# Flat roof exposed beams repair question



## dayton (Jul 14, 2009)

Hi everyone. I'm new to the forum and came in search of some advice. I bought a flat roof house about 3 years ago. It's from 1969 and has a style fairly typical of the modern era...there is a host of these beams that run through the home and extend out, thus making them very susceptible to weather damage and deteriation. 

When I bought the house, the ends were fairly well in tact but there were some cracks that ran through (I was told it was an issue with contraction and expansion since I'm in midwest winter/summer).

Anyway, the ends have been damaged over the years and it's time to repair. I realize that it will be a structural issue after a certain point.
I have painted these a few times but I need to do some serious preservation work on these. 

I was wondering what the best technique would be? 
I don't know exactly what kind of wood it is but on the interior they are flat black, which I'd maintain but it seems like most sealants have a high gloss to them. I used flat exterior latex the last time and it clearly didn't do too much protecting.

Another issue is the cracks that are slowly appearing..some are getting fairly big so I'm wondering if I should use wood putty in those or something like the liquid foam 'Stuff' to put in there, sand down and then paint and seal.

Here's an image of how these things look (this is actually one in better condition) It goes through 2 layers of glass (space in between) and runs the length of the house exposed on the interior.
Much thanks in advance to anyone who is kind enough to offer some suggestions on how to properly paint/seal/rebuild this wood.


----------



## inspectorD (Jul 15, 2009)

Well do do it so it will last, you need to cut the ends flush with the roof overhang. This will change the look obviously, but exposing timbers to the weather as they are is a deterioration issue. If you cut the ends off, you will probably remove all the deteriorated wood and stop the problem from getting worse.
You could then paint the ends and have them covered with a piece of colored/painted aluminum ,just as another saftey measure.
If you want the look, cover the tops and sides with aluminum.(They sell colored flashing for facias and rakes on vinyl sided homes)
This is sometimes an issue where the piece gets nailed, they leak in and you don't notice until it's to late.
No paint will solve this issue.
To replace this roof and beams will get very expensive.
Good luck.


----------



## dayton (Jul 15, 2009)

thanks for the quick response, inspectorD.
Can you suggest a product or process for filling in surface cracks that have already occured? Before I paint and seal them?

I probably won't go the aluminum route just because they've been uncovered since 1969 and have fared fairly well until I moved in. After I get them sealed, I'll just have to be more active about protecting them.

but my main concern is trying to fill cracks from the exterior side before I cut them off and seal them up.
thanks again for your help.


----------



## Nestor_Kelebay (Jul 16, 2009)

Dayton:

     I'll explain what's causing this, and then you can decide for yourself which way to deal with the problem.

     Wood is a natural material that absorbs and evaporates moisture into the surrounding air.  Neither the absorbtion of humidity from the surrounding air, nor the evaporation of humidity from the wood into the surrounding air does the wood any harm.  If you look at the wall studs of an undrywalled garage, you'll see that the wall studs look as good as new.  Ditto for the roof rafters.

     When wood is exposed to the elements outdoors, what happens is that it absorbs liquid water (the rain) or water from wet ground.  And, wood both absorbs liquid water and evaporates it back into the air 15 times as quickly through it's end grain as it does on any of the sides parallel to the grain of the wood.

     Wood cells are shaped like long drinking straws, and they're about 40 to 80 times as long as they are wide.  When wood gets wet, initially the absorbed water goes into the wood cell WALLS.  As this happens, the cell walls swell up (get thicker) and get softer.  Because of the shape of wood cells, there are many more wood cell walls going across the grain of the wood than along the grain of the wood, and the result is that the wood swells, predominantly ACROSS it's grain.  The relatively few cell walls along the grain of the wood mean that expansion of the wood along it's grain when it gets wet is negligible, and is typically ignored in most applications.  Thermal expansion of wood from winter to summer is much smaller than even the moisture expansion of wood along it's grain, so when you suggested the "expansion/contraction" of the wood and then mentioned "winter/summer", it suggested to me that you thought the deterioration was due to thermal expansion, and nothing could be of less importance here than thermal expansion of the wood.  It's the swelling of wood cell walls when they get wet that's causing all of your problem.

