Window sill repair - best way to form Conserv 200

[bobmcc]

I am in the process of repairing the sill under a large picture window.  I have cleaned out the rot, soaked in a borate, and treated with the conserv 100 consolidant. 

I was wondering about the best way to complete the repair with the conserv 200 - should I mix it thick enough so that it can be put in free-form and shape it, or should I build a form and mix the epoxy to a somewhat thinner consistency and shape it against the form? Part of the front edge of the sill is gone, and the form would probably help me get a straighter vertical face.

I recall seeing the latter done with an epoxy on an episode of This Old House.

If a form is best, does plastic sheeting make an adequate mold release, or do I need something else?

Bob

[Paul Marlowe]

Bob,
I prefer to thicken the 200 patch enough to shape the profile as best you can with the first application.  This allows you to work without forms.  Using clean sharp plastic putty knives to apply the patch, enhances your ability to accurately shape it and match planes and profiles.  You can carefully overfill areas after the shape is close, if you choose to.  Simple equipment such as the Mini Hawk 900-MH allows you to keep the knives clean by striking the edge after each stroke to remove the patch from the knife onto the hawk.  When fully cured, tool the patch and add a second coat in the low spots or voids as needed.  For tricky fills a third or even a fourth coat may be needed to achieve exact duplication of the original fabric.  This will depend on your abilities and the level of perfection desired.  You will find that a sharp block plane and in some situations a rabbet plane, chisel, razor knife, sand shark or other cutting tools will be very helpful to remove excess patch prior to sanding with dust control.  Sanding is necessary but be careful not to oversand and remove to much adjacent wood.  Remember this step should be done after each coat cures so you only apply more patch in the areas that need it.  Therfore each coat will use less epoxy hence need less tooling.

Forms can be used but don't make the mix to thin and make sure you pack the patch carefully to avoid air pockets.  You can use poly (plastic sheeting), clear wrap, wax paper or a thin film of paste wax on the form as a release agent.  Since shaping the epoxy patch 200 is easy when it is mixed to the right consistancy, sometimes the forms are more trouble than they are worth, but on rear ocassions they are helpful and could possibly save one coat by quickly achieving accurate results from the first application.  You will possibly still need a total of two or more coats of patch, but remove the form after the first coat is cured.

Marlowe Restorations LLC recently completed a large two story arched bay window sill restoration that had serious damage in one third of the upper sill and checking throughtout.  We used approximately 3.5 gallons of epoxy 100 consolidant and epoxy 200 patch combined, plus wood fillers which were consolidated and encapsulated into the patch.  Three applications were needed to achieve excellent results.  The first application included 100 and 200 wet on wet (which creates the best chemical bond) along with the wood fillers.  Each succesive coat (of 200 patch only) was smaller and applied only in the areas that still needed filling.  The results were impressive and no forms were used.   

[bobmcc]

Bob,
I prefer to thicken the 200 patch enough to shape the profile as best you can with the first application.  This allows you to work without forms.  Using clean sharp plastic putty knives to apply the patch, enhances your ability to accurately shape it and match planes and profiles.  You can carefully overfill areas after the shape is close, if you choose to.  Simple equipment such as the Mini Hawk 900-MH allows you to keep the knives clean by striking the edge after each stroke to remove the patch from the knife onto the hawk.  When fully cured, tool the patch and add a second coat in the low spots or voids as needed.  For tricky fills a third or even a fourth coat may be needed to achieve exact duplication of the original fabric.  This will depend on your abilities and the level of perfection desired.  You will find that a sharp block plane and in some situations a rabbet plane, chisel, razor knife, sand shark or other cutting tools will be very helpful to remove excess patch prior to sanding with dust control.  Sanding is necessary but be careful not to oversand and remove to much adjacent wood.  Remember this step should be done after each coat cures so you only apply more patch in the areas that need it.  Therfore each coat will use less epoxy hence need less tooling.

Forms can be used but don't make the mix to thin and make sure you pack the patch carefully to avoid air pockets.  You can use poly (plastic sheeting), clear wrap, wax paper or a thin film of paste wax on the form as a release agent.  Since shaping the epoxy patch 200 is easy when it is mixed to the right consistancy, sometimes the forms are more trouble than they are worth, but on rear ocassions they are helpful and could possibly save one coat by quickly achieving accurate results from the first application.  You will possibly still need a total of two or more coats of patch, but remove the form after the first coat is cured.

Marlowe Restorations LLC recently completed a large two story arched bay window sill restoration that had serious damage in one third of the upper sill and checking throughtout.  We used approximately 3.5 gallons of epoxy 100 consolidant and epoxy 200 patch combined, plus wood fillers which were consolidated and encapsulated into the patch.  Three applications were needed to achieve excellent results.  The first application included 100 and 200 wet on wet (which creates the best chemical bond) along with the wood fillers.  Each succesive coat (of 200 patch only) was smaller and applied only in the areas that still needed filling.  The results were impressive and no forms were used.   

Thanks Paul - I'll try my hand without the form.  As far as wet on wet goes, I applied the 100 in 2 coats on Sunday, and then the weekend ran out and it was back to work for the week.  By this weekend the 100 should be fully cured.  Is there value in applying a third coat of 100 before applying the 200?

Bob

[Paul Marlowe]

Bob,
There is no problem applying 200 to fully cured or partially cured 100.  Sometimes this is necessary, as in your case due to scheduling.  One of the good things about this system is now your raw wood is sealed and shouldn't absorb rain if it gets behind a temporary cover.  Since the wood is sealed there is no need to apply any more consolidant because it won't penetrate the cured product.  You can simply continue with the 200 patch.  I have done this many times.  You shouldn't notice any problem with bonding to the 100. 

[muntinman]

Another method I have started using which is fast and cheap and uses recycled materials is to form my epoxy with pasteboard which can be folded and stapled at the corners for strength. When the epox is set you peel off the paper and sand to a finished shape. The wax etc. would work to prevent sticking but you take a chance of waxing a surface you want to hold paint.
The pasteboard is available from friendly printers' scrap or cereal boxes depending on how much you want and the size of your repair.

[johnleeke]

I'll often form up just one or two sides of the repair void. This gives me easy access to the interior of the void for filling it with the paste filler.

John Leeke
www.HistoricHomeWorks.com