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How to finish this Cottonwood/Poplar

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Forum topic by Craigils posted 01-06-2021 06:25 PM 553 views 0 times favorited 12 replies Add to Favorites Watch
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Craigils

3 posts in 56 days


01-06-2021 06:25 PM

Topic tags/keywords: cottonwood poplar staining crack

Hi everyone,
I am about to embark on a journey of creating a living Edge table. This will be my first time working with a big piece of wood like this.

Any and all advice would be greatly appreciated since I am such an amateur, but I have a few questions to begin with.

1. Is this the same Cottonwood that any of you are familiar with? It was sold as Cottonwood, and also referred to it as our (South Africa) local Poplar tree. I’m wondering if this is the same as the Poplar that is native to the Northern Hemisphere, or if we just call a different tree the same name. I’m afraid that I follow information based on Poplar wood if this is actually something entirely different.

2. What should I do about the crack at the bottom? Is it best to cut the bottom off above the crack? Should I epoxy it? Or is it safe to just leave it as is.

3. Any advice regarding oil vs water based finishing would be appreciated. The guy at the shop recommended water based sealant, but I’m curious to know the pros and cons.

4. If this wood is the same/similar to the northern Poplar wood, I have read that it is not very good for staining, because it stains unevenly. Do you guys agree? I read elsewhere that it is fine to stain it as long as you use pre-stain first. Wondering if I should avoid staining it or go the pre-stain route.


12 replies so far

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TDH

19 posts in 2363 days


#1 posted 01-06-2021 07:24 PM

This is what I do with woods such as Poplar, Pine etc. First coats are with shellac then topcoat of lacquer. On poplar sometimes use cherry stain then lacquer topcoat but always shellac first. I spray all my finishs.

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CaptainKlutz

4158 posts in 2506 days


#2 posted 01-06-2021 08:41 PM

#1) Species:
One pic makes any comment on species a guess? :-)

There are many species of cottonwood:
http://www.hobbithouseinc.com/personal/woodpics/cottonwood.htm

Also easy to confuse cottonwood, and poplar lumber:
https://www.wood-database.com/wood-articles/poplar-cottonwood-and-aspen-whats-what/

The slab core looks like black poplar, but bark does not match Populus nigra?
In US, can find both white poplar (cottonwood species), or yellow/tulip poplar (Liriodendron tulipifera)
http://www.hobbithouseinc.com/personal/woodpics/poplar.htm

#2) Crack:
Check moisture content. If less than 10-12%, then stabilize it, or cut it off as needed. Need to stablize cracks in slabs is normal due thickness and internal stress of tree.
If need full length of slab, need to stabilize the crack with bow tie insert, slow cure epoxy, or both. Otherwise, cut off the crack, making sure there is not cracked beyond the open portion.
If slab is more than 12% moisture, the crack might grow as it dries further. Then need to seal ends, and wait many months for it dry out and stop moving before dealing with crack(s).

#3) Finish:
Pick one you like. Solvent base has advantages, so does water base. Neither one is better or worse for large thick slabs. Only suggestion is finish both sides to ensure even movement as humidity changes during use.

#4) Stain:
Difficult to stain or blotch prone woods make adding color more difficult. Cottonwood tends to have stringy/fuzzy grain and can be challenge to sand smooth and stain evenly. Yellow popular will botch, but is easier to finish with blotch control.
There is no difference between lumber and/or slab regarding use of stain? Personally, I think large slabs are best left natural with clear finish. If wood color is not a match your home these, then pick another slab and let beauty of wood show.

Best Luck!

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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Aj2

3680 posts in 2809 days


#3 posted 01-06-2021 09:44 PM

Why do new woodworkers always want to stain. It’s such a difficult path to start on.
The board doesn’t look like poplar to me.

-- Aj

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Ruscal

73 posts in 190 days


#4 posted 01-06-2021 09:58 PM

The OP is talking about wood from South Africa. I think it is like our cottonwood.

-- Have a hobby? You should have a business.

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Craigils

3 posts in 56 days


#5 posted 01-06-2021 10:27 PM

#1) Species:
One pic makes any comment on species a guess? :-)

Thank you for your information regarding the different types of trees.
I have discovered that this is likely Populus Canescens, a South African Poplar plant. Called Cottonwood due to its cottony texture.

