# Possible ways to lower water absorption of MDF?



## IHPE (Sep 19, 2015)

Hi guys,

Just for some home projects, in which I've been using MDF jigs (I believe the water absorption is something like 8-12%)

I can look at other materials but they'd need to be machinable with wood cutting tools, I can look into plastics which are inexpensive with a water absorption of around 3%, also looking at any finishes/coatings for something like MDF I could look at to bring the water absorption down to something like 3%. 

Any input would nice, maybe point me in the right direction, new to all of the more science side of things.

Thanks!


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## GeorgeC (Jul 30, 2008)

I do not understand. Just what type of water absorption are you concerned about? Jigs being used in your shop environment would not normally be a concern. 

An introduction of yourself would also give us some idea of who you are and what are your woodworking skills.

George


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## mark_f (Sep 13, 2015)

I'm no expert but I wax all of my MDF surfaces and I would think that would inhibit moisture intake.


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## IHPE (Sep 19, 2015)

Ok I will do some explaining 

I've been making some hardwood decks in my spare time (Used to work at a decking company in France, Now I work within a kitchen company) just looking at some extra income for myself, so I've put some money into making some samples, I've noticed the jigs I am using are swelling (all MDF) and yes its just down to the weather, but they are moved into different environments (from storage, to where I work with them) So I am ending up with some slight issues, but I've been working on some humidity control, the problems are easily worked around if the jigs are all MDF, but I'm having some issues using full depth seams (atleast If I want to figure out a clean, quality minded process when I'm stuck for time to make the actual deck) I'm using tape at the minute to release the caulking from the jig but want to look into building a Jig that is practical, cost effective and has the caulking release built in, I'm using TDS caulking. EDIT: I use acetone before caulking, which is why I am looking at nylon (acetone resistant).

So far I'm looking at nylon as a possible plastic that the caulking won't bond to (still yet to test, still looking at the science side...again this side is all new to me) but if I was to put strips of nylon (assuming it worked) into the MDF where the caulking will sit and cure, the difference in water absorption between the Nylon and the MDF will cause a lot of issues I'm guessing.

just trying to solve (on paper) one problem at a time, might end up with nothing...who knows, yes I've done it for work but I was never anyone substantial at the company just working my own personal experience, kinda looking into everything else now and what my options are. 

And thanks for the answer Mark, not sure I wish to cover my jigs in a wax, just for handling issues and having to re-apply it etc.

Literally been stabbing in the dark on some of these issues, trying to solve one issue...which brings up another issue...etc etc...Just seeing what information I can gather


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## Steve Neul (Sep 2, 2011)

Can you put a finish on the jigs. It just needs something to seal the humidity out. A better solution would be to use a different material. At one time I used cheap Chinese plywood but it got to delaminating from humidity so I now use exterior plywood. It cost more initially but if you plan to save the jig is worth it in the long run.


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## MEP1 (Aug 14, 2015)

If you're up for rebuilding your jigs, use MDO (aka signboard) next time. It's very water resistant especially when painted or sealed.


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## mengtian (Nov 8, 2012)

I use Birch or red oak ply wood for all my jigs. Other than that use poly or paste wax.


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## NickB (Sep 24, 2013)

It seems like the obvious answer is just to put on a few coats of poly-urethane, paint or another film coating. Most of the commercial jigs I've seen have a plastic laminate surface - phenolic, melamine, etc. Since that's probably impractical for a small shop, I'd weigh durability, ease of application and cost effectiveness to choose the best coating.


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## IHPE (Sep 19, 2015)

Thanks for all the responses guys! One thing I forgot to mention, I acetone before caulking, hence the nylon (its acetone resistant) I will look into all of these suggestions and see what I find, If I could just find a paint or varnish that acetone wont defect and the TDS won't stick to I will be flying, as I could use one material for the jig and it cuts out the water absorbing issue using 2 materials.

Thanks again!


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## NickB (Sep 24, 2013)

IHPE said:


> If I could just find a paint or varnish that acetone wont defect and the TDS won't stick to I will be flying, as I could use one material for the jig and it cuts out the water absorbing issue using 2 materials.


Most surfaces aren't affected by brief contact with Acetone. I don't entirely understand the application, but for the portion that you'd don't want caulk to stick to, I'd probably use Band-It melamine off a roll.









Really good caulk will still bond to it as it will to most everything...


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## IHPE (Sep 19, 2015)

NickDIY said:


> Most surfaces aren't affected by brief contact with Acetone. I don't entirely understand the application, but for the portion that you'd don't want caulk to stick to, I'd probably use Band-It melamine off a roll.
> 
> 
> 
> ...


Its just minor chemical reactions which could make the bond minor to a bit stronger or something, basically if the caulking would release from the nylon easier than the hotglue to the jig then it should be viable. thats what i'm looking at. 

trying to get away from any tapes, but will keep that in mind! thanks.


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