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crack in wood top2/3/15
please see the picture.
we have a client in new england that was home one evening a couple years ago when they heard a loud pop. that pop was their countertop cracking because their contractor (discovered later) had installed this top by screwing it in tight, not allowing any room for expansion/contraction. this was in the winter time.
i told him to see about putting some pipe clamps on the end and using epoxy in the joint. i hadn't heard back from him so i thought this worked.
yesterday he emailed to let me know that the joint never came back together so he had a large, epoxy-filled joint along the crack. well, the epoxy is failing and the crack is now moving further inward.
he's now thinking of cutting this section out and replacing it with an inset cutting board. i think this sounds like a fine idea and one that will get rid of the expanding crack. however, he pitched this idea to a local cabinet maker and he essentially said new england is no place for a wood tops and he should strongly consider replacing it with stone.
i cannot see why his idea of the inset cutting board wouldn't work but would like to get some more opinions before we go this route.
I just wrote a report about this issue and it will be in the ASK THE WOOD DOCTOR column in FDM & Cabinetmaker magazine in the next few months. Here is the article with a few added comments for your specific case.
Let's start with a crack in the top the first winter that it is put into use. This crack developed because the air was drier than the wood, so moisture left the wood and the wood shrank, or tried to shrink.
In the summer with the more humid conditions, the top wants to swell and close the crack back up. In your case, the epoxy repair makes it impossible for the wood to close the crack the first summer after the repair. So the wood tried to swell and being unable, it created pressure. This pressure caused the wood cells (hollow tubes is what the cells look like) to be compressed. So, in the late summer, the wood fits around the repaired crack. The compressed cells are essentially compressed for life (unless subjected to wetting with liquid water). Now, when the drier wintertime came again, the wood wanted to shrink bit as it dried, and with the compressed cells, any shrinking resulted in a increase in the size of the repaired crack beyond the size of the crack the previous year. We could say that the crack grew larger because of the repair. Without the repair, the summer swelling would have closed the crack and then winter shrinking would have reopened it back to its "normal" winter size.
So, what you need is something that will give and take easily as the wood naturally moves from summer to winter (humid to dry) annually. Another piece of wood is a good idea if it can be glued in and if it is not installed in the middle of winter when the wood is the driest. Putty will work, except that it must be flexible, which means in the summertime it will be squeezed out forming a ridge (objectionable?) and then back flat in the wintertime. Neither option seems too good.
A third option is to let the entire panel move without restraint. That is, the best option is to design the fastening system to allow the entire panel to move seasonally rather than trying to hold it and prevent movement. This floating along with a good finish, top and bottom, to retard or buffer moisture changes (there are no perfect sealers for wood) is the best we can do.
A simple system uses screw holes that are slotted and screws that are not too tight so the screws will move within the slot as needed. Of course, there may be a crack between panels or at the wall, so molding is a good idea.
NOTE 1: Wood is wood and we cannot stop wood from moving unless we have a constant humidity year round. The maximum movement is when we use the end grain design you have, as each piece is moving in both directions. With long strips, there is no (or rarely very slight) movement in the lengthwise direction, just across the grain.
(Note 2: Epoxy must be a thick joint to develop strength. If it is too thin, there will not be enough heat generated to thoroughly cure the epoxy. So, the pipe clamp idea could easily result in excessive pressure.)
NOTE 3: Remember that wood does not shrink unless its moisture changes. So, a crack is evidence of shrinkage and so we know that the moisture was higher, prior to the development of the crack, than it is now. You can measure the MC now, but that does not tell you what the MC was. For that reason, it is critical to take MC readings prior to shipment. Do not assume that the wood is 6.0% to 8.0% MC or that the wettest piece is no wetter than 7.5% MC. Measure the MC yourself- -measure the lumber and the final product, and even during the manufacturing process. Also, measure the plant humidity and make sure it is no more humid than your customer's home or office (oftentimes 30% RH or even lower in the wintertime). Humidifying a shop in the winter can reduce problems in manufacturing, but actually, it often just pushes the problem to the customer, and then it is expensive to fix compared to catching the problem before shipping or getting lumber at the right MC right away.
Note 4: At my age, you either preach or reminisce...HOPE I WAS NOT TOO PREACHY.
Why in the world would you want to get involved with this? You are trying to fix something you had nothing to do with. Let them get the stone!
dr. gene - not too preachy and i have read those same comments by you and others on this forum before. we have a specific set of installation instructions that dictate proper installation (over-sized holes and screws with washers). unfortunately, our installation instructions were ignored by the contractor who installed the top and this is the result.
i also understand about the summer and winter time periods and when it would be best to take action. i'm going to suggest delaying this latest round of "treatment" until late spring/summer.
question for you - so if i understand you correctly - you agree with our plan but think we should glue the new piece in place. is this correct?
the new piece will be finished with mineral oil. this is vs. the film finish on the rest of the top. would a different rate of expansion and contraction between the two pieces (plus the new piece won't be accumulated to his house when initially installed - unless he waits a couple months) potentially cause the new piece to expand/contract at a greater rate and, assuming we make the new piece fit tightly and glue it, act like a wedge, furthering the potential for future cracks?
i was thinking we would cut the new hole for this cutting board slightly larger to allow for a different rate of expansion/contraction. we'd make the cutting board thicker than the original top so we could rabbit three sides to conceal this wiggle room. i guess we would have to step the cut-out in at the edge of the countertop to make the fit tighter to make it look good. obviously, this part could bite us later but i would hope that there would be enough flex in the wiggle room elsewhere that the countertop might flex during the summer time but not develop future cracks. i'd think we would do all of this in the summer time and keep the new piece independent (not glued) of the existing countertop.
sound like a plan?
al - this is another opportunity to service my clients and expand my knowledge in my profession. this client has acknowledged 100% that his contractor created this and i'm not to blame. however, this is the stuff that i enjoy and the minimal effort (forum post, replying to him, making the cutting board, and coordinating the completion) are nothing compared to the potential opportunities that a very happy customer will present. and besides, i would love to be treated like this and it makes me feel good to treat my clients like this.
I would glue the new piece in and then the entire region would behave as one...although a different finish could offset this objective.
As far as your future plan, wood will move...at least 1% summer to winter. So any design must accommodate this movement and also allow the piece to move freely.
I also agree with you about why we do this...I am motivated to help others, partly because others have helped me and partly because that is why I am here on earth. I do see an increasing level of selfishness within our nation, including some of our government. People need to appreciate that someone's lack of selfishness (such as in WW II) is why we are here today. We do not have the right to be selfish.
I looked at picture again and see it does go to edge, sorry for not seeing that.
Okay thanks Gene. Google, you asked a question and I answered with an opinion not relevant to your question. I usually wouldn't do that and actually don't like when people get off topic like I did.