Whether to Build a Big Order of Slab Doors

      A long and informative discussion of the risks inherent in constructing cabinet doors as glued slabs made up of solid wood boards. November 14, 2014

I am starting a big multi-unit condo job (kitchen and bath cabinets) for a customer who is persistent on going with slab doors (solid 4/4 soft maple net 13/16 thick). It is for upscale condo's being built for city living. It is not about cost, it is just the style they want. I tried everything to talk them out of it because of the possibility of warping. I explained that banded plywood or MDF would be better for the application to no avail. They want the solid wood.

I have been at this 25 plus years and I know the properties of wood. Some of these doors are going to be 24"-wide and 42"-tall. That size door in 4/4 is not only possible to warp, but probable. I could do some re-designing to lower the risk but even with, I would still have many doors at 16 x 42, etc. The entire job is around 750 doors plus drawer fronts which are not of concern. That is a whole lot of doors to replace should these things start warping up on me! I haven't made any decisions one way or the other on how I will proceed with this. I am calling out to everyone with hopes that you will share your experiences, wisdom, and recommendations for this.

Things I have considered:

1. Disclaiming warp tolerance I will guarantee.
2. Bracing the door backs with some wood rails (size rails?)
3. Certainly assuring to reverse the grain cups if we do it.
4. Is moisture content of essence?
5. I'd imagine staining/sealing them immediately upon manufacturing would be helpful.
6. Should I go so far as to consider sealing inside the hinge cups?
7. Other?

Help me out guys. What would you do? What does AWI say about this application? I'd like to know any and everything you could contribute about this. In case it helps for you to know, I am planning to outsource the doors to one of the door specialists rather than gluing and milling this stuff in my shop. Any and all feedback will be well appreciated.

Forum Responses
(Business and Management Forum)
From Contributor C:
If you are planning to outsource this, will the door manufacturer warranty them for warpage? If so, fine. If there is a problem, see how they will deal with it. Then, think about adding a clause that says the doors are covered by the manufacturer, but the labor to replace them is not. (Or, will the door manufacturer cover your labor costs if there is a warranty issue?) If not, then pass that information along to your client and include it in your negotiations, proposal, contract, etc. The third option is to add money to cover the risk to the contract price. These are just my thoughts. I have never had to actually do this.

From Contributor E

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It's a scary prospect. We outsource our doors, and our supplier flat doesn't guarantee slab (plank) doors. When we need that style we always use a veneered, MDF core product. Quarter-sawn material might help, if you can find it, but it still seems kind of iffy.

From contributor J:
You are right. Seven hundred plus solid wood slab doors is a scary thought. Even plywood doors this size would be problematic. Don't do it. As you said, you know better. You’re the expert. Sounds like you know more than 9/10 people on this forum. The client is not informed, nor an expert. He/she has no clue, and he/she is likely misinformed. I would consider trying a pair of doors if a client really insisted, and only because I could still eat that, re-do and make a profit - certainly not a kitchen full and absolutely not 700.

If they want slab doors, they need to be veneered, period. Even with a waiver odds are they could still argue that you had the duty to refuse to do this, as you are the one with 25 years of experience. They would get one of these expert witness types with a PHD in wood science, to rip you to shreds for even doing it. Their lawsuit would claim you were negligent to even do this. Stay away from it. If they insist let them hire somebody else to create a mess.

From contributor O:
I would insist on veneered panels or at the very least frame and panel type doors. You could make flat floating panels the same thickness as the stiles and rails. I typically shy away from work that I feel will get me in trouble but I am proven wrong on a regular basis by the many who will do what I consider to be risky business.

From Contributor W

There is an architect and an engineer on this project right? Solid wood no way, unless out sourced with the express written amendment releasing me from all liability for the doors, balanced panels. Maybe, if it is known and expected to have some deflection understood (in writing) by the owner and compensate for same.

From contributor F:
You could determine an estimated failure rate based on size, apply the failure rate to number of units, add trip charges to each unit, fab and setup times and then add to the price with a deductive alternate that includes the cost of replacing failed doors plus the cost savings to choose a veneered door, maybe a substantial amount of savings will sway the customer; if not you could have enough money in the project to replace doors for one or two years. Or explain to the owner you will need to build a failure rate into the price to cover high replacement costs.