#2) Crack:
Check moisture content. If less than 10-12%, then stabilize it, or cut it off as needed. Need to stablize cracks in slabs is normal due thickness and internal stress of tree.
If need full length of slab, need to stabilize the crack with bow tie insert, slow cure epoxy, or both. Otherwise, cut off the crack, making sure there is not cracked beyond the open portion.
If slab is more than 12% moisture, the crack might grow as it dries further. Then need to seal ends, and wait many months for it dry out and stop moving before dealing with crack(s).

Thanks very much for this. I didn’t know about methods of measuring wood moisture. My search results say I can either use an oven to dry a piece out and compare weights, or use a moisture testing tool. Using a tool seems much easier, and it looks like they can be as cheap as R300 (about 20 USD). Am I likely looking at a bad tool not good enough for the job? Or would this be fine?
https://www.builders.co.za/Tools-%26-Protective-Wear/Measuring-%26-Marking-Tools/Electronic-Measuring-Tools/Ryobi-Moisture-Meter/p/000000000000700855

To be honest, since I bought the wood from a reputable wood company, I expect that it has been sufficiently dried. Or can I not take that for granted?

Lastly, if the moisture content is still high, and I cut the cracked part off, will it just continue to crack anyway? So there’s no way to stop the crack if the wood does still have too much moisture.

#3) Finish:
Pick one you like. Solvent base has advantages, so does water base. Neither one is better or worse for large thick slabs. Only suggestion is finish both sides to ensure even movement as humidity changes during use.

Thanks for the advice about finishing both sides. Very valuable to know. And thanks for assuring me that there’s no right or wrong answer with oil vs water base

#4) Stain:
Difficult to stain or blotch prone woods make adding color more difficult. Cottonwood tends to have stringy/fuzzy grain and can be challenge to sand smooth and stain evenly. Yellow popular will botch, but is easier to finish with blotch control.
There is no difference between lumber and/or slab regarding use of stain? Personally, I think large slabs are best left natural with clear finish. If wood color is not a match your home these, then pick another slab and let beauty of wood show.

I think youre right about leaving the slab to keep its natural colour. I got caught up in all of the info about the challenges of staining and forgot about the option of just leaving it with its natural beauty.

Is there anything more to clear coating other than just the clear coat? Should I be pre-coating it with something before the clear coat? Or putting anything on top of the clear coat?
I’ll probably be using something like this
https://www.fired-earth.co.za/wood-works


Why do new woodworkers always want to stain. It’s such a difficult path to start on.
The board doesn’t look like poplar to me.
- Aj2

You’re right. As mentioned above, I have decided to keep it simple and not stain the wood


The OP is talking about wood from South Africa. I think it is like our cottonwood.

- Russell Hayes

You’re correct. I have since discovered that this is Populus Canescens, a South African derivative of the Poplar tree

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splintergroup

4708 posts in 2234 days


#6 posted 01-06-2021 11:11 PM

Looks like cottonwood to me (smells “peppery”)

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CaptainKlutz

4158 posts in 2506 days


#7 posted 01-06-2021 11:40 PM

To be honest, since I bought the wood from a reputable wood company, I expect that it has been sufficiently dried. Or can I not take that for granted?
Ask your supplier? Any reputable supplier will have moisture measurement equipment, and/or can provide kiln drying measurements, or certification data. In US, Kiln dry certification is required for export or commercial transport across state lines; due to invasive species prevention.
Regarding moisture meter for home shop, there are many choices. Wagner, Delmhorst, and Lignomat are considered top of line units for serious wood worker? Suggest you search forums for more information, as too much info post here.

Lastly, if the moisture content is still high, and I cut the cracked part off, will it just continue to crack anyway? So there’s no way to stop the crack if the wood does still have too much moisture.
If moisture is too high, best to seal ends with timber sealer like Anchorseal, or some other paint to slow the evaporation from ends of log. This reduces the tendency to split/crack. There are several threads on LJ discussing this topic also? US government has handy ‘bible’ on lumber drying if you want dig deep into topic.
IME – Cottonwood tends to have higher wet moisture content than other hardwoods and is more prone to split/check issues. Might want to seal ends with latex paint while the slab equalizes to shop RH, if not working the slab immediately.

