# Who Back Caulks?



## TBFGhost (Oct 9, 2008)

I am working a job as an employee for another company and I am doing exterior trim and siding on a large addition. These guys do something they call back-caulking. 

After we prime our end cuts in the cedar clap board, we apply a bead of caulk to ends and install it allowing the caulk to get squeezed out inbetween the boards. This is done at all field joints and were the clap board butts into the corner trim. It seems like a really good idea as it gets the caulking down inbetween the parts instead of just sitting on top....we do it ever to the boards that are sprung into place....

I had a small fence gate I just finished up and I ended up applying caulking between the framing and pickets before I assembled trying to keep the water from going inbetween the two....

Anyone else do this?


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## Tom Struble (Mar 2, 2007)

i'm not convinced that doing it that way dosn''t trap as much moisture as it keeps out,you can never get a perfect seal that way imo

i caulk the trim to the wrb,let it cure, then install the siding tight to the trim and let it drain the way it's going to drain

caulk should be used in the proper sized gap,useing backer rod as a bond breaker if needed,any other way and it's bound to fail


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## woodworkbykirk (Sep 17, 2008)

i back caulk exterior window and door trim be it wood or azec. i also do it with aluminum cap flashings around the edges

never had any leaks, but had some messy fingers when i goto to re-adjust peices when i get my fingers into the guck

as for back talk, im looking at brutus


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## Tom Struble (Mar 2, 2007)

iv'e found that when iv'e pulled apart joints like that they are usually damp,better imo to make sure the areas are primed


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## Chris G (May 17, 2006)

I don't think it's a great idea. Water in relative terms isn't a problem. But creating a spot for water to gather and not evaporate is. Eventually the caulking will give out, and then you've got a crevice bounded by a membrane of caulk, so the moisture sits there and creates mildew and mold.


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## TBFGhost (Oct 9, 2008)

Then wouldn't a tight fitting joint create the same problem of letting water and and then not back out?


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## FRAME2FINISH (Aug 31, 2010)

yea thats how i do it too, it doesn't take any longer and it looks good like ya tried atleast,


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## rock16 (Feb 25, 2010)

After installing a good WRB I want it to perform as designed. The WRB should keep water out of the structure without any caulking at all. Squishing caulking all over the WRB is bound to affect it in a negative way, most likely like Tom explained trapping moisture.
I think of caulking as secondary and separate from the WRB and treat it that way.


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## aptpupil (Jun 12, 2010)

seal and back caulk is best in my opinion.


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## TimelessQuality (Sep 23, 2007)

TBFGhost said:


> ....we do it ever to the boards that are sprung into place....






I did a house w/ abtco cement, and 'back caulked'...
After a couple years, through the seasons, it's spitting out the caulk:whistling


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## Tom Struble (Mar 2, 2007)

TBF Ghost said:


> Then wouldn't a tight fitting joint create the same problem of letting water and and then not back out?


maybe,Tom but i think wood will have the tendency to absorb it and eventually dry to the outside,even tight fitting joints will move somewhat,like i said,i was always taught to back caulk too but after you see enough failures you start to rethink things and that has been my experience anyway

i do like the idea of trying to keep water from under the trim,so i guess i use a modified back caulk,but i don't set the wood into wet caulk


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## jkfox624 (Jun 20, 2009)

I'm sure its wrong but anytime i've run clapboards i always slid a piece of tyvek 6 or so inches wide under each piece to span where 2 pieces but. Cut it flush with the bottom of the siding and i dont caulk the seams. I always figured with the primed endcuts and a piece of flashing to drain and water that gets in out onto the next lap was a good way to go. The open joint still allows it to dry. Just my 2 cents that prolly don't even have that value.


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## Tom Struble (Mar 2, 2007)

it's not wrong imo:noldtimers call that a ''spline''


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## TBFGhost (Oct 9, 2008)

tomstruble said:


> maybe,Tom but i think wood will have the tendency to absorb it and eventually dry to the outside,even tight fitting joints will move somewhat,like i said,i was always taught to back caulk too but after you see enough failures you start to rethink things and that has been my experience anyway
> 
> i do like the idea of trying to keep water from under the trim,so i guess i use a modified back caulk,but i don't set the wood into wet caulk


Maybe I explained it wrong, but I am doing what you have there...just on the end of the board, not behind it. I am not bedding the full length of the board in caulk....just the end grains.




jkfox624 said:


> I'm sure its wrong but anytime i've run clapboards i always slid a piece of tyvek 6 or so inches wide under each piece to span where 2 pieces but. Cut it flush with the bottom of the siding and i dont caulk the seams. I always figured with the primed endcuts and a piece of flashing to drain and water that gets in out onto the next lap was a good way to go. The open joint still allows it to dry. Just my 2 cents that prolly don't even have that value.


