My friends have a floor made of 2’X2′ squares of 1/2″ MDF glued down over 1 1/4″ plywood subfloor. The sanded grout they used between the squares has cracked crumbled loose two times. The other part of the floor that has 4’x4′ squares with the same grout has held up fine.
Any suggestions as how to replace the bad grout. Would you recommend a specific flexible grout or switch to caulk. Thanks for any help.
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Replies
I would expect grout in mdf to crack. I can't explain why one did and the other didn't.
Reason I would expect cracking is that the products are not compatable. Grout is intended for ceramic tiles and other types of brickwork. it is cementious based product. It cures in place when mixed with the right amt of water and/or modifier additive.
The moisture must remain in the mix while it cures. Since mdf would be prone to such that moisture out of the mix before curing takes place, the cure would be weakend and no bonding with teh mdf would be secure. I would hesitate to try it, but if forced, I would seal the mdf before installation to stop it from sucking moisture out of the mix. I would probably also use a bonding agent to secure the bond between the dissimilar materials.
Admixtures will also be a benefit in that they allow some minor flexability in the grout, along with increased bonding action.
another difficulty to overcome is that wood and cementious materials will move at different rates with changes in humidity and temperatrues. No gaurantees bnut some possible solutions there are to seal the mdf first to reduce the amt of moisture it absorbs, and to keep temperture constant.
Nowthen - satiosfy my curiousity to help me learn.
Where did they get the idea that mdf and grout were good together?
Where in the house is this used? room? floor or wals?
Is this exterior mdf ( MEDEX) or common kind?
is it painted?
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Thanks for the input. The cork sounds like it might be a cool idea. I have trouble imagining that watco and sawdust would hold up. This is a floor and it is the entry way and gets alot of traffic. Dogs, Kids etc. As far as I know it is just standard MDF and I have no idea where they heard about the idea. The finish is a wood stain covered in polyurethane. It actually looks very nice (other than the grout) and fits in well with the style of the house.
For an application like that, I would probably have used Minwax Wood filler. It is a two part epoxy mix filler made for wood with great wear and bondfing strength. It cures blonde and would contrast nicely with the dark MDF and accept the polyurethene surface.
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Here's an interesting approach.
http://forums.prospero.com/tp-breaktime/messages?msg=2383.8
And here's one with a reference to cork spacer grout, but no source.
http://forums.prospero.com/tp-breaktime/messages?msg=50238.1
Google returns 3 hits for "cork grout", 17 for "sawdust grout".