From contributor M:
I'm 40 plus years in the business and I'd run from that job in a heartbeat (despite it being such an attractive contract given the size of the job). Your heart, your head, your experience and your just plain old common sense gave you an answer before you ever posted this question here in the forums. You've received several confirmations of your own fears validating a genuine concern. Don't mess with wood. It will leave you splintered...

Print all these responses and show them to your client. Let him know how foolish it would be to build these doors out of solid wood slabs. Let him read the confirmation of your peers. Even if he signs a disclaimer - I'd still run from the job before building doors up to that size with solid wood. I'm sure despite any disclaimer a good lawyer would make mincemeat out of your contract because you are a professional and should know better.

From contributor K:
Breadboard ends work. Rear battens with sliding dovetails work but only appear as slabs on the front. Solid wood mitered banding on veneer cores with thick shop veneer faces work. Don't get hung up on what you know won't work. Certainly don't get hung up on the price point for what won't work. Just figure it out, or pass.

From contributor J:
The failure rate from this could very well be 100% depending on the climate. That is if the client were expecting tolerances expected for quality slab/euro doors. Bottom line, I have never seen a wood panel that never moved. The expansion/contraction will require greater reveals. You’re going to have some degree of cupping/twisting no matter what. Maybe the rate of failure would be much lower if the customer were not expecting much, and while they may say that now see if they still think so five years down the road. There is a very damn good reason why five piece doors were invented. Otherwise, I doubt anybody would have gone to the trouble to make them.

Disclaimers may or may not protect you. There is a chance they could be thrown out due to technicalities and deemed unenforceable. There may be laws that require you provide a warranty. If you go this route, sit down with a lawyer and have them write these contract terms. Otherwise as soon as the client’s attorney sees DIY legal work, they know an easy target when they see one. That being said, I have seen solid wood slab doors that work, but they were smaller, and made for one-off pieces of furniture, where it is possible to carefully select only the best material for the panel. Most commonly these have been tapered coopered doors, made from many staves. Even still there will be movement that must be allowed for.

The design must not rely on many tight, narrow, reveals and etc. Certainly not something I would ever recommend attempting in euro cabinetry. I would not want to have to warranty more than a handful of doors. I could deal with one-two but 700 would be a nightmare waiting to happen. The other application would be entirely rustic. To me the majority of the time rustic is just an excuse for poor workmanship or limited capabilities due to lack of tools. That is a side note, not related to this discussion.

From Contributor R:
Hard to believe - by all means, pass up this job! You are far too insecure and/or lack the basic knowledge to do the work. Let someone do it that knows how it is done. I agree with the others - walk. It is a good skill to recognize when to walk.

However, there are hundreds or thousands of these doors made all the time and some have been hanging around for 100 years or so. Cabinet doors, passage doors, entry doors, castle doors. This is the oldest form of wood doors there is, beyond a wood slab leaned in front of the cave. I believe woodworkers made them all, and still do today. If it was truly a failed design, it would not be done. How many conventional five peice panel doors warp in a year and do we still make them? Do we follow rules or guidelines to make them successfully? The shop that does make these doors will know the way. T and G is the first thing to consider, along with battens and gaps. Gaps will be determined by a visit to the Shrinkulator. The attached photo is of an exterior plank door out in the weather 24/7 for 12 years now. Looks as good - and performs as well - as it did the day it was set. The assembly details are slightly different - easier - for cabinet doors, but the basic principles of wood construction are still relevant.

Click here for higher quality, full size image

From contributor I:
Quartersawn soft maple, best hardwood supplier you can find, triple the price on the job for future trouble and replacement, and very specific contract that spells out acceptable tolerances for what is considered not flat. Maybe have them spell out the flatness tolerances. Make the money. You didn't mention if they are overlay or inset, but if you insist on quartersawn, that won't make much difference.