Yup, I do the same, but with 15 lb felt...or vycor when I ran out of 15 lb felt.:whistling


Also can anyone explain the rumors of Tyvek is a no-no behind cedar?


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## chris klee (Feb 5, 2008)

i have seen tyvek rot away behind cedar. not sure why. i have heard that you have to put firing strips over the tyvek and nail the cedar to that.


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## WarnerConstInc. (Jan 30, 2008)

Today's wood sidings have gots to breathe.


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## Tom Struble (Mar 2, 2007)

TBFGhost said:


> Maybe I explained it wrong, but I am doing what you have there...just on the end of the board, not behind it. I am not bedding the full length of the board in caulk....just the end grains.
> 
> 
> 
> ...


well it's one of those half truths,the oils in cedar can react with tyvek in the presence of moisture and form whats called ''surfacants''...sort of like a soap

the other half of the truth is it can do that with any wrb including felt


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## festerized (May 19, 2007)

Around here we call it “blind caulking”


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## Seven-Delta-FortyOne (Mar 5, 2011)

If I understand you correctly, yes, we've done that on just about every siding job I've been on. We caulk the scarf joints between boards, and the ends where they butt to the trim. I guess it's extra protection, but I'm just not sure about the widespread use of caulks these days. Buildings have stood for hundreds of years before caulks were developed. I guess it's all about the details.


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## William James (Mar 5, 2010)

In my limited experience with cedar siding, I've done as you describe. I caulk the side of the window or whatever, slide the siding in, squish out the caulk, and caulk over the sides when done. 

Never caulk the bottom. But the paint seals it anyway. If the paint isn't connected/tight then moisture will cause it to start peeling. Any better suggestions?


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## TBFGhost (Oct 9, 2008)

Yeah, no caulking on the bottom of the siding...and the cedar is primed 6 sides to try an keep it as stable as we can.


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## [email protected] (Jan 10, 2010)

I do the same as Tom seal the trim to the membrane top and sides. I try to use caulk on everything but field joints on the surface. I never have liked the idea of blind caulking everything, it might look better but does not perform the way it was intented as theres no tooling or bead to flex. I use either bear skin of a tyvek strip with a shadow line in the middle for the joints, never ever caulk the field it always looks like garbage IMO. The purpose of caulking to trim is to keep water out from behind the siding, if the caulk is behind the siding what is it doing besides acting as a wrb.


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## Remodelor (Nov 5, 2010)

I usually prime all sides of my exterior trim, and then when I cut a miter, I prime the exposed wood before I put it up to help seal it. At that point, I just caulk the joint normally from the outside.

That is if I'm actually using wood. 90% of my exterior trim is vinyl nowadays.


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## stp57 (Dec 12, 2007)

Instead of caulk, I tend to use PowerGrab adhesive in the joints. Great stuff & cleans up with water. Best thing I've ever used with pvc trim too. When I trim out exterior columns I don't even use nails anymore. Years later & the joints are perfect with no cracks.
Steve


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## NaeGan (Sep 8, 2009)

That's the way I do it. Siding expands and contracts during the summer. I leave about 1/16th at each end then set it in an elastomeric caulk. It keeps the end grain sealed. Primer isn't designed to be exposed to the elements any longer than 90 days. It begins to deteriorate.

I don't fur it out on the studs, but most ship lap will be warped just a little bit, so I double up two strips of roofing felt to create just a bit of breathability. Everyone has seen what the old paper underneath old siding looks like. Almost always it has had condensation under the siding and deteriorated the paper.


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## nickangel (May 25, 2011)

I find proper flashing and tuck tape around the Tyvek is the way to go. If the flashing is wrong, water is just going to get in there, caulked or not.


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## TBFGhost (Oct 9, 2008)

C[email protected] said:


> I do the same as Tom seal the trim to the membrane top and sides. I try to use caulk on everything but field joints on the surface. I never have liked the idea of blind caulking everything, it might look better but does not perform the way it was intented as theres no tooling or bead to flex. I use either bear skin of a tyvek strip with a shadow line in the middle for the joints, never ever caulk the field it always looks like garbage IMO. The purpose of caulking to trim is to keep water out from behind the siding, if the caulk is behind the siding what is it doing besides acting as a wrb.


