LumberJocks

Kerfing Cedar Planks for Sauna: Bad Idea?

  • Advertise with us

« back to Wood & Lumber forum

Forum topic by Groundstar posted 06-05-2020 01:07 AM 288 views 0 times favorited 13 replies Add to Favorites Watch
View Groundstar's profile

Groundstar

17 posts in 41 days


06-05-2020 01:07 AM

Topic tags/keywords: kerf cedar sauna

https://photos.app.goo.gl/7g2qrSHehBHXWvB99

We are planning on converting an old Airstream trailer into a sauna this summer. Airstreams have those tight concave ends with compound curves. Straight shiplap cedar boards can handle the basic curves up the walls and around the ceiling. But it’s those transitioning curves in the corners that are really tricky.

We were thinking of possibly kerfing and tapering cedar boards to handle the curves on the end walls of the trailer. The kerfs only leave about 1/8-3/16” of material where the cuts are. Would it be a bad idea to have such thin areas of wood exposed to a sauna? Most sauna builders recommend at least 11/16 thick cedar.. Is anyone familiar with the effect kerfing would have on temperature and humidity tolerances for cedar long term?

If it’s not a good idea, any suggestions on how to get cedar planks to follow these curves nicely without steaming?


13 replies so far

View Groundstar's profile

Groundstar

17 posts in 41 days


#1 posted 06-08-2020 07:49 PM

No one with much kerfing experience in this forum I guess? Maybe I posted in the wrong forum? If so, which forum might be best to answer this question?

View Steve's profile

Steve

2082 posts in 1363 days


#2 posted 06-08-2020 08:10 PM

I would look up the member shipwright on here. He’s probably the resident expert on kerfing.

View Aj2's profile

Aj2

3112 posts in 2579 days


#3 posted 06-08-2020 08:15 PM

Your asking the forum a question that’s sound more like a experiment then a typical woodworking joint.
I’ve heard kerfing used for bending plywood. I’ve also seen videos where kerfing is used to take the warp out of unruly boards.
To me it sounds like your trying to find a alternative to coopering the boards. Nothing stopping you from testing it out.
Or do you want to trust a bunch of strangers?

Good Luck

-- Aj

View Lazyman's profile

Lazyman

5493 posts in 2168 days


#4 posted 06-08-2020 08:17 PM

I’ve never done it but I don’t think that 11/16 cedar would kerf bend all that well. It seems sort of brittle to me for that. If you zoom in on the picture below from your link (I assume this the example not you solving the problem already), it looks to me like they are using something more like the thickness of veneer to do that curve at the end. It sort looks like the guy is using a heat gun to help bend it? I certainly don’t see any sort of saw that could be used for kerfing?

BTW, you are more likely to get responses if you embed the pictures than just posting a link. People are a little hesitant to follow a link from a new member because they tend to be marketing or scambait.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Groundstar's profile

Groundstar

17 posts in 41 days


#5 posted 06-09-2020 02:12 AM



I would look up the member shipwright on here. He s probably the resident expert on kerfing.

- Steve

Thanks man. I’ll give him a shout once I reach the 5 post minimum to send a message!

View Groundstar's profile

Groundstar

17 posts in 41 days


#6 posted 06-09-2020 02:29 AM

I ve never done it but I don t think that 11/16 cedar would kerf bend all that well. It seems sort of brittle to me for that. If you zoom in on the picture below from your link (I assume this the example not you solving the problem already), it looks to me like they are using something more like the thickness of veneer to do that curve at the end. It sort looks like the guy is using a heat gun to help bend it? I certainly don t see any sort of saw that could be used for kerfing?

Yes, that’s right. All those photos are just inspiration photos for the project, we haven’t started any work yet. Traditionally to bend wood it seems you want to use thinner pieces and steam or heat them to mold them into shape. In our case we don’t have any tools or experience to steam or heat wood. The project will also be happening in a remote place in the woods. So our first thought was that kerfing was the easiest thing we could do given our circumstances.

I have already tried kerfing some thick cedar boards and I’ve been able to figure out the spacing to get the curves we need without putting extra stress on the boards, so I’m not worried about that so much.

It’s just that most sauna builders recommend a minimum thickness of board. So I was wondering if the kerfs would weaken the boards in a sauna environment. However I’ve also read that kerfing is used to relieve stress from wood if you need to bend it back into shape or to protect it from warping/expansion/contraction in the long term. So perhaps the kerfs would actually make the cedar boards more resilient in the sauna? I just don’t know.. this is where I was hoping someone with some kerfing experience might be able to enlighten me.


BTW, you are more likely to get responses if you embed the pictures than just posting a link. People are a little hesitant to follow a link from a new member because they tend to be marketing or scambait.

Thanks man. I’ll do so next time.

View Groundstar's profile

Groundstar

17 posts in 41 days


#7 posted 06-09-2020 02:42 AM


Your asking the forum a question that’s sound more like a experiment then a typical woodworking joint.
I’ve heard kerfing used for bending plywood. I’ve also seen videos where kerfing is used to take the warp out of unruly boards.
To me it sounds like your trying to find a alternative to coopering the boards. Nothing stopping you from testing it out.
Or do you want to trust a bunch of strangers?