Lately my computer's been crashing, so I'm going to explain the problem in short posts so that I don't lose a lot of work if it crashes at the wrong time.

     Now,


----------



## Nestor_Kelebay (Jul 17, 2009)

Now, once the wood cell walls have absorbed all the water they want to, that condition is called the "fiber saturation point", but it doesn't mean the wood won't continue to absorb water.  In fact the wood will continue to absorb a lot of water, BUT:

a) Any further water absorbed will go into filling up the hollow wood cell interiors, and

b) Any further water absorbed won't result in any further expansion or swelling of the wood.

So, first the wood cell walls and then the wood cell interiors will fill with water, and when both are full of water, then the wood is in a condition similar to what it was when the tree was alive.  Drying of the wood is this same sequence in reverse; first water is lost from the wood cell interiors, and once the cell interiors are dry, any further drying results in the wood cell walls losing moisture, getting thinner and stiffer (and the wood becoming stronger as a result of the stiffening of the wood cell walls).  It is only that range of moisture content (from about 16 to 30 percent) where the moisture is coming from the wood cell walls that results in any dimensional change (swelling or shrinking) of the wood (primarily across it's grain).

Now, there are two things happening in your case:

1. The beams are cracking at their ends.  You will find EXACTLY the same thing if you look at the 2X12's at any lumber yard where the ends of the 2X12's have not been painted.

What's happening is that the end grain of your beams are absorbing rain water.  That end grain absorbs water like a sponge.  When the end grain gets wet, then the moisture is most rapidly transported along the grain deeper into the wood.  Water simply moves more rapidly along the grain of the wood (presumably by capillary action) than across it's grain.  But, after a rain, while the moisture in the wood is migrating along the beam toward the house, the clouds part, the sun comes out, and moisture is also starting to evaporate from the end grain of the wood, too.

So, what happens is that the wood at the end of the beam swells up, and the beam continues swelling at it's end as the water is absorbed deeper and deeper along the grain.  But, as the moisture then starts to evaporate from the end grain (the end of the beam), then you have wood further from the end that wants to swell, but wood at the end that now wants to shrink.  It's that shrinking force at the end of a swollen beam that causes the end of the wood to crack to accomodate the shrinking right at the end of the beam.  This is the reason why any wood exposed to the elements will often show large cracks at the end.  Just visit your local lumber yard and you will note that every 2X12 they have in their yard will be split at the end for a foot or two.  And, it's entirely because the end grain of the wood both absorbs and loses moisture faster than any other surface of the wood, and the loss of moisture below the fiber saturation point results in shrinkage of the wood.  That shrinkage at the end grain while the wood further in is still swollen is why your beams are cracking at the end.


----------



## Nestor_Kelebay (Jul 17, 2009)

2. The other thing that's I think is happening is that the paint you're applying isn't protecting the wood from the UV light from the Sun.

I'm thinking that whomever sold you the house probably painted those beam ends prior to selling the house, and you just never noticed the deterioration until his/her last paint job started deteriorating on you.

Latex paints are made with tiny blobs of plastic suspended in the water.  In better quality latex paints, those tiny blobs of plastic will be made of polymethyl methacrylate, or Plexiglas.  That means, without solid tiny coloured particles in the paint, all latex paints would dry to a clear or transluscent film.  Plexiglas is darn near transparent to UV light from the Sun, so EXTERIOR latex paints have to have transparent iron oxide pigments in them that are opaque to UV light, and shade the underlying wood from the UV light from the Sun.  Without those UV blocking pigments in the paint, then UV light from the Sun will travel so easily through latex paints that exposure to intense sunlight will cause the paint to peel off the wood.  That is NOT because the UV light has deteriorated the paint... it's because the UV light has so deteriorated the underlying wood that there is nothing solid for the paint to stick to anymore.

