Techniques to inhibit wood decay

[Paul Marlowe]

The new wood most available today for exterior applications is prone to rot from decay fungi.  There are some species not grown in monocultures or force fed with fertilizers that better resistance to decay.  I think many of us especially those only familiar with the common modern day woods, probably believe it is normal & acceptable for wood to first shed it's paint then begin the decay process w/in 5-10 years of installation.  After all we may have been taught to simply remove it, replace it w similar wood & techniques, then hope for better results.  This is a cycle that can be stopped.  Exterior wood should be designed to last for decades w good preventative maintenance.

Take notice of peeling finishes.  This is often due to water being absorbed into the end grain of permeable wood in vulnerable areas.  The fungus spores settle in & begin consuming the wood.  These wood decay fungi need to be controlled by not allowing the wood to stay wet.  This will keep water from penetrating deeply so the wood has a chance to dry out fast.

Specifications to stop this from happening can vary slightly for different species & are especially important in locations that porous end grain is exposed to excess water, such as window trim, jambs, sills etc.  (I won't discuss frame rot now though similar principles apply).  Some simple specs. that will greatly lessen porosity & decay are as follows:

1. precut the wood pieces, apply liquid borates especially to the end grain, dry below 20% moisture, apply epoxy consolidant 100 to end grain using multiple coats if it absorbs fast then an option of top coating w epoxy patch to better fill tiny end grain voids

2. the pieces could then be set aside to cure or they can be fastened as normal w the wet epoxy patch 200 acting as an adhesive but especially as a sealer for the joint to lower it's porosity    

    

[johnleeke]

I agree with Paul.

Back in the early 1980s we began treating the end-grain of exterior wood with epoxy. We did not know if this would have good results, so we did several projects over during the 80s where we applied epoxy to some ends and not to others. Through the 90s we went back to examine the results. These side-by-side comparison field tests proved this is an effective method and we have been using it ever since.

John Leeke
www.HistoricHomeWorks.com

[Paul Marlowe]

House sills, barn sills etc. can often be restored with wood, preservative and epoxy.  The sills usually rot from the bottom outside area and the decay fungus works it's way up and into the sill.  If there was a membrane such as EPDM below the sill, the rising damp would have condenced underneath and went back into the foundation hence minimizing the chances for the fungus to take hold and breakdown the wood.  

Replacement of sills is not always the best option.  Once the sills have been exposed from the outside and preferably 1'-2' above the sills so the stud and post bottoms are in view, a better analysis can be done.  Criteria for restoring them could include  1. visibility of the historic fabric from the inside  2. stud and post connections on top of the sills  3. condition of the foundation below  4. whether there are intersecting joist and girders plus the condition of these perpendicular members if they exist  5. the extent of decay and settling in the sill itself  6. whether the specifications include lifting the wall above to correct the elevation.  The question of cost to replace verses restore will probably be answered after professionally analyzing these six criteria.

A technique I have found to be successful when the sill is to be restored is as follows:
1. prepare the wood by removing most of the decay
2. cap or repoint the foundation top as needed
3. cut and fit EPDM membrane over the exposed foundation and wedge it under the sill when possible
4. if large voids exist, cut dry wood filler pieces to very loosely fill the voids, number and mark their locations
5. apply borate preservative to all fillers and any framing that has had decay and is prepared for epoxy, including stud and post bottoms, in order to contact and kill fungi that probably still exists in the wood
6. verify the wood is below 20% moisture then apply epoxy consolidant #100 on all the surfaces of wood that will be getting filled
7. apply epoxy patch #200 into the existing sills and on top of the EPDM, fill the large voids approx. 50%-70% then press the consolidated fillers into place and allow the patch to ooze out and around encapsulating the wood fillers
8. the epoxy patch should be mixed thick enough to hold it's shape without slumping so you can fill all voids in plane with the surrounding wooden fabric, this includes stud bottoms if they need to be filled
9. if there are large voids under posts that carry heavy loads, you could use the #600 epoxy thickened with #200-1D (fumed silica) prior to, after or in conjunction with the work above.  The #600 can intersect cured or uncured #100 or #200 epoxy.
10. once the epoxy patch #200 is cured it can be tooled as needed to maintain the plane and a second coat applied as needed
11. treat the #200 patch as if it were wood and proceed with the restoration process, using fasteners through the 200 as you wish