where the edges don't quite align. I've got the odd split at the ends due to the nails and may need to chisel out the splinter and reface if the little glue I snuck in doesn't hold and I can't sand and fill it flush without chiseling a notch. I've got to fill the set finishing nail holes too. These may be in the same region as the repairs, otherwise I wouldn't mention them; I'd just use poly, or filler if I have some ready.
I have the gaps at a lot of the corners. They cannot be ignored. You could put a match in one corner. Others aren't parallel. What do I use to fill these fitting errors in so that they will not crack and fall away. I will paint over any repair that I do. I have heard of the use of caulking around casing, possibly to fill the gap to the wall . Is this what I need to use? I have never used caulking for anything other than sealing gaps around windows, water spouts, electrical etc. What type do I need (e.g. latex) and how do I apply it and when do I work it. Does it need to be specified as paintable &/or should it be white in the first place?. If it were like silicone I cannot see working it, it is always springy and won't make or form a shape that I know. Do I need to let it set a little and go back and work it, and with what kind of tools? Do I need to use the slippery finger technique? Can it be cut with a razor blade, sanded? Is it gonna be good, or should I stick with woodfiller or poly and hope for the best? BTW I will also be doing four doors and four windows with all the casings in a matter of weeks. Same thing? Actually I HOPE these will be better, and I can just use some poly. The trim is twisty and isn't backed the same as the casings will be. More finicky, and I didn't finnick too much.
Polyfilla or the like I can only assume isn't flexible enough and will eventually crack, and you can't use fiberglass paper in the limited depth.
Bondo is great but I can only assume it isn't flexible enough and will eventually crack. Dries like JB Weld, no!?
Wood filler, or glue and sawdust I can only assume it isn't flexible enough and will eventually crack. Dries like JB Weld, no!?
Thanks mucho in advance. I'm gonna need a solution soon.
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I should have mentioned: the inside beaded corner round L} is 1/2" x1/2", & the outside corner L is about 7/8" x 7/8"
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From the size of the post you may assume I have a problem. Nope. Just some average trim, with some average gaps.
An idea: maybe if I glued the corners together ( I could get help w/ a syringe) I might be back in the realm of wood filler?
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Latex caulk. Pretty good bridge, adheres well and moves.
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Yep. I've found Dap to be the best brand, but I buy the 30-year stuff when the cheaper would prolly do the job. You should use wood filler (last time I used Minwax brand) for the nail holes. A guy I used to work for used some stuff (I think it was Dap) that was extremely sticky, and cut it with baby powder. Stuff worked like a charm.
For application, yes, the slippery finger (?) method will work. Squeeze a bead on, then run your finger over it to fill.
Good luck.
-Phil Crow
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Painters flexible caulk. Caulk a bead into the corner and smooth over with your finger by sliding your finger down the crack over the caulk. Stare with a small opening in your tube of caulk and if you find gaps after spreading with your finger, make the hole a little larger. If you start with too big of a hole you will end up with a ton of waste on the end of your finger.
Additionally, the ORANGE and CHEAP caulk guns at HD have an automatic pressure release that makes the caulk stop coming out after you stop squeezing the handle. These are great guns and usually cost less than $5.
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Leon wrote:

I agree 100%. I use Alex Plus, It's a latex painter's caulk from DAP. It works well and is very durable. It also has a pretty good adhesive quality. Although nothing will last forever in a cross-grain situation like you described AND this caulking WILL shrink some, so it's not the ideal thing for me on flat surfaces.
On knots and nail holes I use Elmer's wood filler in the little plastic tubs. It dries hard enough to sand. It works really fine on flat surfaces.
Tom in KY, building, refinishing and repairing, it never ends.
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Also keep with you a rag and a bucket of water (with a bit of detergent added) to immediately clean the caulk build-up off your hands and re-wet your finger as needed. Watch out for splinters and any surface roughness that can abrade your water-softened skin. I like Polyseamseal brand latex caulk with silicon additive.
I'm going to check out those pressure-release caulk guns; thanks Leon.
David Merrill

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Keep in mind that the Orange guns look like a typical cheap caulk gun. The difference is a small spring loaded bolt and lock nut located just above the piston shaft. This set up causes the piston to back off just a bit when you release the handle.
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