Take a close look at your beam ends and see if there is a marked change in appearance of the paint and underlying wood where the beam becomes exposed to direct sunlight.

I'm even thinking that whomever painted those beams may have used INTERIOR paint on the outside just to ensure uniformity of colour and gloss of the beam along it's entire length.

So, what I think is happening to the paint at the beam ends is due to both the swelling and shrinking of the wood there due to absorbtion of liquid water at the beam end grain, and the deterioration of the wood UNDER the paint due to exposure to UV light from the Sun.


----------



## Nestor_Kelebay (Jul 17, 2009)

If it were me, I would:

0. Cover the exposed beam ends with a piece of sheet metal laid over them and overhanging them by several inches.  Now, just allow plenty of time for them to completely dry.  Metal is the most opaque material known to man.  You can stop more light with a single sheet of aluminum foil than you can with any other material of equal thickness.  That will both keep the Sun off the beams and protect them from rain as they dry out.  Maybe have an 8 foot long piece of thin sheet metal cut at any sheet metal shop and have them bend one edge downward at 45 degrees a half inch from the edge to ensure that water dripping off that sheet metal drips off the edge rather than runs under the sheet metal.  Maybe seal the points where the beams are with plumber's putty to ensure water doesn't drip through at the joint onto the beams.  And, maybe place a rock on the sheet metal over each beam to hold the sheet metal in place.  Any other material besides sheet metal will work equally well.  The point is to protect the wood from getting wet again during the time you allow for the beams to fully dry out.

1.) Use a sharp paint scraper to scrape off any loose paint that's not putting up a respectable fight to stay on the beam.

2. Use a paintable latex caulk (like DAP "230" "Advanced Latex Sealant") available from Home Depot (or competitor's equivalent) to fill the cracks in the beam sides and end.  Latex caulks, like latex paints, allow H2O molecules to pass through them, but not liquid water.  (Post again if you want to know how they do this.)  The latex caulk will allow moisture to pass through the caulk, thereby allowing the beam to continue drying, but won't allow liquid (rain) to enter the beam at those cracks.

(When using latex caulk to fill cracks in wood, the best thing to do is squeeze the caulk into the crack using a caulking gun, press the caulk into the crack using a narrow (1 inch wide or so) putty knife, and then immediately wipe down the crack with a damp sponge to remove all caulk except that in the crack.  Rinse out that damp sponge frequently in a small pail of water.  Latex caulk shrinks as it dries, so it will be necessary to apply caulk at least twice, the second time to fill in the shrinkage of the first application.)

3. Prime the end of the beam with an exterior alkyd (oil based) primer.  That means both the sides and the end grain.

4. Paint the end of the beam with an exterior alkyd (oil based) paint.  Flat oil based paint is fine; it doesn't have to be gloss oil based paint.  I've been DIY'ing for over 20 years now, and oil based paints simply stand up better outdoors than latex paints.  And, oil based paints protect the wood against UV light better than latex paints.  When an oil based paint deteriorates from exposure to UV light, a whitish film will form on the oil based paint.  That means that the oil based paint is absorbing the hit from the UV rays from the Sun and deteriorating as a result rather than have the UV rays go right through a latex paint and deteriorate the underlying wood instead.

Another option would be to paint over that alkyd primer with an epoxy paint that would be much more impermeable to moisture from the Sun.  I really don't know how well epoxy paints stand up to UV light, tho.

In my humble opinion and based on my actual experience, once the wood is dry and any cracks filled with a latex caulk, then any good quality exterior oil based primer top coated with any good quality exterior alkyd paint will last much longer than an exterior latex paint over a latex primer.  Your US government may be telling you that latex paints are as good or better than oil based paints in every respect, but that's ONLY because they're more concerned about the environment than they are about your beams.