From Contributor U:
We had a very similar insistence from one of our clients. As others have stated it is possible to do successfully, but it is very risky. What we ended up doing was buying random leftovers from veneer logs from our supplier. Then we veneered the doors but made sure we completely randomized which log was used for each piece. It actually looked pretty cool and the client was satisfied.

From contributor J:
I would certainly agree that a board and batten door can be built properly. I would certainly end up charging more than a five piece door to do it right. However I am not sure that is the exact type of door in question. As the term "slab door" in cabinetry is an industry standard term related to euro style cabinet doors my impression is that the original poster was asked to build euro slab doors from solid wood - essentially glued up panels. Not old school board and batten doors.

In that case, I really don't think it is appropriate, for the application, or a quantity of 700 plus doors no matter how skillfully they are built. As I pointed out there are most definitely situations where it is done. I would not do this with euro cabinetry. Board and batten doors can certainly be done skillfully. The mahogany door in the picture is certainly a fine example. My experience is that they are pretty rare in cabinetry. The only ones I have seen in kitchens are in older/dated cabinetry that was being removed. That being said, I think some door manufactures do list them in their catalog. For design reasons, my opinion is that a board and batten cabinet door would be inappropriate for euro cabinets. I have only ever seen them as partial overlay doors with a face frame.

From contributor L:
Bread boarding is cross grain construction. It works fine as long as there is no change in moisture content. Otherwise it is sure to fail in one way or another. There just has to be a way of accommodating wood movement.

From contributor D:
Make some samples of what he wants. Make a few banded samples the way you will guarantee a door and use some nicer looking plywood for the panels. They may say that looks fine. I would say making the doors finish out thicker maybe 7/8" - 15/16" and narrow laminations I want the crown out so a panel that does curve in width may not show from the face, instead of a wildly two directional warp when wider boards get used.

From contributor L:
Banded plywood panel/slab doors seems like as bad an idea as solid wood panels. Long ago someone convinced me to use lumber core for slab doors, equally bad idea. I don't consider a T and G door a slab door so all that discussion doesn't go anyplace if I understand what your customer wants. The problem with making something that you know is likely to fail and using a disclaimer to cover your behind, is that in court you will find that a customer can't legally give away his rights to sue. If you make them to the customer's specifications you are agreeing to warrantee them. Making them to AWI specifications gives you some protection but you can still get sued. Being forced to replace 700 doors would be really expensive! I'd pass if you can't get them to go with an AWI spec.

From Contributor R:
You can completely avoid lawsuits if you get them to sign a contract that has a mandatory arbitration clause. Make sure you get to choose the arbitrator and they pay for it. Most every contract you sign for real estate, credit cards, cell phones, even employment contracts, have these clauses now. Most people ready to sign have no idea what they are giving up when they sign. That does not give you freedom to make crap. Or does it?

From contributor N:
I'm sure you'll agree that even sawn, narrow width veneer looks different than a glued-up panel. What about using 5/8 A-4 MDF core but use the good side as the back of the door then glue up 3/16" plus thick panels that you could laminate to the front side? Edge band before you laminate the front on so you avoid seeing the glue line. You’d still would need to leave what could be considered excessive gap around the door but this could mitigate the warpage to a (hopefully) acceptable level.

From contributor L:
Probably not a good idea Contributor N. What you are suggesting is an unbalanced panel, sure to warp. 3/16" is probably too thick to work as a veneer. At any rate whatever you do to a core do the same front and back.

From contributor N:
3/16 was to reach the stated spec of 13/16 and is a pretty common thickness for stave core stile veneers. A4 is already technically unbalanced but I'll trust your judgment since I have never actually tried laminating just one side with a thin panel and I know you have more experience than I do.

So then glue up 1/4"plus/minus panels and laminate to the 5/8 MDF front and back after edge banding. It might even be best to use a rip off the panel material to band it with so it matches better. I have made this type (two sided) of panel before and starting with the extra thickness in the panels makes the whole process much easier. After all is glued up, plane/sand to final thickness. The final product looks much more like a solid wood panel than a commercially veneered panel does even if you order sawed veneer. Plus you can hide the glue line a lot easier when it is on the side of the door rather than staring at you in the face from the front.