 
The siding is also getting surfaced caulked.


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## Tom Struble (Mar 2, 2007)

how are you keeping all that caulk off your assualt pouch?:blink:


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## dibs16 (Nov 30, 2010)

I was taught put a thick bead where tomstruble does, but we never let it cure we just put the clapboards right on top, let it ooze out and wipe it off. Obviously I was not taught the right way.. Great thread I just learned a ton about siding.


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## Tom Struble (Mar 2, 2007)

whoa tony.i didnt mean to say anyone was wrong.i may have but i didn't mean too


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## dibs16 (Nov 30, 2010)

Nope you didn't. I did. I like your way better. Seems logical and cleaner. Thanks for the tip as always!


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## TBFGhost (Oct 9, 2008)

tomstruble said:


> how are you keeping all that caulk off your assualt pouch?:blink:




lol..I didn't. I has a few spots on it


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## Kerf It (Jul 16, 2011)

Leave gaps at end cut for swell with the elements, H-clips for field joints and caulk the ends on a cool dry morning, is how i was shown. We ususally use the pre-finished.


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## woodworkbykirk (Sep 17, 2008)

H clips? for siding?


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## Kerf It (Jul 16, 2011)

Not roof sheathing clips, field joint clips (we just use the term h-clip) they slip between the joint and are engineered for swelling, much easier and faster than felt, clean look too.


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## TBFGhost (Oct 9, 2008)

Kerf It said:


> Not roof sheathing clips, field joint clips (we just use the term h-clip) they slip between the joint and are engineered for swelling, much easier and faster than felt, clean look too.




Do you have a photo or a link to a manufacture's page?


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## Dirtywhiteboy (Oct 15, 2010)

Yes, Yes I've too have used the H clips, It's a gizmo like the tin corners:blink: I don't like ether one:no:


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## Dirtywhiteboy (Oct 15, 2010)

Here, at the bottom of the page H molding:whistling
http://www.appletonsupply.com/aluminumSiding.php


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## Kerf It (Jul 16, 2011)

http://www.cedarsidinginc.com/about.php


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## Kerf It (Jul 16, 2011)

We only use the H molding, all the other stuff is crap in my eyes, less metal more wood(or wood based products)


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## parkers5150 (Dec 5, 2008)

I've torn out almost as much stuff as i have installed in my days and the single most common denominator is Excess Caulk = Excess Damage


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## skyhook (Mar 17, 2007)

TBFGhost said:


> ....we do it ever to the boards that are sprung into place...?


If the board is sprung into place, there is NO room for expansion and the boards will spring out when the weather changes. 
Back caulked or not.


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## Tom Struble (Mar 2, 2007)

wood clap doesn't ''expand'' in length,it's movement is across the grain,corner and window trim will move and change the joint


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## jeffaah (Apr 3, 2008)

Tom Struble said:


> wood clap doesn't ''expand'' in length,it's movement is across the grain,corner and window trim will move and change the joint


I'm still amazed at the amount of "carpenters" that don't know this. 

Then explain that PVC trim can move on all directions and watch the confusion make there brain explode.....


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## jeffaah (Apr 3, 2008)

Back to caulk....

I try not to touch it until it's absolutely necessary. When it comes to weather proofing I try to rely on deflection and drainage. 

Don't kid yourself..... water WILL get in if it wants to. Surface tension will carry water up and around sills, soffits and other trim. Since water WILL get into places you don't want it to be, you need to allow it to get out. 

Flash windows and doors so that any water that gets between the trim and siding can escape. I usually allow water to escape at the last course below a window etc. 

I little thought about how to let water escape is better then caulking the crap out of everything and thinking water will never get in.....


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## skyhook (Mar 17, 2007)

Tom Struble said:


> wood clap doesn't ''expand'' in length,it's movement is across the grain,corner and window trim will move and change the joint





jeffaah said:


> I'm still amazed at the amount of "carpenters" that don't know this.
> 
> Then explain that PVC trim can move on all directions and watch the confusion make there brain explode.....





skyhook said:


> If the board is sprung into place, there is NO room for expansion and the boards will spring out when the weather changes.
> Back caulked or not.