Is there anything more to clear coating other than just the clear coat? Should I be pre-coating it with something before the clear coat? Or putting anything on top of the clear coat?
I’ll probably be using something like this: https://www.fired-earth.co.za/wood-works
Getting into specifics of finish options and choices will be difficult for me, since I do not live in or use S. Africa materials? lol

But, the Wood Works stuff looks a generic water base acrylic top coat. Acrylic tends to be soft finish, and not something I would use for durable table top in house with kids; but works ok for static ‘show’ furniture. Looks similar to GF High Performance sold in US. Being a Klutz and part time chemist, tend to use most durable finish I can find. Table tops needing durability get a commercial grade conversion varnish, catalyzed lacquer, or polyurethane in my shop. Sprayed some Renner WB poly recently, and it is so tough, that cheap sand paper doesn’t scratch it. Have to use high grade abrasives like Zirconium to sand away a mistake. Scuff resistance is amazing too. :-)

Use of sealer all depends on finish used, and desired look. Most clear coats are self sealing, and don’t need a sealer; unless you want to fill the grain for perfectly smooth surface, or want to highlight figured grain?

Most WB finishes are water clear, and while this can be good for some species; I prefer a warmer amber/yellow toned finish provided by solvent based coating for most projects. WB will not highlight any radical grain figure, which means might use; diluted dye, shellac, or BLO/Danish oil; as your ‘sealer’, before final WB top coat(s).
Finishing is another large subject, and suggest you read and learn more about all options.

Best Luck.

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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Foghorn

1046 posts in 398 days


#8 posted 01-07-2021 12:49 AM


To be honest, since I bought the wood from a reputable wood company, I expect that it has been sufficiently dried. Or can I not take that for granted? Ask your supplier? Any reputable supplier will have moisture measurement equipment, and/or can provide kiln drying measurements, or certification data. In US, Kiln dry certification is required for export or commercial transport across state lines; due to invasive species prevention.
Regarding moisture meter for home shop, there are many choices. Wagner, Delmhorst, and Lignomat are considered top of line units for serious wood worker? Suggest you search forums for more information, as too much info post here. Lastly, if the moisture content is still high, and I cut the cracked part off, will it just continue to crack anyway? So there’s no way to stop the crack if the wood does still have too much moisture. If moisture is too high, best to seal ends with timber sealer like Anchorseal, or some other paint to slow the evaporation from ends of log. This reduces the tendency to split/crack. There are several threads on LJ discussing this topic also? US government has handy bible on lumber drying if you want dig deep into topic.
IME – Cottonwood tends to have higher wet moisture content than other hardwoods and is more prone to split/check issues. Might want to seal ends with latex paint while the slab equalizes to shop RH, if not working the slab immediately. Is there anything more to clear coating other than just the clear coat? Should I be pre-coating it with something before the clear coat? Or putting anything on top of the clear coat?
I’ll probably be using something like this: https://www.fired-earth.co.za/wood-works Getting into specifics of finish options and choices will be difficult for me, since I do not live in or use S. Africa materials? lol

But, the Wood Works stuff looks a generic water base acrylic top coat. Acrylic tends to be soft finish, and not something I would use for durable table top in house with kids; but works ok for static show furniture. Looks similar to GF High Performance sold in US. Being a Klutz and part time chemist, tend to use most durable finish I can find. Table tops needing durability get a commercial grade conversion varnish, catalyzed lacquer, or polyurethane in my shop. Sprayed some Renner WB poly recently, and it is so tough, that cheap sand paper doesn t scratch it. Have to use high grade abrasives like Zirconium to sand away a mistake. Scuff resistance is amazing too. :-)

Use of sealer all depends on finish used, and desired look. Most clear coats are self sealing, and don t need a sealer; unless you want to fill the grain for perfectly smooth surface, or want to highlight figured grain?

Most WB finishes are water clear, and while this can be good for some species; I prefer a warmer amber/yellow toned finish provided by solvent based coating for most projects. WB will not highlight any radical grain figure, which means might use; diluted dye, shellac, or BLO/Danish oil; as your sealer , before final WB top coat(s).
Finishing is another large subject, and suggest you read and learn more about all options.

Best Luck.