From contributor Y:
I have seen what Contributor N is proposing at the local large University. Before my time they had their lab furniture cabinets and doors built this way. Fir ply (or similar) core and 1/8" thick solids laminated on both faces. They have and still will hold up for years. I would imagine this would be very expensive to do. I am not equipped for it that's for sure.

From Contributor W

Realistically when you consider all these responses the potential for a large problem is very high. The risk factor could be as low as 25-45% failure to a guaranteed of failure. This math would have already made this decision for me.

From contributor K:
To contributor L: My above suggestions weren't questions; each type works. I have jobs in service for 5-13 years of each type. The point is a difficult or out of the norm spec is a chance to use your knowledge, and make some real money. And yes: that last part is possible as well.

From contributor L:
I agree it is a "a chance to use your knowledge." That's exactly what I'm offering. I try to learn from my mistakes. Some of my mistakes haven't failed, doesn't mean they weren't mistakes.

But I'd like to pass on all my comments and let Gene Wengert settle the discussion.

1. Solid lumber slab doors, best way to make them?
1.1 Bread boarding?
1.2 Battens?
1.3 Alternating annual ring orientation?
1.4 Sawn thick veneer one side?
1.5 ?
2. How thick of veneer will still work as a veneer & not as a solid?
3. Un-balanced construction, is it a worthwhile bet?

All these have been suggested as solutions. What is the best solution?

From Gene Wengert, forum technical advisor:
Thanks for the referral Contributor L. The response of others about this project, especially the early responses indicated that there is close to zero chance that this will work. Indeed warp will be the issue. So, with all the good advice about this project, I cannot add anything new, but just support what has already been said. Well, one new item: You could put a metal rod or two in each door to keep it from warping. I have seen this done with long windows to avoid warp and cracking glass and seals - expensive indeed. Of course, the attempted warp might crack the wood, but at least the warp would be minimal.

From contributor N:
Contributor L - the shop I used to work at completed a lot of doors in the 70's with thick shop-made veneers on both sides of a stable core with good success. I tore out a couple of their jobs in the late nineties that were done this way and the doors were still holding up over 20 years later. So this is not untested theory. I'll readily admit for my first suggestion I did not think things through, was trying to cut out some labor. I know that I personally do not have the knowledge or experience that you do. On this particular issue I was taught how to do it properly by a third generation woodworker who has seen this system hold up in the real world over the course of several decades.

From Contributor R:
This is not rocket science - or is it? How could so many see this so differently and be so afraid of it? The ruts we are in (myself included ) are deep, but do they prevent us from using good basic wood principles - from seeing out over the edge of the rut? If not board and batten, then simply veneer over MDF core, preferably with 1/8" edge band first - will do the job. Veneers could be 1/16" to allow for sanding and limiting edge band telegraphing. Or go old school and add a layer of cross band under each face. As one sane individual above stated, these have been made for many years, and perform predictably and reliably. Next thing you know, the process will involve a full moon and rooster blood!

From Gene Wengert, forum technical advisor:
I do agree with the approaches using laminations, but the original request was for solids, so that is why I suggested, albeit tongue-in-cheek, the metal rods.

From Contributor R:
Even solids are not out of the question as I see it, if that is what the customer wants. These would require some sort of cross grain batten on the interior side, dovetailed, screwed with expansion slots, etc. If solid and inset, make up a sample with clearances indicative of what the doors need, and show this to those that are making the request. Remember: wood moves in response to changes in moisture content. Buy good lumber that is dried and stored correctly. Provide a good environment for fabrication, and insure that the job site is stable and ready for the cabinets. No full moon or metal rods required.

From Contributor U:
I couldn't agree with you more Contributor R. It is not the case that I am afraid to build something like this, it is rather a case of budget (I assume a project with 700 plus doors the client is budget conscious) and risk. I think the three variables that you commented on in your last post is what makes it problematic for me, as only the second is the one over which I have direct control. The others are just as likely to make the job a service nightmare, hence my random match veneer suggestion.

