Sealing Exterior Door Bottom

[Erich Stoeff]

I've received conflicting advice on this topic. Respected painter friend says prime all sides including bottom & hinge mortises. Old school German carpenter advisor said never prime bottom or hinge mortises, use water-proofing sealer that soaks into the wood. Primer (he says) traps moisture while sealer allows door to breath. I've never liked priming hinge mortises anyway & have always used polyurathane but this wasn't based on any valid advice, just the way my old boss told me to do it. Revisiting 15 yr old projects at least show this has held out water pretty well but some discussions I've seen online cast some doubt as to the longevity of this approach. I've always primed door bottoms, but I'm looking for a consensus to validate. Specific project at hand involves mahogany french doors under small overhang with gutter so I'm not so concerned that it's going to get hammered water-wise. Any suggestions? Thanks.

[Peter Quinn]

How about seal, then prime, then paint? I followed this schedule for some fir bead board that raps the inside of my porch rail about 4 years ago and it has held up well. The sealer was some nasty stuff, oddly a water based product but with lots of warnings about skin contact and breathing. I actually tanked each piece and dried them before installing, priming and painting.

The most durable product I have used is Smith's CPES from Jamestown distributers. This is an epoxy penetrating sealer meant as an undercoat for alkyd paint or oil based varnish/polyurathane and a number of other top coats. May be overkill for a well protected door, but it SEALS for real and penetrates deep, then keys the top coat in. The application schedule specifies to apply the first layer of top coat after the solvent has evaporated but before the epoxy has fully cured for maximum adhesion of the top coat. I used this system on the porch floor and have yet to have a problem in four years.

I can tell you the first place to rot on any door or window I have witnessed is the end grain on the bottom of the styles. Seems worth protecting before installation. Maybe the old German gentleman was right.

[chris cartwright]

I have used West System for sealing the end grain of door and window stiles with great success, even rejuvenating some that had already started to rot, but were dry. If it is warm and lighter viscosity it will penetrate even better; to cool and it just sits on top w/o penetrating. Don't put it in the microwave to warm it up; you will be exiled to the doghouse. (Don't ask me how I know this):mad: West system exudes a waxy substance when cured that must be abraded to allow a good paint bond.

[Erich Stoeff]

Thanks for the input. I'm onboard with either product, but do you think either one, by itself, would be enough to keep the hinge mortises protected? It may be my psychosis, but I really like the idea of keeping the mortises as clean as possible without a layer of primer gumming them up. I can see the benefit of sealing the bottom of the stiles with sealer, primer & topcoat assuming Gert is wrong about the "sealing moisture in" aspect.