----------



## Nestor_Kelebay (Jul 17, 2009)

A very good alternative would be to go to Lee Valley and buy an "epoxy wood repair kit" like the one shown below:

Lee Valley Tools - Important Announcement

This kit costs about $45 and comes with a resin and hardener that's similar to a thick paste in consistancy, and a resin and hardener that's very thin and suitable for absorbtion into wood.  The thin stuff, in the tall bottles, is meant for painting onto rotted wood.  You mix equal parts of the thin resin and thin hardener together and the resulting thin liquid will be absorbed (wicked in by capillary action) into rotted wood where it will cure and harden, thereby restoring the strength of the wood.

Mixing both the liquid epoxy resin and liquid epoxy hardener would make for an excellent epoxy primer to paint over the end grain of the wood to both seal that end grain and prevent any moisture absorbtion or evaporation from that end grain.  That is, painting the ends of the beams with a liquid epoxy would both prevent moisture from being absorbed into and from evaporating from, the ends of the beams.

That Lee Valley kit also  includes two thick jars of paste; one epoxy paste resin and one epoxy paste hardener.  Mixing equal quantities of the paste resin and paste hardener will result in a paste that can be applied to wood and dries to form a solid that's similar to wood in most respects; it can be painted, sanded, cut and painted just like real wood.

What the kit does tell you is that you can mix equal quantities of the epoxy resin and hardener liquids to make an epoxy paint, and that you can mix that epoxy paint with equal quantities of the epoxy paste resin and epoxy paste hardener to make an epoxy paste that will look and feel like real wood so that it can be sanded, primed and painted like real wood.  When that epoxy paste is mixed with epoxy "paint", then the resulting soft liquid epoxy slurry will be suitable for filling cracks in wood.

What I would do is to mix up some epoxy liquid from equal parts of epoxy resin and hardener in the film, and then use that epoxy solution to "thin" a mixture of epoxy paste resin and epoxy paste hardener to make a paste that's suitable to fill the cracks in your overhang using a 1 inch putty knife.

will don't tell you is that you ALSO mix the epoxy paint liquid (made by mixing equal parts of the liquid resin and liquid hardener) with the epoxy paint paste (made by mixing equal parts of the paste resin and pasted hardener) to make an epoxy putty that you can use to fill cracks in the joist ends.

And, you can mix equal parts of the epoxy liquid resin and epoxy liquid hardener to make an epoxy paint that can be applied to both the end grain of the beams and any bare wood on the beams.  This coating of clear epoxy will prevent any further absorbtion of moisture at the beam end grain.  And, by mixing the epoxy "paint" (liquid) with epoxy paste, you can make a thin epoxy slurry that can be used to fill cracks in the wooden joists once they're completely dry.


----------



## inspectorD (Jul 17, 2009)

Thanks Nestor for the wood class 101. :agree:
The only issue I can forsee with the epoxy route is that it is temporary. And maybe that is what he wants.
The epoxy will fail over time due to your area climate. Any water that gets behind the paint and epoxy will freeze in the winter over time, this is why I say temporary....but you can monitor it over the years and fix it when you have issues. Just remember if water also gets trapped in there it will decay the wood, fungus will grow and you could be back to replacing the roof at a later date.
It's like vinyl siding...it looks good and covers up lots of problems...but when you look behind it, sometimes you have major issues.

Good luck.


----------



## Nestor_Kelebay (Jul 17, 2009)

I'm thinking just scraping off any loose paint and applying an exterior alkyd primer and exterior alkyd paint would help preserve the wood much better than is happening now.

If the original poster is concerned about any water getting trapped behind epoxy paint, one good solution would be Impel or Cobra rods.  Impel rods are made from borates, which have almost no health effects on mammals, but which are highly toxic to fungi, including the wood rot fungi, Serpula Lacrymans.