From contributor K:
A mistake that's yet to fail:

1. 5/8" multiply core: cut 1/4" undersize on all edges, cross-grain orientation.
2. Band with 5/16" finish material, mitered corners.
3. Calibrate on widebelt.
4. 1/8" shop veneers (finish material) taped and vac bagged to both faces, vertical grain orientation.
5. Trim to size.
6. Widebelt.

Components: Wood and glue.

From Contributor B:
The customer wants solids, why is there continual talk of veneering? I am in a house regularly which has IKEA boxes with slab maple doors and fronts (solids). Large doors too. Some of the upper doors are likely 42"h x 20"w. 4/4 edge glued, 1x3 battens screwed on the backs. The doors were made by someone locally and are nothing fancy and not pretty (in my opinion) when opened, I guess I just don’t like the battens being there, but from the exterior all looks fine and dandy. This is a rural area too so I’m sure the maker was far from a rocket scientist but surely could have just been lucky.

From contributor D:
I would build a solid slab door and a 3/4 veneer out of the same material and have a meeting. Give them both doors and ask them to identify the solid one. If they can they obviously understand the difference and shouldn’t be hard to put some type of clause in the contract that you would not be responsible if it should happen. My guess though would be that they won’t identify the right door and you can then explain that if they don't know the solid from a MDF core how would the end user and again win them over to the correct type of door.

From contributor A:
If you do go the solid wood route, here are my suggestions in making them. Rough cut all your parts and let them sit at least a day so they release all of their tension. Then face joint and plane them. If any of the cut parts are more than 1/8" out from straight, don't use them. Twisted parts will be your biggest enemy. When you joint the edges, make sure to flip your parts over for each edge so you maintain a flat panel when you glue up. When you glue up, make sure it is in a way where the panels stay flat. At the end of each day, make sure you sticker all of your parts and panels. This will help reduce any uneven exposure to humidity and temperature changes which can cause warping. Expansion of the doors will be the biggest headache when it comes to your gaps. Make sure they are big enough to allow for this.

From Contributor S:
We have done a lot of slab table and desk tops (both 8/4 and 4/4) and use our CNC to cut a dovetail slot across the grain and then slide in 22mm wide solid rails. Holds flat. Not as flat or certain as a veneer method as mentioned soundly above, but reasonably stable. I would avoid screwed battens - if the wood shrinks there is the likelihood of cracks developing between screws. Use larger than normal gaps between doors to allow for expansion. If you can get them to allow a heavy rounded edge that will provide a little forgiveness for some warpage. As you surely know it is essential to finish both sides of slabs 100% same steps - don't short shoot the inside.

I'd skip the metal rods - too much trouble especially on 4/4 thickness. The original questioner is no newbie but has 25 years experience in the trade and wisely is asking for input on what is a challenging application. I think this was a refreshing question (hence the multitude of responses) as it is not some basic question from a newbie but a genuine challenging question from a technical and business perspective. Kudos for the wisdom to ask.

From contributor G:
Until the mid-90s, I ran a strictly solid wood shop, with the exception of drawer bottoms, cabinet backs and bed underlayments. I was on the way small side compared to some of you, but made a lot of solid wood doors. If you are used to them, they aren't that hard. If you only know veneered MDF, best leave them to someone else. Don't make 700 on your first time out. You can get around warpage pretty easily with battens, but you can't keep wood from shrinking. Make sure the design accommodates the movement.

There's a trick to keeping the panels from splitting between the batten screws, since someone was worried. Don't tighten the piss out of them, and put a washer under the head, over the oversized or lengthened hole. Make sure the washer has a hole that's large enough to allow some movement. Read the shrinkulator to find out how much. Check your moisture content and humidity to figure if the doors are at their maximum or minimum width when you are making them, or in between, and adjust accordingly. It's pretty common sense, but you have to appreciate the rules, and they are a bit different for solid wood.

A tip to selecting boards: Some wind is caused by twisted or reaction wood. The rest is in boards that are just fine, but sawed at a diagonal to the growth of the tree. The "cup" of the end grain shifts from one end to the other, so as they cup during the humidity cycle, one pair of opposite corners move more than the other. Don't use the reaction wood, it will take multiple rests to come to equilibrium. Straighten out the other type of wood and it will be just fine.

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