- CaptainKlutz


I’ve tried a couple of WB finishes in the past and always detect a very slight blueish tinge on light colored woods. YMMV.

-- Darrel

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Craigils

3 posts in 56 days


#9 posted 01-07-2021 10:22 AM


The Wood Works stuff looks a generic water base acrylic top coat. Acrylic tends to be soft finish, and not something I would use for durable table top in house with kids; but works ok for static show furniture. Looks similar to GF High Performance sold in US. Being a Klutz and part time chemist, tend to use most durable finish I can find. Table tops needing durability get a commercial grade conversion varnish, catalyzed lacquer, or polyurethane in my shop. Sprayed some Renner WB poly recently, and it is so tough, that cheap sand paper doesn t scratch it. Have to use high grade abrasives like Zirconium to sand away a mistake. Scuff resistance is amazing too. :-)


Thanks so much for all of that info. It is greatly appreciated.

Does this product seem more appropriate than the WB acrylic top coat I had linked before?
https://www.woodoc.com/en/products/woodoc-20-indoor-polyurethane-sealer-gloss
Or perhaps this one
http://novacoatings.co.za/nova-17-2/

I’m a little bit overwhelmed by the choices you mentioned (Polyurethane, Catalyzed Lacquer or Conversion Varnish). Is any one of them better than the others? Or what are the basic properties of them so that I can make more of an informed decision.

I’ve also seen Tung Oil and Danish oil mentioned. Are those alternatives to the above options? Or do they serve an entirely different purpose.

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CaptainKlutz

4158 posts in 2506 days


#10 posted 01-07-2021 08:38 PM

Craigils
Not enough information available from web to draw clean/clear comparisons to finishes sold in US? Especially the ‘ZA’ standards for SDS are lacking information compared to what USA SDS are required to share.

Both of the solvent based Polyurethane coatings linked above seem about same? Without having a can of each in front of me, no way to offer any further advice. The literature makes them appear to be similar to several older style brush on Polyurethane Varnishes sold in US that were popular over 20 years ago? Wipe on versions of Poly finishes have been popular since then.

IMHO – Suggest best way for you to learn more about all wood finish options is read some literature on wood finishing. There are several outstanding authors of finishing books in US, but each has slightly different background and focus; which makes it hard to suggest just one?

‘Understanding Wood Finishing’ by Bob Flexnor is guide used my many. He has other books as well.

Jeff Jewitt (Transtint) is a master finisher that has written books like ‘Complete Illustrated Guide to Finishing’.

‘Best Finishing Techniques’ by Fine WoodWorking Magazine is another good reference, as it is a collection of in depth articles originally published in magazine by many different authors.

PS – Spent a few minutes looking for Industrial/Commercial mfg of wood coatings I know that might have distributors in ZA. These sort of folks are generally focused on commercial cabinet/furniture mfg; but many happy serve serious wood working hobbyists here in US? :-)
Note: Commercial finishes are not meant for retail sale, and require proper health and safety precautions. But industrial coatings offer a wider choice of materials for finishing wood than available to general consumer.

Random links in random order:
These folks sell Lacquer, CV, Poly, and WB products from several mfg: https://www.speccoats.co.za
AkzoNobel distributes wood finishes under the Dulux brand in ZA: http://www.dulux.co.za/
Another broad product range supplier is Morrell in UK: https://www.morrells.za.com/
PPG has large presence in ZA, suggest you look for PPG Proluxe Cetrol wood finishes also.

With some luck, maybe our UK/UE members can comment on above mfg, none of these brands are sold in US.

Best Luck on your finishing education!

-- If it wasn't for bad luck, I wouldn't have no luck at all, - Albert King - Born Under a Bad Sign released 1967

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splintergroup

4708 posts in 2234 days


#11 posted 01-07-2021 08:50 PM

I only made one item in the project gallery here

BLO, shellac, lacquer FWIW

View Robert's profile

Robert

4450 posts in 2492 days


#12 posted 01-07-2021 09:14 PM

Cutting off the crack (correctly termed a check) is no guarantee is will not continue. The best way to handle it is by inlaying a butterfly (you can easily research this on net).

It can be left open or make a dam at the end and fill the crack with epoxy.

-- Everything is a prototype thats why its one of a kind!!

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