The house (wood structures) will breathe when the weather changes. 
Wood siding will buckle when installed too tight,
windows and doors will stick and jamb when installed too tight, without thought of expansion and contraction.
I'm surprised how many "carpenters" don't know the difference and ignor this fact. 
Back caulking helps bridge the gap when the caulking shrinks and this happens.


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## jeffaah (Apr 3, 2008)

skyhook said:


> The house (wood structures) will breathe when the weather changes.
> Wood siding will buckle when installed too tight,
> windows and doors will stick and jamb when installed too tight, without thought of expansion and contraction.
> I'm surprised how many "carpenters" don't know the difference and ignor this fact.
> Back caulking helps bridge the gap when the caulking shrinks and this happens.


Agreed.....

I know a lot of carps that don't think. I'm all for allowing for movement. 

I've seen a lot of caulk jobs that TRAP water in and cause rot. Don't get me wrong there are places where a correctly applied sealant is needed. But I think water can be kept out using different flashing methods.... Both exposed and under cladding.


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## Tom Struble (Mar 2, 2007)

all good points,i was just trying to clarify how and what wood is moving and it's not in an end grain direction which leads me to the conclusion that caulking the trim to the wrb and leaving the end joints primed but not set into caulk is the way to go jmo

but we really gotta stop saying houses breathe,that implies in with the good and out with the bad and that is just not true

a better way to put it is that houses pressurize and depressurize


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## Tom Struble (Mar 2, 2007)

NaeGan said:


> Primer isn't designed to be exposed to the elements any longer than 90 days. It begins to deteriorate.
> 
> .



the ''primed'' end is not subject to u.v degradation,it is only used to seal the wood fibers which it will do probably indefinitely


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## ATXwoodman (Jul 2, 2011)

So if you're back-caulking siding jobs, you better apply the caulk in some repeated-S pattern that allows the air to dry ALL of the caulk behind the siding material. Forever-wet caulk sounds awful!


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## Tom Struble (Mar 2, 2007)

no woodman i don't think your following right,back caulking means setting the ends or sides of the siding[if using shakes] in to a wet bead of caulk,not setting the back of the siding in it

some caulk doesn't ''dry in the air'' but is actually moisture cured


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## Kerf It (Jul 16, 2011)

We suffer from severe humidity around these parts so the allowance of expansion is crucial whether it be in length, width, or thickness, some finesse of the caulk gun, and proper gappage will go far. unless you enjoy buckle-ling.


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## Tom Struble (Mar 2, 2007)

again wood doesn't''expand'' in length from moisture


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## woodworkbykirk (Sep 17, 2008)

my personal favorite is the guys who caulk the seam between siding and the head flashing so water cant get in.......... it doesnt get it but any water that gets behind the siding higher up the wall is now going to sit on top of the flashing behind the siding..... 

then these same guys cant understand why the peice of siding over the window is rotting plus the drywall inside is turning to mush plus the interior trim is moldy


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## jeffaah (Apr 3, 2008)

woodworkbykirk said:


> my personal favorite is the guys who caulk the seam between siding and the head flashing so water cant get in.......... it doesnt get it but any water that gets behind the siding higher up the wall is now going to sit on top of the flashing behind the siding.....
> 
> then these same guys cant understand why the peice of siding over the window is rotting plus the drywall inside is turning to mush plus the interior trim is moldy


So true......

It's usually the painter that caulks EVERYTHING. 

it is also unfortunate that when you tell people not to caulk certain places to let water out......they think your a hack because water can get in.


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## yo mama (Aug 28, 2011)

TBFGhost said:


> I am working a job as an employee for another company and I am doing exterior trim and siding on a large addition. These guys do something they call back-caulking.
> 
> After we prime our end cuts in the cedar clap board, we apply a bead of caulk to ends and install it allowing the caulk to get squeezed out inbetween the boards. This is done at all field joints and were the clap board butts into the corner trim. It seems like a really good idea as it gets the caulking down inbetween the parts instead of just sitting on top....we do it ever to the boards that are sprung into place....
> 
> ...


There must be a better way of doing this.


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## tanthony (Aug 10, 2011)

*no back caulk*

SOmetimes to much is to much. I have done jobs where people seal their trim all the way around and I preach against it. if you seal the lumber it will rot because nothing can escape. many deck joist that I find prematurely rot because the owner paints the under side and sides of the joists creating a bowl. I do alot of timber work and if you want color then use a solid body stain.www.coloradospringsdeckbuilder.com


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