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I've been told that baseboard, unless done so already by the sawmill, should be kerfed before installation to prevent warping in the future. Is that really necessary or just a good thing to do?

I plan to buy plain (meaning no beveling or grooving) maple 1x6 to use for baseboard. I asked the lumber yard and they said they are not pre-kerfed.

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I thought the reason for trim having a kerfed back was to make it easier to lie 'flat' against uneven framing/finishing (ie, the door casing and the sheetrock) – DA01 Mar 17 '14 at 20:32
@DA01 - pretty much my experience, baseboard isn't that substantial. – Fiasco Labs Mar 18 '14 at 0:23
up vote 5 down vote accepted

The main reason the recess is in the back of all moldings is to "thin" the wood, reducing the amount of continuous rings in the wood that helps control cupping.

There is a fringe benefit of that relief in the back of trim, it helps get past some irregularities in the wall. I have had more problems with that relief cut than benefits when it come to base. The tapered edge of drywall at the floor coincides the relief cut in the back of the base, which then requires a shim to keep the base in plane with the wall. Not a terrible thing, but an extra step to do.

It is my belief that the relief cut or kerf as you have referred to it as, now a days has more purpose to go over irregularities, than to control cupping, since houses have better climate control than the old homes did when the technique was created. The trim is machined from wood that is kiln dried, which also helps in the reduction of wood movement.

In a nutshell, I would not hesitate to use 1X6 off the shelf, instead of 1X6 base. I used both 1X6 base and off the shelf 1X6 poplar for the base in my home. You cannot tell one from the other. I stained it too, looks pretty good if I do say so myself. The rest of the trim in my home is poplar to. FWIW.

The maple you speak of can take stain decently too if the wood is treated first with a wood conditioner.

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To prevent warping in the future, put a coat of finish on the back side similar (or the same as) what you put on the front side. Kerfing is only needed to make it bend more easily where the wall is curved, if it does not conform to the wall with a reasonable amount of pressure.

The other stock piece of word-warping-wisdom (since unlike pre-shaped baseboard, your plain 1x6 has two sides that could face out) is to put the "heart side out" (look at the growth rings on the ends of the board - figure out where the center of the tree was relative to this board, and put that face out.)

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