mdf nightmare

[Shire]

just made some shaker doors from mrmdf, and painted with symphony coatings woaterbourne paint.I have been getting blue spots appearing all over the doors? and on investigation the paint has not stuck to the mdf, scrapes off back to mdf.sanded back ,panel wipes with acetone, blue spots still showing!!!!!!!
mite have to make fresh doors and start again.any ideas please
Steve

[ispraywood]

Either one of two things, most likely silicone contamination of some sort, either from transfer from your tools or more likely during transport. You can add a anti silicone additive to your paint which depending on the level of contamination can help, failing that there isn't really a quick fix.

There is an old saying, that if you want to rob a spray shop you don't need a gun, just a squirty can of silicone.

I would avoid using silicone in your workshop at all and use alternative forms of lubrication. Wurth make a great product called wood slide that is great for machine beds etc.

[ispraywood]

Also some pictures might help to further diagnose the problem. Also, what paint are you using?

[senior]

I've had the blue spots before, it's something in the MDF, we just gave it an extra coat. Ours was in medite

[Shire]

the board is medite Mr, the spot sbleed through , I have stripped the old paint off. cleaned with acetone ,sprayed again 2 primers,2 top coats and spots on 10 doors , board is 22mm and 9 mm,you can see the spots in the board and on the surface.going to ring Medite tech support, but bet it's my fault,of course?
will post picture tomorrow
going to make new doors,as last resort,and paint with pre cat. nice

[Wood Finishes Direct]

Hi,

Some types of MDF have a blue or green tint which comes from an added stain to indicate the type of MDF i.e. moisture resistant. Problem is that If the surface of the MDF is sanded or scuffed, it breaks the seal and the coloration can leach out into the finish.

There are various primers / sealers that should cure this problem, try something like Zinsser Bin White Primer & Undercoat - available from B&Q, Screwfix, Amazon etc.

[mailee]

Only problem I have had with MDF has been the normal 'fluffy' stuff especially the 6mm as it became very fluffy on the face once given a coat of primer. I also use Medite and have not had any problems like this so far (Touch wood) I always give it a wipe over with panel wipe before starting to spray.

[Shire]

thanks for all the suggestions, sent some photos to C F Anderson that's where the boards came from,also spoke to the tech man at symphony coatings he said to try ,two pack pu spray, sand back with 240 grit and start again with primer and top coat, never used two pack ?. going to denim and try senior's idea first and if not. Will go for two pack, or a different rapper!

[Tomyjoiner]

Ive had blue spot with medite, same as senior just an extra blow over with 2k primer sorted it.

[mark270981]

Don't mean to sound condescending - but please only use those with the right extraction and masks - especially with the PU lacquer!

[Tomyjoiner]

Give some zinsser a go first with just a very light de-nib if ur using waterbased.

[Shire]

mdf update.spoke to CF Anderson medite rep taking away sample Tuesday,de nibed panels coated again. hope blue spot goes. dose any one know if I can coat over waterborne with pre cat? would it be better than waterborne?

[Shire]

tried zinner after Tommyjoiner advise, blue spot gone. but finger print.must check how long things take to dry.

[templecarpentry]

I've had the blue spots before, it's something in the MDF, we just gave it an extra coat. Ours was in medite

This . Medite is the best but does have pigment bleeds. More coats of primer hides them

[promhandicam]

I was priming some medite doors today and noticed a slight blue tinge even before the primer was dry. This was using zinser 1-2-3 primer sealer.



























Although come to think of it, the primer may not have been as white as some that I've used

[Shire]

mine was a better shade of blue than that.I have finally got rid of the blue spot! bin zinner saved the day.
Had enough of painting for a time

[Tomyjoiner]

Good to hear its sorted

[Shire]

if it wasn't for bad luck I wouldn't have any luck . lately