Impel Rods, information, uses, pricing

What you do is drill a hole in the end of the beam slightly larger than the impel rod (cuz the rod expands slightly when it gets wet).  Slide in the Impel rod, and then plug the hole.  I use port plugs available from any company that sells hydraulic equipment or even O rings used to repair hydraulic or pneumatic equipment.  (When they overhaul a hydraulic or pneumatic valve, they stick plastic plugs into all the valves ports so that dirt doesn't get inside it.  These would well on wood, too.  YOu could also just plug the hole with plumber's putty and paint over it.

When the Impel rod gets wet it dissolves, and the borates that are released are highly mobile in wet wood.  So, if the wood gets wet, the Impel rod inside it starts to dissolve, and releases borates that migrate throughout the wood to kill any fungal growth in or on the wood.  In fact, the reason why Impel rods are popular with log home owners is that Borates are the only wood preservative that will migrate through the entire cross section of a log.  No other wood preservative will distribute itself throughout the wood to protect it's entire cross section like Borates.  Telephone companies use Impel and Cobra rods to protect telephone poles as well, and it's because the borates will migrate throughout the whole cross section of the pole to protect all of the wood.

I use Impel rods to protect the wood window frames in my building, but I don't use the huge rods.  I use a total of three 1/4 inch diameter by three inch long Impel rods at each bottom corner of each wooden window frame; two in the bottom horizontal part of the frame near the corner and one in the vertical side of the frame near the corner.

If you put Impel rods into the ends of those wood beams, then it won't matter even if you clad the end of the beam with sheet metal.  If water gets behind that sheet metal, then by the time the wood gets wet enough for long enough to start to rot, then the Impel rods will be dissolving in that wet wood and distributing borates to protect that wood from rot.


----------



## dayton (Jul 17, 2009)

Nestor,

Thanks a MILLION for the informative, very thorough explanation. I truly learned a lot about what's going on and what to do about it. I've taken some vacation time to spend solely on catching this stuff where it is so your links and suggestions are INVALUABLE to me, as I'm a new home owner with very little experience, esp. dealing with stuff like this.
Much, much thanks....you have made my day by taking the time to set me straight on the whole thing.


----------



## Nestor_Kelebay (Jul 17, 2009)

Dayton:

Thanks for the fan mail.

I skimmed over that post and I should explain that statement:

 "It is only that range of moisture content (from about 16 to 30 percent) where the moisture is coming from the wood cell walls that results in any dimensional change (swelling or shrinking) of the wood (primarily across it's grain).

The fiber saturation point is typically around a 30 percent moisture content.  Below that ALL of the water that evaporates from the wood comes from the cell walls.  If you put the wood in an oven and bake it, you can drive it down to a 0 percent moisture content.

It's just that under typical indoor temperatures and relative humidities, wood will typically maintain a moisture content of approximately 16 percent.

So, if you dry wood below a 16 percent moisture content, the moisture will come out of the cell walls and the wood will therefore shrink.  It's just that 16 percent is typically what it will dry out to under normal conditions because that's the stabilized moisture content under comfortable indoor living conditions.

Here's an excellent paper on wood shrinkage:

Minimizing Wood Shrinkage Problems

It's written by Dr. Stephen Smulski who used to teach at the University of Massachusettes in their "Building Materials and Wood Technology" program.  It's basically university for carpenters.  If you have a question about plywood or Oriented Strand Board or house wraps or engineered wood joists or a variety of other wood building related topics, you'd do well to check here first.  It's a good source of reliable information:

UMass Amherst: Building Materials and Wood Technology » Publications


----------



## WallyPop (Jul 18, 2009)

I'm sealing the edges of 4'x8' plywood roof sheathing prior to applying a drip edge on my flat roof deck.  It's called AnchorSeal, variations of which are applied to the freshly cut ends of valuable logging woods to prevent such moisture checking as you've experienced.


----------

