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Finger jointed primed pine - Shrinkage

shimster's picture

Similar posts prior, but here's mine: I live in Coastal CT, and have hot water radiator heat.  Mid-1800's house.  I like to use FJP pine trim (1x4 thru 1x10) because it's pre-primed, and tends to be straight / true.  I would only use this product on the interior (see other posts re: FJP on exterior).  Here's my deal: I'm experiencing some substantial shrinkage.  Maybe it's due to the high humidity in the Summer (we have no A/C), but it's mid-January now, and EVERY ONE of my caulk joints (baseboard, casing, whatever) is opening up.  Season to season as well.  Not just the work I've done recently.  I'm beginning to think I need to pre-prime all end cuts even on the interior work.  This must be the softest/ youngest wood in the yard, and bottom line: it's a sponge.  I'm talking 1/4" shrinkage or more on a 1x5 door casing.  Massive.

 

Any thoughts/ experience welcome.  Again, this is an INTERIOR situation.  Thanks!

You likely have a lot of (post #207334, reply #1 of 6)

You likely have a lot of seasonal variation in humidity.  (Hard to keep a house that old tight.)

And softwoods tend to have more trouble with this than hard woods.

But there are tricks.  For door or window trim, don't nail off the ends of the pieces, but leave them loose (from the framing) for the last 6-10 inches and glue/nail/screw the ends together so that the trim can flex laterally rather than opening up at the joints.

And if you still have a lot to do, go ahead and buy the trim now and let it acclimate in the house for as long as possible.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

shim (post #207334, reply #2 of 6)

The moisture content in the wood was evidently too high upon assembly and with radiator heat and little or no added humidity-you are going to see shrinkage-And I assume you mean in width.

If those joints are mitres, there's uneven shrinkage as you go from tip to heel. 

So, what kind of joints-butt or mitre?  Did you glue them as well?  if so, you effectively sealed the cuts.

With trim that wide, did you bisquit the joint as well?   Might try pocket screwing the joints together on the bench, then place and nail off.

I don't know anything about leaving the last 8-10 inches not nailed and have been doing this for over 40 yrs.

Moisture content and changes in humidity are the things we try to control.

 

As to the wood itself-and I've had no problem with it-could it be what is called paulonia here?  Chinese "pine" type import, great prime coat-very light in weight and straight as an arrow, little or no cupping?

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Reply to original post... (post #207334, reply #3 of 6)

Thanks all.  I am doing butt joints on the door casing (head casing is capping both jamb casings), and I am not glue-ing them.  The end grain of the head casing is obviously painted in the end, so I suppose that is getting sealed.  It's more the vertical casing that is shrinking in width (and some slight length).  It is also happening in baseboards.  The width of the board is reducing (~1/4" over a 1x8).  Mostly up off of the flooring.  Regarding have a tight house, I suspect I have the least tight house in CT.  Single pane windows, no storms to speak of, and the unrenovated rooms still have no insulation whatsoever, so I suspect a relatively large humidity change (punn intended) is the culprit.  I love the idea of glue-ing all end cuts, more as a sealer than anything else.  My 50+ year old carpenter wouldn't give me too much of an earful on this one, as opposed to busting out a paint can to keep next to his chop saw!

shim (post #207334, reply #4 of 6)

1x8 shrinking at a 1/64th per inch of width-would certainly give you an eigth shrink.  The 64th isn't even on my tape-nor is a 32nd.  It doesn't take much.

 

You need to know the ambient moisture content in your area/home at time of install.  Along with that, what is the MC of your wood?   Acclimating is what is taught, but the reason behind it is often left out.  To bring the MC of the stock more in line with where it is going.  If it's too dry and you introduce it to a moist (constantly) environment-it'll expand and ............

Too wet on install and it'll shrink.

In a home with wide varying humidity, all bets can be off.  The sealing of all sides helps, but most of the coatings breath a little-so keeping a more steady humidity is really the only way to assure long lasting joints.

Along with that, proper technique on install.  I would have at the minimum, bisquited or splined your trim.  Probably would have preassembled and pocket screwed them on the backside.  Just sitting them on top and gluing with a couple nails will at the minimum, guarantee a paint line crack with seasonal change.  Not so bad with stain, butt ugly with white paint.

Take a look at this and plug in some numbers to see what changes you can expect in wood trims.

http://www.woodweb.com/cgi-bin/calculators/calc.pl?calculator=shrinkage

If I can find it, or perhaps you can look for it-there's a formula for how much width a board will shrink for every percent of MC it loses.  The wider the board, the bigger the loss in width. 

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Shim (post #207334, reply #5 of 6)

USE GLUE.

and one question-where and how was this material stored/stocked in the home?

If it was acclimating, did you cover it?

thanks.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.


http://www.quittintime.com/

 


Even though it's (post #207334, reply #6 of 6)

Even though it's "pre-primed", you might want to give the trim a coat of paint or primer on the back side before installing.  (Don't paint before acclimating or it will cup.)  The extra paint will help slow moisture change.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville