Finishing choices for non kiln dried slab of very sappy fir

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Forum topic by Rob77 posted 05-11-2017 07:22 PM 1173 views 0 times favorited 5 replies Add to Favorites Watch
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2 posts in 984 days

05-11-2017 07:22 PM

Topic tags/keywords: finishing fir epoxy sap live edge

I have an air dried live edge slab of fir that once brought into the shop began to ooze substantial amounts of sap from numerous pockets throughout. The slab is to go into a commercial bar so it will incur a lot of wear. My main concerns are containing the sap and giving the fir a tough finish to stand the wear and tear. Ie. daily wipe downs from alcohol spills and the inevitable hits from watches rings etc due to customers sitting at the bar.

I have read that kiln drying the slab will set it and it will then be easier to work with regarding finishes but there isn’t time for that nor money in the budget.

The slab has been in the shop for two weeks now drying under ambient temperature of around 19-24 deg C or
66-75 F. I know the summer temperatures will go beyond that and my limited knowledge of sap tells me that it will run further once it goes above said current ambient temperature. Based on the amount of Sap running at this time (puddles of it on the floor) I am uncertain on how to proceed.

My best solution found thus far is to clean out the pockets the best I can using 5% Phosphoric Acid and try to set the sap by way of torch. After that a de waxed shellac or 5 minute epoxy to fill and seal the pockets of sap. My next thought is to seal the entire slab in an epoxy coat such as System Three’s Mirror Coat.

It’s imperative that no sap seep through in the upcoming summer and I just would like confirmation I guess that I am proceeding in the best way considering all options.

Do let me know of any other ideas

Many thanks in advance,


5 replies so far

View mahdee's profile


4291 posts in 2372 days

#1 posted 05-11-2017 07:30 PM

Try lacquer thinner/acetone it diluted it up pretty good then you can wipe. Maybe apply it liberally and cover with plastic to avoid evaporation. Epoxy is a good solution for the top. I would use a scrap and do to it as you do to the slab and when you think it is ready, apply the system 3 to the scrap and wait a few days. Repeat as necessary.


View HerbC's profile


1801 posts in 3463 days

#2 posted 05-11-2017 08:02 PM

I’m afraid you will find that all your efforts to contain the sap leakage will fail. The ONLY reliable way to “set” the sap is to elevate the temperature of the wood to a point higher than the anticipated highest ambient temperature and to hold it there for several hours. Typically this would be done in an actual kiln. If you don’t have access to a kiln, perhaps making a temporary kiln using a box large enough for the slab and a heat source such as one of the “jet” heaters used on some construction sites might suffice. Bring the temp up high (I’d personally take it up to somewhere between 150 and 175 degrees F and hold the temp for at least 24 hours. What you are trying to do is evaporate the volatile portions of the sap which make it liquid at the lower temps. I would hate to be staking my reputation as a woodworker on the possibility of sap leaking through the finish using the methods you’ve suggested.

Good Luck!

Be Careful!


-- Herb, Florida - Here's why I close most messages with "Be Careful!"

View Rob77's profile


2 posts in 984 days

#3 posted 05-11-2017 08:17 PM

Thanks mahdee and HerbC for ur replies.

I understand my options are a potential fail in wait but I’ve yet to find a better way which is why I am here asking the cumulative knowledge base. It’s tough even to find forum topics on the matter I’m guessing because no woodworker would work on a runny sap slab in the first place….smh…nevertheless I said I would take this on and do it to the best of my ability. All I’m really interested in knowing so I satisfy my own need for due diligence is are there other options…? Am I moving forward in the best possible way factoring the wood I have to work with and the final use of said slab…?

Thanks again for the input…


View Tim's profile


3859 posts in 2565 days

#4 posted 05-11-2017 08:31 PM

I really don’t see any other options than kiln drying that will set all the sap. You could make a solar kiln and depending on your latitude it would work pretty quickly and effectively. I suppose its possible that you could get the temperature high enough just with a few layers of plastic sheeting if you seal the ends and have a black background of some sort.

View Aj2's profile


2649 posts in 2402 days

#5 posted 05-12-2017 04:52 AM

Even Kiln dried fir can still ooze pitch.I made several Veritcal grain fir doors and one pushed the pitch right thru the paint.I had to repaint the door for free.
Its a small price to pay for working with my favorite wood.

-- Aj

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