Yes, I guess it’s a bit of an experiment! I’ve searched and searched for examples of saunas that use curved wood that was kerfed but have not found anything specific yet. Also it seems that not many people have converted their Airstreams into a sauna either so that will be a challenge to make sure we ventilate and drain things properly.

Most kerfing projects I’ve seen use plywood as well. We really want to extend the traditional sauna look around the whole trailer so we’d rather not transition to a different material in the tricky spots if we can help it. We think it will add a great aesthetic to maintain the cedar boards and accentuate the curves of the trailer.

As for advice from strangers.. well I was hoping that by dropping this question on a few good woodworking forums I might find someone who knows a thing or two about kerfing and/or bending wood around curves and be able to confirm that our approach should be OK or recommend a better idea.

View Dave Polaschek's profile

Dave Polaschek

5461 posts in 1363 days


#8 posted 06-09-2020 02:49 AM

When building teardrop trailers, most of the tutorials suggest kerfing boards for the interior corners. I don’t see why it wouldn’t work, especially if you layer up two (or more) layers so you have your cedar for show, and something more flexible behind it (and to support it through the curve). It’ll be more work, but I’m assuming you want this to last, and as Nathan said, cedar seems more brittle than I’d try for those tight curves. Do a small experiment and see.

-- Dave - Santa Fe

View Lazyman's profile

Lazyman

5493 posts in 2168 days


#9 posted 06-09-2020 02:51 AM

Kerfing on that many boards sounds like a ton of work. It is one thing to cut kerfs on a few sections for a corner but it would seem that you would need them along the entire length. If you follow this design, you also have to cut of them into a wedge shape which means that they probably aren’t shiplap. I cannot imagine trying to cut shiplap edges on every custom cut piece and fine tuning for a good fit.
I just looked at the picture a little more closely. It looks to me like he is using a calk gun to apply construction adhesive or some other adhesive to glue them to the wall. Also, the pieces laying on the floor appear to be about 1/4” thick at most. They certainly don’t look like they are almost 3/4” thick. I really think that in the picture they are thin enough to bend without kerfing or any other steam or heat bending.

EDIT: One other thing just occurred to me after I read Dave’s comments. Most kerfing cuts I have seen are made on the inside of the bend not the outside as these would be. Having never tried it, that might still work I suppose but I have just never seen it done that way?

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Groundstar's profile

Groundstar

17 posts in 41 days


#10 posted 06-09-2020 03:14 AM


Kerfing on that many boards sounds like a ton of work. It is one thing to cut kerfs on a few sections for a corner but it would seem that you would need them along the entire length.

Yes, it is some added work, but when I experimented on some boards already it only took about 1-2 minutes to cut the kerfs with a jig in place that guides each subsequent kerf.

If you follow this design, you also have to cut of them into a wedge shape which means that they probably aren t shiplap. I cannot imagine trying to cut shiplap edges on every custom cut piece and fine tuning for a good fit.

Yes, the wedging will be the trickiest part I think. But we can cut extra wide rabbets with a dado blade on the table saw, which will give us a little room for error. Cutting the rabbets should be simple enough after we have our wedge.. you just push it straight against the fence and run it over the dado blade.


I just looked at the picture a little more closely. It looks to me like he is using a calk gun to apply construction adhesive or some other adhesive to glue them to the wall. Also, the pieces laying on the floor appear to be about 1/4” thick at most. They certainly don t look like they are almost 3/4” thick. I really think that in the picture they are thin enough to bend without kerfing or any other steam or heat bending.

Yes the photos are just examples of the effect we are trying to achieve. I’ve already experimented kerfing some cedar boards and I can get the curves we need without putting the board under stress – so that should work. The kerfing, wedging and rabbets are all something that were are sure we can do, and we’re willing to put in the extra work to achieve the aesthetic. It’s really just a question of whether the kerfed boards would be resilient or compromised in a sauna environment.

View Groundstar's profile

Groundstar

17 posts in 41 days


#11 posted 06-09-2020 03:21 AM


When building teardrop trailers, most of the tutorials suggest kerfing boards for the interior corners. I don’t see why it wouldn’t work, especially if you layer up two (or more) layers so you have your cedar for show, and something more flexible behind it (and to support it through the curve). It’ll be more work, but I’m assuming you want this to last, and as Nathan said, cedar seems more brittle than I’d try for those tight curves. Do a small experiment and see.

- Dave Polaschek

Thanks, Dave. I’ve tried kerfing some cedar already and I’ve got the spacing figured out such that I can bend 11/16” boards to the curves we need. You are right, these boards will require some backing so I think we may reinstall the original walls that are already curved (and thin which will help make the transition smooth) so we have something to support them.

View shipwright's profile

shipwright

8562 posts in 3579 days


#12 posted 06-09-2020 03:34 AM

Sent you a PM.

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese! http://thecanadianschooloffrenchmarquetry.com/

View Groundstar's profile

Groundstar

17 posts in 41 days


#13 posted 06-09-2020 04:21 AM


Sent you a PM.

- shipwright

Thanks very much!

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com